How much is too much ?

[Lee Thompson]

How much is too much ? I run 21-22 psi max. Does anyone run, or know of anyone running more boost on a hot air car and gaining anything by it? I have tried 25-26 psi with no gain from it. Is it just my car, or is this the norm with these cars? Thanks Lee

 

[cool 84]

What size turbo are you running? Mine's intercooled so this probably doesn't apply but when I put the T64 on as soon as is hits around 22psi the car REALLY wakes up and I can feel a big difference for every pound after that. I've gone to 26psi and it was awesome. With my old 49 it would keep getting faster but I had to really concentrate to feel any difference at high boost.

 

[Twins]

I don't really see any difference in the 1/4 times above 22-23 psi.

I can't tell if that was a problem with my car or if it was just the 33 running out of air.

 

[JDEstill]

On a theoretical basis, you should still be able to go faster with more boost.

Holding the compressor efficiency constant at 70%, going from 21 psi to 25 psi should give an 8% increase in charge density. Yes, it's hotter, but the increased pressure still makes it a net gain. Even if the efficiency drops from 70% to 65% there is still a 4% gain...

All else being equal, the actual change in air flow should mirror the change in charge density, ie 8% more density = 8% more air flow = ~8% more power.

So if you aren't seeing an improvement, I would suggest that you are either running out of compressor (maybe the efficiency is dropping too fast?), or maybe the turbine is becoming a restriction (maybe plumb a gauge and watch the backpressure?). Or maybe there's something else going on... but it appears you ought to be able to go faster.

What size turbo do you run now?

John

 

[Lee Thompson]

PSI

My turbo is a hybrid built by John Craig. I hope I am close here, T-61 or T-62 compressor wheel and the same turbine wheel as a 70. John said he could not go any bigger on the compresor side without going through the housing (84-85 housing ). He did say it was tested and was most efficient at 22psi. I would think I would still see some gain at a little higher boost. Maybe I need more turbo. I like my turbos like my cams BIG. A turbo is too big when you can/t close the hood, a cam is too big when it won/t go through holes in the block

 

[CoolAir85TNX]

LOL!!! - your'e killing me Lee.
YouDaMan - Dennid

 

[CoolAir85TNX]

Dennis - see im laughing so hard i cant spell!

 

[WFO]

Re: PSI

Originally posted by Lee Thompson
. A turbo is too big when you can/t close the hood, a cam is too big when it won/t go through holes in the block

yeeeeah buddy!that's what i'm talking about.


maybe the problem is the stock 84 housing itself.there is a significant difference between 84 stuff and 87 stuff.check this out.


http://www.gnttype.org/techarea/pictureguides/turboguide/8485vs8687.html


i was looking thru this stuff the other day and i was surprised at the difference.


maybe you should try a precision exhaust housing?i betcha that big exhaust wheel would like the extra room.


later,sean

 

[TType85]

Get rid of the 84/5 housing

Theres supposedly a way to put a 66 wheel in a TA (86/7) housing. Thats the way i'm going. This 54 is too small

What A/R exhaust housing are you running? I'm running a PTE .85 housing on my 54 and the car was pulling real hard on the top end of the track even at 17psi in street trim. (although the car only ran 112mph like that it still had a ton more in it).

 

[cool 84]

This reminds me of what I was told when I ordered my TA62 in the stock housing. I was told that at a certain flow rate the small housing would cavitate (I think that's the word he used) and would flow no more air. I was also told that I would get a 30hp gain by going to an 87 comp housing which is what I have on the 64 right now.

 

[Lee Thompson]

Psi

80 housing

 

[TType85]

Maybe you could go to a .96 housing? It will kill the bottom end a bit, but maybe give you a bit more on the top end?

 

[JDEstill]

cool 84 -

Cavitate isn't the right term here, that's just for liquids turning to vapor in a pump suction.

What you probably mean is "choked", when the suction volume flow hits a maximum and it just can't flow no mo', even if you spin the impeller faster.

John

 

[cool 84]

You're probably right, I talked to him 2 years ago but I remember he seemed to think the 62 wheel could never be taken full advantage of in that housing. The way it was explained was at a certain flow/boost, the car would actually slow down due to the housing.

 

[TX87GN]

ain't seen him in a while...

Lee, last time I talked to Drew Carlton (ATEAV8) I think he said he was running somewhere in the 25lb range. I actually saw him run 18-20lbs on the street on pump gas, If I'm not mistaken.

John C.

 

[REDS HOT AIR]

heck im pushing up to 22# with the stock turbo ....

but its really backed up on the ext. side ..looks kinda neet at night when i make a full pass on it and the ext. and turbo housing is glowing so bright you can almost see thru it..

i have every thing sitting in the garage to tap a pressure fitting in before the ext housing on the turbo but im afraid of what i might see so im gonna wait till i get my 12 second time slip with it then im going to do some testing just for reference

my turbo is WAY-WAY to small...good thing i said turbo...

 

[ATEAV8GN]

Boost it!

How much is to much is always different for every car... How big the, turbo, heads, cam, intake... blah balh... Every car is different. And each car will have its own "sweet spot". Even if your got 2 cars, botled thexact same parts on it, each would have its own "tune" to it.

I was running about 23-24 psi with my TA33. I too run a big cam like you Lee, 218/218, seriously ported 4.1 casting heads, and a Turbomotion V1 intake. But,as of tuesday of last week, the fabrication was finished to get the TA54 on the '85 and a set of MSD 50's went in yestrerday. So far I've got the car set at 19 psi in street trim, 93 octane, ZERO knock, with O2's in the 830's with fuel pressure at 42 static. So yes I've got more tuning to do, but there is more there for sure. In race trim I think this turbo can go 25-26 psi easy.

Two weeks ago I went to the track with the 33 still on the car (it hada bad oil seal on the compressor side mind you) and with only 20 psi, 26 degrees timing, 117 octane, 10 psi launch off the t-brake, the car went 12.148 @108.51 , 1.669 60', 7.647 @ 88.26 1/8th.

The car feels even stronger than ever before and once I get it a little more tuned I will be heading to the track to hopefully get kicked out for not having a cage I will update ya'll as soon as I know anything more.

Best of luck to everyone!

Drew H. Carlton
'85 GN, 12.148@108.5, NO IC, NO SPRAY

 

[Jerryl]

Another GREAT thread for those who are just tuning in ............

 

[Boost231]

thanks for the bump. havent read this thread in a really long time

 

[charlief1]

Thanks for bringing it back. This is some good info.