86944turbo

There is nothing that Rage2 mentioned that was incorrect. An excellent point he made was turn down the boost. He has also taken the time to map in better fuel mileage at part throttle W/lower boost. Not easy to accomplish. If your static comp. is 8:1 and your running 18 lbs. with fairly decent effeciency, you're well over 17:1 comp. ratio. If you're A/F @ max. rpm's and max. boost is in the 11's, you're leaving reliable H/P on the table. As well as accelerating ring wear, etc. Timing is critical. So, just adding more fuel may well reveal nothing. My AFR @ WOT changes dramatically throughout the RPM band, as does timing. 13.5 will fry my motor, even on race fuel and w/ex. valves that can take a lot more heat than stock sodium filled, inconel, etc. And, of course, race fuel, not the low grade tuolene from ACE, helps. .82 @ 7000 w/ 20lbs. Comp. over 20:1. Tremendous amount of work done to head. Not just for flow, but flame propagation. Even moving most of the plug out of the way. Rage2 has done his work and tested it on the track. Not just a dyno # and not by theory alone. Due to the fact that my motor is fairly effecient (at least for this comp.) it will produce a few more ponies if it were leaned out a bit. Very effecient N/A racing motors have run much leaner than stoich. More H/P. Even w/push rods and 2v heads, Winston Cup cars @ restrictor plate venues (where every pony is priceless) have run well past 16:1 in A/F. Some have reported as high as 17.5:1. Again, these are very effecient motors. 110% and more.

rage2

haha actually, made a small typo. I meant 13.7, not 14.7 .

The reason why we can't run that lean is because of 2 things. First, EGT's will be really high, and most valve material isn't designed to withstand more than 1650F temperatures reliably. Second, the high EGT's also increases the octane requirement. If we were running on pump gas at max boost, a 13.7:1 A/F ratio would knock like you would've believe .

So to work within real world limits, we make our maximum reliable HP at around 12:1 A/F ratio. This allows managable EGT's (additional fuel is a source for cooling) and of course, realistic octane requirements.

An interesting note... Formula 1 engines run about 1850F peak EGT's. It'd be interesting to see what kind of valve material they use .

FSAEracer03

F1 racecars use titanium-alloy valves

Bengt Sweden

This picture, which I have taken from the Halmeter Brochure ( TWM Induction), shows at what mixtures you typically get max power or max fuel economy. Most of my references claim 13.2 for max power but the curve is very flat in that area so probably this differs from engine to engine. As stated before, we would normally want to run richer for cooling purpose at WOT.


I am not familiar with winston cup racing but in many cases fuel consumption plays a big role in racing ( number of refuellings and weight).

I have been running a Volvo turbo engine for several hours at WOT in a dyno at EGT of 900C = 1650F. Volvo told me that this was about the limit for the turbo as well and in the long run the turbine blades would deform due to heat and centrifugal forces, resulting in less efficiency. I am still amazed at what kind of abuse an engine can stand if it is run in steady state.

Bengt

Mike S

Is that for turbo motors only? I was under the impression that Danno and some others had found more power at leaner ratio's on the NA's. Just trying to figure out if this applies to both or just the turbo.

Bengt Sweden

With very efficient swirl you can make sure that most of the oxygen is used with somewhat less extra fuel, approaching stoichiometric conditions but not leaner.
Swirl will also make combustion more rapid leading to that the fuel is burnt when the pressure can be used for pushing the piston.

I don't know if forced induction makes any difference.

Bengt