[Brent Flynn]

Originally Posted by screamingchief

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.

I figured i could get 10 to one or more outta that setup...i know, i have to mill the intake side of the heads too... i would go zero deck or even maybe .005 out.

[Cliff R]

"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"

We provided the "recipe" to make 1hp per cid from the 400 engine with unported heads.

Following a "recipe" is much like making a batch of chocolate chip cookies. If you leave out the chocolate chips, you will certainly have a less than desirable result.

Lowering the compression to the "low 9 to 1 range" would not be following it. Those are pretty "big" cams for 400 engines. Low 9 to 1 compression would certain result in giving up quite a bit of power. You might loose more if the cam wasn't degreed to spec?

The test engine used unported #16's, zero deck, and the 60916 camshaft. We used high ratio rockers and degree'd the cam to 108ICL. Nothing else "special" was done for the built. That engine made 419hp/453tq.

The larger 60243 cam made 424hp/465tq.

With unported KRE aluminum "D" port 65cc heads 430hp and 440hp respectively.

They even dropped in a larger 60919 camshaft, and it only made 10 more HP than the 60243, but idled poorly and pushed the power pretty high up in the rpm range. Interesting how a 400 with that much compression still didn't "shine" with the RAIV sized camshaft in it. Nearly as I can remember is made about the same average torque as the smaller cam.....Cliff

[462ta]

Cliff not doubting you at all , just a simple statement "dont expect an automatic"
Man i wish i lived closer to you and i would drive the car to you as i'd love to find the 80hp and tq im missing somewhere
Compression was at 9.5 but is down little now as i opened up the chambers when i unshrouded the intake valves when porting.
i advanced the cam 4 deg and lost power so i put it back straight up and degreed
Both these engines are basically the same and make about the same power so were missing something, cant remember exactly what the AF was on the dyno but it was OK and steady across the run.(built the carb using your book)

[bobzdar]

Originally Posted by 462ta

Cliff not doubting you at all , just a simple statement "dont expect an automatic"
Man i wish i lived closer to you and i would drive the car to you as i'd love to find the 80hp and tq im missing somewhere
Compression was at 9.5 but is down little now as i opened up the chambers when i unshrouded the intake valves when porting.
i advanced the cam 4 deg and lost power so i put it back straight up and degreed
Both these engines are basically the same and make about the same power so were missing something, cant remember exactly what the AF was on the dyno but it was OK and steady across the run.(built the carb using your book)

Do you have some HP curves to post? Could tell if there's a valvetrain issue or something.

[Cliff R]

Compression is important in power (torque) production. Once you get past mind-set that a "perverbial brick wall" of 9.5 to 1 exists for these engines on pump gas,, the engine builder can use the compression to get these engines to manage larger cams.

The problem with this line of thinking, is that you can lower the compression and still manage the same cam. The larger cam takes a LOT of "wind" out of the lower compression engine, specifically down in the "normal" driving range, low rpms and at idle.

If you drop out a half point or so compression, to get the engine to run compariably to the higher compression one, at the same cid, reduce the cam duration by about 10 degrees.

In other words, a cam down around 214/224/112 would have been a better choice all the way around......Cliff

[462ta]

will have to look to see where the dyno runs are then figure out how to post, Cliff just ordered couple air horn gaskets , ripped mine at the prim rod hanger.

[BruceWilkie]

Percentage wise, horsepower gain from compression is at a greater percentage from 9.2 to 9.7 than from 9.7 to 10.2. And 10.2 to 10.7 is even less of a percentage gain. Any engine!

Also valve job detail especially how its blended into the bowl and gasket/port match and blend can add up to big hp differences. Usually the valve job done well is worth more than a modest compression increase alone. VE is the king when it comes to making power.

[slowbird]

Originally Posted by Cliff R

In other words, a cam down around 214/224/112 would have been a better choice all the way around......Cliff

We ran a cam very similar to that in our first 400 ran great. Ended up run 12.7s I believe with that cam, and untouched 16 heads.

