so, i have a 91 RS.. 305 tbi... that is NOT an HO right?

what are the -specific- differences between a normal 305 and a 305 HO ?


also will HO heads fit on a non HO motor?
i happen to see some locally for sale, and i have a cracked head.

are the HO heads better than what came on the 91 rs 305 TBI ? (question doesn't matter if they won't fit, but feel free to answer anyhow)

thanks guys

 

I want to say the HO had flat top pistons and that was it but don't quote me.

 

hmm... seems like there should be more to it than that... but..... i wouldn't doubt there's truth to it.

thanks for the quick response

 

Sorry I didn't really read what you asked.
Yes the heads will fit. I can't imagine them being much better (if at all). They might have ran a slightly different cam than the none HO... but than again your 91 probably has a different cam than the older 305s.

If you give me the casting numbers for your heads and the HO heads we can let you know which ones are better in stock form. I had a set of HO 305 heads that were lightly ported and deburred on a 350 and it felt like it had a very good amount of low end grunt.

 

thx. yeah i haven't bought the HO heads, and, the the other ones are still on my car until i find time to yank them off.

i'll probably just go with a direct replacement.. i may venture into the idea of having them ported before i stick them on, but, it really depends upon what they charge me to do it. and it also depends upon if i need to re-tune the computer for a minor head port.

which i think is a separate thread in itself

 

i heard and dont quote me that the 305 ho, was a mid 80s version till fi. it had the 416 heads, rv cam and the flat top alum slugs, the intakes are different as you have the tbi swirl port heads

 

416 heads a waste, get 113 vette aluminum heads they have 58cc chambers so same as 416 chambers. But much lighter and probably flow better. Ditch the precat exhaust for shorty headers and maybe dual cat exhaust, also the cat back would be a improvement.

I had a 1990 L-98 vette short block with with 083 head (083 heads for calif. smog) then used 1990 F-body TBI system, 83-84 5.0 h.o. exhaust sytem. Stock 5.0 ecm calibration and a 5 speed trans in my old 82 trans am and it ran pretty strong.

 

https://www.thirdgen.org/forums/faq-...5-engines.html

JamesC

 

If you have a dremel and cartridge rolls you can always disassemble the heads and debur any rough spots in the castings on the intake runners and exhaust ports. It won't make a huge difference in power but will do something.

 

You should get some casting numbers. The LB9 TPI 5.0 is listed in every RPO list (including "The Third Gen RPO Decoder" offered here at TGO) as an HO motor. So, those heads would fit your TBI. However the pre-87 carbed HO heads won't fit. But there is a strong possibility that whoever is selling those heads have misrepresented them as HO heads anyway. You should get some casting numbers.

 

yeh im going to skip out on the heads on cl, i found them locally, the same ones i have ON the car for less completely rebuilt and ready to go, 99 each, just gotta yank my old ones and take them in.

i have about 6 motorcycles i have to have done for customers and am trying to finish my powder coat oven so i can get some of those finished, and more things coming in every day...

finding the time to dismantle my camaro is kinda difficult... maybe next weekend lol.

which actually brings me to a slight shameless advertisement. if you guys need powdercoating, sorry, don't flag me....


so apparently there are 3 or 4 different heads that went on the motor in 1991, and i'm not sure what the casting is on mine, can any of the castings go back on it?

 

The casting on your tbi should be 14102187. how do you know what they are selling are the same as you have now if you don't know what you have now? Ask them what casting number they are selling. Post it here and someone will verify compatibility.

 

Why won't pre '87 heads fit on any SBC??

They will fit.

 

Difference in valve springs I'd imagine from tappet to roller. They would PROBABLY work but roller cams have a higher spring pressure.

Physically any small block chevy head (gen 1 which ends with the L31 Vortec heads) the issue comes in 1987 when GM switched cams/rockers/springs.

 

On lazy factory cam profiles it's a non-issue.

 

Wasn't aware. Never switched a cam out without rebuilding the heads.

 

If he's buying generic replacement heads I would assume he would want them to "fit" his intake manifold without wallowing out the 4 inner bolt holes.

 

X2


That is true. However, the OP might want to know that is an option and make that decision himself. To say "they won't fit" on a Gen I SBC is not stating all the info, IMO. "They fit but you need to oblong 4 bolt holes, which takes less than ten minutes." -Certainly, that opens up a lot more options for the OP.

 

im not buying generic replacements, they are rebuilt used heads.. and... i'll know the casting when i have time to tear my car apart and get the heads off of it. then i will verify what they are selling etc.

but, shouldn't any casting from that time period fit ?

like.. from 89-92 or whatever.

 

All Gen I SBC heads will fit on your block.

'86 and earlier will require either an "< '86" intake, or you to oblong the center four bolt holes in your intake, and also require perimeter bolt valve covers.

All '87-'95 Gen I SBC heads (except Corvette) will fit on your block and your stock intake will bolt up w/no modifications.

The "305 HO" ran from '83 - '86, used old style intake and perimeter bolt valve covers. So to use them, see above.

 

The only difference in the heads as far as fitment on the pre 87 small block and the newer one is the angle of the center two intake bolts, but a Dremel will fix that in short order.

 

The "H" and the "O".

 

10 years later...

 

And repeating what was already stated, no less.

 

all GEN 1 heads will bolt on, not all will work with a 305 (and other small bore SBC's) if you use a set of heads with 2.02/1.60 valves and don't cut reliefs in the cylinder walls, the intake valves will hit the cylinder walls, and let's not even go into shrouding issues with any intake valve 1.94 and up. also once you start getting into cc bigger than 57cc your compression drops off really quick

 

 

...Needed to be confident the gasket sealer was really cured before bolting those heads on.