mods are in the sig, i was just curious because someone at the track told me i should put a carb on there that really does something, as apposed to the stock. are the stock carbs really that bad and will there really be that big of a hp gain from replacement
ya i think a new carb would make the car run alot better and give you a few more horse power as well, espically if you are running the stock carb. the new carbs have alot more technology than the old ones so it should help quite a bit. with the mods you have i probally wouldent go bigger than a 600 cfm carb.
Well with that "mild head work" you're probably not seeing any power gains due to the stock carb not flowing a whole lot of air, also, if you're running a stock intake. My car still has the stock intake and carb, but i 'think' the carb has had the jets sized up or something because it just runs like a bat out of hell....it's probably the best tuned carb i've ever driven (i wish i had tuned it...previous owner)
Anyways, i'd say hell yea it'll make a difference, especially if you get a matching intake to go along with it. If you've got the cash to spend, i'm planning on getting an RPM Air Gap intake since it's about the best duel plane intake on the market, and a BG 650 Speed Demon carb. Even if the carb flows a bit more gas than i need, just get a FP regulator and be done with it.
I priced the intake at my local speed shop for about $239.00 which is what most of the mail order places want. I havent got a price on the carb yet but those Speed Demons are a work of art...Plus unless you plan on building the hell out of your motor, it'll probably be the last carb you ever buy. If you're planning on a stroker kit or something in the future, buy a 700-750 and regulate the fuel pressure down so it doesnt run rich, then you'll have your extra fuel in the future when the need comes.
A very easy way to see if that carb is holding you back is to simply hook up a vaccum guage and see if you have any intake manifold vaccum at WOT. Theoretically, if your carb is large enough your intake manifold vaccum should be zero at WOT.
If you are still running factory pieces, I would guess that the carb is NOT holding you back. The port work you have done should require nothing more than a jet change. If you put a set of aftermarket headers on it and a different intake, then it might be a different story. As far as "old technology" there is very few differences between a current-production base model holley and the piece on your car; aside from the emissions and blocked idle screws of course. If you went with one of the higher-end carbs, then yes, there are certainly upgrades/benefits.
The holley 4bbl's that came on those cars were tuned extremely well, you'll spend a lot of time on an aftermarket carb to get the same response and fuel economy you have w/ your stock carb. Of course this is assuming that your existing carb is in good shape and tuned correctly.
In summary, if you aren't planning anymore upgrades I would spend some time with a rebuild and holley tuning kit on your existing carb. BTW, I own an '85 GT. If you are interested in any stock pieces PM me b/c I am considering parting out the car.