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Old 09-15-2010, 02:44 AM
Nicks67GTO Nicks67GTO is offline
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Default iron head compression and pump gas

What is the maximum compression recommended for 6x-4 heads to run reliably on pump gas?

I'm considering a set of heads for sale by a forum member. They are 260cfm ported 6x-4 heads with 93cc chambers. I ran some numbers and found that if I run a

-4.185 bore
-4.25" stroke
-flattops with 5cc reliefs
-a head gasket with a 4.3 bore and .039 compressed height
-0 deck
-93cc chambers

I'm going to be a touch under 9.8:1 compression.

Did I calculate that right? Is this too much? I will be running a good aluminum radiator and a MSD digital 6 ignition box so I should be cool and I should have a relaible hot spark.

This is a stickshift, 95% street car. I do not want to have to run race gas under any circumstance and want to be ok on 89 octane if I need to.

So is 9.8:1 too much for the old iron heads?

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Old 09-15-2010, 06:28 AM
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Quote:
Originally Posted by Nicks67GTO
So is 9.8:1 too much for the old iron heads?
Depends a lot on who's answering that question,as opinions vary on that subject.

Me,I see no valid reason to push the CR envelope for mostly "street" oriented cars.

And I almost never recommend it to anyone I dont really know that well either,as the higher one chooses to push that deal,the more important it is that they cover every detail possible to make it work without any problems.

Is this a shortblock that's already assembled?

Or is it a shortblock your planning on building??

I ask because KB/Icon has a 10.5cc dish forging for that 4.25" stroke/6.8" rod combo (#KB938),and that would help to bring the CR just a bit more inline for an 89 octane iron head pump gas combo.

I dunno,that should get you down to like 9.5:1 or so I believe,I'll admit that's not a drastic difference,but every little bit helps if you ask me.

With good tuning that should be able to tolerate 89 octane in a pinch.

Beyond that CR,I'd wanna feed it strictly pump premium myself.

But I'm sure some others here will feel differently than I do.



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Old 09-15-2010, 08:38 AM
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Some of us base our "opinions" on FACTS, by actually doing things, others on information they come up with reading stuff on Websites.

The cam chosen is a key player here.

My last 455 used the same 6X-4 heads, 9.98 to 1 compression, and ran for years on 89 octane, or any other pump gas I wanted to put in it. It also made great power, dyno'd a 455.4hp and pushed my car to 12.0's at 112mph in full street trim.

My car wasn't as "refined" at that time in the suspension or exhaust as it is now, or we'd have easily posted some 11 second timeslips with it.

Anyhow, choose the cam carefully. Avoid lobes with short seat timing events, early intake valve closing points, and tight LSA's.

The best cam out there would be the no longer available Wolverine 5059 cam. A real RAIV cam, or Crower 60919 is a very good choice. I've seen a few other recent offerings that look good as well. Ace has a flat cam that's not too far off the old 5059 grind that looks pretty attractive, if you are looking at flat hydraulic grinds?

Quench distance is another player, shoot for .035", give or take .about .005".

Not sure if it helps, but I polish the tops of my pistons and work the chambers some as well, by removing any sharp edges, smooth things out as much as possible, etc.

I've seen folks get into PLENTY of trouble with running hot/overheating/detonation at lower compression ratios pissing around with "modern" lobe profile camshafts designed to build cylinder pressure and make power early in the rpms range.

Compression can be your friend, as it allows for a much larger camshaft to be used while offsetting some of the negatives associated with a lot of overlap and seat to seat timing.

To this day, I do not understand why folks continue to stay below the proverbial "brick wall" of 9.5 to 1 SCR, then throw tiny little cams in these engines to salvage decent idle and low speed power? I go the other direction with my builds, lots of compression larger well chosen camshafts on wide LSA's, then reap the benefits from good flowing heads, broad power curves, and vehicle set up to use this sort of power.......Cliff

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Old 09-15-2010, 09:02 AM
Nicks67GTO Nicks67GTO is offline
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Quote:
Originally Posted by Cliff R View Post
Some of us base our "opinions" on FACTS, by actually doing things, others on information they come up with reading stuff on Websites.

The cam chosen is a key player here.

My last 455 used the same 6X-4 heads, 9.98 to 1 compression, and ran for years on 89 octane, or any other pump gas I wanted to put in it. It also made great power, dyno'd a 455.4hp and pushed my car to 12.0's at 112mph in full street trim.

