As most of you know I am putting together a race car. Well after buying parts and such I ran into a few snags that caused my compression to be higher than planned. I was aiming for about 10.7:1 static and 8.5:1 dynamic. Now I am looking at about 11.2:1 static and 8.9:1 dynamic, but I have a nice tight 0.036" quench. I know this is pretty high for dynamic so I am looking for options. I am getting close to finally firing it up and looking into my fuel options. I was hoping to run 93 pump gas in it but I dont think that is going to work out right? I can get 100 unleaded at a station about 40 min. away, but that will almost triple my expected fuel bill. What are your thoughts on a bottle of octane boost vs mixing 100 with 93?

 

If you do a search on Google on "home brew high octane" you will find some ggreat reading and the facts on boosters and what can and cannot be expected from the wide variety of admixtures available to the avg guy.

Moth *****...truth to the story. Napthalene. Its available in liquid at most paint stores. Problem is that it has a limit on how high it can boost and cost becomes impractical.

Painters alcohol....probably one of the ost economical but we all know what high alcohol fuels do to many rubbers and plastics scattered thru the engine.

Its worth reading. I've experiemented with some home brew and had good results, but was afraid to go too far for fear of the law of unintended consequence showing up when I could least afford it.
Another consideration is water/alcohol injection. I did that and its cheap, systems are available for few hundred $$$ and it WORKS. I had a system that sprayed only at a pre-set throttle opening, so the water/alcohol was not wasted until I stepped in it hard and it prevented the destructive knock and kept combustion temps to a safe level.

Do the search..there are some good solutions out there. Its just a matter of whats best suited for your needs..The fuel reading is interesting...
Good luck.

 

While those sound like great ideas, I should add that "home brew" fuel is illegal in my race class, and I cannot do a water/alcohol injection. My only options would be a mix of 100 and 93, or a bottle of octane boost.

 

I personally think it'll be fine on straight 93octane.

You got alot of things going for it on a race car that street cars don't.

Make sure the temps are up when your doing the final timing curves.... Just pay attention to the knock counts.

If you want to home brew some octane booster just buy a few gallons of Toluene... But I honestly don't think it'll be necessary for safe operation. It'll defiantly make more power - but you can slight the tune enough to make it run well on regular 93 octane as is.
Will

 

This is what I was hoping to hear! The issue is I am not tuning it myself. Alvin at PCMforLess is going to tune it by mail. He sent me my start up chip and when the car is running I am going to do some data logs. Anything special I should do on my end either in the data log or in documentation form for when I send the chip back to Alvin? I will be sure to log the car warming up at idle, doing a short cruise and then a WOT run or two to show hopefully all the engine parameters under a variety of conditions.

 

Octane boosters in auto parts stores-junk

Real octane booster http://www.wildbillscorvette.com/OctaneSupreme01.htm

Brings my avg down to about 6/gal cant complain

 

A lot is in the tune yeah. I wouldn't spend the money for 100 octane and would (and did) use E85 instead. If it's making enough power the timing chart can be dumbed down so it's safe. Without a WB I wouldn't do any WOT.

 

I dont have the pump or injectors to support E85 I dont think. I do have a WB that I will hook up prior to driving it.

 

Will was saying (correctly) that you need to get it hot, not just warmed up. Whatever the hottest temps you can get (e.g., race situation) that's what you need to log and be tuned for.

My car is a good example. I tuned it at "temp". By that, I mean 195-deg where it normally "lives". On the dyno, I ended up doing several back-to-back pulls (with time for a quick reburn/rechip between each pull). By the end of the session, my temps were running 25-30 degrees hotter and I was getting into some knock counts at peak torque rpms.

Instead of retuning to that issue, I decided to leave and figure out how to keep temps in the 195 range. Really, either philosphy is fine -- but if you're going to hit situations where the temps go up and you're not tuned for that, you're gonna be pulling timing and probably end up running slower than getting it tuned to that situation.

When my KS kicked in (on dyno day), it was pulling 30+ ft/lbs of torque throughout peak. There was an obvious dip in the power graph. I know it would have stayed up and been more linear with tuning for that situation.

This summer, I corrected that by backing it off 1.5 deg in the higher load/higher rpm range. I didn't put it on a dyno again, but it runs out better. For you, that means tune it for race conditions.

 

That makes sense. I have a fan wired to a seperate switch so I can let it get hot and log before turning the fan on. Thanks!

 

My 12:1 ,8.7 DCR 383 with a .040 quench runs fine on our 95 octane which is equal to your 91