X compression ratio increase = X HP increase

kstylianos · 05-21-2003, 12:20 PM

Yesterday I talked to the machinist who is completing the work on my top end and we got talking compression ratios, etc. I have an 82 SC with a Porsche rated 9.3:1 CR. He explained to me the Porsche rated CR's are actually .25-.50 less than stated, so my 9.3:1 CR is actually around 8.9:1 due to CIS piston dome size, valve cut out, etc. So I asked him about the JE 9.8:1 pistons, and he said these are true 9.8:1 pistons. This would be close to a whole CR point increase which would be a 'very nice upgrade and would complement the porting and new cams nicely'.

My question is, what would be the equivalent HP (approx.) increase if I performed this mod. I have the Alusil cylinders which would need to be Nikasil replated to work with the JE pistons....a $1900 total cost for both P/C's. If I'm going this far, why not a 3.2 P/C upgrade with the 9.8:1 CR. Would this work well with CIS? Just want some input and suggestions.

Thanks...

BTW: Also posted in the rebuilding forum.

82SC · 05-21-2003, 12:37 PM

i remember seeing some nikasil cylinders for sale on the classfieds...that would be a cheap way to go

if you decide the 3.2 route...I figure it will start snowballing...why not get 3.2L heads...maybe get Motronic instead of CIS...might was well double plug...maybe go with a EFI setup...etc...

good luck...keep us posted

MJ

Superman · 05-21-2003, 12:49 PM

Yep. '82 is right. You're walking down a slippery slope. If you want to use that engine case and get more horsepower, more than you get from just advancing the timing, etc., then you can:

1) Change P&Cs, cams, fuel system, port heads. Maybe get 250 hp.

-or-

2) Drop a 3.6 in there. Get 260+ hp right out of the box.

Approximately the same price.

kstylianos · 01:36 PM

The modified heads and cams are a done deal. They have been matched to work well together along with the SSI's and the sport muffler. My ears perked when I was told that increasing the CR will complement this setup. I probably wont go with the 3.2, but just curious what a 9.8:1 CR will bring. I'll search around and see what I can find.

Dan Owens · 05-21-2003, 02:03 PM

Charlie,

Just curious on who's doing your work?

kstylianos · 05-21-2003, 02:06 PM

Walt Watson @ Competition Engineering

Cams by Elgin

911pcars · 05-21-2003, 02:22 PM

Just curious. What does Elgin get for a set of cams? Reground factory cams? Rewelded?

Thanks,
Sherwood Lee
http://members.rennlist.org/911pcars

1fastredsc · 02:45 PM

Don't quot me on this, but i think with your horsepower and torque stock, you can expect about an extra 10-15ftlbs. Which depending on your new torque curve will either give you say 5hp or an extra 20 hp. If your getting your head ported and matched to cams, you should port out the cis runners as they are significantly smaller than the older 78-79 ones and will restrict your motor's breathing during high velocity air flow (high rpm). Therefore making your improvements only noticable until you get above like 5,000 rpm, then it'll start giving up on you. And if you do plan on going 9.8:1, you should twin plug unless you have resources to decently high octane fuel.

kstylianos · 05-21-2003, 02:49 PM

$275 for welded, ground and hardened to any profile.

Can't find the .html for their different cam grinds. Probably need to call and ask.

http://www.elgincams.com/main.html

kstylianos · 03:06 PM

Quote:

If your getting your head ported and matched to cams, you should port out the cis runners as they are significantly smaller than the older 78-79 ones and will restrict your motor's breathing during high velocity air flow (high rpm).

The runners are getting ported as well to match the intake. 93 octane is avail. here in Virginia. Was told with the ported heads and runners and the matching cams, the engine will pull hard up to and past redline. Leaving the exhaust ports as is will give enough back pressure to keep it torquey down low.

Thanks for the input guys...keep it coming.