[72LuxuryLeMansLa.]

Originally Posted by 70 Dream

I have to make my rebuild decisions soon. What I want is a stock rebuild for my 400 cid. We all know the stock 10.25 CR is too high for today's gas . . . . but if I go for say a 9.5 CR, will that be too high, even for 93 octane?

I am supposed to tell my engine builder what I want, but I am quite sure that I don't know what it is that I'm supposed to tell him.

I'm not even sure what questions I should be asking in this post. Do I want the highest CR I can get away with on pump gas? If yes, what is it? Do I pick a lower, safer CR that I won't have to worry about? If yes, what is it? How high is "too high?" And is there such a thing as going for a CR that's "too low?"

Next to cam selection (totally confusing), this is my most frustrating issue. I don't really care about performance as much as streetability and reliability.

Thanks for any and all opinions . . . . .

I'm certainly NOT an Experienced engine builder. but if you have some decent automotive knowledge, this article may help you as much as it did me to understand what steps to take to build an engine that will meet your goals.

This is written by Jim Hand:http://www.pontiacstreetperformance....mpression.html

[bobzdar]

Originally Posted by Cliff R

"What power does the raIV make with unported dport heads?"

It will make great power with unported "D" port heads, especially in a 455 engine.

We built and dyno'd one a few years ago with untouched 1973 # 46 heads. We did outfit the with 2.11/1.77 valves, but not sanding roll or grinder ever touched them, not even a port match.

The engine made over 440hp on the dyno and 530tq.

In a 400 engine, you simply need compression to effectively use the RAIV cam, and plenty of gearing and converter.

3.73's would be the absolute minimum gearing I'd want to see with that cam used in a 400, and at least 3000rpms stall speed, or stick shift. 3200-3400 stall would be even better.

It's not really about making more power over a 744 cam, which it will, it's about where in the rpm range it's going to make the power.....Cliff

So 440hp vs. the 425hp a 60916 made in a 400? So could be looking at ~15hp?

I really don't care where in the rpm range it happens, horsepower is horsepower. I'm running 10:1 compression with a 4 speed so if it gives me 15hp, It'll be worth the swap. I just haven't seen dyno results on unported dports with an 041 in a 400. Maybe those that complain about the cam in a 400 are afraid to rev it high enough to make use of it?

[mechanic17]

Bobzdar, you need pete mccarthy's article "Tweaking the 400" published in HPP many moons ago. Someone has linked to it on these forums somewhere. He was happy with the results and made over 400hp, as I recall, but then went on to install a more "modern" profile and make more power. Unported D-ports.

When younger, I really liked the experience of high-revving a motor, but that was before replacing several. Now the lower the power comes in, the better I like it.

[mechanic17]

Found this in a 6-year old thread:
"Pontiac guru Pete McCarthy did some comparisons on a 400 engine & the results were in HPP magazine April 92. He compared the RA IV cam with a slightly larger Comp Cam 236/244 @ 050, with 108 LSA. The RA IV was 231/240 @ 050 with 113.5 LSA. With the CC cam advanced to 104 degrees, it made 456 f/lb @ 4300 pk tq; aver tq 3500 to 4500 was 444 ft/lb; aver power 3500 to 4500 was 338hp. For the RA IV the corresponding figures are; 438 @ 4400;427 aver tq; aver power 326. The RA IV had slightly higher pk power @ 418 v 402, but lost out in the lower ranges.
Pete's comments on the RA IV cam: ".... the power curve generated by the IV cam is not particularly broad, but rather peaky. It packs a wallop from 4500 to 5800 rpm, but outside that range, it ius not much beter than the 068HO or 744 RA III cam. [ HPP Feb, 92 ]"

So there is a case where a "15 hp gain" (for the 041 cam) on the dyno would definitely be a case of reduced performance in the real world, unless the car was optimized in the narrow 4500-5800 rpm range--certainly NOT on the street.

Anyone know the grind # on Pete's Comp Cam? Remember, I believe these numbers were just with unported, 72cc d-ports--so approaching 10:1 SCR. He didn't mention detonation, as I recall. What kind of ETs could this engine see in a heavy car?

[bobzdar]

Originally Posted by mechanic17

Bobzdar, you need pete mccarthy's article "Tweaking the 400" published in HPP many moons ago. Someone has linked to it on these forums somewhere. He was happy with the results and made over 400hp, as I recall, but then went on to install a more "modern" profile and make more power. Unported D-ports.

