[Ryche400]

I have been a die-hard Holley carb guy for years. But I just came across a Quadrajet that I took off my old Trans Am years ago. Could anyone tell me what size it is. I want to try it on my current 400 Pontiac set-up. Its got these #s on it 7045274 T9 1405. I want to see how good these carbs really work. I believe it came off an early to mid 70's 400. Anyone care to convert a Holley guy to a Quadrajet guy???

[Ryche400]

I have been a die-hard Holley carb guy for years. But I just came across a Quadrajet that I took off my old Trans Am years ago. Could anyone tell me what size it is. I want to try it on my current 400 Pontiac set-up. Its got these #s on it 7045274 T9 1405. I want to see how good these carbs really work. I believe it came off an early to mid 70's 400. Anyone care to convert a Holley guy to a Quadrajet guy???

[Hattmann68]

I've got a 7045264 pontiac carb.Its a 800 cfm model, good carb except in 75 they used a adjustable tapered rod and fixed jet to supply extra fuel to the primary main jets which gives you an adjustable jet. I've never had good luck fine tuning these carbs and usually plug these ports off. Everything else about the carb is pretty good.

[Cliff R]

The 75 carbs are oddball units. They make excellent carbs but it requires removing the aux power piston/rod and plugging the jet followed by complete recalibration. The end result is as good as any other late style 800cfm carb......Cliff

[Ryche400]

Sorry, my quadrajet experience is limited to stock rebuilds. I have done quite a few in my day, but never really "hot rodded" a quadrajet. Do you think just rebuilding it it will work fairly well. Its a 400 6X heads, mildly ported and shaved .030, Flat top pistons, Summit 2801 cam, Performer intake, Hooker super comp headers. Anyone care to make a guess one C/R? I have done many Chebby's, but not very many Pontiacs, so im still kinda learning as I go. Thanks for the reply's guys..

[Cliff R]

I've never been happy with any of the 1975 carbs that used the auxilary power piston set up. Even correctly rebuilt they often don't work well. Probably why they were only used one year and the aux power piston, rod, jet and oddball APT system was replaced with the later style APT that was retained until the M/C solenoids and TPS started showing up.....Cliff

[Ryche400]

Thanks Cliff. I guess I'll stick to my HP Holley till i can find a better Q-jet. What about an Edelbrock Q-jets?? Any luck with those?

[Cliff R]

Edelbrock chose to copy and use the late style Chevy side inlet carbs. They have the single main airbleeds in the airhorn and use a "teardrop" shaped airhorn gasket at the main boosters. They have labeled the RPM carb an 850cfm unit even though they are no different than any front inlet q-jet made after 1974. This is probably a marketing ploy to steer folks in that direction. I've custom tuned quite a few of them here and ran them at the track. The Edelbrock RPM units have a very generous (rich) idle curcuit, a bit lean on the primary side and WAY rich at full throttle. KRE's dyno testing has confirmed this on a few that have been tested there.

Even so they make a very good foundation for a really nice q-jet if you don't mind the price and that they are side inlet. We have seen quite a few quality control issues ranging from holes not drilled at all to holes drilled and missing the intended target. This was mostly with accl pump holes in the airhorn and the secondary enrichment holes just above the airflaps. All in all they are decent carbs, but no performance advantage whatsoever over a correctly prepared 1975 or newer Pontiac carb......Cliff

[burnt chicken]

Weren't most Q-jets after 1975 800 cfm? Why not visit the local boneyard and find one from another 400... I picked up a spare from a 1976 Buick 455 for about 40.00. Other than the throttle linkage being different, it works out well.

[burnt chicken]

..oh, had to change the choke, too.

[Hattmann68]

Almost all if not all 75 and later Pontiac Carbs are 800 cfm.Most 75 Buick and Olds front inlet carbs are 800 cfms.Chevy carbs are a mixed bag. The only real way to know is to look in the primary bore near the venturi look for the bulge. I like the 76&above quads because of the electric chokes ,apt, better castings and cheaper to buy than the earlier overpriced and sometimes restamped to get more money carbs.

[Ryche400]

Cool. thanks for the input. I have a 4 day weekend. Might just give the q-jet a try. Hell all it will cost me is a carb kit, and a little time. Cause lord, knows Ive got more time than money....