92 Auto AWD w/ 20g + liquid ic. drag report

[GDNF2ET]

I put in a set of HKS 272's last week and it totally screwed up the launch...the car wouldn't make it past 2400rpm/3psi no matter what the tune. I put AFR between 13:5 and 9.5 and had ign timing at that point between 0* and 30*..it barely made any difference. It would sit for 10+ seconds at that 200-2450rpm and 2-3psi with no change.


So I pulled the 272 intake cam, put a stock 2g intake cam back in...bingo...now it will whip up to 3500+ and 15+psi (limit of my testing with street tires...it goes up in smoke with even that much power on the brakes).

Was that a 2g, stock, turbo, auto cam ? I've been tempted to try a pair of 1g, 2.0, NT auto cams just to see how it does...I would imagine the NT cams would be more aggressive since there's no turbo for power...
Good info here !!

 

[autotalon]

I put in a set of HKS 272's last week and it totally screwed up the launch...the car wouldn't make it past 2400rpm/3psi no matter what the tune. I put AFR between 13:5 and 9.5 and had ign timing at that point between 0* and 30*..it barely made any difference. It would sit for 10+ seconds at that 200-2450rpm and 2-3psi with no change.


So I pulled the 272 intake cam, put a stock 2g intake cam back in...bingo...now it will whip up to 3500+ and 15+psi (limit of my testing with street tires...it goes up in smoke with even that much power on the brakes).

Im guessing the overlap was just too much at 2400rpm.

With 2 stock cams I would see (at 22psi street boost) about 36-37lb/min and peak power seemed to be about 6400rpm. Easy spool to 15psi on converter in like 4 seconds.

with both hks 272's...I was seeing 41-42lb/min up top with the same boost settings and power seemed to hold up top to 7500, peak maybe around 6900-7000. But it will not launch!

With just the 272 exh cam, it seems like a good compromise. Still seeing 40lb/min and peak power looks about 6700rpm and falls off a little less than with stock cams past 7000. It will hit 15psi/3400rpm on the converter within 8 seconds now. acceptable I guess.

Going to the track tonight if the weather holds out. MAx boost, slicks, E85, working IC water pump, rewired fuel pump, and starting with the last tune that should be close. Basically set to kill from the start.

planning to make one run without launch to test mph/tune/log and then go for a full pass & likely the boot from track mgr.

I had the same trouble for a while. Do you have adj. cam gears? I ask because I have been told to run more overlap to help with spool. +2int/-2ex. I also found leaning out the afr helped too. I also had no effect playing with the timing. I was also running a re stalled stock converter.

 

[Nate Crisman]

Was that a 2g, stock, turbo, auto cam ? I've been tempted to try a pair of 1g, 2.0, NT auto cams just to see how it does...I would imagine the NT cams would be more aggressive since there's no turbo for power...
Good info here !!

Stock 95 turbo manual cams.

 

[Nate Crisman]

I had the same trouble for a while. Do you have adj. cam gears? I ask because I have been told to run more overlap to help with spool. +2int/-2ex. I also found leaning out the afr helped too. I also had no effect playing with the timing. I was also running a re stalled stock converter.

Still have oem gears and I haven't changed the gears yet because Iv been swapping the cams via "zip tie" method of keeping the belt to the gear. But next time I have the head off or tbelt apart, I will put in the 272 intake with a set of adj gears. Then I can experiment to see if I can find a better compromise to get the higher airflow and rpm spread and still keep it able to whip up.

 

[rhamlinii]

Still have oem gears and I haven't changed the gears yet because Iv been swapping the cams via "zip tie" method of keeping the belt to the gear. But next time I have the head off or tbelt apart, I will put in the 272 intake with a set of adj gears. Then I can experiment to see if I can find a better compromise to get the higher airflow and rpm spread and still keep it able to whip up.

Any new Times?

 

[jrohner]

Is that track really that terrible or are your slicks not actually that good? I run just some random street tires I found laying around that I put on my 1G auto and I launch at about 24psi with my 16g. Also, doing a burnout helped my times.

