Looking for input on a V8 swap, stock heads or Vortec?


Asked by Feb 23, 2014 at 06:39 PM about the 1991 GMC Sierra 1500 K1500 4WD Standard Cab Stepside SB

Question type: Car Customization

Hi, I own a 91 GMC Sierra 4WD Standard Cab Stepside with a 4.3 litre V6 and 5 speed transmission. I've put a lot of work into her already, as I do bodywork for a living. I plan on doing a V8 swap this summer, the motor will be from a 93 Chev 3/4 ton, it ran fine the last time I checked. I want to do some upgrades before it goes into my truck, so I get a bit more horsepower and attempt to keep some gas milage. Right now I plan on adding a mild cam, cold air intake, throttle body spacer, Edelbrock Performer intake, shorty stainless steel headers, 2.5 inch exhaust, and a full gasket kit just as a precaution. I dont want change the heads, but everything I can find online tells me I should swap the old ones for some Vortec heads. I was planning on porting and polishing my originals, which way should I spend the money? At the machine shop, or junkyard Vortec heads? And I know the intake manifold has to be different for the Vortecs, thats why I'm asking before I buy anything.

6 Answers


I take it you'd be keeping the throttle body setup. Personally I don't like the vortec heads, but my info is limited to complete Vortec engines. We have major issues with head's cracking. Personally I would sit down and see what you want for flow increases and go aftermarket.


Yes, Im keeping the throttle body. I've read in a couple places about them cracking, something to do with thinner walls when they cast them so they dont handle heat as well. I just dont want to double my budget by buying new aftermarket heads. If you know of any cheaper ones, everything Im finding are around $1000.


$1000 is average. If your worried about budget here is what I would do. Since your running the tbi I would make small changes to the motor and concentrate on the efi. 1.) As per your deleted answer. Yes port your heads (not so much polish the tumbling air helps mix the fuel, polish on multiport). Port match your intake to your heads. 2.) Get headman or another header brand with thick flanges and use locking bolts. The 2.5 should work nice but 2.25 isn't bad either on a 350. 3.) Since all your mods will increase the air flow you need to tune your ECM or you will be running lean. This is where I would concentrate.


I was worried about the fuel mix, I can fix that with an aftermarket chip though. Can't I?


I'm sure you researched the swap and know that almost everything is bolt in and a memcal (chip) change to the 350 your good. Most aftermarket chips are a waste of money, it might run better than the stocker. They only use small generic changes. I strongly recommend getting an ALDL cable to read the data from the ECM. Mine was about 70 off ebay, the software is free To start off I would upsize the injectors, try junk yard 454's (rich is better for the motor), there is a size in between 454 and 350, can't remember where though. Once you get familer with the cable and software you can tune. About 400 I think for a chip burner and a wide band 02 that works with the software. Or datalog and get someone else to tune. At least if you setup this way you can always tune for new heads if you add them in the future.

Best Answer Mark helpful

Yeah, I've been wanting to do this for a couple years, its just come together now. I apperciate the advice about the chip and injectors, I may have to allocate funds a bit differently but if it will help get a better result thats what I want.

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