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LS Swapped C4 | Torque Stall & Diff Ratio Help Needed!
Hey all,
Trying to sort out the right setup for my LS Swapped '84 Auto C4. Right now I'm running into some flat spots in the power curve (around 2200-2800 RPM) and haven't had the car out of 2nd gear yet based on a few factors so looking for some advice on what RPM Stall and Gear Ratio I should be running. Here are the details of the drive train currently:
- Engine and Fuel: LQ4 block with 799 heads, LQ9 Flat top pistons, Elgin SS2 .585 Cam, BTR .600 Spring/Trunnion kit, Dorman 615-901 Intake, LS3 Injectors, MSD Street Coils, Holley EFI Fuel System, Walbro 255 Fuel Pump, Hedman 1 7/8 LongTube Headers, 3" exhaust with cat delete (x-pipe). Running ~10:1 compression, dyno'd at 415 RWHP
- Transmission: Rebuilt 4L60e with Covette Servo and 2400 Stall
- Diff: Auto Dana36, not sure if it's the 2:79 or the 3:07 but based on performance I'm guessing it's the 2:79 because I pulled 126mhp on the Dyno in Second Gear!!
All of that said, I'm getting competing answers on where to land on Stall RPM and DIff Ratio. I don't drag the car, it's mostly for spirited street driving and road course lapping a few times per year.
Question is: 3.73 or 4:10 for the rear end? 3200RPM Stall? Higher? Any advise is hugely appreciated! Thanks all!
Stall I don't think will matter for road course so pick what you like for around street. 2400-3000 stall probably. Gear ratio though I suggest you don't shift to fourth and look at what max speed will be at the track you will run. The last C4 I used at Road America could not have more than 3.07 in the rear diff without a shift to fourth. This was around 6500 rpm at 150 mph. A track with say you'll get to max speed 125 mph could have 3.73 or ? You will need to use a gear calculator and play around a little bit. The below calc works great!
For a streetcar generally a 10 to 1 Ratio is considered ideal. Since your trans has a 3.06 first gear if you were to install a Dana 44 with a factory stock 3.33 ratio that's going to put you at a nearly ideal 10.19 ratio.
All '84 automatics came standard with 3.07s and 3.31s were the only option...and they are extremely rare! If your D36 has 2.59s/2.79s, they are not original to the car👍
My opinion is you need more stall. I have a very similar motor to you in my 84. LQ9 with T.E.A. stage 2 ported 243 heads and Summit stage 2 cam (226/238 .600/.600 lift 113 LSA) with PAC springs and an LSXR intake. I have an FTI custom made for my car converter. They say it has a max stall speed of 3600 rpm. But in Corvettes converters always flash on the low side. It seems as though it really flashes around 3200. I'm doing all this with a Dana 44 with 3.73 gears. I know custom built converters are expensive. But FTI made mine after a ton of questions about the car. And it was still under $1000.
The other problem I see from your pic anyway is your sucking hot under hood air. Do a data log with your Holley some time and see what your air intake temps are. Then check and see at the point you feel it run flat what point on the timing map are you? You might find some correlation. For example, Is it feeling flat at a point that the ECU is trying to give you timing but the air temp is over 100 deg. A lot of default Holley tunes pull timing based on high air temps. I was losing lots of power until I started pulling air from in front of the radiator. It sounds simple but it's a big deal especially in an LS. Those 799 heads flow a lot of air but depend on air density to do it.
If your considering a gear swap you might consider swapping over to a Dana 44. You are way past the breaking point of a Dana 36 and especially the Dana 36 that was used in an 84. The 84 Dana 36 was weaker than the Dana 36's of other years. You could sell off the Dana 36 and put that money towards a 44 and swap in the gears you want. Or better yet find one with the gears you want. For a street car I would go 3.54 if you do a lot of highway driving and 3.73's if not. I love the 3.73's but I'm using a 4L80e so my trans gear ratios are different.
By far the most important item in that list is the stall speed, if you cannot get the engine into its power band when you hit the throttle it will be doggy until it gets to the power band no matter what rear gear you have. The correct stall speed will make all rear gears better and make driving the car so much better. I would target a 3200 RPM stall from a good company, Once you have the stall taken care of you could try a Dana 44 with 3.45 gears since they are fairly easy to find. Order of importance is stall and then gears.
You will be surprised how much better the car will drive with the correct stall. The cam manufacture recommends a stall speed of 2800 for that cam or higher, I would go 3200 with lock-up, but your call.
I also agree that you should try and get cold air to the air filter.
It certainly appears to be a very clean and attractive install. Converter and a D44 for sure but with so few miles, I believe you get cool air to it and drive it as is for a while. How recent is the 4L60e build?
Just not happy with the performance based on the gearing and stall. It's sluggish from around 2000-3000RPM which is so frustrating! Trans was built about a year ago. Only one season running on it so far.
