The only way I know of to convert a TH400 to OD is with a Gear Vendors unit, or other units. They add length to the transmission, and will require the driveline to be shortened. This can be a problem in some cars, if you already have a short driveline.
Considering the cost of buying/building a TH400, and then adding a Gear Venders OD, it would save money to just start with the 4L80.

 

I'm amazed that this is even getting discussed in detail. The only, and I mean only reason a TH400 is better than the 4L80 is I am assuming you can buy them on the cheap. I didn't have to think about it, why would I put. $3-4000 three speed behind my 600hp motor when I could put a four speed for like $1000 more and I know that it's built for the power I have. My 4L80 is better in every way. $1000 difference is like 1% of the total that I have put into the car.

 

On a side note (well actually the main note of this thread) I was driving my car today and it was running like complete garbage. It kept flooding out and stalling on me after I would punch it. I really hope my carb isn't leaking somewhere as I know nothing about them, nor do I know of someone around here to rebuild mine.

Luckily I am thinking it's my fuel system. My Holley pump died right when we got my car running and we installed an old take off from a buddies project. Also my regulator seems to change the pressure all of the time I think what I will do is install the GMPP mechanical pump designed for this motor and see if it solves it. That's the cheap route and I hope it works so I don't have to spend a bunch right now to get it running again.

Looking forward...

I also priced out the multi-port fast fuel EFI today. Looks like I can get a self learning kit for $4300 USD. My issue with that is by the time I pay duty, shipping and exchange it will be like $6000 CDN. This would be the self learning kit, and when I got supercharged I only need to buy a new ECU and map and it will all work with some tuning. Will have to wait until January when the wife goes back to work before I can pull the trigger on something like this.

Decisions, decisions....

 

no your right 4L80 is the better tranny no doubt an cost more yes you can buy th400 900.00 to handle 500hp + brand new shipped jegs an like 1100.00 for the one that handles 700hp ,some guys want 3 gears an other 4 ,i could go either way for now 3, hope you get that fixed so far i have had no carb issues either ,other then a fuel pump ?i guess i mentioned the th400 4 speed is couse i thought i heard someone say they wanted 4 gears out of the th 400 ,i do have an exstention on mine 6 inches allows me to use my old drive shaft ,that kit sound great alot of money though,i think if you shop can do better ,not to get way off subject i seen a 2007 gt 500 yesterday was unmarked one as far as stripes an gt 500,is a pretty nice car i still like the old ones an or the zl1 ,some of them have 2 superchargers,?would not tpi be better way to go ,that as much as the cost of an engine depending?you got 100.000 in that car,just guesing by what you said above,i dont mind saying i got $12000.00 + in mine an not even close to your build ,other then a pretty powerful engine ,dont take long for money to add up,i also hear you on the geting the right guy for job ,why was it so much easyer untill we grew up ,when i was younger i allways had some guy going bring it bye this weekend

 

Why would some guys want three gears over four? What would the benefit be other than cost savings?

The pricing that I received was direct from FAST, it is the best kit that they have and is able to handle up to 1200HP. I plan on using 1000HP of it in the future which is why I want it so bad. It costs me $1.35 for every US dollar i spend right now. By the time I pay shipping, gst, and duty that kit will cost me $6000CAD which is why I want to wait until my wife goes back to work. You mentioned thats as much as an engine, and yes it is the same price as a lot of them but quality usually isn't cheap.

As for the money into the car, yes, between building this stupid car twice and purchasing it in the first place, we are well over 100k into it. Hell I am 40k for engine/trans/rear/driveshaft/brakes/suspension. My dad and I did the first build back when i was in junior/high school. Most of those components are now sitting on shelves in the shop now. I have a $100 000, $20 000 car. Its not worth anything but it was my first car so I don't feel bad dumping money into it when it needs it. This isn't an investment its entertainment.

 

i undertsand very much sometimes you get what you pay for .what i was told with th350 or 400 ,its about the sound that comes from the car in 3rd gear ,is going to be heard more then one in 4th gear ,the cost for some i think to ,so i guess its just choice ,but i may go to 4 speed one day ,couse i found its about performance more then sound looks is a good thing to ,you got it all with that car ,i guess i would not blame you with the fuel issues you have had ,? do you have a riser plate under your carb ,i hear those only work well with 750 cfm or bigger ,you got 650 right,i have to admit i am a guy who looks for bang for my buck ,but have to be careful with that too,yes a $4000.00 engine is not $4000.00 after you put serpintine pulleys on it among things ,though i paid someone to install mine ,i stil think of a good 1980 roller with the new version of the 406 meening it has aluminum heads estreet with a better crank geting like 475hp ,an a wopping 513tlbs about a 50 more then i get now ,wich feels huge

 

No I don't have a 650, I have an 850. I think a 650 might choke off a 572 a wee bit. No I don't have a carb spacer, it is hard enough as it is to tuck this monster motor in my engine compartment.

 

That's really silly for anyone to use that reason for going to a 3 speed auto vs. a 4 speed auto. Since 3rd gear on a 4 speed auto is the same, if it was just a case of liking the sound of the engine more, the driver could simply leave it in 3rd gear, and still have the option of 4th OD when he didn't care about impressing the crowd with the sound.

 

its ok what one may think is silly another guy does not ,aahh yes i have the same problem with my 406 fitting ,would have to make hole in the hood,an for 4th gear is realey only needed at over 100 miles per hour at least for my car an or highway wich at 10 miles to the gallon is why i have the 3800 now for cruiseing 30 mpg ,but its realy only any good when you need it 4th gear that is ,bearly ever used in the 3800 either,an there is the price not evryone want to spend $3000,00 for a good trany,at $1100.00 for th400 from jegs brand new with everything ,most guys have a budget ,for me life is to short to sweat the small stuff to much ,

 

I'm hoping someone can help me on a carb problem. I'm helping a buddy out at his shop on a pos 80 firebird. I've never seen this much rust before. Regardless, I've replaced the lines, fuel tank and pump and have fuel going into the front of the carb

I think the carb is a two barrel Rochester carb. It's on top of a 4.3l v8. I have never touched a carb before so I don't even know where to start. What's happening is nothing, there is no fuel squirting into the carb. Any ideas on where to start.

Thanks guys