[jgsrna]

Hi i have a 429 cobra jet engine with a 600 carb elderbrock, its been rebuild and everything! but aint satisfied!! it takes 12 to 15 sec to go from 0-60 mph!! and that is slow!!! is something wrong mabey!! and im wondering if i get a 750 carb will i notice a slight difference! or would i have to buy the manifold, cam, carb etc..( which i dont really want to) to see a difference!! please help!!! or anotha thing that engine isnt on a mustang but a thunderbird 68!!! but its still a mustang motor thats why i post it here!!

[caveman]

How much ignition timing are you using? Could need more. Original cam? Could be flat. Aftermarket cam? Could be too big for the intake or designed to operate too high up the RPM range. What rear gears are you using? Stock? Probably 2.70's or 2.80's. Horrible for hard launching. Trans rebuilt? Torque converter could be slipping.

[jgsrna]

Yea stock rear gears!!! and its original cam! and what do you mean ignition timing cause its timed right!! and the transmission has not been rebuilt!!

[cavediver]

Are you saying that the engine is out of a 1971 Mustang 429 Cobra Jet? (1971 was the only year for the real 429 CJ engine) I ask because Thunderbirds never had a Cobra Jet engine. The T-bird 429 was a low compression - low horse power engine.....lots of torque but that's all.

If you do have a REAL 429 Mustang CJ then you have a rare engine worth some serious $$$. if it's a generic T-bird engine, well then you have a nice tame hi-way cruiser engine.

What rear gear do you have? That will make a big difference in performance. What is the compression ratio? What cam is in it? Single or dual plane manifold?

Don't forget that T-bird of yours is as heavy as a tank and it will never be as fast as a lighter Mustang.

We need more information to answer your question.

[jgsrna]

Yea its a cobra jet engine!! not thunderjet!! and the rear end gears are stock, the cam is i think is stock too! and manifold is stock as well!! i thinks its a single plane!! and i know, the tbird is really heavy compared to the mustang!!!

[caveman]

Just because the book calls for 6 degrees advance doesn't mean that the engine will perform best at that setting. Try advancing the timing until it pings, then back off a bit and see if it doesn't run a little better. Mine ran best with 10-11 degrees advance. Also, check the harmonic balancer. Make sure you are timing it from the proper location. If the engraving is worn or hard to read, you could be timing it at zero instead of 6.

[jgsrna]

Oh i didnt know that!!!! thanx!! i always thought it had to be in the proper degree to run good!!but to do that i would have to readjust the carb though right? and about the rear end gears if i get some 4.10 would i notice a difference in getting off the line quicker!!! but i heard itll effect my top end!

[jgsrna]

Ohh i didnt know that!! thanx!!! i always thought you would have to time it where it was the proper way!! but then i would have to readjust the carb though right? and about those rear end gears, thinking of getting some 4.10 would i notice some difference on those getting of the line!! but i heard the downside that it will effect my top end though!! are those a good choice!!

[caveman]

If you want to be able to cruise, you want to use something in the 3.25-3.50 range. I have 3.25's in mine and I cruise around 2400 RPM. I'm about to upgrade to overdrive to compensate. 4.10's would make you launch pretty hard, but would kill your top end. As far as carb adjustments go it should be minimal. You will have to adjust your idle speed screw some but your mixture should remain the same. When you advance the timing, it will reduce your RPM a little so you will have to bump it back up to maintain engine idle speed.

[jgsrna]

k thanks !! so when you put those 3.25 on yours did you notice any difference!! so what about 3.50, how much would those kill my top end?!

[thetvirus]

A T-BIRD is not supposed to be fast, it is a cruising luxury boat!!

[andrewmp6]

The thunderbird had a thunderjet in it which was a watered downed cj.

[66Sprint200]

Originally Posted by andrewmp6

The thunderbird had a thunderjet in it which was a watered downed cj.

Yes, but his 429 CJ is from a Mustang, he said that in the first post.

Hey jgsrna, why do you keep putting exclamation points at the end of all your sentences? In essence that is basically the same as if you were typing in all caps. It makes people think you are yelling.

[cindys_sn95]

3.55s, a little more timing, and a little more carb. should help some.

[jgsrna]

Alright thanks cindys! i hope to do this and see if theres a change in it!! and notice a bit more power!!