the 3/4 350

[89IROC&RS]

Ok guys, heres the lowdown on the 4.3L V6 that Hot Rod magazine put together.

Skip to the power, it made..

301.2hp @ 5,500 rpm
316.6 lbs/ft @ 4,400 rpm

they used a pre vortec 4.3L without a balance shaft, and did the following....

Speed Pro lightweight pistons with a 6.1cc dish
milodon fastners on rods and main bearings
Factory heads with 68cc chambers
pistons were installed .010 in the hole
head gaskets were .041in compressed
the new compression was 9.63:1 (over the stock 8.6:1)
however they planned on running a blower so they milled the heads for additional dish totallying 12cc, lowering compression to 9.08:1
they then installed a windage tray, (a modified small block unit) high performance oil pump and pickup, and a steel pump shaft.
then installed a small block chevy balancer.
they put in a cam from Comp Cams in with following specs
280HR
durration - 224/224
Lift - .525in
LSA - 110

(specs at .050in lift.)

the heads were modified for larger spring seats and screw in rocker studs.
they also installed comp cams pro magnum rocker arms with 1.6:1 ratios increasing lift to .560 in.

the heads were ported and measured at 208 cfm on the intake side and 190 cfm on the exhaust side (similar to a 305 head) (stock flow on the heads were 138/116 cfm) they also used milodon megaflow valves in 2.02/1.60 size.

exhaust was a pair of long tube hooker S10 headers with 1 5/8in primary pipes, 26in tubes, and 2.5in collectors.

Ignition was an MSD distributor with 8.5mm wires and a digital 7 ignition box.

Induction was run twice, first with an edelbrock carb and 2in spacer, and ran 288hp @ 5,400rpm / 303lbs-ft @ 4,400. the second run was with a 650cfm mighty demon and provided the 301.2hp and 316.6 lbs-ft.

so as we can see, there is alot of potential in these engines, with 305 equivilant heads, a compression level thats pretty low on the performance scale, it still broke 300hp naturally asperated, with a set of better heads (as those found on 95 and up vortec 4.3L engines have) and a higher compression, there is even more power for the taking, i plan on firing up the good ol desktop dyno to play with this one a little bit.

however there is one snafu, the vortec style heads on the 4.3L from 95 and up have some sort of difficulty bolting up to the older style blocks, i dont know if its just intake like on the small blocks or if its different water passages or something, so its something to watch out for.

oh and for those of you who are wondering about putting a blower on it, they did, and it made 475hp on 9psi of boost, and 501hp on 12psi of boost, heres the article with the specifics.

http://www.hotrod.com/techarticles/e...own/index.html

and heres the article on the naturally asperated buildup, that covers alot of the details ive left out in this thread.

http://www.hotrod.com/techarticles/e..._v6/index.html

personally, im pretty excited. if i keep the IROC as my weekend queen, this gives me the opportunity to buy a clean RS in the future remove the weezy 305, and put a 4.3L in there that really cranks the hp, and gets good gas mileage to boot. oh and for those who are interested, heres the link to the brackets to put a 4.3L in place of a 305.

http://www.allstarperformance.com/product.htm?prod=334

[Link85x]

WOW!!! That 4.3 is a beast!! Guys you should really look into this. 89, what about the 305 rebuild post you said you were post? I'm gonna stroke it, but what else should i do to build it up, from bottom up?

[89IROC&RS]

lol greedy greedy, wanna know about the 305 geeze, well, ive gotta go do chores, and try to be productive, so ill see about doin a general small block building thread tonight, if you still have questions i can do a thread about building up your 305.

[Link85x]

Thanks 89, you da best!!!! Also, that 4.3 is bad sob, man. What cars can it be found in? Thats crazy, if blown, it reaches near 500?!?! That's amazing!! Also again, your selling your RS to get another one and drop a 4.3 in it, you gotta let us know how that goes. I'm gonna build the hell out of the 305, i whenever i finish and get bored of it i'll give myself another project, like LT1 or LS1 swap, but i'm talking years down the line though.

[Viper_Storm]

lol, so these 4.3l can put out over 500hp and still be easy on the gas?

[Rally Sport]

Originally Posted by Viper_Storm

lol, so these 4.3l can put out over 500hp and still be easy on the gas?

Yes, the thing that 89 is trying to get across is that the 4.3 makes the power of the 350 v8 and the effeciency of a 6er.

[Muscletang]

That's a pretty cool/mean little engine.

[89IROC&RS]

the 4.3L came in trucks starting in i think 88, but im not really sure about that. The vortec headed ones started around 95ish in the S10 and silverado trucks.

as far as the gas mileage of a sixer with that honkin big cam and a blower, im not to sure about that, but the naturally asperated one making 300 hp is probly way better on gas than a comparable 350 making the same hp. and its set back farther in the chassis for better weight distribution.

[Link85x]

A 4.3 in an RS would be perfect, just the perfect sleeper. Any idea what it would sound like?

[89IROC&RS]

not a clue