High air temps and a/f

B

Bobo

Guest
Now that I can log my air temps I'm kinda worried. With around 20-22 psi with a T76 and what I'd call a medium sized air intercooler on a 347 ci sbf, I get between 190-210 at the 1/8 mile. That is high right? I need more power, I want to try 25-28 psi and/or more timing. I run about 23 degrees now on 114 octane. I'm gonna try to get some 117 octane. I'm afriad to try more timing with the boost just where it's at.
How much does the Speed Pro compensate for the high temps? Any guesses as to how much the temps will increase with 3-5 more psi? The a/f ratio doesn't seem to rise much with the air temp increase, but I'm still worried about adding timing or boost.
The a/f ratio goes up and down, and it seems like the boost follows it. The O2 says it is taking away fuel all the time, so I need to take out some fuel from the VE table. When I do that, will my a/f ratio be more of a flat line? BTW, my target a/f is 11.2, way too rich or just a little safe?
One more thing, has anyone ever hear of or tried spraying CO2 or nitrous on an intercooler? I can rig up a set up to spray nitrous on the ic during or just before the run. I can also go to a bigger air/air or I think have mine moddified for water. Any thoughts?
Thanks!
 
The Speed Pro will automatically compensate for the manifold air temperature (assuming you have the air temp sensor after the intercooler or in the intake).
190-210 sounds high to me, a better intercooler would definitely give you some hp. If you get a better IC, the Speed Pro will automatically add more fuel as intake temperature goes down and the charge density goes up.

From what little I know, 11.2 a/f ratio seems pretty rich. I thought 11.5-12ish was more typical for a high boost kinda situation. But then I am a bit ignorant here, don't take my word for it, others will have to confirm that.

John Estill
 
On this subject, do I want to mount my IAT sensor in the air stream after the intercooler or in the intake manifold? I'm worried that in the manifold the reading may be affected by radiant heat from the engine.

Thanks,
 
The heat problem you mentioned is real. The last turbo car we had here in our shop had the air temp sensor in the plenum and the sensor was reading RIDICULOUSLY hot. It was obviously being heated by the rest of the motor. Relocating the sensor to the outlet of the intercooler made an immediate improvement in how the car ran. Put the sensor where you think it will get the best measurement of the temperature of the compressed air entering your motor. It is not my opinion that cold air leaving the ic will pick up a great deal of heat from a hot intake, so I like the intercooler theory myself.

Bear in mind that I run a naturally aspirated motor... I'm only an expert in my own mind! :D :D :D
 
Hmmmm...

I run my MAT in the intercooler up-pipe, about 2 feet before it ever sees the intake...

I've been trying to get DeQuick to send me a replacement core for the V-1 forever... Seems he has his usual sense of urgency about that.. hehe

His thicker V-1 core works REAL good (I've seen data logs from a Fel Pro with a very small rise in charge temps during the run).

Sounds like you need a more efficient intercooler for that thing.
 
Well this may be too difficult to quess, but I'll ask anyway. What I plan on changing is my 2.5" inlet pipes to 3" (worth much?) and doubling up the intercooler. I have a Cartech/Bell Engineering 3 core that gets what I would think would be a good amount of air from the front mount position it is in now. Much of the core is exposed to air.
So here's the $64,000 question, would doubling up on the ic and using sheetmetal ends help much? The new part of my ic will be added to the back of what I have now, so my ic will basically just be twice as thick. Will the sheetmetal disapate heat better too? This will cost $500, cheap when you consider the whole 6 core ic itself costs around $1800. Sound like a good idea? I also plan on 5-8 more psi too. Thanks guys!
 
Hmmm, that's a tough one to answer. It all kinda depends... there are both pluses and minuses...

Pluses:
1. The charge air side pressure drop is cut in half. If you have a significant pressure drop now, that is a Good Thing, since extra pressure drop means the turbo is working harder than it has to, raising inlet temperatures and exhaust backpressures (since the turbine side is working harder).

2. The heat transfer area is doubled, which is a Good Thing, usually means colder outlet temps. It won't double the cooling though; if the current IC is cooling the charge air by 100 deg, the second IC won't cool it an extra 100 deg, for various reasons. The hot air that has passed through the first IC fins before hitting the 2nd IC is one good reason. It would be better if each had its own fresh air flow, but I realize that probably isn't practical.