 

[Nate Crisman]

Any new Times?

Yeah, I went to island last night with a working intercooler pump, an HKS 272* exhaust cam, and the air filter removed. Otherwise the same setup and tune as last time.

Run 1: rolled out with an easy launch
1.807. 4.987. [email protected]. [email protected]

Run 2: launched it harder. Minor change to timing
1.679. 4.763. [email protected]. [email protected]

Run 3: launch just a bit higher. No log unfortunately. Took out timing.
1.613. 4.723. [email protected]. [email protected]

Was warned for no rollbar after run 2, then I went quicker on run 3 = end of night.

 

[Nate Crisman]

Is that track really that terrible or are your slicks not actually that good? I run just some random street tires I found laying around that I put on my 1G auto and I launch at about 24psi with my 16g. Also, doing a burnout helped my times.

I ran 1.4's all last season on those wheels&tires on a similar setup. On the Apr night..track temp was 46*f and I was the only slick tire car. Radial tire cars were dragging water onto the starting line.it was ridiculous!

Last night I did 1.6's with not even a hint of tire spin, coulda done 1.5's if the turbo out spool harder in first or I held brakes harder. Felt like it was creeping last two runs when I left off brake

 

[rhamlinii]

I think I was only running like 31psi because we only had a 3.5bar aem map sensor, and the car had crappy cams with the degree likely wrong. Stock head & low compression. I think the car barely went 131mph off nitrous...pretty pathetic for a 35r alone. It wasn't setup or tuned anywhere close to ideal. At that time I still didnt really know how to tune aem well, didn't have the knock sensor setup right. Likely didnt even have the ignition timing synced right.

Plus with the stock trans and single disk clutch, I was lifting and granny shifting. Lettin the turbo fall off boost every change. I remember the car wouldn't even hit 30psi in first gear at all with the .82 housing.

What I'm saying is that car/setup in 2005 was a disaster, the only thing decent was it ran big mph for a 2005 era little shop built car. I just lucked into a decent tune with the nitrous on actually.

When you sprayed how much did the boost raise with the tial gate and the 35r turbo? I'm thinking of maybe adding spray to my current build. I remember your car being over 3000 pounds. I really want to trap over 150, and I'm a big guy. Any advise to help it servive?

 

[forcefed86]

Nice runs! When that 60' is ft is dialed in it outta scoot! Some of the low viscosity cold climate trans fluids may loosen up the converter at tad too...


On a side not whey would more overlap increase spool time? Does it just make more heat? With the small housing and big boost/backpressure he's running I'd think less overlap would be ideal?

 

[autotalon]

More overlap means the incoming boost air will escape out the still open exhaust valve, giving more to the turbine wheel.

 

[94awdcoupe]

More overlap means the incoming boost air will escape out the still open exhaust valve, giving more to the turbine wheel.

exhaust pressure is higher than intake mani pressure. there fore during valve overlap exhaust pressure moves backwards toward intake. increasing overlap increases this problem.

less overlap traps more exhaust in exhaust manifold for faster spool.

this is why hks 272 cams dont spool fast. they have too much overlap. usually just 10-12in vac at idle.

 

[forcefed86]

More overlap means the incoming boost air will escape out the still open exhaust valve, giving more to the turbine wheel.

Yea the op probably has a 2.5:1 or greater back pressure. I'd want more air in the cylinders for a bigger "bang" myself.

 

[autotalon]

ok, how much of the exhaust is going back into the cylinder when the piston is near TDC of the exhaust stroke? The way I have it, the exhaust closes 2* later and the intake opens 2* sooner. It sounds like you are thinking of the compression stroke.

 

[Nate Crisman]

I'm going to post some datalog screenshots that show how different this clipped 20g performed compared to a standard evo3 16g during spool on the converter and through first gear. I spent some time trying to analyze the difference and I'm very confident now that the clipped turbine wheel is hurting the 60'. I'll also compare the same clipped 20g turbo with stock cams, with both 272* cams, and with only the 272* ext cam. Sadly, Iv had the parts to setup a sensor to log ext back pressure and have been talking about doing it for months now, but just haven't gotten around to it. That would have been excellent info to know since it pertains to the issues Im having.

