I Have A 91 Rs 305 Tbi. I Had An Idea And Was Wondering If Its Possible. Do You Think I Could Get A 400 Small Block And Put A 454 Tbi Unit On Top Of It? The Intake Would Have To Be Bored, But Would The 454 Tbi Unit Use The Same Wiring Harness That Is Already In The Car. With A Custom Chip And A Few Other Small Things Done I Think This Can Be Done. Any Info Would Be Great. Thank You

Adam

 

The 454 TB will bolt on and the wires will hook up, but as you said the throttle bores on the manifold will need to be opened up to match. You could also go for a better-flowing aftermarket intake that already has the bigger bores. You'll need the extra flow to properly feed a decent 400 anyway.

It's gonna need serious tuning....don't trust a mail-order chip to get it right because it probably won't. Either find someone local or learn to do it yourself.

 

I'm not sure the big block TBI bolt pattern is the same as the one on a small block. I would check with the guys over of Thirdgen.org in the TBI forum (if they ever get the board back up and running).

Agreed, you're going to need some serious changes with the chip tuning even if you can bolt it all together.

 

Yep, these guys are right. The 454 TBI unit will physically bolt right on, but you'll need to bore the holes on the manifold or get one with a 2" bore already. Since you want to go with a 400 SBC, you're best bet would be to just get a carburetor intake manifold and just install a TBI adapter plate (which you can get with 2" bores, if I remember correctly). The 454 TBI unit will use the same wires, but I do think you have to change the weatherpack connectors, so everything will connect right.

And, chip tuning is going to be the hard part, for sure. It is going to take a lot of time, patience, and experience to get the chip even close to being right. If you haven't starting burning and tuning yet, you better start now on your stock motor. Once Thirdgen.org gets back up, go to the message forums and search through the DIY PROM and TBI boards to get a good idea of the amount of work and time it's going to take to do it right.

Good luck.

 

Even in the absense of TGO, many of us are over hear lurking while it is down...

1) You will want a 4bbl manifold. I would suggest a single plane, but I am baised.

2) Chip work. depending on the cam, this may or may not be as big as a deal as one might think. Granted I have been doing chip tuning for a few years. A mail order WILL NOT CUT IT. But, with the BB injectors on there, assuming the cam is not out of this world wild (I would suggest a mild cam for this application anyway, as the 454 TB unit will not flow enough air to support a 400 spinning at hit RPMs). Once you set the displacement constant, and injector constant and get a good generic timing table set-up. you can start working on the part throttle fuelling, with help from programs like Jon Prevosts aldltobin program, this is fairly easy. Once it is part throttle is good, and the car is well mannered when cruising and part throttle driving, you can start to tackel WOT. This will require a WBO2 to get correct. But again, with a WB, and some datalogging, that is not that bad of a task. You will also have to probably give the car a siginificat amount of AE, and you will have descent tune (note: I did not say great). From there, you get to work on getting the tune RIGHT, tweaking the timing table, reworking fueling, tweaking the timing, reworking fuel, and so on so forth.

Now, that probably comes accross as being easier than it really is. The learning curve is really steep, especialy if you try to learn after the motor swap. So, here comes my best peice of advance I can give you. Start tuning now, you can learn tons of valuable information and experiance tuning even a stock motor, you will learn what you can change, and how those changes effect things, and what data to look for in the logs. This is experiance you just can't get, trying to learn on a motor that won't even run right.

Hope that helps.

 

I'll probably be hanging out with Prevost tonight, so I'll tell him to hop on here and drop you some advice...

Best of luck with the motor, and let us know how it turns out when you are done.

- Justin

 

You'll never get enough fuel in the engine with two injectors. A freind of mine had a 383 TBI engine with 74lbs injectors, and it was still way lean above 3500 rpms. He swapped to a multi-port single plane carb intake with 8 injectors and gained tons more power.

Save yourself the cost and hassle and just stick with a 350 engine if you want to upgrade your TBI. You can do that with the stock intake, some 64lbs 350 TBI injectors, and a stock 350 TBI chip from a police model Caprice.

 

What kind of tuning did he have done?

If TBI can feed a 454 bbc, a 400 sbc is no problem.

- Justin

 

I agree with Justin...he either didn't use big enough injectors (74pph on a TBI would be good for 350-375hp, tops) or didn't have the calibration right. Probably both.

 

A 454 BBC in a late model truck is a torque engine, not a horsepower engine. Its only expected to make power to 4000 rpms or so, and TBI will handle that. But most people here want to make more horsepower and have their engines rev higher than 4000 rpms. Therefore, a two-injector intake like a TBI will not support that, in my opinion.

The tuning was done by myself and my dad. While I admit we did not spend a lot of time trying to tune the 383 for wide open throttle, it took about 2 weeks and more than 50 chip burns to get the thing to idle and drive right on the street. And that was with a ZZ4 cam. I couldnt imagine anything bigger.

 

the injectors are not a restriction to performance. the later big block injectors(91 and up) were 90 or 95pph and would be plenty capable of handling over 400hp with a little bit of raised pressure and a 255lph fuel pump.
what most people miss out on is proper tuning. the computer and the induction systme are perfectly capable of handling a bunch of power as long as the time is taken to update the tables.

later
tim

 

I know guys with 500+ burns logged, just trying to get the car to drive the way they want it to. And these are guys who KNOW what they're doing, that have been doing it for years. 50 burns for idle and part-throttle drivability is nothing.

I have about 70-80 revisions on my '91Z so far, and it's a bone-stock L98 longblock. The only thing that's been changed is the intake, and the only things I've tuned are idle, part-throttle cruise, and a little bit of AE to help smooth out the transitions. You guys were just getting started good.

You get points for doing it yourself, though. It's the only way to truly get it RIGHT.