[screamingchief]

Originally Posted by pmd400

Just a question from a complete novice. Assuming we have a 455 with iron heads and close to 9.5:1 compression. Which of the following intake lobes would be considered larger?
Xe274-274 advertised, 230 at .050, 0.488 lift
Crane- 288 advertised, 226 at .050, 0.458 lift
I would have assumed the xe274. But does the crane make up for the lose of lift and .050 duration with the extra seat timing?

"Larger" is a relative term.

The one with more advertised duration is typically considered larger due to how that is gonna skew the total overlap numbers higher.

But put one on a tight LSA/early ICL and the other on a wide LSA/later ICL and they can "act" much differently than the specs might suggest,so honestly,it's the sum of the whole cam that determines which is "larger" and which is "smaller",and it's not always that easy to tell which is which,that's largely where problems with cam selection stem from.

And FYI: Any lobe with more lobe lift is going to tend to have slightly more .050" duration than another "similar" advertised duration lobe with less lobe lift,that's just a quirk of lobe design.

It's largely the same dynamic that higher ratio rocker arms exploit.

Originally Posted by llwta76

So ( correct me if I'm wrong) a lot of overlap sends a lot of fuel in to the combustion chamber not only creating a stinky smell( and burning eyes) but washing the cylinder walls (washing oil away and accelerating crosshatch wear) ?

IMO no.

Being too rich puts too much fuel into the combustion chambers,it's the root cause,not the effect of a copious amount of overlap.

Overlap can indeed let some portion of the existing intake charge out the pipes due to over-scavenging,but that typically only happens @ higher RPM when the charge flow is high enough for that condition to rear it's ugly head,that inturn actually creates a lean condition as a good portion of the intake charge is going right out the exhaust pipes and not going towards proper combustion like it should be.

This is often evidenced by the color of the exhaust ports (bone white coating in exhaust ports).

What typically happens with large overlap cams at lower RPM is actually an intake charge dilution situation,where-in the slow moving incoming intake charge gets diluted by the residual exhaust gasses backing up into the intake ports in a defacto "EGR effect" which inturn displaces some amount of said intake charge actually creating a (more or less) lean condition.

This is often evidenced by the color of the intake ports (black sticky goo in intake ports).

And FYI: one can have one/the other/both happening in the same engine.

Originally Posted by tpssonic

That being said, you can also have "stinky" exhaust with a LEAN A/F mixture.

Same is true for a four stroke engine,see ^^^^ above.

HTH

Bret P.

[Dave Bisschop]

Originally Posted by GOAT WHORE

One more shout out to Dave for taking the time to post here. Must have been the visit to Portland that got him back on track. 😁

Probably I had a great time Pontiyaking!!! We've had a rough few years after the landslide and the down turn in the economy but things are going a lot better now so I'm looking forward to getting out and doing some more racing and attending more events again. Just need to clone myself a few times!!!!LOL being a one man show has its challenges especially with the demand we're seeing this year!! (not complaining)

I appreciate all the support we get and I will try and make more time to post on the board when I have a few minutes, but with my overflowing plate its not easy to find the time.

[Cliff R]

Here are the dyno runs from the two cams. I condensed them to one page for easier comparison.

What I left out of all of this is that the dyno shop that built the engine tried to crank up the timing and swapped carbs around in order to try to make acceptable power.

They "pinged" the engine on the dyno after this pull was made and ended up taking out the rod bearings and bent the crank .020"!

The pulls shown were the best pulls made in each configuration. The intake manifold used for the testing was the Edelbrock RPM intake. During the first session they thought at first the problems were due to the custom built Q-jet carburetor that was supplied for the engine, so they side-lined the carb and made all pulls with their Holley 830cfm "dyno carb".

The q-jet wasn't built here, but it ended up getting sent here for us to check it out and run it on one of our engines to make sure it was fine before putting it back in service, which we did.

