Why Are HotAir Cars Slow?

[Boost231]

I think the biggest limiting part on these motors would be the intake manifold. I also agree with the above post talking about the throttle body being a restriction on a hot air due to it not being under boost pressure like the 86/87. Much more sensitive to causing a restriction when the engine is having to suck the air through a part rather than being forced through under pressure like the intercooled motors. It may be something to look into getting a 70mm TB to work on those cars running turbos with larger inlets than 62mm. But with all cars they are not going to run the numbers with out tuning and track time. Since the hotair crowd does not have as much of a following as the 86/87 its seems there are not enough people pushing the envelope or breaking new ground on what it takes to get these cars into the solid 11-10 sec zone. The intercooled cars have been tuned to death. There are many cars running near 10's with mostly stock parts on factory sealed motors. Once someone overcomes the above mentioned engine differances and is dedicated in tuning to the end (suspension too) then Im sure thesecars will run the times everyone wants. Tuning is the biggest factor.

i would think going to a 70mm tb wouldnt do much if the inlet let of the turbo doesnt match. i have yet to take a mic. to see how big the inlet of my turbo is but lets say its a 65mm. i would think if you went with a 65mm tb that would be better since its a nice straight shot with no edges to hit. so lets say i could get a 70mm tb and the inlet to the turbo is only a 65mm. if i could send my compresser side of the turbo to limited or precision and have them bore the inlet to 75 that would work really well i would think. im going to look into this more once i get my hands on a stock 87 tb but i dont think there is much meat on the compressor side to bore it open more. so im going to mic it and see what size tb i really need and go from there.

 

[tb3]

Boost231, have you thought about a even bigger turbo? just curious is all.

also, what about our uppipes? Is there anything to there being a longer distance from the pass side outlet to turbo on our cars, vs the ic'ed cars? Any chance velocity of the exhaust gasses going through the path they have to take (uppipe) could be hampering the turbo from full potential? I'm just swinging in the wind here, but maybe its something legitimate to think about, I don't know.

 

[Way2QWK]

Boost231-

Thats what I was meaning. Utilize the 70mm TB if the compressor inlet is near 70mm. Thoughts in my head just didnt make it to the computer. I would look into getting that housing opened up a bit. Maybe some potential there.

 

[Boost231]

Yes I have thought about a bigger turbo like a TA-64 since that is the biggest Ta version I know of and because I am putting heads on my car. But I think the potential of the 54 is sufficient enough and keeps me in the right efficacy range for my application. As far as the up pipe is concerned there is definitely a factor as far as spool up time due to the fact that the exhaust gases have to travel threw the up pipe into the turbo. As far as the 87 is concerned eliminating the up pipe it is going to spool faster since it has a shorter distance to travel and the turbo is directly mounted to the header. This is just my thought but maybe someone can clear this up due to other factors like egt, turbo location, and other factors.

 

[Way2QWK]

I think the air coming out of the turbo is moving at a fast enough rate that the extra 12" or so of travel through the hot-air up pipe is not going to make a differance. Take a look at cars that have a rear mount turbo setup.... all the way in the back of the car, with the right turbo they have no problems with spool. Anyways, spool time has nothing to do with max power output. At a certain point, the diameter of the up-pipe may become a factor. Thats one area that could use some experimenting to find out when a upgrade is benificial.

 

[1QUICK85]

Does the stock throttle body flow more or less then the stock MAF sensor?
84/85 and 86/87 MAF sensors flow the same amount. So, if the stock throttle body is flowing more then the MAF then is the throttle body really causing any problems in the stock location(it is a bigger throttle body then a stock 86/87)? I think the throttle body is only really effecting throttle response and maybe chocking off the turbo a little, but you probably having to be pushing a lot of power to notice it.
I think the stock turbo, intake, up-pipe, and downpipe are the key factors holding the hot air back from the factory. Those are the reasons the hot airs don't respond as well. My .02 cents, interesting thread. :smile:
-Nick.

 

[Boost231]

i was just thinking something to do with the temp of the exhaust gases and what not but i dont know. i didnt even think of those rear mount setups like the STS but ya. also as far as the throttle body deal i think the stock maf will out flow any tb we put on our cars so the tb is the issue as far as air in.

