Is anyone running 2 seperate tunes for pump gas vs. racing gas and if so, on average, what is the difference in timing??? Do you have any dyno and/or track time to compare the difference in H.P. or E.T.?

 

Hard to believe that no one has run some higher octane race gas thru their motors. Timing and/or boost increases would certainly net some noticable performance numbers.

 

IMHO there is not that much extra power to be made using extra timing and race gas or torco. I fool around with my timing all the time and don't see any drastic increases or decreases adjusting timing. I see large increases in power when the AFR is exactly right.

 

There's plenty of power to be made with more timing.....

I've gotten rid of the car (94 Z/28) but back when I first put the P600Bb on the car and it just made 7lbs of boost and I switched between 24* and 28* of timing it averaged about 15rwhp and 20rwtq throught the powerband. I know that's relatively small but it did make a differnce at the track and also was easy to do.

Now after that motor met it's maker (on the pump gas tune & 24*) I rebuilt it to a 383 w/ D1 19#'s and this is where timing made a huge difference.

The below are all rear wheel numbers from a dynojet.

24*- 571 hp / 535 tq
26* - 604 hp / 552 tq
28* - 630 hp / 562 tq
30* - 654 hp / 581 tq

I drove the car on the street and ran between 22-24 degrees and at the track I used to run it in the 28* range and it ran 10.0 @ 136

The motor did not like 29* or above as it munched a few head gaskets while trying to reach for glory (aka - 9's)

Whatever it was fun while it lasted

Marc

 

What kind of heads do you have on your 383? AFR? I just can't figure out why your combo likes so much timing.

 

Those are the kind of numbers I would expect as I've never seen a blower motor (or most any motor for that matter) not like additional timing providing it has the appropriate octane fuel to safely support the added timing.

Marc - What kind of fuel were you running when it started eating the head gaskts? I would imagine with some 114 or 116, 28 to 30* of lead and 18-19lbs. of boost, the motor would be relatively happy, providing you didn't lug it.

 

97pilot - I was running stock LT1 heads that were ported by CNC.

Before and after pics of the heads are here:
http://www.geocities.com/marc94z28/cncheads.html

Click on the pics for more pics

Boosted - I was running the highest unleaded gas I could get. Don't recall if it was 104 or 107 but somewhere in that range.

I considered running leaded C16 but I was running a FAST system and wide band 02 sensors were not cheap, in hindsight they would probably have been cheaper than doing head gaskets (downtime, parts, headaches etc...)

There are times when I miss the Tomato (the 94 Z) but my 73 Z/28 with an LS1 is not too shabby either Looks better and goes good.

Uncle Marc

EDIT....one more thing....when I put the combo together I went with 9.3:1 compression and I was planning on running between 14-15#'s of boost but I started eating blower belts due to the high quality tensioner that ATI provides so I went to SD Concepts (only 2½ hours away from me) and let them do their spring loaded tensioner on the car....well, when I got it back the boost went up to 19 due to no belt slippage and I could never justify spending $85 for a bigger pulley to go slower

 

Very interesting before and after pics. It really shows how much a good port will clean up lt1 heads.

 

I find that boosted cars need far less timing than NA. I have yet to hear a good explanation. About all I can come up with is that there must be a lot of turbulence in a boosted motor and this increases the burn rate. Centrifugally SC LT1's, other SBC's and SB Fords seem to make max hp with ~26 degrees regardless of fuel used. But the AF ratio must be right. Lean will make more power to a point, going beyone will take out the head gaskets or worse due to detonation. We did an experiment yesterday with my buddies low CR/high boost SBF. We ran it w/o the blower. Power was pitiful - it lost over 400rwhp. It needed a lot more timing. Boosted, max hp is with 24 degrees but w/o boost it wanted 36. My BBC NA alcohol motor wants 40 degrees. High compression BBC's have crappy combustion spaces due to the large dome needed and alcohol burn slow. So, there is an obvious explanation.

Rich

 

My motor peaks out at 26 degrees when boosted and 34 when the belt is off and I run it normally aspirated. I've taken it up to 30 degrees boosted with no appreciable gain. When my AF ratio goes from 11.8 to 10.5 it feels like I'm losing 100hp. This is street tuning at a local airport.

 

Was that intercooled?

 

So then why does my buddies Supra make 600whp on pump gas and 850whp on race gas???

 

Because he is cranking up the boost?

Rich

 

And upping the timing.

 

It doesnt matter because he'll run a 12.4 1/4 either way