[Gmecm] Chevy 350 Carburated to TBI / TPI?
Jake Tucker
jktucker
Tue Jan 9 04:15:35 UTC 2007
The most obvious difference between a square bore and a spread
bore manifold and carburetor is that the secondaries (rear two barrels)
are much bigger than the primaries (front two barrels). The front-back
bolt spacing is the same on both, but the width is smaller on the
quadrajet. When I bought the Holley pro-jection system several years
ago, it came with two adapters, one for a square bore and one for a
spread bore, so they are both available.
I don't believe they ever made a TBI manifold that would bolt up
to the '86 and earlier heads. I agree with Jay below that you can
re-drill the middle holes to make it work (I've used such a manifold),
but it's ugly and requires extra silicon to keep it from leaking. I've
also heard that those manifolds are prone to cracking.
You really don't want to convert to the '87-95 heads either,
because they aren't very good for performance.
-----Original Message-----
From: gmecm-bounces at diy-efi.org [mailto:gmecm-bounces at diy-efi.org] On
Behalf Of Aphelion79
Sent: Monday, January 08, 2007 5:31 PM
To: gmecm at diy-efi.org
Subject: Re: [Gmecm] Chevy 350 Carburated to TBI / TPI?
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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