 

[1QUICK85]

The throttle body is smaller on the 86/87 cars, so I don't think that is a concern for the hot airs. You can only push as much air threw as your motor will allow............intake, heads, headers, downpipe, and stock exhaust. Its a big air pump and the 86/87 setup does it better from the factory with its intake and downpipe.

 

[Jerryl]

Disclaimer:
I am not some engineer who got all this figured out.
Just a rough estimation to try and pinpoint some things.
Sure, some will argue and some will flame, but it is close enough to determine some things. This is ALL theoretical and many of the variables have aready been proven by the experts. (It is late, I am tired, it is compex, but hope you get the idea and see some value in this excecise)

I was trying to pinpoint to see where the bottle neck may be.
There are LOTS of ASS-U-M-ptions made but you get the idea.
There is some value in it I think., So, FWIW ……….

To produce an 11.5@118mph run in a 3700 lb car, requires about 485 hp at the wheels
At 90% driveline efficiency, 539 HP at the crank.
At90% VE, the required theoretical HP is 599 HP (Call it 600 hp for ease)
Turbo flow required is about 900 CFM or 63 lbs/min.

Here are some of the basics;
3700 lbs
Bore 3.8
Stroke 3.4
RPM 5200
Inlet valve size 1.70
Lift 0.384
Boost 15 PSI
Engine eff. 90%
Turbo Eff 75%
Turbo intake temp 80F
Discharge temp 120F


Heads
Stock inlet flow @0.400 lift is right at 150 CFM
Max lift is at roughly 1/4*Dia or 0.425” lift

Inlet Valve speed is 0.624 Mach Index (MI) …. (0.6 = max)
@0.450 lift - 0.533 MI
@0.500 lift – 0.480 MI
This leaves me to believe that more increased lift would be a very good thing

To produce an 11.5@118mph run in a 3700 lb car, requires about 485 hp at the wheels
Ass-U-M-ing an 90% driveline efficiency, 539 HP at the crank.

To produce 539 HP at 90% VE, the required theoretical HP is 599 HP
(Call it 600 hp for ease)

To produce 600 HP, you need about 900 CFM
900 CFM is about 63 lb/min
Again Ass-U-M-ing equal balance, each intake should flow 150 CFM @ lift. Looks like the stock ports are barely up to the task. And a bigger turbo “should” not be of benefit.

TB
At 58mm, air speed is around 555 ft/sec
Sonic is 1120, so it seems ok.

So, Turbo flow required is about 900 CFM or 63 lbs/min.
If you keep the pressure ratio at 2 (15 psi) you get cooler tamp, if that is the efficiency rating of the turbo.

Interesting note is that for every 10 deg drop in temp, a benefit of about 1 PSI is present.
So, say you need 900 CFM at 15 PSI bit the turbo runs at 200F.
If you decrease the temps to 120, you get the same 900 CFM around 7 PSI.

So, you need a BIG turbo and run LOTS of alky, (22 ounce or 660cc /run) and pull fuel. The questions are: Intake and header/exhaust flow.

 

[JOELO'S T-TYPE]

Excellent addition Jerryl!!

I think the key factors were mentioned at the bottom of your post except one (in my humble opinion), Engine Management (tuning).

We all agree that the intake takes away some power producing air flow from our engines. The exhaust system, specially up and downpipe are big power killers. Every inch of pipe travel that we have on our air flow route in and out of the engine affects us greatly, and our "excellent and beloved" downpipe topic should have it's own zip code by now, it's been mentioned almost as much as religion.

I really believe tuning is key to many hidden ponies in our cars.

Great topic!!!!!!

 

[Jerryl]

Excellent addition Jerryl!!

I think the key factors were mentioned at the bottom of your post except one (in my humble opinion), Engine Management (tuning).

We all agree that the intake takes away some power producing air flow from our engines. The exhaust system, specially up and downpipe are big power killers. Every inch of pipe travel that we have on our air flow route in and out of the engine affects us greatly, and our "excellent and beloved" downpipe topic should have it's own zip code by now, it's been mentioned almost as much as religion.

I really believe tuning is key to many hidden ponies in our cars.

Great topic!!!!!!

100% agree. I don’t think 90% of us spend enough time tuning. Engine management is often taken for granted as well and that will make or break any combo.