The peak numbers from the two dyno runs really don't tell the whole story here. The "tiny" HR cam was WAY too good at cylinder filling with the 250cfm heads, even though the compression ratio was under the often recommended threshold of 9.5 to 1. I've seen this before with this exact same engine/cam combo. That cam is WAY too good at cylinder filling early in the rpm range, and makes a low compression engine want a LOT more octane to be happy.

This engine was professionally built with very good flowing heads. Notice how it really shined when they installed a cam that was more suited to what they were doing. What one really needs to look at instead of "peak" numbers, is how much power (torque) the engine enjoyed with the bigger cam across the upper mid-range and top end. It also idled better and made a BUTT LOAD more average power.

This type of engine is very good at moving these heavy cars around without a lot of gearing or converter, and there is no need to run it WAY up in the rpm range to make good track runs. You can shift down around 5000 rpms and still run nearly as well as shifting clear up at 5900rpm's where peak power was made at, just look at how much torque it's making in the upper mid-range. This engine wouldn't care where you shifted at, it would continue to pull like a locomotive everyplace.......Cliff

[tpssonic]

Thanks for posting the dyno sheet, Cliff and for originating this particular post- much appreciated. These two were the exact cams that were "in the cards for me": the engine came with the XR276HR and I could have run it with that. Dave and I came up with the OF on a 114 and GT (blueghoast- thanks Gary!) made the rest of the parts sing in harmony. it is worth repeating that I am so thankful for the people and knowledge on this forum as without them, I would be leaving a LOT of torque/hp on that table and would have probably been chasing the deto, carburetion, stinky exhaust, etc. issues until such time I got educated. Kudos to the Ponti-sages.

[1969GTO]

OK, stupid question here.........
As for the "Stinky Exhaust" what are you saying?
Is it some thing that can be measured with an A/F meter?
If those numbers are correct, then all is good?
I am running a 400/462, stump puller,# 16 heads ported, cast intake as per Ruggles/SDPerformance, RAMAIR Restorations manifolds, 1.6 roller rockers and the DEMON 750.

[tpssonic]

There are no stupid questions,

"As for the "Stinky Exhaust" what are you saying?
Is it some thing that can be measured with an A/F meter?"

I assume (bad thing sometimes) you are talking about at idle. The answer I have is "possibly"- to a point. You can have a decent A/F mixture, but if you have a lot of overlap (both intake and exhaust valves open due to valve timing events) the air/fuel charge can go in the intake and straight out the exhaust (short-circuit). That being said, you can also have "stinky" exhaust with a LEAN A/F mixture. On the dyno when testing two-stroke engines, I know when the mixture at WOT is "right" as verified by highest engine output, plug reading and piston wash reading; there is an acrid smell that burns your eyes that you only get when the engine is "spot on" at full wail. Switching gears here (pun intended) with swimming pools, the reason a pool "smells like chlorine” isn’t because there’s too much chlorine in it; it’s the result of chlorine mixing with various nitrogen and ammonia compounds and creating chloramines. In effect most all of the free active chlorine (available for disinfecting) is bound up; so in actuality you have TOO LITTLE chlorine.

[76 poncho]

^^^^^ x1

[llwta76]

Originally Posted by tpssonic

There are no stupid questions,

"As for the "Stinky Exhaust" what are you saying?
Is it some thing that can be measured with an A/F meter?"

I assume (bad thing sometimes) you are talking about at idle. The answer I have is "possibly"- to a point. You can have a decent A/F mixture, but if you have a lot of overlap (both intake and exhaust valves open due to valve timing events) the air/fuel charge can go in the intake and straight out the exhaust (short-circuit). That being said, you can also have "stinky" exhaust with a LEAN A/F mixture. On the dyno when testing two-stroke engines, I know when the mixture at WOT is "right" as verified by highest engine output, plug reading and piston wash reading; there is an acrid smell that burns your eyes that you only get when the engine is "spot on" at full wail. Switching gears here (pun intended) with swimming pools, the reason a pool "smells like chlorine” isn’t because there’s too much chlorine in it; it’s the result of chlorine mixing with various nitrogen and ammonia compounds and creating chloramines. In effect most all of the free active chlorine (available for disinfecting) is bound up; so in actuality you have TOO LITTLE chlorine.