[mechanic17]

Hey, I've been plugging some of the suggested street combos I've seen in various threads around here into some DCR calculators, and am coming up with numbers well shy of 7.0 to 1. Meanwhile, I'm reading elsewhere that 7.5 to 8.5 DCR max is what's desired for 93 octane (170psi cylinder pressure).

I hate to start another "brick wall"-type discussion, but am I missing something about DCR? I hate to build 6-something DCR into a motor that's still on the stand if it means leaving power on the table--I can buy another cam easily enough.

Also--not the combo I'm talking about above--Cliff, are you saying an actual 041 cam in a street 400 can never get enough SCR to be worthwhile with today's other cam choices? I may have misread you.

[aktattoo]

what you are missing is the static compression. the engine never sees 170psi with the bigger cams and lsa's at 8.5 due to the valve timing.

[screamingchief]

The problem with DCR numbers being "all over the map" is due almost entirely to the fact that not everyone uses the same valve events to get their numbers,some guys use the seat events,and others use the .050" events (often adding a "set" amount) and that results in vastly different DCR numbers being tossed around when talking about the whole DCR thing.

This happens because many cam companies dont even bother to give out the seat events anymore,and many folks dont understand how to convert the seat duration numbers into seat event numbers.

There is a lengthly thread about DCR here that explains all that stuff,so I'd suggest doing a search to study up on that stuff if you really wanna grasp the whole thing 100%.

HTH

Bret P.

[slowbird]

Has anyone actually seen a correlation between DCR and power out put? I haven't seen anything yet.

[screamingchief]

Originally Posted by slowbird

Has anyone actually seen a correlation between DCR and power out put? I haven't seen anything yet.

Honestly,I dont put much faith into the whole DCR theory thing myself.

I mean it's interesting to run the numbers and see where different combos end up and such,but I dont feel it will tell a fella which combos will be 100% trouble free,and which combos will be nothing but trouble,so IMHO it's mostly just a fun toy to play with.

So,I myself would'nt ever build an engine entirely around DCR theory alone,as there's just too much that it does'nt remotely account for.

There still exists a certain "hit or miss" factor despite the whole DCR thing trying explain this whole static/dynamic CR relationship.

But I dont pooh-pooh DCR theory either,if folks wanna play around with the whole DCR theory and it's math & calculators and such,that's cool by me,I'll play along for the most part,no sweat off my back really.

I admit that I feel it's always wise to read up on certain subjects like this so one can make those sorta judgements on their own,and then one can decide just how much merit to give a deal like this.

FWIW

Bret P.

[slowbird]

I'm around 7.2:1 DCR and 145 cranking psi. Engine makes good power and it is temperamental on 92 octane (have to add a little fuel and pull a degree or two of timing out to make it happy). From what I am reading here it should run great on almost any kind of gas. There is a LOT more to than just these simply calculations.

[Cliff R]

"Percentage wise, horsepower gain from compression is at a greater percentage from 9.2 to 9.7 than from 9.7 to 10.2. And 10.2 to 10.7 is even less of a percentage gain. Any engine!"

This statement is spot on IF you use the same cam in both engines, but doesn't tell us the whole story IF you use the compression ratio increase to effectively manage a larger camshaft.

Case in point, at 9 to 1 compression, a 214/224/112 cam (068 size or something close to it) is a very good choice for the 400cid Pontiac street engine.

If you move up to 10 to 1 compression and use a 224/234/112 cam, it will idle about the same, same throttle response off idle, drive about the same, etc.

The increase in compression offsets the losses from the additional seat timing and increased overlap. (Probably a good time to mention octane requirements between those two engines are also about the same)

However, run both engines on a dyno and see how much more power the higher compression engine produces.

At best the 9 to 1 engine is a 380hp deal, probably closer to 350hp.

The high compression engine will make at or just over 1hp per cid.

When we dyno'd the 221/229/112 cam in a plain old 400 with unported 72cc "D" port heads, it made 419hp/453tq.

A slightly larger 228/235/112 cam made 424hp/465tq.