3. The larger pipes is probably a good thing... with your single turbo, I'd like to see 4" i.d. on the suction, 3" i.d. on the compressor outlet (and even 3.5" isn't going totally overboard, the gain at max boost/rpm is slight but it is there), and 3" on the intercooler outlet. I'm figuring that you are moving enough air right now to make 600-700 hp BTW. Moving from 2.5" to 3" on both inlet and outlet is probably worth a good 1 psi of pressure drop saved at 20 psig/6000 rpm, less at lower revs. That seems worth it to me. FWIW, velocity at turbo outlet with a 2.5" pipe is about 275 ft/sec in your case, and with a 3" it's about 190 ft/sec (again, 6000 rpm/20 psig). As a design engineer (and we are a conservative lot) I don't like to see over 200. But, like I said, it hurts worse at high revs, and maybe it isn't worth it just for that operating point.

Minuses:
1. air flow... this could be the giant killer. If the pressure drop on the cooling air side of the core is too much, restricting the air flow, all that extra surface area won't do you any good. Calculating the cooling air flwo through a core is not my area of expertise; I do know it will be a function of fin count and tube count and such. Building a shroud for it will help.

BTW, if you do succeed in running 25 psi boost with, say, a 125 deg IC outlet temp, I forsee the need for big injectors (minimum 70 lb/hr) and making a good solid 750-900 hp! And you will also then be on the ragged edge of that T76, which is very well suited for what you are doing today.

FWIW from this here bench racer...

John Estill
 
Thanks a lot for your insight John. I want to try to get 900 hp out of this T76. The car is mostly drag, so I've considered a water ic, but the price is too much right now. This may sound kinda hard to believe, but they told me a guy with a similar setup to mine picked up 3 tenths in the 1/4 with this same ic upgrade. That guy ran a 8.65 @ 159 I do believe @ around 30 psi. I'm gonna try it and see what it gets me. Hopefully the pluses will outwiegh the minuses :)
 
I was told the car weighed 3150. Sounded high to me. If I remember correct, I saw him run a high 8 in 96 or 97. Not sure of the mph, gonna have to go back and look at my old tapes. I know Cartech built their own Mustang with a T72 and it got low 9's, and in the class they ran it would have prolly been over 3200 lbs. Turbonetics told me the 76 could get 900-950 hp. I figure 159 at 3150 is around 1000 hp? Since mostly Turbo Buicks are on this board, does anyone know what the fasest a TB has gone with a T76? Seems like I read about one in the high 8's? I have to get some real suspension before I start dreaming of those #'s though :)
 
re:

The fastest I recall hearing was ~ 145 in a 3600-3700 lb car. Maybe the owner will comment(?)

PS the T'netics catalog lists the max air flow of the T76 compressor at about 90 lbs mass/min. If you use that as a guide, mixing it with fuel at say 12:1 a/f ratio then that implies 450 lb/hr of matching fuel flow. If you assume a BSFC range of 0.55-0.50 you get 820-900 hp capacity.

TurboTR
 
I don't know how to figure BSFC, but I've heard a boosted motor will be around .55-.65 I think? Are you saying a motor @ .55 can make 820 hp with the 76? I don't know much about figuering fuel flow, BSFC, or reading compressor maps just yet.
 
Originally posted by Bobo
Now that I can log my air temps I'm kinda worried. With around 20-22 psi with a T76 and what I'd call a medium sized air intercooler on a 347 ci sbf, I get between 190-210 at the 1/8 mile. That is high right?

. When I do that, will my a/f ratio be more of a flat line? BTW, my target a/f is 11.2, way too rich or just a little safe?
I just rechecked my last few logs for air temp before posting this. My air temps (MAT mounted in uppipe) at beginning of runs were in the mid 90's....and at end of 1/4 mile run in the high 140's or low 150's. I did the figuring's....53, 51, and 54 degree difference. This is with the PTE front mount with the ambient temp being in the 80's. What temp do you start your run with??

And I just spoke to Dan the man Strezo today. I was running an 11.5 - 1 a/f ratio at the top end and had EGT's of around 1750. I thought this was OK with aluminum heads. Dan figures that's too high and suggested 1600's. So I'm going to fatten it up a bit. I'll try an 11-1 this Sat and see how that does.