So ( correct me if I'm wrong) a lot of overlap sends a lot of fuel in to the combustion chamber not only creating a stinky smell( and burning eyes) but washing the cylinder walls (washing oil away and accelerating crosshatch wear) ?

[1969GTO]

I know it's nice to be able to test this and that, but for us on the slim $$$$, we have to trust those that have done all the testing and go with what they recommend and hope it all works out, and for me I think it has by using the combination I listed earlier in this post by talking to the pros [Butler,Ruggles, SDPERFORMANCE ,Spotts Performance].

[tom s]

As said,my 366 V engine with the single plane intake and a lot of cam for a little CI and lazy ports showed WAY lean on the AFR gauge but had real heavy gas smell at idle.When I went to the dual plane it showed a little richer with no carb change and had less gas smell.Tom

[PAUL K]

Originally Posted by tom s

As said,my 366 V engine with the single plane intake and a lot of cam for a little CI and lazy ports showed WAY lean on the AFR gauge but had real heavy gas smell at idle.When I went to the dual plane it showed a little richer with no carb change and had less gas smell.Tom

Good post! Port design and size effects idle quality, throttle response, torque and horsepower. Keep the velocity high and the ports as small as possible to get the job done, this should be on the priority list before flow numbers.

Also carburetors equipped with an adjustable idle mixture screw at each barrel and screw in air bleeds will make it easier to dial in the air fuels at idle and help with the eye burning and gas smell .

[PAUL K]

I just watched the videos on YouTube and the one titled "1970 Firebird Formula runs mid 10 second quarter mile @ 128 mph in car view " is an excellent example of what can be accomplished when extra effort is applied to keep your car comfortable and you are not worried about adding a few extra pounds to keep your Pontiac a true "street car"!

I think this link will work:
https://youtu.be/9Zk4n3KAawU

[tpssonic]

Thanks Dave for the dyno numbers/specs and thank you SC for the clarification and tutelage. I am very grateful, guys. Race on!

[Cliff R]

Not sure how we got off on "stinky exhaust", but it is a by-product of incomplete combustion, or an overly rich or lean mixture.

Overlap has been mentioned several times. Overlap basically describes the amount of time in crankshaft degrees that both valves are open at the same time. This bleeds off cylinder pressure and lowers dynamic compression, and combustion efficiency at idle and low rpm's. It makes up the lost ground later on, but a lot of overlap can produce a pretty "rough" idle, and stinky exhaust as a by-product.

For he most part cams with tighter LSA's produce more "lope" at idle speed, which is from pulling the lobes together and increasing overlap, but the story doesn't simply end there. Smaller cams on tight LSA's also tend to close the intake pretty early, so you can get what we call "reversion" here. I see this a LOT with short seat timing cams on tight LSA's, especially in the longer stroke engines. They have what I call a "quirky" idle quality, for lack of better words to describe it. Sort of a combination of having a fair amount of overlap and having the events happened sooner in the cycle. When we observe these symptoms those engines NEVER make big power, as the cam is simply too small, too far advanced, and intake closing to early to ever have a fighting change to breath well at high rpm's.

For bigger cams we can yank them down on tight LSA's and still enjoy good power, and that "rumpity-rumpity" sound everyone loves. Pound for pound they don't typically outrun big cams on wider LSA's. It seems like the wider we go with LSA, the better the long strong engines respond to it. We still yank down the LSA when we go out beyond about 260 @ .050", but we've still seen some very good performing engines, and not just Pontiac's, use "big" cams on wide LSA's in street/strip and full race applications and make great power with them.

I think Dave eluded to why in several of his responses, as the reasons some combos work well is more about the total combination of parts, and not just the camshaft, although the camshaft does play a big role with these things.

I started this thread to basically educate those who are venturing into a pump gas 455 or stroker 400 build, and are looking to make good power on pump fuel, and run a moderate to high compression ratio as well. There are cams out there that just leave WAY too much power on the table, and they can get you into trouble quickly with octane requirements, even at lower compression ratios.

