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Remove TBI for Quadrajet

C

CombatWombat75

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I have an 89 GMC suburban that I will be adding 4.56 gears and 37's to this summer and as we are all aware, the 350TBI motor is not a real powerhouse. I have been toying with the idea of taking the TBI off and throwing some Vortec heads, 1.6 roller rockers and a good intake and Quadrajet carb. I already have most of the parts so cost is not an issue.

What are every ones thoughts/feelings on a Quadrajet in off camber situations? The truck is a multi-purpose tool. Camping, hiking, fishing, backpacking and some Rausch Creek/parks. I have read that they are pretty decent and referred to as "poor mans injection", but I would like some real world experiences.
 
I've never owned a carburetor that I liked. I'd swap in the vortec heads and intake and keep the TBI personally. IMO the only downsides to TBI are computer tuning and cam selection, both are very limited.
 
tbi unit is not holding you back in power .

its the TINY cam / lower flowing heads / stock exhaust / lower compression of that engine .

I would install the parts you have and do a few live data drives and have a custom chip made . http://coloradok5.com/forums/forumdisplay.php?f=81

eagle mark here is the moderator for the efi section and also does custom chips .

but yes a q-jet is a good off road carb over a lot of others for its small central located fuel bowl . less chance of flooding .
 
it's more of a pimple rod than a bump stick..
 
;)

I find the BB version to be even moreso than the sb's.. and that's, sadly, saying something..
 
I did think about doing a chip for the heads and exhaust, but if I was going to have a chip burned, I would probably do something more aggressive than that and do a 383 or at least a nice roller cam to go with the heads.

Another option I have been thinking about is installing larger injectors and playing with the fuel pressure to get it where I want it with the heads, intake and exhaust.
 
As a guy that took off a carb for a TBI, DON'T DO IT.

Figure out how to make your motor with FI. Carbs are ok for street driven applications, but off-camber, you will never get a carb to run as good as FI. Converting a FI setup to carb is crazy.
 
good stock cam swap for roller cam if your block is setup for factory roller cam is a LT1 stock cam from a 350 LT1 not the 4.3 v8 LT1 .

and its computer friendly . just need the cam/lifters/link plates/spider. then new cam holder to block and also correct timing chain . then cut down the index pin on the front of the cam were the gear bolts up and smack it all in the engine.
 
Change the cam first. I went w/ an Edelbrock performer cam and 1/6 ratio rockers. It really woke the truck up, much more so than regearing even. Keep the TBI and get a chip for it to match whatever cam you put in. The performer cam puts peak torque right around 1900-2100 rpm, which is exactly where my '89 runs on the highway w/ 35s and 4.56s.
 
I bought a Vortec 454 out of a 2000 Chevy and used it with a new dual plane intake and a Trans-dapt adapter to mount my TBI unit. It will spank a peanut port 454 on any playing field all day for dirt cheap money.

I would buy a Vortec small block, and buy an intake then use the adapter plate. I wouldnt buy GMs Vortec to TBI intake because it costs twice as much, but it is a nice piece. You wont be in it but maybe 1500$ tops. And you can leave it stock and it will have atleast 50hp and 80ft lbs over the TBI clunker any day of the week, and thats a bare minimum increase. Plus you will pick up an extra 1000 RPM from the roller cam the Vortec has.
 
CombatWombat75 said:
I did think about doing a chip for the heads and exhaust, but if I was going to have a chip burned, I would probably do something more aggressive than that and do a 383 or at least a nice roller cam to go with the heads.

Another option I have been thinking about is installing larger injectors and playing with the fuel pressure to get it where I want it with the heads, intake and exhaust.
Click to expand...
Injector size and fuel pressure is not a guessing game, it's all math to calculated HP of engine needs.

The biggest mistake in TBI engine building is cam selection, not that it is limited but TBI can only do as much as a carb. If you choose a cam that starts making power at 2500 RPM? Well don't expect a lot of power under that. Then if it's an Auto trans you could put in a 2500 RPM stall converter but most guys don't want the engine revved that high all the time on the street. Look at cam specs from 1000 RPM -up and you'll be fine with Vortec heads, exhaust and a tuned chip it will idle fine at 750-800 RPM and drive nice with stock converter.

The Vortec heads are a huge improvement, but it's not only fuel needs that change, the entire spark advance table is completely different.

Desktop Dyno build of the engine and parts can give you approximate HP of engine. Then you can calculate injector size and fuel pressure needed. With a 383 I like the BB injectors at lower PSI over 5.7L injectors and higher pressure.

Replacing the intank pump with a bolt in from a TPI or 96 Vortec engine is all you'll need along with an adjustable regulator. Get your injectors serviced while your installing the adjustable regulator.
 
Thanks All. I have actually had a good deal of experience with efi and carbs and realize all of things I would need for a good efi. I know the injectors are math based, but you still have to dial them in and unless you Dyno the motor, you can only estimate the power. That is kind of why I was curious about real world results with a quadrajet. On the street I will take a carb all day long. I know it's a split opinion, but I love the simplicity and at WOT it's all the same IMO.

Back to the burb though, if I don't do a carb because it's an easy and cheap (already have most parts) 40+Ftlbs then I would likely stick to something more advanced like a 6.0 ls1 or 8.1 swap but I am not budgeting that money in any time soon.

Thanks all for all of the advice though and if anyone wheels a carb speak up! Lol
 
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