My car wasn't as "refined" at that time in the suspension or exhaust as it is now, or we'd have easily posted some 11 second timeslips with it.

Anyhow, choose the cam carefully. Avoid lobes with short seat timing events, early intake valve closing points, and tight LSA's.

The best cam out there would be the no longer available Wolverine 5059 cam. A real RAIV cam, or Crower 60919 is a very good choice. I've seen a few other recent offerings that look good as well. Ace has a flat cam that's not too far off the old 5059 grind that looks pretty attractive, if you are looking at flat hydraulic grinds?

Quench distance is another player, shoot for .035", give or take .about .005".

Not sure if it helps, but I polish the tops of my pistons and work the chambers some as well, by removing any sharp edges, smooth things out as much as possible, etc.

I've seen folks get into PLENTY of trouble with running hot/overheating/detonation at lower compression ratios pissing around with "modern" lobe profile camshafts designed to build cylinder pressure and make power early in the rpms range.

Compression can be your friend, as it allows for a much larger camshaft to be used while offsetting some of the negatives associated with a lot of overlap and seat to seat timing.

To this day, I do not understand why folks continue to stay below the proverbial "brick wall" of 9.5 to 1 SCR, then throw tiny little cams in these engines to salvage decent idle and low speed power? I go the other direction with my builds, lots of compression larger well chosen camshafts on wide LSA's, then reap the benefits from good flowing heads, broad power curves, and vehicle set up to use this sort of power.......Cliff
Cliff. Thanks for your post. If i do build a 4.25" stroke engine i would definately throw some cam at it. I doubt you could kill the low end tq of that kind of engine with a little extra cam.

My last car was a Nova that ran 11.1:1 compression on whatever gas i wanted. It was a 350" small block chevy with brodix racerite 200's and a 258/264@.050 .562/.562 lift on a 108. It was a solid FT erson grind. I ran the hell out of that car for 9 years and still have the engine sitting in my garage. Now it never saw temps above 175 and i allways had a good ignition on it. It also had the CNC profile chambers in it wich im sure helped greatly

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Old 09-15-2010, 12:28 PM
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I'm at 474 ci, 95cc's, slightly thicker gasket and a 7 cc valve dish...I "calculated" out to 9.6. I always run 91 or 93 octane 10% ethanol midwest QT gas. Never tried 87 or 89. 32 degrees of timing cuz it doesn't make any more power giving it more......never heard it ping even at part throttle with a bunch of vaccuum advance. You might be ok with the right cam.

Same heads but on old shortblock, 462, KB non-dish piston, UD 280 288 hyd cam......no ping on 93/91 gas.

You're probably fine, but keep attention to the details as you build it.

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Old 09-15-2010, 09:22 PM
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Silly me,,,I thought the OP said this was supposed to be a 95% street car???

Starting to sound much more like it's a 50/50 street/strip car now.

That's what I get for reading & trusting the original post I guess?

Never said a fella could'nt run more CR with iron heads either,I just said it gets a bit riskier as you do so.

Pardon me for being a bit conservative on that deal.

If that .5 point of CR is that important to any of ya'll,and ya' like taking those sorta risks,by all means be my guest,it's not like it's my engine that's gonna take the hit if it does'nt work out,so WTF do I care about that anyways???

And there are no "brick walls" AFAIK,,,only "brick heads" LOL...

I guess according to some folks POV on this topic,anyone & everyone out there that's using less than 9.75:1 to 10.0:1 in their "street" cars,must mean they're complete morons or something of that sort?

WOW is all I can say.

And FYI I never said anything about cams here either...

That was purely intentional too.

As I knew precisely who would be posting on this thread even before I posted my comments here,and I knew exactly what they were going to say too,glad to see I was'nt disappointed either.

Hell,ask me,we dont even know enough about what the rest of the combo is supposed to be like,to even begin make any sorta cam suggestions.

All we know is it's a manual trans car with a 468 cid engine...

Whatever...

If all that is wanted here is "one size fits all" or "cookie cutter" approach to follow blindly,and ya'll only respect folks who's first natural instinct is to ridicule & discredit others for having a mind of their own,well be my guest,that's for ya'll to figure out.

But guess what,your not gonna get any of that dreck from me.

I encourage people to think for themselves and to follow their instincts and learn a thing or two for themselves,instead of just taking the easy route and copying from others verbatim and learning next to nothing of any real value,except how to copy from others.