Called Precision Turbo.
The recommended model to flow 45 lb/hr @ PR -2 is the SC60XXX ~ $1200

I reviewed a few maps and realize there is MUCH more to this than just max flow.
Here are some great maps for research.
TurboByGarrett.com - Turbochargers

 

[cwmccray]

When I first got my 85, I ran the car before learning to tune. I finally got a gauge on the car I found out I was barely get 10.5 lbs of boost.... I was breaking the tires from a standstill and on the shift. I set the boost to 14lbs and the car responded greatly. NOW the bad news.... No knock, but after one run if i can back and ran again I would only get a 10 lbs What did I learn... I could kill stock T/A and Z28's. Only could get in 1 run... From the factory, some HA's got 10-maybe 12lbs of boost. A friend of mine only had 9lbs when we put a gauge on his car. With a K&N, Kenne-Belle Hot Chip and a adj regulator, we got him into the 13.99's. Boost was set to 15lbs. With 65hp NOS, 17lbs boost and a Kenne-Bell Nitrous Chip, he finally ran 12.60. So what did we learn... In 1986, GM had planned to use water/alcohol injection. The problem would be the driver forgetting to fill alky tank... GM choose to intercool. The Kenne-Bell Niitrous chip was ahead of its time.. especially for a Hot Air... Jim Bell found a way to change the timing progressively with nitrous.... The curve of that chip was flat... On a HA.. that 65hp shot was almost 85hp... We did put a Bosche 308 pump at KB recommendation. We would launch the car against the brakes and just before the tree spray the NOS. So in effect the NOS to the place of the intercooler at the top of first and second gear down the track. There was a old timer, Sterling McCullars from Mississippi, he had a 87 GN with a 3 stage Nitrous system. Sterling and Lee Howie (Mr. Twin Turbo from Ohio) came up with a mechanical solonoid system (Rumor was some Coke Drink machines were missing their solonoids ) that sprayed three separate systems in to a STOCK turbo (I know... let the flaming began aka Tim Stockwell). I saw this car run 6.80's in the 1/8 10.70 1/4). This car was a KILLER in the 1990's. Sterling help us get the HA moving. We tapped the inlet adapter. We got the fuel of the fuel rail. We actually started with 35hp shot cause we WERE SCARED . The 35hp actually gave us a little over 50hp. Then we stepped up to 65hp. My friend sold the Lear seated GN and bought a Pace Car GTA. Just a little reminising,,, sorry so long:biggrin:

 

[MoeJr]

Boost231, have you thought about a even bigger turbo? just curious is all.

also, what about our uppipes? Is there anything to there being a longer distance from the pass side outlet to turbo on our cars, vs the ic'ed cars? Any chance velocity of the exhaust gasses going through the path they have to take (uppipe) could be hampering the turbo from full potential? I'm just swinging in the wind here, but maybe its something legitimate to think about, I don't know.

I am coming in late here but TB2 have you thought about flowing the heads and intake to see how they match up? That way you could see what the flow is and where to port in order to match flow for your combo. Just my .02

Moe

 

[tb3]

Have I thought about it? hell yeah I've thought about it! Seriously though, thanks for the suggestion. I'm open for, and appreciate any suggestions or comments that can be thrown my way. Let me just kind of give a little overview of what I'm planning on doing.
My goal is consistant low 12's at the track. Would be nice if I could break 11's. I will not sacrifice any of the options on my car, including ac. I will be running alky of course, I will not intercool it with conventianal air/air intercooler, I have nothing against intercoolers, they DO work, and there are lots of benefits to them. But my car still retains the original turbo/intake setup, and it has been proven that these cars can make it to the 10's with that setup, therefore, i have no doubts about my goals for the car. I've got a few more mods I'll be doing over the next few months. I'll be playing around with turbo selection, My stock injectors should be adequate for now, and they are currently flowing fine. I've got to get my chip situation squared away. I'm going to port my tb. Even though thats also being discussed in this thread, and it may very well not even help me really, (just going on some research I've done), regardless, I've determined that it definetly won't hurt to port it. A few other odds and ends for the summer, mostly doing research and getting sharp on tuning. This coming winter, I'll pull the engine and get serious with it. Knowing me, i'll go over board as far as beefing up the block componets and spending lots of money on the heads. I've got a spare intake that I'll send off to have gutted,welded and ported, then matched to the heads. A big factor will def be (as jerryl has pointed out and you have suggested) is to have the entire system matched as best as possible from air in to air out, for air flow, obviously. (remember the "engine is just a big air pump" idea?) And we'll see how I fair, I'll make some mistakes along the way, but it'll be fun. When I get everything back in, turbo selection, cam selection,and tuning is what I want to be my main focus. I'll be playing around with some differant designs of uppipes that I'll build myself. Theres lots of other details, poly mounts, etc....but I'm just giving a general overview. My big concern right now is getting the down pipe situation squared away. I think a 2.5" dp with the integrated wastegate would be the way to go. From the research I've done, seems like theres always fit issues with the 3" pipes. I don't want to go cutting/hacking/beating on anything to get it to fit. I have no hard data to back it up at this point, but I'd bet a 2.5 dp with the integrated wastegate is going to flow better than a 3" that still uses the stock elbow.

