Well I be able to run 12.1 compression on pump gas for dd with a tune? Oh and its ca 91 octane.

 

Sure why not.

 

It's a stretch for 91 octane, but it is possible. Timing may have to be retarded so that it acts like a similar 11.5:1 engine however.

 

I'll jump in too here. Can you elaborate on this or just re-verify what I think you're saying? I am considering a similar setup with 12.5:1 B20 with stg2 LS cams until I can get my B16 head with pro2 cams together. If I read you correctly, this is OK as long as I retard the timing enough and I'll basically make similar power as 11.5:1?

 

What i'm saying is that when you tune the car, because of the 91 octane's lower ability to resist knock, it doesn't make any sense to bring the car up to over 12.0:1 or 12.5:1, because your tuner will basically retard timing safely to a point where it will no longer knock.. That usually means lowering timing to a point where the car behaves as though it is running as though it were 11.5:1 and not the 12.5:1 that you built the engine for.

In essence, it means, just build an 11.5:1 CR engine and you won't have as much timing retard to do instead of shooting for 12.5:1.

 

Pretty sure I have been doing it daily for the past 4000 miles and couting.

Static compression ratio is not the end all be all.

 

What's the advantage of that if eventually I'll want to get cams that want 12+ compression? I'll have it tuned of course. Is it significantly more reliable?

 

tune it ..yes

 

What engine is this going to be ?

 

Tune is the most important part of the science. Anytime you play with raising the compression ratio in any aspect, a tune is almost necessary to ensure reliability, driveability, and longevity.

 

You're looking at 12+ compression as though its the only thing that matters if trying to make power. It doesn't help that you're using 91OCT. Too many Cali/AZ/KS/CO guys don't understand how important that 2 point increase in the Average RON rating is for fuel to be able to resist knock. Knock hurts timing, which in turn decreases power. You'll be just as fast and "reliable" (assuming your assembly was dead on) with the 11.5-11.8:1 system even more than you would the 12.0:1 system (properly tuned) because the tuner will have less timing to try and worry about. Stop obsessing over the CR ratio that you want to blab to idiots. Get the car running correctly with good fuel (even though it is 91 OCT water) a good tune and enjoy..

 

As a general rule of thumb its better to run a lower c/r with a load of ignition timing then a high c/r where the ignition timing needs to be retarded. Although i don't know your fuel theshodan sounds correct. Always plan c/r on the safe side. Higher isn't always better.

 

Retarding timing just to run higher compression defeats the purpose and costs you power. Either run a lower compression number or nut up for some better gas. My buddy used to run 2 gallons of 100 with the rest of the tank 92 (best you can get at most pumps in WA) to increase the octane 2-3 points with his 12.5:1 LSV and the ignition timing was still slightly advanced and dead on. There are ways around this...just costs a few more bucks. Gotta pay to play.

 

Half the **** posted in here isn't true..but whatever.

A good tune, will yield the proper results, leave it at that. Compression, is just 1/10th the equation to making power. Compression will make up, with what you lack in displacement. Choose the best of both worlds.

Set a goal, get the correct combo of parts, find a tuner that actually knows what a motor is doing.

 

^This

 

The way i see it : If a engine can't hit maximum brake torque (MBT) for the given volumetric efficiency (VE) & running conditions it has been designed for with the octane rating taken into account (either NA or FI) then you have a problem. This is just my view though... Remembering that VE and C/R work side by side.... Only if we had a world of variable compression ratio engines hey.... we could get the best of both worlds...

 

Ive been driving my hatch dailey for 40,000 miles at 12.5 compresssion running 93 octane . I have had to put 91 octane in it and it still runs fine but you can tell the difference in power. The car makes over 250 hp on mid nights dyno when it was 116 degrees in the shop on 93 octane with 12.5 compression. If your cams arnt desighned to run that high of compression then your going to have way to much cranking pressure and there going to have to retard the timing which is going to kill your power. everybody in the honda world builds motors *** backwards . Read up on how the v8 guys do it and learn something . the first thing you need to know is what cam you are going to run then build your motor around that . We had so much cranking pressure that i had to go from stage2 cams to pro2 cams .
A good tuner can tune 13.1 for you to be able to drive on the street but odds are you would make more hp at 12.2-12.5 on pump gas . The only reason i would run 13.1 on the street is because i was going to swap to race gas at the track . I wouldnt go over 12.2 on 91 octane .

 

Ls block sleeved, 84 mm supertech 12.1 compression pistons, stock ls crankshaft, ported gsr head, and planning to run s2 pro 2 cams which I don't have the cams yet.

 

I would use a bigger intake cam for that setup and a 4.785 final drive to take some load off the engine.