I guess having respect for others POV and listening/learning to/from a broad range of opinions are over-rated concepts anyways.

Once again,this has been a hoot!!!

Good luck.



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Old 09-15-2010, 10:57 PM
Nicks67GTO Nicks67GTO is offline
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Originally Posted by screamingchief View Post
Silly me,,,I thought the OP said this was supposed to be a 95% street car???

Starting to sound much more like it's a 50/50 street/strip car now.

That's what I get for reading & trusting the original post I guess?

Never said a fella could'nt run more CR with iron heads either,I just said it gets a bit riskier as you do so.

Pardon me for being a bit conservative on that deal.

If that .5 point of CR is that important to any of ya'll,and ya' like taking those sorta risks,by all means be my guest,it's not like it's my engine that's gonna take the hit if it does'nt work out,so WTF do I care about that anyways???

And there are no "brick walls" AFAIK,,,only "brick heads" LOL...

I guess according to some folks POV on this topic,anyone & everyone out there that's using less than 9.75:1 to 10.0:1 in their "street" cars,must mean they're complete morons or something of that sort?

WOW is all I can say.

And FYI I never said anything about cams here either...

That was purely intentional too.

As I knew precisely who would be posting on this thread even before I posted my comments here,and I knew exactly what they were going to say too,glad to see I was'nt disappointed either.

Hell,ask me,we dont even know enough about what the rest of the combo is supposed to be like,to even begin make any sorta cam suggestions.

All we know is it's a manual trans car with a 468 cid engine...

Whatever...

If all that is wanted here is "one size fits all" or "cookie cutter" approach to follow blindly,and ya'll only respect folks who's first natural instinct is to ridicule & discredit others for having a mind of their own,well be my guest,that's for ya'll to figure out.

But guess what,your not gonna get any of that dreck from me.

I encourage people to think for themselves and to follow their instincts and learn a thing or two for themselves,instead of just taking the easy route and copying from others verbatim and learning next to nothing of any real value,except how to copy from others.

I guess having respect for others POV and listening/learning to/from a broad range of opinions are over-rated concepts anyways.

Once again,this has been a hoot!!!

Good luck.



Bret P.
Bret. Ive been throwing hypothetical engine scenarios out because i dont know exactly what im going to build. I don't understand Pontiacs. I don't get it. They are a completely different animal from what im used to.

I want a very streetable engine that will crack 11 second timeslips but no faster than 11.50. I will not cage my GTO. I want it to idle nice, and drive anywhere on pump gas and be lots of fun. I also dont want what ever i build to tear my 5 speed to shreds in 5 minutes. This also has to be done on a reasonable budget. I know its asking a lot but i think its do-able

The parts i have laying around that i plan to use are the following

-67' 400 2 bolt block
-RPM intake
-750 mighty demon
-1 3/4" super comps
-3" x pipe and ultraflo's

I also have some 2262's and a 3.75" N crank. If i could do this with 400 cubic inches and my 5 speed, that would be great but the way it sounds, a 400 is hard to get enough power out of to run 11's in a GTO and keep it street friendly. My initial plan was to go this route. 400ci, 290cfm Kauffman heads, 10.5:1 compression with a 236/244@.050, .550/.550 lift solid FT cam on a 110 ls {made up cam specs}. I figured that would get me around 500hp @ around 6000 RPM, 500tq around 4000 rpm with a fairly flat curve. I figured it would idle around 850rpm and run hard. From everything ive gathered here i was wrong.

My last car was good for high 11's@ 116 mph out of 350 inches with a 5 speed. I do not want to dissappoint myself and sell myself short on what ever i build.

Im wide open to suggestions and expierence.

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Old 09-16-2010, 12:12 AM
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Nah,it's cool,I was just being more than slightly sarcastic (and just a bit cynical to boot),as both those things are well within my nature.

Cliff & I do this sorta thing from time to time,I dont take it seriously,doubt he does either.

Look,the compression ratio thing is'nt a deal breaker,that was just me throwing out a potential option to consider,as it seemed you were being more than a little hesitant to pull the trigger on the 6X's due to the stated CR you mentioned.

I figured the KB/Icon forgings might be just enough to help ease your fears a bit.

See I'm not rabid about things like CR,I may state my general thoughts/opinions,but I dont feel any subject is as "set in stone" as some others seem to feel they are.

