Yes, I'm stuck with unleaded and I should probably clarify the title by adding "under optimal conditions". Hoping a tuner has tried to tune for high boost with 100 octane unleaded in the past and is willing to share their experience... (Higher octanes are available but not readily so in this area). Does anyone know what boost level can be safely tuned up to MBT (min best timing) with 100 octane? Running 700bb turbos, 3.54L motor, 9:1 compression, with intake temps in the 85-100 degF range. Can I get to 24 psi on 100? 21 psi? (Don't worry Sharif, I won't go anywhere near the limit )

I was looking into mathematical models for predicting detonation, but I cannot find too many engineering documents specifically for the automotive industry (chemical storage and processing predominantly). Here is one link - interesting read and could probably be applied to the automotive industry. Mathematical prediction models might work better than knock sensors alone, particularly with newer flex-fuel vehicles and sensors that can detect octane. But I digress...

EDIT: George, I recall you mentioned the spark plug pressure sensors that last only a single tuning session. I would think those could be used to establish a calibration curve based on timing, air, and fuel, to create a model for pressure vs. time. It would only have to be done once for a particular build spec. but should be good for every engine built to those specs. Although, crap like oil vapor ingestion would screw it up without a sensor of some kind to detect that. Hmmm...

 

First of all, if you are sticking to unleaded I would recommend VP's MS109. It is an oxygenated 105 octane R+M/2

There is so much that goes into timing and detonation I can't see any standard formula applying. Even oddities such as hot spots, piston design, etc. If I am wrong, I would love to have that formula - and so would many others

Regarding max boost, this too is impossible to name a set limit. If you want to push it to the max, you can continue increasing boost and tuning timing, while monitoring knock and torque. You will reach the point where gains are minimal as you max out your fuel.

Regarding spark plug pressure sensors - they are a great idea and I have looked into them before as a solution for high power unlocked auto-trans tuning (it gets very difficult). My conclusion was the only setups I would feel comfortable with cost nearly as much as a Z.

 

Thanks for the fuel recommendation and your experience Hal.

This is the pressure sensor I was looking at (they say inexpensive, but that may be a relative term): http://www.optrand.com/products.htm#apsis

EDIT: Actually I found this white paper on their site that discloses the theory of operation and an indicated price of under $10 per sensor: http://www.optrand.com/Papers/fisita98/fisita98.htm

Too good to be true? Think you could ask for some test samples and try them out for us? I suppose I could use my Innovate logging gear - looks like a linear output with high precision, but not necessarily accurate (good enough for relative determinations)...

 

[/drop mic]?

great info!

 

Ok, never mind on the pressure sensor - looks like the total cost per channel is roughly $1000! $6k is just a bit too much for casual use / academic curiosity. Maybe ok for a shop?

 

If they really work for $1k each, I would actually consider. I'm sure next time I get frustrated with drag cars on the dyno I'll give them a ring

 

Will 100 octane prevent detonation at high boost?

prevent it, not absolutely
reduce it, yes

 

You can definately run a little more boost and achieve more power with 100 octane vs. 93. However, the only way to really know the correct timing valves, is via trial and error on a load based dyno. The MBT method of setting timing requires a way to measure your results (repeatable dyno), and is not as formulaic as something like an suggested AF ratio.

 

I am currently running 11-12PSI on my stock block with 100unleaded fuel. pulled 1 degree of timing up top. and 11:1 4th gear WOT.

 

I was going to rent a dynojet to get my feet wet with tuning for timing. I figured while I was at it, I'd try to tune up boost a few notches - like maybe 18-20 psi? I don't have the experience to identify where/when you reach MBT vs. where/when you reach the detonation threshold first. So, I was only going to attempt it with race fuel - trying to get my hands on 105 octane (VP MS109)...

Sharif, thanks for your input - when you gonna have some time to play with my car again? You're too busy with new customers - lol! Let me clone you here in the lab and your clone can go win races while you teach me what I need to know.

You are recommending a load based dyno, but I only have access to a dynojet. I'll give you a call tomorrow if you've got a few mins...

 

Cool...I want to talk to you about an idea as well...I send you an email today as well.

You can use a dynojet, but a nice way to get used to dialing in the timing, is steady state, and low low boost...or even slight vaccum. While holding the load on the motor, you can click click click and see real-time engine output....very nice. Something you can't do on the DJ.

 

From my experience with low-compression VQs, MS109, and 18-20psi, you will definitely see tq level/fall before you experience knock.

 

Great feedback guys - thanks. Both you guys working late? "Joys" of being single and kid free - ahh well - well I gotta go

 

No problem, and yes... I'm in the lab now, turning up one of my babies

 

Like most have said, the variances from engine to engine won't allow for a mathematical formula. If you think about it, an evo will run 20psi on pump 93.
A built 8.5cr VQ should be good at 20psi with 100 MOTOR octane fuel.

 

Appreciate the feedback and your experience with the evo platform.

However, I'll respectfully disagree with your first point. There's nothing that CANNOT be modeled or explained through mathematics. History has shown that those who disagree with this position are subsequently proven wrong. Just a matter of time, necessity, and ingenuity...

 

what DJ are you thinking about? just curious about the other options around the area.

 

I would love to agree, as I always use mathematics to explain everything. Problem is, you can use/make/work a formula for an estimate or general outcome, but each individual engine combo would need it's own formula to get it right. Deck height, squish, piston shape, even the spark plug or dwell time will play a role in the outcome of the equation. Hence the invention of the dyno. Turn up the boost, set the timing low and work your way up. As long as there's a good HG and a set of headstuds, I don't see an issue.

I specialize in Supra's and things 2J equiped, so a low compression VQ is not my forte, but the principals apply regardless.

 

Craig's dynojet on Guess rd. (Staples Automotive Engineering). Hey, you know any pumps with high octane unleaded? I've sent an e-mail to VP's rep in Fayetteville, but no response yet.

 

i do in charlotte. the pump outside my cousin's has 101 or something like that (i think its a shell station, and i'm sure there are others with Lowes within 30 miles). Around here no. I looked forever last year because my 2t scooter runs on 100 octane.

I use Klotz Hitrate in the scoot now for 100+ octane mix. ~150$ for 5 gallons on concentrate. I think its leaded though.

Phantasm (a ricey tuner shop) in downtown raleigh does 3 pulls on their DynoJet for 60$. I did some pulls there a while back, not sure what their hourly charge is though