I have decided to rebuild my yellow 1g for the shootout this year. (family vacation plans changed to Dec, so August I'm free). My plan is to run DST of course, so what info I can gain from this car will be of service even if I don't continue to make improved runs with the red 1g due to lack of safety equipment. I'm guessing that 11.38 is the quickest this red car is going to run...I'm planning to "de mod" it a bit and use the liquid intercooler system and HKS cams on the yellow race car. This Red everyday car will get stock cams and a typical air/air fmic kit, which should slow it down just enough to be ok without a roll bar. Im actually going to try running it next wed night again on my everyday street tires and pump gas at my 22psi street boost level to see how it goes on that setup. (Im predicting 11.8@114 on 1.8 launch)

The yellow car will most likely be running a standard E3 16g and I guess my goal will be to come in second behind English Racing's grey 1g. hahaha



Did a lot of log comparison between the last two track days with this red 1g auto w/ 20g and comparing it to logs from the yellow 1g w/ 14b/7cm and E3 16g setups with the same stock auto driveline/basic engine/cams.

Basically...on the yellow car with both the 14b and 16g, the car would leave the line and run through the 60' at maximum boost pressure 25 to 33psi and cut 1.4 60' times. The 14b would spool to 25psi at 3500rpm on the converter in about 3 seconds and the E3 16g would do 3900rpm/22psi in about 3.75seconds. (both instances with either his 264/272 or GSC S2 cam sets)

This 15* clipped 20g on the red car takes more like 5-6 seconds to hit 15-17psi at 3500rpm on the converter, but worse off - it takes it 1.4 to 1.7 seconds to hit maximum boost of 27psi in first gear! The car is already through the 60' beam before it's fully spooled up! Not to mention, even with the waste gate solenoid completely maxed, it only hits 26.9 to 27.3psi peak in first gear at 5500rpm+ and falls right off from there to ~24psi. Average boost while moving in first gear is 22.9psi on my best 1.61 60' time with the 20g (not a hint of wheel spin and 100% throttle...leaving at 3900rpm & 17.1psi

On the Evo3 16g took about 3.75 seconds to hit 3900rpm & 22.0psi on the converter. It would spike to 34.8psi and drop off to about 22psi at 7300 during the first gear pull. The crazy thing is the average boost while moving in first gear, in same type comparison to above: Average boost: 29.9psi and the biggest part of that average is immediately at the launch since it will go from 22psi on line to 35psi Max boost while moving within .35 seconds! The car would do 1.46 launches with this much immediate torque off the starting line.

The Evo3 16g holds an AVERAGE boost pressure through first gear that is higher than the MAX PEAK boost the 20g ever produces.

Guess I just quantified my gut feeling that this 20g setup was lazy off the starting line and why it just didn't seem to put down the 60' times I hoped for due to the great difference in spool up & max/average boost in first gear. Not to mention my red streetcar is about 300lb more weight to push out compared to the tin can yellow racecar. The 20g might make more ultimate power at higher rpm, but that doesn't really mean much when it gives up a few tenths at the line. Honestly, I think the unclipped Evo3 16g would be a better choice overall for the streetcar...make close to the same peak power but a huge amount more bottom end torque. Granted, a 20g compressor wheel with an unclipped turbine wheel might be even better compromise, but unfortunately, I can't test that without a $$$ turbo rebuild.

 

[forcefed86]

I was under the impression clipping would just require more exhaust energy to do the same amount of work making the turbo less efficient. Wouldn’t you want to run the smallest housing possible with an unclipped tight turbine to get out of the hole, then bypass the rest with a large WG as needed?

So what differences did you notice “spool” wise in the logs swapping out the OEM Int. cam VS the 272? I’ve got a set of OEM cams I’ve been itching to swap in on my setup. (BC272) Perhaps just an Int swap would be more beneficial