Chris
 
Some things I have observed regarding MAT's:
I have never tried the MAT in the up pipe, but with it mounted in the plenum my car starts a pass at 120 (heat soak), when I launch it drops quickly down to 90's then gradually climbs to 140's. This is with a PT-88 & a V-1. The same combo with a T-70 ran about 40 degrees higher.
This year at BG we made several passes (friends car) with a T-76 and PTE intercooler. The air temps were in the 190's. We swapped to a V-1 and he dropped 40 degrees (the same day). On his car the standard PTE intercooler couldn't keep up. On both of these cars the Turbonetics turbos were putting out all the boost they could (roughly 25 psi) so that explains the high air temps.
On a twin turbo Mustang I just did with a liquid intercooler (mid 8 sec car). When we added ice the air temps dropped from 150's down to 70's. What I thought was suprising is that we only needed 3.5% more fuel for such an extreme temp diference.

I know a T-76 can probably sneak into the 8's if the car is light enough. Lance went a 9.03 with the wastegate closed (25psi was all it would make), but the turbo is going to be working VERY hard to do it and is going to need a REAL good intercooler. At 3600 pounds the fastest my buddy has gone is a 9.4 with the wastegate closed (26 psi).

Just food for thought so go easy on me :)
 
re:

>suprising is that we only needed 3.5% more fuel for such an extreme temp diference

But how exactly did you figure this? 3.5% more duty cycle, 3.5%more of what(?)

TurboTR
 
Re: Re: High air temps and a/f

Originally posted by ChrisCairns
I was running an 11.5 - 1 a/f ratio at the top end and had EGT's of around 1750. I thought this was OK with aluminum heads. Dan figures that's too high and suggested 1600's. So I'm going to fatten it up a bit. I'll try an 11-1 this Sat and see how that does.

Chris

I hate that: car running reasonably conservative A/F, reasonable timing, reasonable boost, VE map on the money... blistering EGT... richen A/F and ET slows. That happened the one time I fattened up the A/F slightly, and I haven't revisited this area. In fact, I'm not sure what else to try under these circumstances. If you pick up with lowering A/F Chris, please tell us about it. I'll probably try this again soon.

Art
 
Re: Re: Re: High air temps and a/f

Originally posted by JoyOf6


I hate that: car running reasonably conservative A/F, reasonable timing, reasonable boost, VE map on the money... blistering EGT... richen A/F and ET slows. That happened the one time I fattened up the A/F slightly, and I haven't revisited this area. In fact, I'm not sure what else to try under these circumstances. If you pick up with lowering A/F Chris, please tell us about it. I'll probably try this again soon.

Art

I think I probably will slow down. I believe Dan was talking more from a "don't damage your engine" point than a "go faster" point.

Personally, since I have yet to up the boost from 17 psia the better ET's should come later (with higher boost) once I get the map and A/F in line.

Chris
 
I assume you mean 17 psi gauge. You say you run 11.5 A/F at the top end, but apparently (?) you haven't come close to operating in the top end in terms of the 3-bar map. What's the A/F @ your 17#, and on a related note, are you running high compression?

At 17#, I don't think my EGT would be over 1550, although I never run the boost that low (8.6 CR). Thanks, just comparing notes.

Art
 
Re: re:

Originally posted by TurboTR

But how exactly did you figure this? 3.5% more duty cycle, 3.5%more of what(?)

TurboTR

It was based upon the car output on a chasis dyno. The 3.5 was 3.5% fuel enrichment on the Air Temperature Correction table.
 
Originally posted by JoyOf6
I assume you mean 17 psi gauge. You say you run 11.5 A/F at the top end, but apparently (?) you haven't come close to operating in the top end in terms of the 3-bar map. What's the A/F @ your 17#, and on a related note, are you running high compression?

At 17#, I don't think my EGT would be over 1550, although I never run the boost that low (8.6 CR). Thanks, just comparing notes.

Art

No...I meant psia on the Felpro. On the gauge I read just under 20. I once had this explained to me that psia "should" be 14.7 under psig...since it's absolute and the gauge "starts" at 14.7 but calls it "0". Since I'm 2.5 to 3 psig over the psia guess I understood it wrong...lol.

Anyway, you make a good point that EGT's should be lower with my lower boost. And my A/F at the boost level I'm at is 11.5. Ya know as a side note, I just looked at my plugs last night....and they look, to my non expert eyes, fine. Slightly gray around the center changing to very light black on the edge. (If I'm reading these wrong someone let me know please.) I would have expected them to be "leaner" lookiing considering my high EGT's. Perhaps return road, putting on trailer then into my shop "richened" the appearance.

Art...what plugs are you running...perhaps mine are too hot?

Chris
 
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