[Formulabruce]

Originally Posted by GTOKIDRH

Thanks for the intel! Again, the stock engine in my wagon has the low compression 8.6:1 pistons as well as the large chambered heads. My thought is I already own the 670 small chambered heads which will only push me into rhe mid 9s compression wise which is still pump gas friendly and I will gain 3% more power than why not? It's free. I won't change the heads until I do the cam swap. I'll be in there anyway. I admit that i know just enough about engines to get myself in to trouble. Still much to learn. Thoughts?

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That 3% Increase in power is NOT going to be in your normal driving RPM range, IF it was, Pontiac would have done it..... ALL, and I mean ALL, Horsepower increases are at higher RPMS, and Most all are Not used in normal driving.
ALL Horsepower is calculated, even at the dyno, its Never measured.
You have a nice car, hate to see it get into "mission creep" and not enjoyed..

[amcmike]

Originally Posted by Formulabruce

That 3% Increase in power is NOT going to be in your normal driving RPM range, IF it was, Pontiac would have done it..... ALL, and I mean ALL, Horsepower increases are at higher RPMS, and Most all are Not used in normal driving.

Actually it is, and today's OEMs do.

Modern engines use much higher compression ratios, enabled by direct injection. The higher SCR increases efficiency even at part throttle, thus increasing fuel economy (in addition to increasing torque under wide open throttle). They can get away with these compression ratios due to the charge cooling as the fuel is injected directly into the combustion chamber (especially with multiple injection strategy at under medium loads and low-mid rpm). This then allows them to downsize the engine displacement (if desired) to further improve fuel economy. This is why OEMs use DI even on small economy cars, not just performance vehicles.

[amcmike]

Originally Posted by amcmike

Actually it is, and today's OEMs do.

Modern engines use much higher compression ratios, enabled by direct injection. The higher SCR increases efficiency even at part throttle, thus increasing fuel economy (in addition to increasing torque under wide open throttle). They can get away with these compression ratios due to the charge cooling as the fuel is injected directly into the combustion chamber (especially with multiple injection strategy at under medium loads and low-mid rpm). This then allows them to downsize the engine displacement (if desired) to further improve fuel economy. This is why OEMs use DI even on small economy cars, not just performance vehicles.

I should have said, one of the reasons. The other of course, being emissions (with the exception of particulate emissions, which is actually higher than port fuel).

[GTOKIDRH]

Originally Posted by amcmike

Actually it is, and today's OEMs do.

Modern engines use much higher compression ratios, enabled by direct injection. The higher SCR increases efficiency even at part throttle, thus increasing fuel economy (in addition to increasing torque under wide open throttle). They can get away with these compression ratios due to the charge cooling as the fuel is injected directly into the combustion chamber (especially with multiple injection strategy at under medium loads and low-mid rpm). This then allows them to downsize the engine displacement (if desired) to further improve fuel economy. This is why OEMs use DI even on small economy cars, not just performance vehicles.

So correct me if I'm wrong. The LS engines before DI were mostly if not all in the 10+ CR range. I understand this was largely due to the use of aluminum as well as the heart shaped combustion chamber with a centrally positioned spark plug tip. Yes DI helps immensely.

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[amcmike]

Originally Posted by GTOKIDRH

So correct me if I'm wrong. The LS engines before DI were mostly if not all in the 10+ CR range. I understand this was largely due to the use of aluminum as well as the heart shaped combustion chamber with a centrally positioned spark plug tip. Yes DI helps immensely.

It's a bit complicated, but I'll try to simplify.

The GENIII passenger vehicles (Corvette, Firebird, etc.) were in the low-mid 10s with aluminum block/heads premium. The small engine trucks 4.8/5.3 were mid-9s, the exception was the 5.3L HO which used an aluminum block and 9.9:1. The 6.0 LQ4 was only 9:1 but was meant for HD trucks that weighed more and would be used for heavier loads and 87 octane. There was a 6.0L LQ9 which was a 10:1 variant of the LQ4 but was used in Escalades and required premium.


The GENIV LS (debuting with the LS2) were still PFI, and saw a bump in compression with passenger cars adding about 1/2 point. For the GENIV trucks, the iron blocks (and some aluminum) were typically 9.5:1, but often had VVT which bumped up the dynamic compression below 3500rpm. Some larger aluminum blocks (like the L92) were as high as 10.5:1 but recommended premium.

With the GENV having DI, compression even with VVT, is typically 11:1 on trucks, and higher for passenger cars (but with premium recommended). And we haven't even talked about Super Charged cars, but the LT4 runs 10:1 with 9.4 lbs of boost.

[PunchT37]

One can’t talk about modern engine specs as a reference to old car building without realizing the fast and powerful computers running them.

[NeighborsComplaint]

I had a '65 Lemans w. 326 2bbl and single exhaust as a kid. A dual exhaust was a big upgrade in performance. I then added a 4 bbl intake and Carter AFB which also made it even better with no other changes. I was amazed at the transformation which included basic, quality tune up parts. It was a 3 spd w. Hurst linkage and would chirp the tires in 2nd and 3rd with ease. If you're up to a cam swap, a Summit 2801 kit with lifters and springs and a new timing set will give a nice performance return on investment. The 670 heads aren't needed for what is just a nice torquey cruiser. The rear gears would be a better investment than the heads if you had to make a choice.

[GTOKIDRH]

Originally Posted by NeighborsComplaint

I had a '65 Lemans w. 326 2bbl and single exhaust as a kid. A dual exhaust was a big upgrade in performance. I then added a 4 bbl intake and Carter AFB which also made it even better with no other changes. I was amazed at the transformation which included basic, quality tune up parts. It was a 3 spd w. Hurst linkage and would chirp the tires in 2nd and 3rd with ease. If you're up to a cam swap, a Summit 2801 kit with lifters and springs and a new timing set will give a nice performance return on investment. The 670 heads aren't needed for what is just a nice torquey cruiser. The rear gears would be a better investment than the heads if you had to make a choice.

I already have the rear end as well as the 4BBL setup and the 670 heads. So.....

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[NeighborsComplaint]

Originally Posted by GTOKIDRH

I already have the rear end as well as the 4BBL setup and the 670 heads. So.....

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Go for it. The potential for detonation will be reduced if you step up to an 067, 068 or Summit 2801 cam.

[Formulabruce]

Originally Posted by amcmike

Actually it is, and today's OEMs do.

Modern engines use much higher compression ratios, enabled by direct injection. The higher SCR increases efficiency even at part throttle, thus increasing fuel economy (in addition to increasing torque under wide open throttle). They can get away with these compression ratios due to the charge cooling as the fuel is injected directly into the combustion chamber (especially with multiple injection strategy at under medium loads and low-mid rpm). This then allows them to downsize the engine displacement (if desired) to further improve fuel economy. This is why OEMs use DI even on small economy cars, not just performance vehicles.

While true on modern cars, The 60's and 70's and most of the 80's were built based on Torque And were built to run on the highway just below their torque peak in most cases, for passing power, and economy.
Would be interesting if ANYBODY started Dyno mapping at 1500 instead of 3K .
My Point is that some things were designed well, and do the job.. well....

[GTOKIDRH]

Originally Posted by Formulabruce

While true on modern cars, The 60's and 70's and most of the 80's were built based on Torque And were built to run on the highway just below their torque peak in most cases, for passing power, and economy.

Would be interesting if ANYBODY started Dyno mapping at 1500 instead of 3K .

My Point is that some things were designed well, and do the job.. well....

I would like to see that as well!

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