Rochester vs Holley

[mustangandy]

My 1971 mustang 429 CJ has a holley 3310-12 carb fitted instead of the original Rochester. I presume its a 750cfm? It's on the original spreadbore iron intake with the appropriate conversion plate/spacer. It was fitted as the PO couldn't get the Rochester to idle at all. I gather the rochester is quite difficult to dial in properly? More so than the holley? The cold idle is still poor with the holley though.

However I do have the original Rochester carb and so was wondering, other than just being historically correct for the car, if there are any advantages to putting it back rather than just leaving the holley on there? Thinking of any differences in HP, torque, driveability, noise, and mpg. Does the fact that the holley is on the rochester manifold make any difference either?

Thanks

 

[7173Vert]

My Opinion...

The Rochester Quadrajet is a good carb if you know how to tune it. I had to get some help with the final tuning on my carb although, I learned that the issue I was having was not actually carb related. Turned out to be a timing and vacuum issue. I then went to a GM engine and tuning expert here in my area. He found the issue quickly and was very supportive of these carbs, again, if you know how to tune them. In his opinion, no harder then any other carb. out there and after going through the process with him, I would tend to agree. I am still trying to dial in my carb, it is close, but sometimes runs a little rich, may need to re-jet once more to complete the tuning.

If you go back to using the Rochester, do you have the original choke pull down assembly? This is a very rare and hard to locate piece. 

If you are looking to keep the car completely original for show purposes, then it makes sense to return the Rochester carb. to the car... if not and the Holley is doing the job, may be better to stay with that. At least you have the original carb. that still remains with the car...

I'll let someone more familiar with the Holly's speak to that end... Good luck.

 

[mustang7173]

The one main issue I have with either carburetors, it heat, time, and vibration take their tolls on their body's. I have rebuilt many carburetors with no better results due to internal cracks that create vacuum leaks. IMO, If the Rochester is in good shape, then I would fix her up, store it and get a brand new Holley.

 

[Don C]

Yes, it looks like the Holley is 750cfm. The adapters are somewhat restrictive, so it is likely not delivering full performance. A properly operating Rochester would probably provide an improvement.

Rochesters are not my favorite carburetor, but not that hard to work on, just got to follow the rebuild and adjustment steps, no short cuts. As long as the throttle shafts and carburetor body are not worn, there are no cracks or porosities in the body that allow air or fuel leaks, it should be rebuildable and usable.

If you want to keep using the Holley I would recommend getting a new aluminum intake manifold, improve performance and shed a few pounds.

 

[donkost]

Seems like it was a common thing to do- replace the Rochester with a Holley. My '71 429 CJ-R has a Holley installed by a PO in place of the Quadrajet. I don't have the original carb, and since I'm never going to have the car judged I'm not going to try and locate one. I had a Quadrajet back in the day on a '68 GTO 400 and a '79 Trans Am 400. Never really had issues with either one of them, and I did some mild tweaking to each.

 

[mustangandy]

Thanks everyone for your thoughts.

I'll unbox the Rochester to see how complete it is. Hopefully all the bits and pieces are with it.

The car is not for show so, in that respect, there's no rush to refit the quadrajet just yet. I think, for now, getting the holley set up properly, timing optimised and running the car, after standing so long, may be best.

Although the holley is, I think, from 1995 it was only fitted 3 years ago as part of a mild restoration and, as covered less than 200 miles since then, it should hopefully be in decent shape but how would I be able to tell if there were any vacuum leaks? Perhaps a rebuild kit would be a good investment?

I'd wondered as to whether the holley would sit correctly onto the original quadrajet iron manifold. Although she seems to run well (though I've no way of judging either way) it would make sense to get an appropriate and correct intake manifold. Presumably the iron SCR one's are like hens teeth? As I have ram air that limits the choice of after market aluminium intakes I believe due to height issues? As I likely won't be hunting the red line every time I take her out (well not yet anyways as the original untouched 47 years old, 52,000 mile engine that I am really not familiar with) I'd probably go with the edelbrock performer intake. However I've checked their site and it says that this manifold won't fit a 429 CJ - though I presume it's because originally a quadrajet would be fitted and the two wouldn't line up? Am I right in thinking this and that it would be OK with the holley carb?

Lastly would anyone know what, if any, performance gains, or losses, might result in changing the intake manifold over?

