Generation IV Internal Engine - 434,11.8:1,262/266 cam,compression 182-185 across board. Normal?
08-15-2012, 12:12 AM
Engine is ERL sleeved 434, 11.8:1 compression, cam is 262/266 .624@113+3...car seems low on power and trying t find cause. I have almost 3k miles on engine and I did a compression check and it's 180,185,185,185,185,180,182,181. Does this seem too low? Or normal for a car with this compression and cam?
08-15-2012, 05:12 AM
Ive seen 220, but with that cam Im not surprised. Its very large. Your intake is probably choking it because it will need mega RPM to generate its power. Overlap and valve timing means you are not compressing as much at the cranking speed you use to check pressure.
If you want to drive it around town take at least 20* off the durations, if not a bit more.
If its not a daily, then whats the intake/exhaust setup? What are you spinning it to? Where is the dyno graph? Its going to be RPM limited by the looks, probably because of heads/intake etc. But not enough details to make any specific guesses :)
08-15-2012, 11:48 AM
Define low on power.
08-20-2012, 11:49 AM
comp numbers are fine.. that cam is around 310+ at 0.006" which is a lot of cam. It will lay over earlier as hyd valve train setup is very critical. Spring pressures and valve weights also u would require limited travel lifters to stop bleed down in order to run as much spring pressure as u would require. your cam would be equiv of a 270+ mechanical roller! What cylinder heads do u have. This cam with a head around 2.8 inch choke would not start working till 6500. You dont have a lot of lift focus on spring choice /setup and shoot for 200 on seat and 550 + open thats where u need to be. OR run a smaller cam with eps lobes or similiar. If the cyl heads are good always look at the valve weight/spring setup 99% of time it will be the culprit. Easy fix. Look at Morel limited travels. and PAC 1209X shimmed 60 thou from bind+ 3/8 pushrods. You can run bolt on non adjustable rockers just have to try a few size pushrods till u get the right crush
Your cranking compression is good for the actually eombo but down for best power because you are down on DCR. You are down on DCR because your cam is too large for the SCR you chose. You want a cranking compression around 200-210psi or a DCR of atleast 8.5 from my experience for a large camed street motor. With out actually using a calculator I am thinking that you would need between 12.5-13.0 SCR for that cam with 93 octane. My cam was in the high 240's int and low 250's exhaust on a 112 lobe sep with 12.0 SCR and still only had 8.5 DCR. People way under compression their large cam street motors and give up a lot of power and tq in the process. As long as your DCR is good you will be good on pump gas.
08-20-2012, 08:54 PM
What kind of head do you have on it, dyno #s? Exhaust setup? Intake? Need more info
08-20-2012, 10:37 PM
TFS 245s with extra exhaust cnc porting for nitrous, our dyno doesnt come in till the 31st so ill know then.. 1-7/8 headers,dual 3" exhaust with an X through borla XR1s, fast 102mm intake..4" intake pipe with LS7 MAF.
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