[Gmecm] Chevy 350 Carburated to TBI / TPI?

Tue Jan 9 01:40:17 UTC 2007

Hopefully someone will have a better answer, but the QuadraJet is a 
spreadbore carburetor, while the Holley is squarebore.  I *think* the 
holes were closer together at the front than at the back on my 
QuadraJet, but I've had TBI so long (and sold the carburetor) so I 
can't verify it.

On Jan 8, 2007, at 7:30 PM, Aphelion79 wrote:

> It shows the
> "HOLLY MANIFOLD BOLT PATTERN ONLY
> Q-JET MANIFOLD HOLES ARE NARROWER"
>
> Is there a schematic for that or what is the "narrower", and which 
> holes?
> I do believe the Chevy does in fact have a QuadraJet...
>
>
> Jay Vessels wrote:
>> Hi there!
>>
>> Here is the adapter on the FTP site:
>>
>> ftp://ftp.diy-efi.org/uploads/tbiadapter.jpg
>>
>> Or, if you can handle the file as a drawing:
>>
>> ftp://ftp.diy-efi.org/uploads/tbiadapter.dwg
>>
>> Jay Vessels
>> 1982 Chevrolet S-10 Sport, 2.8V6 TBI
>> 1984 Chevrolet S-10 Blazer Sport, 2.8V6 (TBI pending)
>>
>> Aphelion79 wrote:
>>> Ok, well I guess it is best to look at adapters then, I'll check the 
>>> website and see if I can find that schematic you spoke of earlier 
>>> guys....
>>>
>>> Chris Reynolds wrote:
>>>> TBI was not introduced until 1987 on Fullsize trucks with V8s.  
>>>> That means that all of them had the later style "High Swirl" heads 
>>>> on them.       You can however often find the 454 TBI adapter used 
>>>> on the early 454s for a song.
>>>>
>>>> Aphelion79 <aphelion79 at cox.net> wrote:
>>>>   Whoops, to finish that... so at the Junkyard look for a TBI'ed 
>>>> truck, latest model being a '86, for the whole setup... anyone have 
>>>> pictures of the differences or is there some big obvious thing I 
>>>> could notice?
>>>>
>>>> Aphelion79 wrote:
>>>>
>>>>> Yeah, depending on prices of the adapters (compared to prices, if 
>>>>> I can find any, of some junkyard intakes for the correct years) 
>>>>> I'll probably go that route... The engine is brand new with less 
>>>>> than 300 miles on it... so everything about it is currently in 
>>>>> near pristine condition last time I checked...
>>>>> Jay Vessels wrote:
>>>>>
>>>>>> Hi there!
>>>>>>
>>>>>> No need to swap heads. There are several options for the 
>>>>>> TBI-specific intake:
>>>>>>
>>>>>> 1) Grab an adapter to bolt the TBI to an existing 4bbl. intake. 
>>>>>> Holley, etc. make them, or make your own -- there is a drawing on 
>>>>>> the GMECM website's incoming directory somewhere.
>>>>>>
>>>>>> 2) Grab a stock TBI intake from a mid-80s fullsize truck. These 
>>>>>> are likely to be hard to find, since by '87 GM went to centerbolt 
>>>>>> valve cover heads which have a different angle on the four center 
>>>>>> intake bolts.
>>>>>>
>>>>>> 3) Grab an intake from a newer ('87-, but not Vortec) car/truck 
>>>>>> (i.e. F or B body, or fullsize truck) and redrill the center 
>>>>>> boltholes. I've done this but do not like it at all. Getting the 
>>>>>> bolts drilled right isn't fun, and I made special washers to sit 
>>>>>> under the bolt heads to make sure there was enough surface for 
>>>>>> clamping. Personally, I would not do this again.
>>>>>>
>>>>>> 4) Buy an aftermarket intake for a TBI and older heads. Holley 
>>>>>> 300-49 is a choice.
>>>>>>
>>>>>> If I was on a tight budget or if I had a really nice intake, I'd 
>>>>>> do #1. I might do #2 if I got really lucky in the salvage yards. 
>>>>>> Otherwise, I'd do #4.
>>>>>>
>>>>>> For TPI, it's a similar issue. 1985-1986 baseplates will bolt to 
>>>>>> the heads you have, but after that they're designed for 
>>>>>> centerbolt heads. These may be easier to modify, or mix-and-match 
>>>>>> runners/plenum/baseplates based on what you dig up.
>>>>>>
>>>>>> Jay Vessels
>>>>>> 1982 Chevrolet S-10 Sport, 2.8V6 TBI
>>>>>> 1984 Chevrolet S-10 Blazer Sport, 2.8V6 (TBI pending)
>>>>>>
>>>>>> Aphelion79 wrote:
>>>>>>
>>>>>>> Is this possible? I have a 79' Chevy C20 sitting in my back yard 
>>>>>>> with a carburetor that sucks. About 300 bucks for a new one... 
>>>>>>> so I was wondering can I take the head off of a newer model 
>>>>>>> truck with a 350 and TBI (or off a car with TPI) from the 
>>>>>>> Junkyard and if it will bolt on directly without any problems?
>>>>>>>
>>>>>>>
>>>>>>> *I realize I also need the wiring harness and computer (I've 
>>>>>>> done a few FI swaps on vehicles already, but this one seems to 
>>>>>>> be the easiest looking like everything will bolt right on...)
>>>>>>>
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