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| Replacement intake/exhaust Values (86 GT) (Page 1/1) |
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Darthscooby1001
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SEP 19, 11:19 AM
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Hi guys,
you don't hear from me very often. I am currently renovating an 86 GT, quite literally replacing everything that is needed and making several upgrades and mods! The engine was tired, but I have decides to keep it (no swaps) and want to change the valves. On Rock Autos there are two sizes of valves listed, one being slightly bigger for cast iron heads only. Of course I bought the other ones before reading that 86 only had cast iron heads. My question is do I actually require the slightly bigger (for cast iron heads only) or the original I purchased. My confusion comes from there being two choices when as far as I believe, there is only one head!
Links if people wish to look and understand what I am talking about!
Exhaust
Intake
And obviously if readers know of a better solution or price, then please advise me.
Thank you
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olejoedad
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SEP 19, 02:05 PM
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All 2.8's in Fieros had cast iron heads.....
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MarkS
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SEP 19, 03:14 PM
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82-T/A [At Work]
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SEP 19, 03:15 PM
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Yeah, as Joe said... I don't really understand why it's listing smaller valves. The Fiero V6 that was in 85-88 all used the same heads, and they were the larger "H.O." heads. I'm surprised really that Rock Auto even lists them. They're usually really good about this stuff, but once in a blue moon they get it wrong.
Sorry man, you want the larger valves. Anyway... you could probably make them work, but you'd have to rebuild the valve seat as they're ground for the larger valves, and you'd lose horsepower anyway with the smaller valves... which you don't want.
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Darthscooby1001
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SEP 20, 12:18 PM
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Thanks for that link, I may just shop there. I can assume though that a set is both intake and Exhaust?
Thanks
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Darthscooby1001
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SEP 20, 12:20 PM
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Thanks everyone. I can return the smaller ones (plus the front engine mount - I don't have a front engine mount, it's a shock) and go large 
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82-T/A [At Work]
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SEP 20, 12:22 PM
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| quote | Originally posted by Darthscooby1001:
Thanks everyone. I can return the smaller ones (plus the front engine mount - I don't have a front engine mount, it's a shock) and go large |
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OMG, I totally forgot about that front engine shock!!!
My 1987 had that... are you sure that yours doesn't have that? it was supposed to help soften the abuse from the engine during hard shifts. When the "dog bone" would go bad, the front engine shock absorber would start to take all the abuse, and it would often lead to that bracket breaking... especially in manual transmission cars that would often get abused a lot.
EDIT: Back when I was like... 20 I think (~25 years ago)? I bought a used 1985 Pontiac Fiero GT from either Darrel Morse or David Rodebaugh off Peter Zurich's Yahoo Fiero Mailing List. It had decked heads on the 2.8 V6 to about 9.2:1 compression, a 4-Speed manual swapped out from an 84 2m4 SE w/ 4.10:1 gears... and in really good tune, just weathered looking on the outside. I did a 6k clutch drop from an intersection (as a 20 year old might), and the engine LURCHED back and ripped that little shock absorber RIGHT off the engine. The car basically sat there doing a burn out without me applying the brakes. I shifted into second and it still continued to burn out for what felt like 20 seconds. I finally had to let up off the gas just a little bit for the tires to connect, and it raced through the intersection with the tires squealing the entire way until I finally let up.
The old man in the Toyota Corolla next to me beat me, but only because he wasn't doing a burn out, and was just trying to make his way to the Mexican restaurant across the street... hahaha....[This message has been edited by 82-T/A [At Work] (edited 09-20-2023).]
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G-Man
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SEP 20, 06:49 PM
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The carbureted versions of the 2.8L had smaller valves. Anything fuel injected (like the Fiero) had the larger valves from the factory.
Didn't Fiero Store have some kind of high-flow valves for the 2.8 with the stem cut back in the bowl area?
Gary
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82-T/A [At Work]
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SEP 21, 08:36 AM
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| quote | Originally posted by G-Man:
The carbureted versions of the 2.8L had smaller valves. Anything fuel injected (like the Fiero) had the larger valves from the factory.
Didn't Fiero Store have some kind of high-flow valves for the 2.8 with the stem cut back in the bowl area?
Gary |
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Yeah, the "SI" Stainless Steel "swirl" valves. They are really hard to find now. ARI Racing has a couple sets of them, but only if you order them with the cyl heads. I just ordered a set of cyl heads with them, and had them port the heads as well. The valves are stainless of course, which typically makes the valves last longer. But there are a couple of differences between these and normal stainless valves. They have a swirl finish to them that is supposed to work with the natural direction of how the air would be coming into the combustion chamber (from what the sales brochures said when I looked it up). They are also narrowed a bit (as you say, right at the stem) which uniquely increases the amount of air that's able to get into the combustion chamber (and get out of it), since the stem is narrowed and allows for more volume.
Based on all the research I did after plunking down $1,200 for a set of heads with these installed... I saw several posts on here that it increases anywhere from 2-5hp, but also improves fuel economy. I can't really speak to the fuel economy, because I have to ask myself... if you're changing out the valves, what was wrong with your car before and what are you comparing it to? But there were some dynoed results (I saved the images from somewhere) that showed a horsepower increase in the mid to upper rpms.
I also had the cyl heads ported by them, so hoping that'll make a difference too. Still, I think the biggest bottle neck is still literally... the "neck" of the intake plenum.
Here's a horrible graphic, but you can just make out the swirl finish on it, and the narrowed stem.
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