Pray

iTrader: (7)

I thought my 383 dynoed a little low so I wanted to check the health of the motor. It is brand new with only 1,400 miles on it. I set it up to run at almost max for pump gas. It mathmaticly has a 11.8 SCR and 8.7 DCR. The confusing thing is that all the cylinders came in at 175psi cranking compression with 0 leak down. Which I think is way low. My stock Z06 with a 224/228 cam came in at 205-210psi and when I swapped to 59cc AFR's with a .054 head gasket with a 228/232 the CC was 220psi or so. Both of these cams were on a 114+4. The current combo is a 383 stroked bottom end. 4" crank, 6.125 rods, 3.905 bore with -7cc Diamond pistons. 59cc AFR 205's, .040 Cometics. The cam is a 239/244 .651/.612 112+2. So what's the deal? I figured my CC would be around 200psi or so. I also ran 29* of ignition lead on the dyno with no detonation. That was my first clue. So my conlusions.

1. Heads are not 59cc.
2. The calculator I use was not correct.
3. DCR means nothing and I needed more SCR.

What do you guys think.

Brett

1989GTA

If you did not actually measure the cc's of the heads, the cc's of the piston or measure how far your pistons are from the deck then yes your compression ratio could be off from what you thought it was.

PewterZ28

iTrader: (1)

That is almost identical to the setup I am about to go with but I am using a TH350 with a 8" converter and a 12 bolt with 4.10's. I was hoping to put down close to 480 rwhp since I put down 443 rwhp on the stock bottom end with valvetrain issues. I figure without the valve train issues I probably would have put down 445 to 450 and the 37 extra cubes should give me at least 30 rwhp. I hope I'm not wrong. I'll quit racing all together if I don't put down more power than my stock bottom end did.

FYI my setup is:
ETP 225 small bore heads, 58cc, larger valves
237/241 cam with .632/.612 lift, 113 LSA, 109 ICL
11.65 SCR
8.77 DCR
.035 Quench

Almost identical to your setup. I just hope I make more power than you did.

PewterZ28

iTrader: (1)

P.S. How are you coming up with 11.8? How much is the piston coming out of the hole? If I use -.005 I come up with 11.6 (not like 2 tenths of a point is going to make a big difference). 5 thou out of the hole puts you at .035 Quench. To get to 11.8 you'd have to be coming 10 thou out of the hole but that would drop your Quench down to .030.

Pray

iTrader: (7)

Don't let the power numbers fool you. The car went 127 in the quarter with the traction control pulling all my timing (I have an issue with it, I didn't leave it on) with a bad slave cylinder causing me over half a second on each shift on street radials. I couldn't really get into it untill well into second. There is also more power coming as I maximise my combo. Just remember that you are stuck with a small bore that can only take so much air. So making more peak hp may not happen like we all want it to. But the whole curve will pick up substantialy. Plus you will be running through an auto which shine on the track but suck on the dyno. Good luck with your project. Keep me updated on how it turns out.

As far as the SCR numbers. I just used PianoProdigy's posted calculator and that is what it came up with. I think it has the pistons .008 out. I am not sure though.

Brett

PewterZ28

iTrader: (1)

I looked up your dyno thread and saw that you still need to get a better intake & TB as well as a better set of headers. That could be a big reason why your numbers aren't as high as you were hoping. I'll post my numbers in the dyno section in about 4 to 6 weeks.

Pray

iTrader: (7)

I hear you on the intake and headers. I have some customized LG's from a big name on here that will be here today and go on by tonight. They should be worth a few. As far as the intake I am kind of stuck right now. Two grand is alot of money for an intake. (although I want a ported Mamo 90/90 so bad I am about to go into debt to get one) I can get a whole ported L92 top end for that much. Then sell my AFR's and buy a LS2 block and some new pistons. So for my total investment of two grand I could have a ported L92 headed 402. I have to weigh my options. My dyno tune also left some to be desired. I left it rich on purpose with the sensor in the tail pipe and dynoed through a Vararam. On the track with the air being rammed in there, I was in a whole different part of the tuning cells that you can't duplicate on the dyno. I didn't have a WB hooked up so I didn't want to mess with the tune. Now that I have my WB 02, EFI live, new slave cylinder, and the headers I think the car is going to pick up substantialy.