Quote:
Originally Posted by Nicks67GTO
My initial plan was to go this route. 400ci, 290cfm Kauffman heads, 10.5:1 compression with a 236/244@.050, .550/.550 lift solid FT cam on a 110 ls {made up cam specs}. I figured that would get me around 500hp @ around 6000 RPM, 500tq around 4000 rpm with a fairly flat curve. I figured it would idle around 850rpm and run hard. From everything ive gathered here i was wrong.
Yeah,first thing first that kinda solid cam would be waaayyy too small for that sorta deal.

It would take a solid cam up closer to 245° to 250° intake and 250° to 255° exhaust duration to have a chance in hell of making 500 hp from 400 cid engine like that.

And that's gonna have a fairly lumpy idle likely too.

That 400 cid combo would'nt make as much torque as the big inch 468 combo will,but run anything hard enough and it can tear up the drivetrain parts no matter what engine is in front of the given driveline.

Honestly,those 6X-4 heads are a fairly safe bet if the price is right,and if your remotely concerned about the CR deal,that's easy enough to fix if you really want to,see silly me that's why I asked the questions I did (is it already built/or just being planned),instead of just dictating some sorta mandatory manifesto for all to follow on CR for street cars.

The other thing is cams,ahh yes,cams,well the problem there is one can easily think they're getting one thing,when in fact they're getting something completely different,so when I hear terms like "throwing cam at it" I get more than a bit leary of where that talk is gonna take a fella.

It takes a huge change in IC event timing to make the sorta difference that rates the "best" to "worst" choices on a combo like this.

Typically your talking about a range of like 15° to 20° of intake closing difference.

That's a LOT.

An 041/RAIV style hydraulic is gonna close the intake @ like 81° ABDC.
A cam like the SD ol' faithful is gonna close the intake @ like 72° ABDC.
A cam like the Crower #60243 is gonna close the intake @ like 70° ABDC.
And a cam like the XE274 is gonna close the intake @ like 63° ABDC.

All are pretty close @ .050",but they're worlds apart on the actual seat/advertised intake closing event timing.

But unless you really understand cams,and you dont watch the actual valve event timing,it's easy to lose sight of all that.

And me personally,I dont like to use the cams to "crutch" any compression ratio choices,that is not unless there is simply no other possibly choices/options to address the compression ratio situation itself.

Not to "bleed off" high compression.
Nor to "pump up" low compression.

Pick them both wisely,and you should'nt ever get into trouble.

If I were gonna look for solid flat tappet cams for something like this,I'd probably look at the Crower #60311 solid (IC 74° ABDC),and as a side note that solid cam is actually very comparable to the SD racing ol' faithful HR cam if one looks at the actual valve events and such.

Of course the solid FT cam would require 1.65 rockers to match the lift of the HR cam with 1.5 rockers,but other than that they are a dead heat in most all respects.

I'd bet $$$ those two cams dyno'd in the same engine would be within 10-15 hp of one another.

And I could'nt tell you which one would be the winner either.

So there is more than one way to skin that cat as well.

Me,I see this sorta thing as a infinte number of possibilities.

While others seem to choose to see but a few of those.

Which is fine really,different strokes for different folks.

(pardon the pun,,,yeah I know that was rrreeeaaalllyyy bad...)



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Old 09-16-2010, 06:17 AM
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"Cliff & I do this sorta thing from time to time,I dont take it seriously,doubt he does either."

Bothers me not is the least. I think most folks have figured out by now that I do this for a living, and my car runs under the legal roll bar rule on 89 octane piss-water gas with 11 to 1 compression, in full street trim, full/quiete exhaust system, factory intake manifold, factory Q-jet, stock HEI distributor, and using tiny little DOT tires. No T-II or Victor intake, Dominator, big HP Holley, 2" headers or any other "special" components typically associated with cars this fast.

We campain another car out of my shop that uses iron heads and even more compression, and it's daily driven and needs a roll bar as well. I put it together to show folks you don't need aluminum heads to run nearly into the 10's with near stock drivetrain components.

You can give all the advice you want, but I'd listen closer to someone who's actually doing it, than to someone who hasn't had a car that moves in at least 10 years....FWIW.....Cliff

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Old 09-16-2010, 11:33 AM
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Cmon Cliff, why you always gotta bust out the same old chest banging routine.... I wanna hear more about this iron head pump gas car that runs "close" to 10's with "near stock" drivetrain componenets and is "daily driven". That sounds like a recipe for broken 10 bolts, u joints and driveshafts, any car that runs under 11.50's is gonna need some drivetrain beefing up, so please don't lead us astray with veiled statements like "near stock drivetrain components"......I know what your idea of "daily driven" is....on and off the trailer once a week.....LOL!!! Now I'm busting out the sledgehammer!