My opinion is you need more stall. I have a very similar motor to you in my 84. LQ9 with T.E.A. stage 2 ported 243 heads and Summit stage 2 cam (226/238 .600/.600 lift 113 LSA) with PAC springs and an LSXR intake. I have an FTI custom made for my car converter. They say it has a max stall speed of 3600 rpm. But in Corvettes converters always flash on the low side. It seems as though it really flashes around 3200. I'm doing all this with a Dana 44 with 3.73 gears. I know custom built converters are expensive. But FTI made mine after a ton of questions about the car. And it was still under $1000.
The other problem I see from your pic anyway is your sucking hot under hood air. Do a data log with your Holley some time and see what your air intake temps are. Then check and see at the point you feel it run flat what point on the timing map are you? You might find some correlation. For example, Is it feeling flat at a point that the ECU is trying to give you timing but the air temp is over 100 deg. A lot of default Holley tunes pull timing based on high air temps. I was losing lots of power until I started pulling air from in front of the radiator. It sounds simple but it's a big deal especially in an LS. Those 799 heads flow a lot of air but depend on air density to do it.
If your considering a gear swap you might consider swapping over to a Dana 44. You are way past the breaking point of a Dana 36 and especially the Dana 36 that was used in an 84. The 84 Dana 36 was weaker than the Dana 36's of other years. You could sell off the Dana 36 and put that money towards a 44 and swap in the gears you want. Or better yet find one with the gears you want. For a street car I would go 3.54 if you do a lot of highway driving and 3.73's if not. I love the 3.73's but I'm using a 4L80e so my trans gear ratios are different.
Thanks for the great advice here. Tough part right now is finding a D44 with 3.73's. Will have to adapt a manual diff and batwing I think.
By far the most important item in that list is the stall speed, if you cannot get the engine into its power band when you hit the throttle it will be doggy until it gets to the power band no matter what rear gear you have. The correct stall speed will make all rear gears better and make driving the car so much better. I would target a 3200 RPM stall from a good company, Once you have the stall taken care of you could try a Dana 44 with 3.45 gears since they are fairly easy to find. Order of importance is stall and then gears.
You will be surprised how much better the car will drive with the correct stall. The cam manufacture recommends a stall speed of 2800 for that cam or higher, I would go 3200 with lock-up, but your call.
I also agree that you should try and get cold air to the air filter.
Very nice looking install!
Glad the consensus so far is 3200 stall. I think that's what I'll do. Appreciate the advice!
Thanks for the great advice here. Tough part right now is finding a D44 with 3.73's. Will have to adapt a manual diff and batwing I think.
I believe you maybe shop a 3.54 or 3.45 already built if you don't find a built 3.73. The D44 would be a very straight forward install. You would need just a D44 C-beam, the rear and if you could find a D44 drive-shaft a slip-yoke change to fit the 4L60e. The 4L60e has the corvette extension already?
Can you do a D44 rebuild yourself or is it something you would need to 'hire'? If you can do the build you can disregard the ratio maybe.
Glad the consensus so far is 3200 stall. I think that's what I'll do. Appreciate the advice!
FYI, My wife's Camaro runs a Yank 3800 RPM stall convertor with lockup in a 6.2 with a slightly smaller cam and it launches very hard. The 3800 stall is a little sloppy around town but with lock-up it still cruises great.
Glad the consensus so far is 3200 stall. I think that's what I'll do. Appreciate the advice!
Before you take our word for it. I wouldn't just run out and buy a 3200 rpm converter. I know it's tempting. But I doubt you're going to be happy with a generic off the shelf converter. This is a custom application. A good converter needs to be made for the car. If you're going to spend the money on one anyway give a couple companies a call and see about having one built for your car and more importantly your driving style. I started when I first LS swapped mine with an LS6 and a 4L60e. I put a Circle D converter in with a 3200 rpm stall. I called them and talked to a tech for a while about the car. That's the one he recommended and he had a lot of very good reasons why. Then when I swapped out to a 4L80e I called around. Circle D didn't really have an option that fit my needs very well. But FTI sure did. They built me a billet converter that perfectly suited my cam and RPM range of the car in a street application. You can't get that kind of detail in an off the shelf converter. I wouldn't worry about the advertised stall speed. Call a good company and have them give you a recommendation. Also ask them how much a re-stall would cost down the road. With FTI the first one is free. This is because maybe down the road you want to change the cam to something bigger. And having a company who will re-stall that converter to match the new cam is a huge benefit.
You should be able to find a good custom made billet converter for under $900. Unless you want triple disk lock up. I wanted it pretty bad in mine but it just jumped the price up too high. (Over $1300) I wanted to hit the 250 shot of nitrous with the converter locked. But I had to keep the costs down somehow.
LS Swapped C4 | Torque Stall & Diff Ratio Help Needed!