When younger, I really liked the experience of high-revving a motor, but that was before replacing several. Now the lower the power comes in, the better I like it.

For my purposes (at least right now), I'm limited to factory cams and unported dports. I may be able to run aftermarket grinds if I decide to only run one sanctioning body, but would still be limited to hydraulic flat tappet and the unported dports. If that is the case, it opens it up to the crower 60916, 60919, 60243, comp xe274, summit 2802, Crane H-288, 294, 296 and probably a bunch more. Of all of those, the dyno numbers I've seen on stock dports are 425hp for the 60916 and 440hp for the 041 (albeit on a 455, but should be around the same on a 400 barring valvetrain instability) both from Cliff.

I'm limited to stock valve size (and length), rockers and pushrods but not valve springs - Another reason to stick with the factory cams at this point, though others won't have those limitations.

Still, I'd like to see what the most power somebody has made on a 400 with unported dports and pump gas. I think it's relevant to the thread. With the parts available these days, there's no reason to fear revving a pontiac. Even my stock bottom end 400 has held up to 6000rpm shift points, so with the good rods and pistons that are out there, there should be no issue. I'll have to search for that article.

I went and found part of the article here: http://forums.maxperformanceinc.com/...carthy+article

The 041 made 417hp, both of the aftermarket cams made less horsepower but more midrange. I actually commented in the thread - can't find the full article, though. Did they test the 744 and/or 068 as well?

[mechanic17]

I'm assuming the rules allow headers? If NOT, I'm pretty sure the wide factory LSAs are the only way to go anyway.

Every time I've "cammed up" an engine with a factory exhaust, I've felt like the exhaust manifolds were acting exactly like a restrictor plate (though I've no scientific data to prove it. ) Conversely, I've busted my butt to get headers/duals on cars with mild factory cams, and felt no improvement at all there either--though the noise will try to fool you.

I've not seen much testing on the 744 cam, which seems like a controversial piece (people who favor either the 068 or the 041 are dominant camps). Have always wondered about that one.

[bobzdar]

We must have posted at the same time . But, I'm road racing, so power from 4000rpm to 6000rpm is where I want it. I'll take the 17hp. If you're running a 4 speed, that rpm range (other than the launch) is where your car will operate when getting after it - street or anywhere else unless you shift like a granny.

Would like to see the 744 and 068 results as well for comparison.

[bobzdar]

Headers are allowed. I'm currently running the 744 and am happy with it - mph indicates around 370hp flywheel. I also have an 041 sitting in my garage, if I can get another 15-20hp, it might be worth the swap. Current info doesn't quite support me doing it yet, we'll see if anyone else has some numbers comparing those sized cams with unported dports (like 60916 vs 60919 or xe268 vs xe274). First I'm going to do some testing with a torker I and do some racing before I decide.

[mechanic17]

Oh, one thing occurs to me about the idea of "unported D-port heads." I occasionally read that a good valve job is worth as much as a good port job, to a point. Pete's 041 400 peaked at 418hp, Cliff's at 440hp.

Since most of the 72cc heads flow very similar numbers, and assuming the exhausts were equally unrestrictive, I'd be willing to bet the difference was in the valve job and not the bottom end parts (different pistons-SCR, etc.) Of course, they weren't on the same dyno either, same intakes, etc.

To at least mention CR (the thread topic), unless I've misread his posts, I think Cliff would say go right up to 11:1 SCR with your competitive situation and iron heads, as long as you optimize the quench. Zero-decking and planing the head a bit would accomplish it, if that's legal.

Wish I had a local shop I'd even trust to work on my Pontiac heads.

[Skip Fix]

When you figure the NHRA stockers and smogger 78s are running mid 11s "unported" D ports and low compression can do OK in the HP area. Granted they have to run stock lift cams(.364 or .407 depending on the HP motor/class) and duration is wide open and open headers. But still the mph/HP is amazing. They have some very trick valve jobs to help it out.

[Skip Fix]

When you figure the NHRA stockers and smogger 78s are running mid 11s "unported" D ports and low compression can do OK in the HP area. Granted they have to run stock lift cams(.364 or .407 depending on the HP motor/class) and duration is wide open and open headers. But still the mph/HP is amazing. They have some very trick valve jobs to help it out.

