boredomkills

has an anyone ever built a 4.3 tbi unlike the tbi V8s the heads on them are very good from the factory as long as it is a vortec head
(the v6s had vortec heads with tbi and the multi port) but anyways hot rod did a build ona carbed one a few months ago that made three hundred horse and since i am going to be buying a 89 blazer (the small one based on an s 10 not he fullsize) and lifting it i think it might need some more pwoer witht eh bigger tires

Dewey316

My good friend is cloning that motor from the Mag, and we are topping it with TBI. I'll let you know what happens, when it happens.

Fast355

iTrader: (2)

Only the vary late TBI 4.3s like about 94-95 had vortec headed TBI engines and then only in the S-Truck/M-Van. The older 4.3s all have the same swirl port heads as the 350, just with two cylinders chopped off. I built up a 4.3 TBI for a late 80s Safari Mini-van used to pull a 5,000 lbs trailer about a year ago. A friend of mine was tired of being underpowered, even after a gear swap from 3.08 to 3.73 it was still a dog pulling the weight. He needed more, at first we were talking V8 swap, but money and time ultimately won out. A spare 4.3 was located and rebuilt. Bored the block .030" over, used the balanced stock rotating assembly (crank turned of course), I bought 6 pistons for a 350 from Jegs (they gave 10.3:1 compression with 64 cc heads. The stock swirl port heads were cleaned up with some minor port work, the exhaust was worked over a little, Z28 springs, 3 angle valve Job, cut for 2.02 & 1.60 valves. Then I added the crane compucam 2020 made for the 4.3. 256/266 advertised duration, 194/204 @.050, .407/.429 lift, 112* lobe center with a powerband of 800-4,600. On top of that was the edelbrock intake (Edelbrock says it won't fit an Astro which is BS, maybe if you keep the stock riser for the air cleaner). On top of that was an Ultimate TBI moded TBI, with 305 injectors and a GM VAFPR. On the exhaust side of things the Astro had the Factory Tubular exhaust headers and the larger 2.5" exhaust. We carried the 2.5" exhaust all the way rearward and fitted the van with a highflow muffler and cat. We also used the air filter lid from a fullsize van and used a K&N filter equivelant to the Fram CA192. We added a Corvette TV sleeve and plunger, .500" Boost Valve, Corvette Servo, and recalibrated the governor in the 700r4 to shift at 5,000 when mashed. We pulled the 2,000 rpm stall out of the 700r4 and put in one for a full size van that stalls at 1,400. This thing would fry the tires like you would not believe and ran awesome on the Edelbrock Supplied 4.3 chip(Just told them it was in the same year S10). It would make more power with a custom chip. He reports that pulling the trailer is no longer a battle for the Safari and fuel mileage is about the same as stock (probably largely helped by the Corvette TV Sleeve and Plunger as it keeps the transmission in OD until 85% throttle).

Ran some quick DD2000# on the 4.3 (Modeling the factory tubular headers as HP Manifolds and Mufflers)

RPM------HP------TQ
2000-----108-----284
2500-----138-----289
3000-----168-----294
3500-----190-----285
4000-----204-----268
4500-----209-----244
5000-----201-----211
5500-----182-----174

Edit-forgot the .030" overbore and to mention, those are close to stock 350 TBI numbers from a very mild 4.3.

boredomkills

well that kinda sucks that i wont get hte better heads but thank you for the info you seem to know what you are doing very well from your other posts that i have read this will help me for sure when i get that blazer

Fast355

iTrader: (2)

Want power, with vortecs, and don't have emissions. Go with this intake, vortec heads, and a Holley TBI-4 bbl intake adapter.

IROC-Turbo

I have a set of those tubular headers in the building i pulled off a 4.3 a while back.Always wondered if they came factory or not since they had heat shields on them.Thanks for letting me know.Still have no use for them though lol.

kdrolt

1. what cam was used in the above model?
2. what headflow #s did you use in the above?
3. what are the #s if you assume that the 4.3 swirl port heads can be ported to the same level you (Fast355) obtained on the 193 "garage" ported heads, and using the same cam modeled in the above?

FWIW the L35 4.3 had raised runner intake ports, no swirl ramp, and heart-shaped chambers with deep-projected central plug position.... all aimed at good flow & fast burn. The name "Vortec" was used with these, and IIRC they were used in 1996+ (same initial year as L31). They were v6 clone versions of the L31 Vortec head.

The heads that preceded these were the v6 clone of the 350 193 casting swirl port head. I think GM refered to them as "vortex" heads because the ramp induced a rotation to the intake flow, and a vortex is a rotating flow. I'm not sure of what the year breakdown was for these heads, but they were used on LB4 4.3 v6 engines, probably 89-95 (same years as SP heads on C/K/G trucks and vans)... and perhaps even earlier than 1989.

The 4.3 heads preceding the SP version would be 1988 (?) and earlier.

The S10 web site(s) have a lot of info on the head flow for the above, including porting the L35 Vortec heads (L31 clones), and porting the swirl port LB4 heads too. The data is scattered somewhat so you have to dig through the forums using the search button. HTH.

Fast355

iTrader: (2)

1.)The cam was the crane 2020
2.)Those were the flow numbers from a different set of 4.3 heads that were treated to a similar setup. I have no way of knowing exactly what the ones on this engine were flowing. These had 2.02 and 1.60 valves in them with a mild port job.
3.)I will run some numbers based on my heads and different cams later on.