Thanks again

 

[Canted 393]

http://www.cobranda.com/1x4duplcojet.html

Try this 1 its a blue thunder, my 71 torino cobra with a 429 cj had a performer on it  works with a lot of Permatex , it was on there when I got it. I switched over to this intake and its night and day difference and yes I have a shaker.

 

[Hemikiller]

Quadrajets are a very good carb. Small primaries for great low end response, huge secondaries for top end. They can develop a "bog" when the secondaries open, hence the "Quadra-Bog" knickname. Probably swapped out for "more performance" or the owner didn't understand how to rebuild a Q-jet. I rebuilt a bunch of them during my stint as a professional mechanic in the 90's. I could practically rebuild those 80's feedback units in my sleep. Biggest problems I saw were just dirt, dried up gaskets and bad accelerator pump diaphragms. Lots of places to get any manner of parts out there.

http://429mustangcougarinfo.50megs.com/new_page_6.htm

http://429mustangcougarinfo.50megs.com/new_page_2.htm

 

[mustangandy]

Quadrajets are a very good carb. Small primaries for great low end response, huge secondaries for top end. They can develop a "bog" when the secondaries open, hence the "Quadra-Bog" knickname.  Probably swapped out for "more performance" or the owner didn't understand how to rebuild a Q-jet. I rebuilt a bunch of them during my stint as a professional mechanic in the 90's. I could practically rebuild those 80's feedback units in my sleep. Biggest problems I saw were just dirt, dried up gaskets and bad accelerator pump diaphragms. Lots of places to get any manner of parts out there.

http://429mustangcougarinfo.50megs.com/new_page_6.htm

http://429mustangcougarinfo.50megs.com/new_page_2.htm

Thanks Hemi. Properly set up, do you reckon the quadrajet is as good as the holley throughout the rev range? What's the 'trick' to overcome the bog? I'd like to try and rebuild it myself  - if I'm up to it!

Cheers

 

[Fabrice]

I have the original Rochester and seen it in action when my friend the PO had it.

The car ran very fine with it. Replaced by a 750 Holley. It did not really ran better. But in the early 90's having a Holley was cooler and there was more doc on how to tune them vs the Rochesters. I know the car ran back then with the Rochester with the unrestored original engine up to 220 kmph without much efforts.

Suspension/steering were the problem. With both the car was a fuel monster.

@mustangandy, I don't know if you plan drive it lots, but if you do, I'd really ditch these ancient tech for an EFI.

Du 40 ou plus au cent, ca amuse pas longtemps...

Here's a pict of mine if you need compare.... As the car is matching number, I keep it for the sake of be able to say I have it, same for the 1 ton intake or the ridiculously heavy air filter casing and all original parts that I will not reuse.

 

[c9zx]

I would at least try to reuse the Q jet. If it can't be made to work, get an intake to match the Holley. Chuck

 

[TommyK]

I would at least try to reuse the Q jet. If it can't be made to work, get an intake to match the Holley. Chuck

+1. I ran a Q-jet for several years on an Edelbrock Performer RPM and it worked fine. FYI the Edelbrock Performer RPM has a flange that will accept either the Holley or q-jet.

 

[mustangandy]

I would at least try to reuse the Q jet. If it can't be made to work, get an intake to match the Holley. Chuck

+1. I ran a Q-jet for several years on an Edelbrock Performer RPM and it worked fine. FYI the Edelbrock Performer RPM has a flange that will accept either the Holley or q-jet.

Thanks Tommy. I have ram air though so I think the rpm is too high? Maybe the basic performer will fit but not sure if it offers (other than 30lb weight saving) any real advantages over the original iron intake?

 

[mustangandy]

I would at least try to reuse the Q jet. If it can't be made to work, get an intake to match the Holley. Chuck

Thanks Chuck. Yes I'll try to reuse the quadrajet (not bothered about emissions stuff) if at all possible. Am I giving up any performance with quadrajet manifold and adapter with the holley now?

 

[Don C]

Yes, the adapters are restrictive.

 

[c9zx]

+1 on Don C's post. The adapter is a poor solution. Chuck

 

[Hemikiller]

If you want to get rid of the adapter and still run a Holley, they made a 4165 spread bore carb as a direct replacement for the Q-jet.