Quite a bit more power than the little 214/224/112 or an 068 sized cam will make in the same application.

The best numbers I've ever seen from a 389 or 400 with one of those cams in it was exactly 380hp, and that engine had MORE than 9 to 1 compression (9.8 to 1) to be exact.

These facts are why I continue to mention that compression can be your friend, if you choose the camshaft accordingly.

"Also--not the combo I'm talking about above--Cliff, are you saying an actual 041 cam in a street 400 can never get enough SCR to be worthwhile with today's other cam choices? I may have misread you."

I don't know how much compression one could use in a 400 with that cam and still manage pump fuel? I simply never spent the time building and testing one.

If I had to guess, I'd say EASILY 10.5 to 10.8 to 1 compression on pump gas with iron heads, and 11 to 11.5 to 1 with KRE aluminum "D" ports.

I say this because my 455 using the Crower RAIV camshaft was fine at 10 to 1 with iron heads on 89-90 octane, and 10.48 to 1 with KRE heads. I even installed a HR camshaft which raised dynamic compression some, and it still ran flawlessly on pump gas for years and hundreds of dragstrip runs.

Interesting that my iron headed 455 cranked at 160psi with that cam, and 170psi with the KRE heads.

My new engine cranks at 198psi, so out the window goes the theory that you need to be around 160-170psi cranking pressure for pump gas.

My new engine actually got a steady diet of 87 octane last year, as my son was filling the gas cans for the shop on parts runs, and can't follow simple instructions.

The only hint I had that low octane fuel was being used, was once in a great while it would "run-on" at shut down on a really hot day and fully heat soaked.

Never pinged once, and ran flawlessly on the street and at the track.

At least we know with good heads and an efficient chamber, that we can easily manage pump gas at a solid 11 to 1 compression ratio. Keep in mind that I have FULL control of timing and fuel curves, and my engine has very tight quench, with polished piston tops and combustion chambers (if that makes any real difference?). I also installed the cam at 109 ICL instead of 108, which can be the straw that broke the camels back, in terms of cylinder pressure at lower rpm's that may induce detonation on any given octane.

Some quickly write me off on these things and say that I "push the envelope" too far.

I say that you will NEVER be able to make progress with these things without gettin off the sofa and doing some testing. You guys can research this stuff to death, and do all the fancy DCR and computer sims you want to...the ONLY real way to find out the limitations, is to go out and do it! I just do NOT buy into the deal where folks fall back on statements saying you can make just as much power at a lower compression with a smaller whiz-bang camshaft.

I've had these engines in here to tune, and have seen PLENTY of them at the track, even helped a few folks optimize them for best ET/MPH etc. Most are wondering where all the power is at, and examples where folks are running these deals nearly into the 10's up over 120mph are as rare as hens teeth!........Cliff

[bobzdar]

But if you were after power, why wouldn't you use the same cam in both? Then the power difference is more like 10hp instead of 40-50hp. I don't know why you'd give up 40-50hp on the top end to gain 10hp on the bottom end unless you're building the car for your grandma. The loss of driveability is less than what people think if you tune it properly, difference on my 400 from 8:1 to 10:1 was 2" of vacuum with the 744. If you're on the very edge of power brakes, then it might make a difference, but I don't think pulling out 20 degrees of duration even going down to 8:1 is necessary vs. say a raIV.

Pontiac themselves use the raIV cam in an 8.4:1 engine before having to swap it for the 744 due to emissions in the SD. I've never driven an 8:1 400 with a raIV, but if it works in a 10:1 engine, it should work with an 8:1 engine with a loss of 20hp ish through the rpm range. It'll be more noticeable on the low end as a loss of 20hp at 2000rpm is equivalent to around 50 lbs ft of torque, but as you get over 4000rpm it should feel similar.

If you're married to 2.56 gears and 8:1 compression, then maybe a smaller cam is good. But if you are building ground up and are matching the drivetrain to your engine instead of vice versa, I don't know why you'd use anything less than a 744 unless you're towing.