Heck John Schloe is in the 10s with his 69 Bird,although not low CR.

[Brent Flynn]

Originally Posted by Cliff R

"That's what I've always suspected. I bought the engine already re-built. It has always seemed to lack some firepower. I think a stroker kit and higher CR would wake it up quite a bit. I've never done any serious diagnostics/tuning. Just timing."

Install some flat tops with 2 small valve reliefs, zero deck height, shave the heads for closer to 11 to 1 compression, and your RAIV cammed 400 will have an entirely different "attitude as far as power production is concerned.

It simply takes some compression when using a 400 and a cam with that much duration, 113.5 LSA, and over 80 degrees of overlap.

We've worked with quite a few pure stock set-ups using the RAIV cam in the 400 engine, and they make fantastic power, and the vehicles they are installed in run great at the track. They also require plenty of gearing, and a stick shift or high stall converter to effectively use it.

Even with that said, we get more complaints from that CID/cam combination to our shop than any other, simply because they either don't squeeze them hard enough, or use enough gearing/converter behind them........Cliff

Would running a set of the domed TRW floaters in a 400 with a set of 6x's(98cc) milled some to get the compression up to approx 11 to 1 work the same as long as deck height is zero, or does it matter as much since there are domes on the pistons?

[screamingchief]

Originally Posted by Brent Flynn

Would running a set of the domed TRW floaters in a 400 with a set of 6x's(98cc) milled some to get the compression up to approx 11 to 1 work the same as long as deck height is zero, or does it matter as much since there are domes on the pistons?

You would still hafta mill the $#!t outta those 6X-8 heads to get those to a chamber size that'll net close to 11.0:1 CR with the TRW/FM L2279F dome pistons.

It would take something like some 6x-4's milled to like 85cc's on a zero deck shortblock to get close to 11.0:1 CR with those pistons (that's like 10.94:1 CR).

The dome on those pistons is pretty dang small,only like +10cc's compared to the flat tops that are -6.6cc's or so.

FWIW/HTH

Bret P.

[72LuxuryLeMansLa.]

Originally Posted by 70 Dream

I have to make my rebuild decisions soon. What I want is a stock rebuild for my 400 cid. We all know the stock 10.25 CR is too high for today's gas . . . . but if I go for say a 9.5 CR, will that be too high, even for 93 octane?

I am supposed to tell my engine builder what I want, but I am quite sure that I don't know what it is that I'm supposed to tell him.

I'm not even sure what questions I should be asking in this post. Do I want the highest CR I can get away with on pump gas? If yes, what is it? Do I pick a lower, safer CR that I won't have to worry about? If yes, what is it? How high is "too high?" And is there such a thing as going for a CR that's "too low?"

Next to cam selection (totally confusing), this is my most frustrating issue. I don't really care about performance as much as streetability and reliability.

Thanks for any and all opinions . . . . .

Here is another link for you to read about cr, dcr, cylinder pressure and the like.

http://www.empirenet.com/pkelley2/DynamicCR.html

[462ta]

just a FYI on the 60916 cam dont expect an automatic 400 plus HP out of this cam simply by dropping it in a 400 , I did and so did a buddy and both our 400's are nowhere near 400HP, now we dont have the building/tuning abilities of the pros but the best we can get out of our cars on the dyno are in the 260-275RWHP which is nowhere near 400hp. I built mine based on info gained here 406 zero decked,forged KB pistons,5140 rods,13 heads,68 intake,quadrajet and tri-y headers to 2 1/2, low 9's compression

[bobzdar]

Originally Posted by 462ta

just a FYI on the 60916 cam dont expect an automatic 400 plus HP out of this cam simply by dropping it in a 400 , I did and so did a buddy and both our 400's are nowhere near 400HP, now we dont have the building/tuning abilities of the pros but the best we can get out of our cars on the dyno are in the 260-275RWHP which is nowhere near 400hp. I built mine based on info gained here 406 zero decked,forged KB pistons,5140 rods,13 heads,68 intake,quadrajet and tri-y headers to 2 1/2, low 9's compression

How much tuning have you done? Just curious as I picked up a solid 50hp between when I first put my engine combo together to when I had fuel delivery problems fixed and jetting/timing dialed in.

[slowbird]

400hp from a 400 isn't hard at all, in my opinion.