I have been driving my "racecar" for the last 4 weeks now, as the real "daily driver" has been in the shop with multiple issues. It may not even come back!! So If I may boast a little here too...I have driven my GTO to the repair shop, to the grocery store, to the gig, to work, to my girlfriends house, to the hardware store, I loaded mulch in it, hay for the yard, 100watt marshalls and 4x12 cabinets every weekend, and I put gas in it. Like every 3 days $45 worth of pump gas 91-93 octane and burn through it, at part throttle on the hwy around 2200, stomp on it sometimes onramp, torrential rain, 90+ degree heat........I'm still driving it everyday and it's fine! I could drive it to the track, change tires and run some 11.70's at 117mph if I wanted to, jump right back on the hwy and drive it for another 4 weeks. Never open the hood.

Those 6X-4's sound like a great deal for a 400block stroker kit engine. I would not hesitate to run them just because the comp might end up around 9.8 to 1. You could try and open the chambers some unless they have already been reworked. Butler has a gasket that compresses at .042. You could bleed off some with the cam, lots of ways to make them work. Sure beats the heck out of $2000 plus for some aluminum heads.

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Old 09-16-2010, 12:53 PM
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because this is in a street forum im going to ask a question of Cliff and any other pro engine builder.Would you build a engine with iron heads and more than 9.5 CR AND gurantee it for daily street driving?Not knowing how hot the weather will be,quality of gas to be put in it etc etc.Will the car be sitting in 100 degree traffic etc.Tom

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Old 09-16-2010, 01:03 PM
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Heh-heh! You guys are funny!

Stickboy - welcome to my world! And a lot of the guys at the local 1/8 track joke that most of the cars there don't have half the engine I have in the daily driver!

My last iron head engine, 400, 30 over, believe they were #16 heads, was right around 9.98 static as I recall. I ran a few different cams in it, and for me, it was walking the line of detonation. Granted, I may not have the knowledge many here have regarding cam selection, but have done enough to know what works for me (over the last 25 years). That 400 would ping if it was hot outside and being in traffic, sensitive to the gas I ran from station to station, and had to be in perfect tune the whole time. That engine, .5 CR would have probably made all the difference in the world, and doubt I would have given up much either. I know if I would have gone to a larger cam it would have made things better, but it's a power brake & A/C car, something I wasn't going to give up. That is probably a real-life scenario you'd be most likely to hear through the 'general' ranks of Pontiac guys I would think, take it for what it's worth.

.

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Old 09-16-2010, 02:10 PM
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"Cmon Cliff, why you always gotta bust out the same old chest banging routine...."

Interesting, I didn't see anyone yanking your chain, and didn't see you start a post with a big disclaimer before we had to read a page and a half of vague information barely even related to the original thread right to start with.

I think SC and I can throw some mud in each others direction without any assistance, but thanks anyhow.

Having SUCCESSFULLY campained three 10 to 1 or higher CR 455 engines that effectively managed 89 octane fuel with zero issues anyplace, I just figured I could share some of those experiences to help a fella out who seeking some modern, up to date info on the subject.

Each time I've upgraded my engine combo, we've also increased the static compression ratio. We went from 9.98, to 10.48, to 10.99, and still use whatever octane fuel we feel like topping it off with. Each time we have been rewarded with smooth idle qualities, and no loss anyplace of off idle or low end power, even though we kicked the cams specs up some. (there is a hidden message in that statement for those who look close enough) It appears that the increased CR is complimented nicely by a few more degrees of camshaft, or visa versa, depending on how you are looking at it.

I drive this car DAILY, it is only trailered to distant tracks to save the DOT's, no other reason. I always drive to our local track, lower the tire pressure, and start making runs. Even in hot/humid mid summer weather, no need to cool it down before, or between runs. I've even got involved with the Friday night box/no box Gamblers Race, and taken home all the bananna's, then stopped by my favorite watering hole on the way home to spend some of the winnings on adult beverages. My suspension system is a close to stock appearing as you will find. Not single traction bar, or anything else being employed in that area.

