Anybody know if running a built turbo b-series motor around 14.7 A/F on pump gas is ok? Car is capable of around 370hp on pump gas. I have heard that since turbo motors run hotter than stock, cruise A/F should be a tad richer but wanted some thoughts from the masters. Check my sig for engine specs.

I have been playing with my cruising fuel values, but don't want to go so far as to hurt the cylinders/rings/internals. I have been running 14.7 for a while, and the car doesn't overheat or anything, but that is because I'm running an oversized radiator, and I'm getting really good mileage at this ratio. (Close to 30mpg)

My main concern is that even though the car doesn't overheat, the cylinder temps be kept safely under control. Or is this one of those - "Everybody's setup is different, check your plugs" - things?

I also assume that it doesn't matter as much with E85 due to the cooler burn characteristics of the fuel? Thanks dudes.

 

Reading your plugs is the fastest & cheapest way to see what's happening in your combustion chamber. Generally speaking, steady state cruising in vacuum, 14.7 or 15.0 on pump gas should be fine.

Alcohol based fuels have a wider tuning "sweet spot," partially due to it's chemical make up and partially due to the extra volume required. For example, if your car makes peak power between 11.6:1 and 11.8:1 on gas (any richer or leaner decreases power), E85 or methanol might make peak power between 11.3:1 and 12.0:1 (converted). + the cooling benefits, knock suppression... overall, alcohol based fuels are just much more forgiving for tuning.

You're asking the right questions and you're on the right track - so props to you!

 

i, too saw this on the default target lambda table on the S300



I feel its unsafe to continue at 14.7:1 PASS the 3rd column (-20.7" vacuum) on a turbo motor or an high compression NA motor. Possibly richen it up to around 14-14.2 by the 4th column (-17.3" vacuum) maybe? 13.6-13.8 for the 5th-7th ... what would you guys suggest as a good target lambda values?

 

blah, my turbo car cruises between 14.7-15.3:1. if its leaner just have a tiny bit more timing to match. an egt will be helpful. mess with the timing/fuel settings until you can get the egt to stay stable and not continue to rise.

that said anything under like 12" should be in the 14's and below 5 or 6" in the 13's. it really depends on your fuel, compression ratio, efficiency of your cams/exhaust etc...

 

It doesn't matter if its NA or FI, at cruise its the all same load on the engine. You can lean the crap out of it like 16-17 AFR and advance the ignition in the cruise cells. Feel safe to experiment with the light load columns. You will never hurt anything under light load like cruise.

 

thanks, ill give it a shot and see if i can get some better mpgs. so even on a high compression NA motor on pump gas, the light load is safe? which columns should i watch out for ? obviously 7 and above , but what about 4-6?

 

Yes you'll be fine. You'll need to figure out which load columns you cruise around in, likely column 4 and its neighbors.

 

my experiences tell me that there is a difference between cruising and light acceleration like 18" vs 12". on high compression pump gas you may not be able to run a lot of advance much past column 6.

knocksense or another knock detection method will help you maximize it if you are indeed dealing with a high compression motor.

muckman, i know its been a little while but what did you use for knock detection on the high comp boost motor?

 

Knocksense. I used it primarily for the warning light but am now logging the 5v analog output.

 

well, ive tuned a high compression motor , and there was a lot of poppin noises whenever i get below 14" (column 4-5) if i kept the air-fuel anywhere near 14.7 . the poppin went away when i got the air -fuel to around 13.8 . Because of that, i never ran that much ignition advance after column 3, and have always been conservative with the air-fuel even when tuning less aggressive setups after that experience.

 

That is most likely because it wasn't tuned right to begin with. There are a lot more tables to deal with than just fuel and ignition.

 

Light load I cruise around 16:1 with high advance. Just get your tip ins sorted and watch the leftmost column for really off-throttle behavior (it can cause bucking on/off light throttle if you have it tuned badly) and you should be good.

 

Just curious what conditions usually cause bucking under light load? For me its usually caused by a decel value that is set too high where you can trigger it during light cruise.

 

I understand that tuning a car correctly requires the tuning of each and every parameter, but when the car is warmed up, on open loop, and pops when the engine lightly accelerates from 2.5K rpm to 4K at 14.7 air fuel, and stops when richen up to 13.8, i fail to realize how that could be any other table. please elaborate.

raene, when i cruise at column 2 (20" vacuum) its fine. i have the tip-ins set, and it decels fine. ive encountered the bucking before and like muckman, ive found it was the tps decel set too high. my problem with that particular to tune lies at the very light to light accleration .. which is column 3-5 for me (17" to 13")

 

There are many software and hardware possibilities that could cause that but lets not derail this thread.