I've known about this for years, but just about every time I've mentioned it, someone quickly takes the thread off course and calls me the Comp XE "cam basher", then the whole thing turns to poop.

The dyno sheets tell the story of what's going on here, and expect even WORSE results if you have a similar build and are using the smaller XE262 and XE268 flat cams in them......Cliff

[Matt Meaney]

can anyone post a video of what these engines sound like at idle and maybe a drive away? so, you can hear how it's not revving to the moon before it moves. if you can, list all the particulars with it too. cam, idle rpm, static compression, timing, what exhaust, convertor, etc. the more info the better.

[PAUL K]

Originally Posted by Matt Meaney

can anyone post a video of what these engines sound like at idle and maybe a drive away? so, you can hear how it's not revving to the moon before it moves. if you can, list all the particulars with it too. cam, idle rpm, static compression, timing, what exhaust, convertor, etc. the more info the better.

If you want to click on the Facebook link on the bottom of this post and go to the video section, there are short idling videos of a RAIV Trans Am, my 80 T/A that uses a 259 duration cam with 108 LSA mentioned previously and my 74 red Firebird with a 275/283 108 LSA mentioned previously you.
Also there are several videos of them at the track but unfortunately the noise from the race cars drown out the sound of our cars in most of the videos. If you search on YouTube under "pkmusclemotors" there are a couple of good Go-Pro videos of my brothers 70 Firebird using a 455 with RAIV heads and mid 270 duration cam ground on a 106 LSA. The video that he races a 64 GTO has some pretty good sound from inside the car.

I just watched the videos on YouTube and the one titled "1970 Firebird Formula runs mid 10 second quarter mile @ 128 mph in car view " is an excellent example of what can be accomplished when extra effort is applied to keep your car comfortable and you are not worried about adding a few extra pounds to keep your Pontiac a true "street car"!

[ta man]

Originally Posted by Matt Meaney

can anyone post a video of what these engines sound like at idle and maybe a drive away? so, you can hear how it's not revving to the moon before it moves. if you can, list all the particulars with it too. cam, idle rpm, static compression, timing, what exhaust, convertor, etc. the more info the better.

I don't have a video of mine,its similar to Cliffs,mine has a steady strong idle,when I say it drives like a stock 301 Trans Am..believe it ,with the Continental Convertor you can put the car in reverse or drive and it will move..no revving up of the engine to get it going.

[Cliff R]

Here's as close as I can get, with a clip of my car at the track. Notice who smooth it idles, rpms barely change at all when it's put in gear.

https://www.youtube.com/watch?v=6zVdoLR-VzM

Timing is only set at 10 degrees, no want or need for any additional timing from the vacuum advance, although I use one to add about 10 degrees timing at cruise via ported vacuum.

In this clip the engine is actually "de-tuned" slightly, 100 lbs added to the trunk and short shifting at 5000rpms to stay roll bar legal and keep the track Officials happy.

The time slip below is 1/8th mile, in hot/humid weather, and shows the potential of the combination better than the video of the track run.

My combination is the very popular KRE heads by Dave at SD ported to around 295cfm, 455cid, and his "Old Faithful" camshaft. Mine is the 112LSA version, and the ICL is set at 109.5 degrees.

No "lope" at idle or "stinky" exhaust here, the engine is very efficient, and actually gets excellent fuel economy although I don't drive it long distances very often due to running DOT's on it that cost over $400 a set!.......Cliff

[firechickenman]

Great thread! A lot of god info here! Click the link in my sig for a video of mine. If you click on my name or pic below the video, I have several videos of it. In car and outside. Comp 290B6, 290/304 dur. 255/266 @ .050 106 LSA installed at 103 ICL.

[PAUL K]

Originally Posted by firechickenman

Great thread! A lot of god info here! Click the link in my sig for a video of mine. If you click on my name or pic below the video, I have several videos of it. In car and outside. Comp 290B6, 290/304 dur. 255/266 @ .050 106 LSA installed at 103 ICL.

You might want to look at post #73 . Maybe you can by-pass running deeper into the ten's and go straight to the low ten's.