LT1 POWR

So I've got a 2800 vigilate which I think is too tight cause at idle my car dies a couple times until I warm it up for about 5 minutes. If I don't as soon as I put it in gear it dies. I think this is the problem, but it might be in the tune too. Anyway what would be the ideal stall size for my setup?

Also I've got a 3 channel strange 12 bolt with 4.11's and its pretty bad. I'm in OD by 35mph and 1st gear is useless. Whats a good rear end ratio to go with.

Before I change out the stall, I'm going to look into the tune and make sure everything looks good.

RealQuick

What gears are offered for a 12 bolt? I would go low... like 3.00

Orr89rocz

Gear it like any other combination... whats your rpm range and goals for the car? Power?

Loking at your sig information, you have a 383 witha tc78 making about 600hp on 10psi? Whats the peak rpm?

If you are going for 1/4 mile like performance, you'd want to trap at around the peak hp rpm so you'd gear and tire to match.

My 401 was so mild that I shift by 6000 most of the time and I ran 26" tires with 2.73 gears behind the TH400 trans and a 4000 stall. Traps 140 on good day so that works out fairly well. I went high on the converter to help brake stall it higher to hopefully get some boost off the line but unfortunately havent seen any yet. Brakes wont hold the car and the tune is abit off yet. Now I'm going much bigger in heads/cam so I should shift by 6800-7000 perhaps, so I'll want 3.23's because I expect my trap speed to be much higher...150 plus. It will fit the rpm range well.

2800 is not causing your idle issue. You need some work to the tune.

96capricemgr

The LT1 b-bodies had a 1400rpm stall and they ran fine at idle, then again they were tuned right. Another thing to look at is IAC position, if it is maxed out then maybe you need to drill or enlarge the IAC bleed hole.

Gear ratio will depend on use of the car and anticipated top speed in the quarter(if you want to race) stall in a turbo car is very hard to nail down as I understand it, a friend runs a speed shop and he was talking about how they always have to get them restalled a few times because it is such a fine line between building boost and blowing through the converter. For the street just stay mild as you seem to have and it will drive and behave fine, might have a hard time getting it to make proper boost at the tree though.

Orr89rocz

Its hard to get a real low stall speed in a turbo car as mentioned above. I had to get my converter restalled because the first custom one was too high. Turbo cars are like nitrous cars in that they have alot of torque...mainly alot of power coming in very quickly over a short amount of rpm.

My converter now will stall about 3000 rpm on motor but 4200 when boost hits. HUGE difference in torque between all motor and booost so the big variance in stall speed is seen.

Thats the great thing about a turbo car..normal driving the converter acts so mild but it really opens up when boost is on WOT. You get 2 converters in one basically. Street and race because the power level on boost will open up the stall.

Spend your money on the converter, as it will make all the difference in the world. Often times it helps to slightly overestimate your power levels so the converter guys will tighten it up more, so if they do make an error, it wont overstall as much. I use PTC who have a good reputation on theturboforums.... seems to do well on my combo. We shall see how it handles the new heads/cam. If it stalls abit higher that will be ok by me as the new combo needs it.

LT1 POWR

Right now its geared perfect for 1/8th mile, which is what I have locally, but I'll only run it once or twice a year. At 65 its about 2500 rpm, which isn't too bad as 65mph is really the fastest I cruise at anyway. The lowest I can go in a 12 bolt is a 3.08.

I'll have to talk to my tuner to see what my IAC counts are. I know when the idle drops to around 300-400, it jumps back up to around 1000, so I don't think the IAC is maxed out. What kind of idle rpm should I be at? I think we have it set pretty low like 600-700. It idles fine when its warm, but the first minute or so I have to elevate the idle or restart it 2-3 times.

LT1 POWR

Also, I think it shifts at around 6000-6200.

Orr89rocz

3.23's is what I'd run.

How big is the cam? 3000-3500 stall usually works well on a 383 but all depends on the cam/heads. If it peaks in the 5800-6000 rpm range then 3000-3600 ish should be ok.

LT1 POWR

Cam specs. 224/224 .577/.582 114 LSA

Looks like I'll stick with the 2800 stall and work on the tune some more.

Here is the dyno graph on 10 psi and about 20º timing on 91 octane.

Orr89rocz

600whp is stout. That should push you well over 130mph in the 1/4 mile if the car is around 3500lbs, even 3600. My buddy's heavy 02SS went 130 with 550whp or so but that was on a mustang dyno that in our area, has been known to throw down very low numbers compared to the dyno jets in the area.

130mph with 3.23 gears and 26"tall tire is 5428 rpm assuming no converter slip. Most converters remain open while in the 1/4 mile, so there can be up to 8% slip or more depending on the model. 8% would be 5862 rpm...so you are almost trapping at your peak hp.

If you go any faster than 130, which is very likely 134-135mph, then your rpm will be even higher. Perfect match IMO.
BUT if you raise the boost for more power, you will start to run out of gear. May need 28" tires at that point. Or 3.08 gears.

LT1 POWR

I've got 27" slicks which is what I'm using for gear calculations. I plan on upping the boost at the track to 15psi if the turbo will support it. Also thinking about going to E85. And the race weight is around 3460 lbs.

LT1 POWR

Gearing for the 12 bolt goes from 3.08 to 3.42. I don't think there is a 3.23 option like for the 10 bolt, unless I'm not looking hard enough. I think if I go with the 3.08 gears, that'll leave plenty of room to add power down the road, plus I'll stay in boost longer an have better cruising rpms. I'll miss those 4.11's though.

Orr89rocz

3.08 will leave some room down the road... I mean you arent far off in weight and power from me. I ran 134mph on 10psi which was around 600whp on a mustang dyno. 12psi I went 137 which was 640. 14psi I went 141 which was around 670-ish guess from the dyno.

MikeGyver

I've heard you really need a custom built converter for a turbo car or you might have issues since it changes everything.

MikeGyver

Automatic turbo cars don't go 'out of boost' during shifts. I'd definitely go with the 3.42s since with the auto you only have 4 gears.