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post #1 of 7 (permalink) Old 11-21-2017, 07:19 PM Thread Starter
 
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hi,

i just bought a 1970 trans am with a 400 RA 111 and TH 400. it was restored in 2012. as with many restorations for big collectors, more time and money was spent on cosmetics. also, i realize that there is also a trans am forum or 2, but this GTO forum has some knowledgeable members. my initial questions are mechanical which are common with GTO's.

just starting to evaluate, but the performance seems anemic compared to other 68-70 muscle cars i have owned. assuming a leakdown test doesn't reveal the need to rebuild, the power will have to increase in order for me to want to drive it much. since this car appears to be original (build sheet was included), i need to leave it as much stock appearing as possible. i think that a 75-100 hp increase will be adequate.

what are any members thoughts on such a power increase? i can do almost any engine mods, but would like to stop short of a complete engine out rebuild.

thanks,

dave
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post #2 of 7 (permalink) Old 11-21-2017, 11:29 PM
 
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That car should move pretty good. I have owned a TA powered by a 1970 RA III with an automatic and it was pretty quick. (Mid 12 quarter mile most days...). Some mods but not extreme. What gear ratio does your car have? If the car hasn't been driven much by the previous owner then a carb rebuild might be in order.
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post #3 of 7 (permalink) Old 11-22-2017, 09:57 AM
 
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Originally Posted by Shake-N-Bake View Post
That car should move pretty good. I have owned a TA powered by a 1970 RA III with an automatic and it was pretty quick. (Mid 12 quarter mile most days...). Some mods but not extreme. What gear ratio does your car have? If the car hasn't been driven much by the previous owner then a carb rebuild might be in order.
Good recommendation. Also you might be interested in the Ames PY forum as there are all kinds of Pontiac people there, most of whom have Firebirds/TA's. I try to get as many opinions as possible. Pontiac - Street - PY Online Forums
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post #4 of 7 (permalink) Old 11-22-2017, 10:31 AM
 
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Shake-in-bake's reply is spot on. Q-jet work, adequate fuel pressure, distributor work, verifying leakdown. With a little teardown, what cam has been installed. Is the TransAm equipped with factory AC? Non AC cars makes it a lot easier to pull the cam.

Under wide open throttle, a '70 factory PQ Turbo 400 equipped TransAm should automatically shift from 1st to 2nd gear in the 5200-5400 rpm range. Had a never bored stock '70 TransAm YZ 400, PQ T400, stock converter, in my '80 T/A for a while in the '80's, mid to low 14 sec car, with 3.08 gears out back, minimal exhaust work. I ended up pulling the original 12 cyl heads & installed a set of fresh "64" casting 70 455 heads & the T/A ran even better, as I could run a full advance curve w/o detonation.
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post #5 of 7 (permalink) Old 11-22-2017, 07:03 PM
 
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Garage
Agreed with above - do the basics first. Compression test & adjust valves - zero lash using polylock rocker arm nuts, ensure you have a free flowing exhaust system and no collapsed mufflers or restrictions (check the exhaust manifold heat riser if so equipped). Good gas, tune-up, rebuild/tune the Q-jet, adjust the timing curve for best performance.

Often, the secondary air flap on the Q-Jet does not open soon enough or has been adjusted too tight. I would make sure the air flap is snapping open, but not too soon as to cause the engine to bog - that's how I adjust them. Getting this correct is very important to engine's power and responsiveness.

If you do not already have it, suggest you invest in Cliff Ruggles book, How To Rebuild And Modify Rochester Quadrajet Carburetors. It will show you the small set screw, spring, and the screw to adjust the tension on the secondary air flap, as well as the vacuum diaphragm (which I always tossed away) that pulls down on the air flap.

Once you feel you have the engine performance tuned, then if you wanted to play around with other items to improve HP, then I would look into other add-on items.
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post #6 of 7 (permalink) Old 11-22-2017, 08:26 PM
 
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The quest for power

I had a 1973 455 T/A in 1981 and it would fly!

I used to delight in torturing the young boys with their 77-81 T/As.

Good luck in finding the hidden power in your car.
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post #7 of 7 (permalink) Old 12-12-2017, 03:38 PM Thread Starter
 
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Thanks for the responses. Have repaired trans shift modulator, RA flapper solenoids, fixed some exhaust rattles. Now trying to increase fast idle speed. Looks like solenoid has threads so i will disconnect electrical and turn. Have not found a good write-up on this so just have to figure it out.

Car has 3.31 posi 12 bolt, auto, 400 YZ RA 111 and claims rotisserie restored.
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  Pontiac GTO Forum > The 1964-1974 Pontiac Tempest, Lemans & GTO > 1964-1974 Tempest, LeMans & GTO Engine Tuning and High Performance

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