Maximum Boost on Turbocharged SI Engines

[wxman]

I challenged a post on pickuptruck.com about turbo gassers being "the ultimate in power and torque". See the last few posts in this thread . I am pretty familiar with turbocharged diesel (CI) engines, but admit I have little knowledge of turbocharged gas (SI) engines.



According to this guy ("turbobill"), "... Indy type cars are probably running the highest boost levels for turbocharged spark ignition engines, somewhere around 90 psi I believe. " The "I believe" makes me pretty skeptical. Can anyone verify if this is in fact true? What type of fuel is used? What is the max boost pressure of a SI engine using gasoline as a fuel?

 

[JoshPeters]

Looks like a bunch of Ignorant gassers to me! They'll learn sooner or later!



Josh

 

[RBratby]

i just went on an indy car website. according to the website the rules say boost is limited to 22psi. the website says they burn methanol.

 

[NPloysa]

"If a gasser (spark ignition engine) would be as good or better than a diesel why is it that all the 18 wheelers are diesel??

Could it be that while producing the hp and torque needed to pull heavy loads the diesel also uses less fuel??"





That's a quote from FamilyMan. Yes, all current 18-wheelers are diesel, and almost all are inline 6s, yet he is driving a Sick Point Oh V8!

 

[wxman]

Thank you all for your responses and for the supporting post(s) on PUTC. It appears that the 90 psi boost on Indy cars is an "embellishment"!



What IS the highest boost levels that anyone has seen on a turbocharged gas (SI) engine?

 

[RustyJC]

What IS the highest boost levels that anyone has seen on a turbocharged gas (SI) engine?

I would check the Formula 1 engines back in the late '80s and '90s (up to the current naturally aspirated formula). Some of the 1. 5L turbo engines were making 1200 BHP in qualifying trim. This was back when they allowed "designer" fuels, though, so the stuff they called gasoline was unlike anything you'd ever find at the corner stop-n-rob!



Rusty

 

[MrWinkey]

I'm running 22 psi on a 2. 2L dodge 8v head. Cound run more but ran out of injector. Already have 52 pph injectors so I guess I'll have to start putting a 5th and 6th injector.



I have a couple friends who run about 45 psi with the same bottom end. I think the biggest reason that you run a diesel is that it lasts much much much longer than a gaser. Around 200k on a gaser is fantastic. On a motor like our Cummins it's just barely broke in.

 

[JoshPeters]

Well I may not be a member of that site for long..... hehe... I'll see if I can make this guy realize how stupid he is.



Josh

 

[HoleshotHolset]

45psi on a turbo Chrysler? That must be Gary Donovan.

I never went above 10psi with my 'bathtub 287' head casting equipped 2. 5L turbo minivan. That thing was an absolute blast to drive... .



The old F1 turbo gassers used to run about 40psi.



If you want to see high PSI on a "gasser"... look at the alcohol fired pulling tractors. They're converted diesels that run alcohol...complete with gasser style fuel injection, low compression, etc. They run upwards of 150psi...



Matt

 

[snowracer69]

Do airplanes count?



Rare-bear and Dago Red both run upwards of 130-150 inches of manifold pressure (Hg) which equates to anywhere from 64-74 psi. Of course, they also run ADI and nitrous at the same time. If either pulls the throttle back too fast, or advances it too quickly, the engine will destroy itself instantly.



Fastest motorsport in the world...

 

[wxman]

Guess I still don't understand how the autoignition (detonation) problem is overcome in these highly turbocharged SI engines. 45 psi is ~3 atmospheres, so you're essentially tripling the compression ratio (effectively). So 9:1 compression ratio becomes 27:1 effectively. Maybe you could lower the compression ratio to something like 4:1, but that would make it impractical to run at anything much less than "full throttle" (wouldn't it?).



I understand about the "designer fuels" with very high autoignition temperatures, but it still seems to me that there would be a fairly low limit on the boost on engines running nothing more than 93 octane fuel.



Where am I going wrong here?

 

[JoshPeters]

So as Wx and I try to beat some Diesel common sense into this guy... . anyone else have something they want me to post?



Josh