TBIThrottle Body Injection discussion and questions. L03/CFI tech and other performance enhancements.
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This is the problematic adapter plate. As you guys can see, the tbi is moved too far foward. I "opened" it up, and cleaned it up a little when I had it on the old engine, but there is no reason the same can't be done on a custom adapter plate. I believe this piece is part of the reason my 383 bit the dust, in that the fuel distribution was messed up
__________________ '91 RS L03 auto Red w/T-Tops
'91 z-28, 383 tpi underconstruction.....
'99 Trans Am m6
LME 416...trap speeds of 129mph n/a- now to get the launch down
Originally posted by r90camarors This is the problematic adapter plate. As you guys can see, the tbi is moved too far foward. I "opened" it up, and cleaned it up a little when I had it on the old engine, but there is no reason the same can't be done on a custom adapter plate. I believe this piece is part of the reason my 383 bit the dust, in that the fuel distribution was messed up
could you not have a new one cut at a machine show with the throttle body placed further to the rear?
__________________ 1989 WS6 Formula Firebird T-Tops
L03 305 TBI 5 speed
SLP takeoff 3.42 posi rear (was 3:08 open)
Ultimate TBI mods
1/4" injector pod spacer
MSD 6A ignition (switched back to stock, AC/Delco distributor, coil and wires and picked up 3hp!)
'84 Trans Am functional cowl induction with K&N element
SLP 1 3/4" shorties w/air
Dual 2 1/2" converters
Custom 3" cat(s) back
Flowmaster 40 series muffler
Spohn weld-in subframe connectors
Lakewood control arms
Hotchkiss adjustable panhard bar
KYB shocks and struts
170 rwhp, 263lbs. ft. torque
best 1/4 mile: 15.62 @87 mph
Originally posted by r90camarors This is the problematic adapter plate. As you guys can see, the tbi is moved too far foward. I "opened" it up, and cleaned it up a little when I had it on the old engine, but there is no reason the same can't be done on a custom adapter plate. I believe this piece is part of the reason my 383 bit the dust, in that the fuel distribution was messed up
What kind of intake did you have on the 383? Some GM TBI's from the factory came with slightly different sized injectors in the pods to compensate for "factory" distribution differences. If your manifold isolated the injectors to specific cylinders, this might have helped things along.
There's another adapter plate that appears to allow the TBI to be mounted over either the "front" or "back" spreadbore intake bores. For bolting a TBI on a stock spreadbore GM intake, it seems like a good way to go.
Believe it or not, I'm actually having a hard time finding a machine shop to do it. But I'll probably just fab one up myself.
Also, this is the 2" tbi to squarebore adapter. Spreadbore adapters are easy to make because the bores can be bored straight down and will not overlap the intake. Squarebores, as seen in the picture, need to be angle in which makes things a little trickier.
Originally posted by r90camarors This is the problematic adapter plate. As you guys can see, the tbi is moved too far foward. I "opened" it up, and cleaned it up a little when I had it on the old engine, but there is no reason the same can't be done on a custom adapter plate. I believe this piece is part of the reason my 383 bit the dust, in that the fuel distribution was messed up
I have one thats offset and Ive noticed a tad more varnish toward the rear of the intake but didnt see much evidence of a problem from the plugs. Jsut out of curiosity, how did the rear combistion chambers compare to the ones in the front?
The real thing I had against the offset is that it made hooking up the linkages a pain and my trans never worked right with the tbi set further back to the rear of the motor and my gas pedal mysteriously lost half its travel.
The rear 4 cylinders were pretty bad. The number 6 ring had about a 3/4" piece break off-which unfortuantly made it's way around the block. The number 6,7, and 8 valves were burned and needed to be replaced. They were Manley valves. The number 5 valves were close but cleaned up ok.
The only problem with the turbo city adapter plate is that it is for the 1 11/16" bore. For the extra grinding needed and $40 plus shipping, I think I'm just going to try to fab my own.
i have a howell adapter (2.00 inch) squarebore. with 1/2 inch spacer above it. i forget the offset but will GUESS it was about 5/16 inch offset. if you like i can measure and post the actual number. it is no where as great as the holley. i assume some offset is a good thing but that photo seems a bit much.
i have that exact adapter plate on my edelbrock performer manifold, i did notice my rear cyls running leaner then the front but i never really did anything about it... I thought it was from puddling of the manifold and the adapter being so far forward, now with my new heads i was thinking of going to a single plain intake with that adapter to see if the distrib of fuel to each cyl would be closer... i was thinking maybe about going with the torker 2 manifold, or maybe just a bored out performer tbi intake manifold... dunno yet...
__________________ 96 SS M6 Track only car
88 Iroc Z - sounds stock but it aint stock...
Last edited by Formula305FI; 06-28-2004 at 09:40 PM.
The best/ easiest way to make an adapter plate is::::
Get a carb spacer (spread or square bore) (1/2" or 1" and bigger if your hood clearence will allow), Then get a 1/4 alum plate. Trace the 2" bores onto the plate, trace the bolt hole locations, drill and tap the holes. For the bores use a hole saw. Once the 1/4 plate is done, bolt it to the spacer, and simply smooth out the spacer sides to allow for a nice transition. When you done there probably wont be room for a gasket between the plate and spacer, so either take it down and have it welded together on the outside, or use a good silver colored silicon around the outside.
Thank you Low1500, that is actually what I was thinking.....hopefully my fab work on the two pieces doesn't look to bad. I plan on using the spreadbore to squarebore as the base
