[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. 😁

[Steve C.]

Overlap calculator:

http://www.wallaceracing.com/overlap-calc.php

And note the use of advertised duration, not .050" duration.

Calculating Overlap:

http://members.uia.net/pkelley2/Overlap.html

Note the comment at the bottom regarding the valve timing overlap ranges that are most likely to work correctly.


.

[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?

[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) ?

[Dave Bisschop]

Originally Posted by 72LuxuryLeMansLa.

Dave,

I know it is difficult to boil it down to generalities because each combo is specific, but is there a range for street overlap vs. street/strip vs. strip only that novices can use? For instance I told you I wanted to make in the area of 450hp with my daily driver 433(4"stroke .030" over 400 block) with iron heads and intake, also using RARE manifolds instead of headers and you said the Stump Puller was the cam. In my calculator it has 63.5° of overlap. Would 75° of overlap be way too much? Is ther a sweet spot for manifolds vs. headers? What does it take to figure out how much overlap?

Thanks much for spreading the wisdom!

Good question and while I'd love to tell you I have some magical formula that I use the reality is all my knowledge in this area has been from trial and error testing on the dyno. That being said using the Wallace calculator (Thanks Steve for posting the link) the old SP cam shows 64 deg, new one shows 61, OF on a 112 is 73 and the OF on a 114 is 69. I haven't done a manifold vs. header test with the new version of the SP, but I think it's safe to say it will work well with the RA manifolds since the old version the most we ever saw on the dyno back to back was 8hp less with the RARE GTO 2.45 manifolds vs. a Hooker SC 1 3/4" header. We had a 491 on the dyno a number of years ago with a set of our 300-305 KRE D ports, Performer RPM etc. with the OF on a 114, the engine made 567hp with the manifolds and 582hp with the headers, previously we'd seen a good 30hp spread comparing headers to manifolds in another engine we tested with the OF on a 112. So looking at the data I'd say when you start to go beyond 70 deg. overlap using the Wallace calculator the hp difference is going to get into the 20+ range quickly as the overlap increases. Under 65 deg. and the difference is more like under 10hp. Years ago we did a manifold vs. header test on a iron headed 9.5 to 1 467 with an Ultradyne flat tappet cam 263/271 @ .050 on a 112, the manifolds killed 45 hp at peak and 75hp at 6000rpm, using the .020" rated duration numbers the overlap calculates to 76 deg. I think this gives a general idea what to look for when deciding if a cam is a good choice to run with the RARE manifolds.

[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.

[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].

[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.

[72LuxuryLeMansLa.]

Originally Posted by Dave Bisschop

Good question and while I'd love to tell you I have some magical formula that I use the reality is all my knowledge in this area has been from trial and error testing on the dyno. That being said using the Wallace calculator (Thanks Steve for posting the link) the old SP cam shows 64 deg, new one shows 61, OF on a 112 is 73 and the OF on a 114 is 69. I haven't done a manifold vs. header test with the new version of the SP, but I think it's safe to say it will work well with the RA manifolds since the old version the most we ever saw on the dyno back to back was 8hp less with the RARE GTO 2.45 manifolds vs. a Hooker SC 1 3/4" header. We had a 491 on the dyno a number of years ago with a set of our 300-305 KRE D ports, Performer RPM etc. with the OF on a 114, the engine made 567hp with the manifolds and 582hp with the headers, previously we'd seen a good 30hp spread comparing headers to manifolds in another engine we tested with the OF on a 112. So looking at the data I'd say when you start to go beyond 70 deg. overlap using the Wallace calculator the hp difference is going to get into the 20+ range quickly as the overlap increases. Under 65 deg. and the difference is more like under 10hp. Years ago we did a manifold vs. header test on a iron headed 9.5 to 1 467 with an Ultradyne flat tappet cam 263/271 @ .050 on a 112, the manifolds killed 45 hp at peak and 75hp at 6000rpm, using the .020" rated duration numbers the overlap calculates to 76 deg. I think this gives a general idea what to look for when deciding if a cam is a good choice to run with the RARE manifolds.

Got it. Thanks Dave, great info for the board!

[Steve C.]

These might be of interest....

Reviewing Reversion

http://www.hotrod.com/how-to/engine/...ine-reversion/

http://www.hotrod.com/how-to/engine/...ake-reversion/

http://bestdamngarageintown.blogspot...reversion.html

.

[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

[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.

[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