 

[Jerryl]

First off, my goal was a mid-high 12 DD.
That Has not changed.

“IF” I had to do it again with a different goal, I would have a high lift cam (0.500), bigger turbo (?) /converter (3400), AND raise the compression to 9:1. The cam would allow flow at the valve below Mach Index, the larger turbo would allow flow at much lower boost level, the converter would spool the turbo, and the increased compression would allow for increased performance at lower boost.

 

[cool 84]

Biggest problem is all of the little problems.

1. Turbos- We can't get anything near the CFM flow of the intercooled turbos. TA 33 is the biggest common I believe for the HA cars.

2. Intake- You hit the nail on the head with that dissection.

3. DP- Until you can get the 90 degree bend out of the elbow on the turbo it will not ever be close.

4. Colder Air- More fuel to burn, Alcohol helps tremendously, but not as much as a colder air charge getting sprayed with Alky.

My 2 cents.

You can put turbos capable of mid 10s on the hotairs.... I'm running one.

Ported gutted intake flows more than a stock 87.

 

[cool 84]

The throttle body is smaller on the 86/87 cars, so I don't think that is a concern for the hot airs. You can only push as much air threw as your motor will allow............intake, heads, headers, downpipe, and stock exhaust. Its a big air pump and the 86/87 setup does it better from the factory with its intake and downpipe.

Problem is you can push more air through a given opening than you can suck.

 

[cool 84]

Does the stock throttle body flow more or less then the stock MAF sensor?
84/85 and 86/87 MAF sensors flow the same amount. So, if the stock throttle body is flowing more then the MAF then is the throttle body really causing any problems in the stock location(it is a bigger throttle body then a stock 86/87)? I think the throttle body is only really effecting throttle response and maybe chocking off the turbo a little, but you probably having to be pushing a lot of power to notice it.
I think the stock turbo, intake, up-pipe, and downpipe are the key factors holding the hot air back from the factory. Those are the reasons the hot airs don't respond as well. My .02 cents, interesting thread. :smile:
-Nick.

It's about pressure ratio. Any restriction on the intake side of the turbo has a huge effect on the outlet temps. That TB mounted on the inlet side of the turbo hurts the hotairs-- especially modded hotairs more than you think, including spool and power.

 

[tb3]

Cool84
are you running a intercooler? Looks like it from your sig. Just wondering is all

May flow better once gutted. But what about the equal air distribution to each cylinder? Wouldn't a 86/87 stock intake still have the advantage with the RJC power plate?
I'm a little lost on the pushing vs sucking comment. Whats the differance? Isn't it all about delta p? High pressure always flows to low? Which is why I have been wondering of late why the focus hasn't been on bigger turbos. A bigger turbo to pull more air through and force it down. I know its way more complicated than that, and a bigger turbo can be restricted of its potential because of the size of the throttle body and the intake, and the dp. and then theres the temp thing

I quit.
I need more exp before I can contribute any more comments to this thread, I'll just read from here on out.

 

[Boost231]

well

i know as far as my gutted intake all the ports dont flow even thats why i want to get my on a flow bench and get it matched. the #1 and #6 cylinder are alittle rich compared to the rest. well i will let you guys know what happens with my car when i put the new heads on. right now the car has gone 12.6@107 with little tunning. im going to be putting GN1's on the car probley and have the intake ported to match since its gutted and gasket matched to the felpro gasket already. we will see what happens.