[Ragtop Man]

Maybe a better way to express it is that longer overlap cycles and longer exhaust duration drain effective cylinder pressure, all other things equal. This gets back to the dynamic CR issue.

What is clear from the thread is that if you choose fuel quality as the constant in the equation, you will have to vary camshaft timing with the CR ( as well as exhaust scavenge and port filling efficiency ) to arrive at a final answer for the combination

I could easily see 10:1+ static CR a long-cammed (041/744-like) car with a slightly rich mix, good scavenge and good ignition running just fine on 91 Octane Cali gas in a light car with good street gears, and be a stone pig in a heavier car with no convertor, gears or tuning.


What is also clear, at least as a free opinion, is that if your engine builder cannot give you a reliable recommendation for your desired combination and results that you need a real specialist Pontiac engine builder.

The cost is not that much more for the priceless knowlege that what they are doing not only works, but kicks ass.

[mchell]

Originally Posted by 462ta

just a FYI on the 60916 cam dont expect an automatic 400 plus HP out of this cam simply by dropping it in a 400 , I did and so did a buddy and both our 400's are nowhere near 400HP, now we dont have the building/tuning abilities of the pros but the best we can get out of our cars on the dyno are in the 260-275RWHP which is nowhere near 400hp. I built mine based on info gained here 406 zero decked,forged KB pistons,5140 rods,13 heads,68 intake,quadrajet and tri-y headers to 2 1/2, low 9's compression

thanks for some real world #s.......I made a high of 300 RWHP with an xe 268 on my old 400 combo...iron intake, qjet, 9 to one comp, ported #96 heads, RA manifolds, 2 1/2 inch exhast with X and dumps.....started at around 280ish and worked it from there over a year or so......still nowhere near 400 flywheel HP...was running consistant 13.00 and even a few very high 12's sprinkled in with my 4000lb sled....

[BruceWilkie]

Originally Posted by Ragtop Man

Maybe a better way to express it is that longer overlap cycles and longer exhaust duration drain effective cylinder pressure, all other things equal. This gets back to the dynamic CR issue.

Intake closing point determines number of degrees in compression. Overlap has nothing to do with it.
The overlap window is the time to purge the chamber of ex charge with fresh intake charge. Proper exhaust tuning(design) plays large here.

Exhaust opening point is touchy too. Too soon you lose power to CE losses, too late you lose VE to pumping losses on the upsweep. Ideally you want the exhaust to open as fast as possible right about the time the piston reaches max speed approx 75 deg ATDC on a 400. At high speed opening a bit sooner will still result in more hp as the VE increase with less pumping loss can exceed the CE loss. The more exhaust pressure you can relieve before the piston leaves bdc dwell the less pumping loss you will have.(ideal would be only swept volume on the upstroke side of exhaust event) Opening exhaust after max piston speed is reached offers no additional power from combustion(it does help emissions). Less pressure in cylinder on the exhaust upsweep also affects overlap requirements because a reduced pressure allows the intake charge to begin moving sooner into the cylinder. When exhaust first opened it sent a high pressure wave somewhere down the exhaust pipe. Behind that initial high pressure is a lower pressure which helps pull higher pressure (atmosphere) charge from intake across the chamber and purges the chamber. Thus the cylinder starts filling before the piston leaves tdc dwell. Closing exhaust too soon(or excess backpressure or wrong collector lengths) allows excess residual exhaust to contaminate fresh charge and hurts power. Closing it too late wastes fresh charge and kills off intake charge velocity that normally would help fill the cylinder. The piston does not suck the charge in, atmospheric pressure pushes it in.

And I am NOT discussing high speed scavenge tuning above. Same principals apply to granny's economotor.

Also keep in mind that although a 2.5" exhaust system can support near 500 hp, exhaust pipe on the end of your collectors makes them part of your collectors. Pipemax suggests a 3" od collector for a 406 with the 60916 cam.

I suggest spending the $40.00 for Pipemax for further details. It suggests a 406 at 9.7 compression 60916 cam 5200 rpm pk power at 400 lowest point - best case 432 hp.

Kauffman used to advertise a similar stock head good valve job 406 that dyno'd 418hp at 5100, 453 ft lbs at 4200. 72cc dports w/2.11/1.77 valve, 60916 cam, 750Holley and RPM intake.

Pipemax suggests similar combo needs 1.575-1.7" OD headers. Suggests 93-94 octane as well.