70mm TB & 1 5/8 shorties too big for stock motor?

90LX5spd

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Aug 13, 2005
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A buddy of mine with a '91 GT is getting ready to order a TB and unequal length shorty headers. His ride has all the usual bolt-ons (pulleys, cat-back, off-road h-pipe, MSD, Edelbrock Performer, 3.55s) but doesn't plan on installing heads anytime soon (he just installed a new stock long-block). He wants a 70mm TB and 1 5/8 headers but I caution him it might hurt his mid-range torque output. Would a 65mm TB and 1 1/2 headers better suit him? If he does get heads (the stockers being true major restriction in the package) will these smaller pieces still support descent power or would they become a restriction at that point? Thanks.
 
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IMO, stock tb works the best on stock heads n/a. i originally bought a 70 when i bought my cobra intake. i ended up putting the stock on back on beacuse it drove much better. i had the 70 on my current combo and ditched it for the 65. 1 5/8 headers will be fine
 
So it seems the larger headers are fine but stay conservative with the TB. Good torque is something 5.0s are known for and I'm betting my buddy doesn't want to lose that in favor of a few ponies here and there on the top end.
 
The parts will be fine.

TB can effect driveability issues like tip-in if you go big...

Don't neccessarily believe in the bigger is better clause...seems like your on your way!

Keep what you got for now
 
1 5/8 is generally the normal primary tube size...i think 1 3/4 is the next step up for moderate HCI cars and then 1 7/8 for stroked HCI's and up. So the headers will be perfect but i would suggest a 65mm tb. With stock heads i think intake air velocity is more important than intake air volume so going with a bigger TB might actually hurt your performace/driveability. I have heard that a 65mm tb is good up to about 300 rwhp maybe a little more. good luck man