We are really in the infancy stages with our new 455 set-up, so not much information to share currently. We have some suspsension "issues" to overcome, as it really hits the tires hard. We have managed some improvements in that area, going from 1.88 or so 60' times down to 1.70, but it's still spinning HARD on the launch, so there is a lot more ET awaiting for us when we start hooking it up. When we get that deal all ironed out, I'll put up ALL the specs on it. For now, we're running mid 11's at over 117mph spinning hard on the launch. The compression on that engine is really high, so we are "weaning" it onto pump gas, not starting it out on pump gas so we can put a few pistons in the oil pan while we dial things in. As mentioned, we wanted to do an iron headed "basic" engine, with some really good heads, and a lot of compression, to see just how much the iron vs aluminum deal really plays a role in all of this?.....Cliff

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Old 09-16-2010, 02:12 PM
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here is where I have a problem and maybe im stupid.We put larger cams in our engines to make more HP?I know they bleed off comp at low RPMs BUT they MUST add more in the mid to upper ranges SOOOoooo I guess if you drive a car with a big cam at idle it wont be detontation sen. BUT I seem to drive my cars in the mid RPM ranges where I might have a problem?Tom

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Old 09-16-2010, 02:19 PM
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That sounds like quite a setup you're working on Cliff. I'll be waiting for the results and the specs.

I was initially concerned about my 406 but after discussions here with you and others I don't think I'll have any problems, if I can zero in on the tune. I'm hoping my experience and some good advice received here will aid me in that endeavour. And I'm only at about 9.8:1 with the cam in my signature.

Stewart

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1976 TA, nose converted to 1970 style, 406, ported #13 Heads, '70 iron intake without crossovers, Q-Jet - Cliff style, RARE OS manifolds, Pypes duals w/crossflow, UD 230/238 custom HR 4/7 swap cam with solid roller lifters , Hydro-Boost 4-wheel discs, 4 Speed, 3.23 posi.

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Old 09-16-2010, 02:38 PM
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Stewart,
We are all looking forward to your build running down the street again, hope we all live long enough...LOL

A good friend of mine has a 22 yr. old son that wants to get a project done RIGHT NOW, isn't this the "Now" generation???....LOL..

Only one problem, that stupid money tree, ain't produce'n worth a darn....He wants every thing just so, all the megabuck parts....trying to con dad into spending $$$ on it...the Dad's job right now is barely hanging on @ 3 days a week...Jr. is learning about the real world, quickly...

OH CRAP, I almost forgot, Go Cliff, Go!!!.........LOL

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Old 09-16-2010, 03:28 PM
Steve C. Steve C. is offline
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Some here might remember George Hanks who went by "Witch Doctor" years ago over on the Classical Pontiac board. He has been associated with Pontiacs for over 45 years and I, along with many others, have considered him a genius when it comes to both Pontiac history and specificly his extreme knowledge of combustion effeciancy regarding the factory Pontiac chamber designs and detonation issues. He has written technical papers on the subject. Although George no longer goes onto the internet we talk on the phone frequently and I brought up this very subject yesterday. He again explained why, but in no way could I repeat his tech material presented to me so I'll leave it with his point of view..... for the most part anyone attemting to run over 9.5 compression on a factory iron head in a true street driven car under most circumstances is "NUTS" ! And do note, he is not saying it can't be done. And he is not talking about a vehicle that puts on a big dog and pony show with a few laps around town or short cruise.


Statement from Cliff... "We campain another car out of my shop that uses iron heads and even more compression, and it's daily driven and needs a roll bar as well. I put it together to show folks you don't need aluminum heads to run nearly into the 10's with near stock drivetrain components."

Cliff, who's car is this ? Curious if your speaking about Ray Klemm's '69 Firebird recently featured in HPP Pavement Pounders. At that time he was struggling with 11.80 runs and using 110-octane fuel with his '68 #62 iron heads ported by Dave Bischop.

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Old 09-16-2010, 03:43 PM
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OK Cliff, I'll stay out of your mudfight with SC, maybe we can have a little fray of our own? Check this out, posted 5/1/2010

"In any case, I make about 2-3 local outings a year requiring a 15 mile round trip on the tires. No need for a floor jack, 4 way lug wrench and an extra set of tires on board.

For all other outings I trailer the car. At most the car will see about 100 miles a year street driving. This opens up my choices for tires, just looking for something that hooks good and lasts a bit longer than the MT ET Drag Radials."

I guess you're definition of "daily driven" is different than mine.

Probably different than a lot of guys here on the "STREET" forum.

So let us know how that 11:1 iron head motor likes the 89 octane pump gas (when you get around to putting some pump gas in it and driving it "daily") and I will eat my words.

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Old 09-16-2010, 03:56 PM
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Quote:
Originally Posted by 77 TRASHCAN View Post
Stewart,
We are all looking forward to your build running down the street again, hope we all live long enough...LOL

Only one problem, that stupid money tree, ain't produce'n worth a darn....He wants every thing just so, all the megabuck parts....trying to con dad into spending $$$ on it...the Dad's job right now is barely hanging on @ 3 days a week...Jr. is learning about the real world, quickly...
Hey now! What's the rush? This is a retirement project and I'm not officially retired yet.

Actually I'd hoped to have it back together and running by the end of the month but I got held up because some parts took longer to ship than I figured and I discovered a need for a couple of more new tools. Plus I've run into some other vehicular problems that are taking my time.

I understand the problems with the money tree as well. It must be global warming. Mine stopped producing a while back and I'm almost out of the last pickings. Hope it starts producing again.

Stewart

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1976 TA, nose converted to 1970 style, 406, ported #13 Heads, '70 iron intake without crossovers, Q-Jet - Cliff style, RARE OS manifolds, Pypes duals w/crossflow, UD 230/238 custom HR 4/7 swap cam with solid roller lifters , Hydro-Boost 4-wheel discs, 4 Speed, 3.23 posi.

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  #20  
Old 09-16-2010, 04:38 PM
BruceWilkie BruceWilkie is offline
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Quote:
Originally Posted by tom s View Post
here is where I have a problem and maybe im stupid.We put larger cams in our engines to make more HP?I know they bleed off comp at low RPMs BUT they MUST add more in the mid to upper ranges SOOOoooo I guess if you drive a car with a big cam at idle it wont be detontation sen. BUT I seem to drive my cars in the mid RPM ranges where I might have a problem?Tom
BINGO! Dynamic compression increases with rpm to a point then pretty much levels. There is also a big difference between preignition and detonation. Preignition usually destroys with little to too late a warning. Preignition can be caused by cummulative heat build up and usually occurs damage somewhere around bdc. The mix ignites as the engine is trying to compress it. Sustained detonation can lead to preignition from heat buildup but its seldom the primary cause.
Knock or ping that you hear is detonation. An engine can sustain quite a bit of it. However the duration and intensity affect how long before you kill bearings and eat rings. Preignition WILL burn holes thru your pistons if your lucky and if they dont blow thru first, something else catastrophic will likely occur. (I've burned down the same motor and cylinders 3 times in a 1 month period all 3 were preignition and the problem appeared at seemingly random intervals. Turned out to be compression related though I actually didnt lower the compression ratio till I figured out I had changed dynamic compression ratio. Engine had NOT ONE sign of ping just sudden rapid failure when preignition occurred)

Some more about compression ratio, fuel capability, and ignition needs. Usually "ping" tells us we have spark occuring too soon BTDC. We fire the spark btdc so that the cylinder pressure rise can reach peak cylinder pressure ATDC. Typically PCP needs to occur @15 deg atdc(iirc) or thereabout to reach optimum rod/crank angles for best power. If you are running excess cylinder pressure for the fuel being used it will explode too fast(octane partially controls the speed of this flame travel. Heat of compression also factors into how fast this burn occurs.)
A little too early we hear a light ping of detonation and little else occurs unless its sustained and intense. As we retard spark to prevent the ping we LOSE HP due to the loss of mechanical advantage of rod, piston, and crank positions. It usually ends up excees temp not used to move the piston ends up transfering more heat to your water jackets instead. Often turning your car into a highway boiler at normal road loads when it never did it before you "upped the compression and made compromises to run a less than adequate fuel octane".

I'm in the middle of rebuilding my main pc and there was a related link I'd like to share on there. Hope I havent wiped it.
So I'll summarize that its best to work with known "safe" compression ratios and going beyond them is likely going to require a compromise that overall could = zero net gain or cost you needlessly later.

If your motor is not built yet you can build it with whatever head you chose and tailor the compression to best meet the needs of type head you have and fuel you plan to use. Its good to have safety margin to accomodate the possible bad load of fuel you may get when a delivery truck accidentally starts to pump the wrong fuel in the wrong tank etc.

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