carb change

[jpaz]

I have decided to change the carb on my Q code Mach 1. I have read a lot of different opinions about this and would like to thank all who have shared all the info. I have a 72 Mach 1 w/351 Q code. It has been rebuilt .030 over w/a little larger than stock cam, stock 4300D carb, stock intake & exhaust manifolds C6 trans & 3.25 gears. The 4300D carb was rebuilt about 2000 miles ago, but its already starting to leak & its not that great. I'm going w/an Eldebrock Performer intake & a Holley Street Avenger 770 w/elec choke. I just found one for 356.00 bucks, sweet! Will I have to change the fuel pump? Would really appreciate any suggestions. Thank's!

 

[Jeff73Mach1]

Sounds like a very streetable combo that should be easy to live with. Stock fuel pump should be fine.

That intake is not as good as some others out there, but it should be smooth. I assume you are looking at the Edelbrock 2665 It doesn't really utilize the upper rpm range as well as it could.

I would consider the Edelbrock 7564 Air gap intake as I think it will preserve the upper power band that a 4v engine has and will work better with the engine's overall strengths.

 

[jpaz]

Ya Jeff, I got the 2665. Thought about getting the Air Gap for that reason, but I may add the ram air unit someday. Would I see a better performance gain with the air gap & no ram air? Kinda not sure.

 

[barnett468]

Ya Jeff, I got the 2665. Thought about getting the Air Gap for that reason, but I may add the ram air unit someday. Would I see a better performance gain with the air gap & no ram air? Kinda not sure.

the rpm is likely a better intake than the air gap for your app.

try your performer intake witout and with a 1" open spacer.

curve your ign timing so it is optimal for your engine.

 

[4Vforever]

Not long did the Performer intake change over myself with my 750 V/S Holley on my Q code and it runs a lot nicer and seems heaps better all round. The stock pump is more than adequate. Also don't listen to this crap about port matching because the intake ports are heaps smaller. Edlebrock has done this (rpm and air gap too) to keep better air velocity in the port and not affecting the higher end revs, because the old type design with the larger ports would be doey down low. The only thing you may have to do is run a spacer as the accelerator linkage may hit the intake, I run an inch spacer for clearance. My Q code engine is stock (91 000) and this, a double row timing set and a Pertronix kit in the dizzy are all that's done to it, (until the rest of my exhuast system arrives) and it performs quite well and gets pretty good milage out of it too.

 

[jpaz]

Thank's for the input guys! I can't wait try this out. Was pretty disappointed with the hesitation & boggy traits of the 4300 carb.

 

[Jeff73Mach1]

I think the air gap is a better performing manifold, but I run an old Torker single plane and an 850 double pumper that has been massaged a bit. That being said, the manifold you have is not a bad manifold and has its advantages.

Ram air doesn't really add power that can be measured, but it sure looks cool. I'm going to stick some led's in mine behind the flapper for night time operation. If I needed nitrous it would be a good place to run the purge lines too!

 

[c9zx]

As others have said the Performer can't utilize the potential in a Q code engine. It will "sign off" at about 5400 RPM. You would be better off with the air gap. And as Jeff said, the ram air is mostly "cheese cake". Chuck

 

[jpaz]

So with the Air Gap the redline will be @ 6500 rpm? Can I safely rev that high w/stock valve train? I already bought the Performer manifold, was on sale, but it's not on yet. Should have done a little more research I guess. What about milling the dividing wall down a bit like the Air Gap is? Saw a video about that & they were able to get just about the same hp & torque from the Performer as the Air Gap. Or just add a 1" spacer? You guys are right about the ram air, more of a cool factor than anything. Should probably use the money for a posi unit instead.

 

[Jeff73Mach1]

Posi unit is a great upgrade!

Air gap will prevent some degree of fuel percolation in the bowls of the carb. If you could return, exchange or sell at a minor loss, I would do so.

6500 rpms is probably pushing the limit of a stock valvetrain and it is the manifolds range-not necessarily the engines. The Performer will hurt the engines top end performance while the Air Gap will not. I would not run a stock valvetrain much past 6000rpms regularly, though the Cleveland Valvetrain is made of decent factory components. I would not hold a stock Cleveland at or above 6000 for any significant length of time.

 

[jpaz]

Ok, thank's so much Jeff, that's what I thought, about 5500-6000 max. I'm just running it on the street & to a few shows. I don't plan on running over that & the Performer was 95 bucks cheaper, guess I'm a cheap wad. I will probably try a 1" spacer under carb after I try it as is, and see if there's any difference. I read somewhere today that a guy that worked as an engineer for Edelbrock & he said runner lay out is exactly the same. But I'm sure the Air Gap has to be cooler. Interesting. Anyway, thank you for the advice. My new carb just got here!

 

[jbojo]

So with the Air Gap the redline will be @ 6500 rpm? Can I safely rev that high w/stock valve train? I already bought the Performer manifold, was on sale, but it's not on yet. Should have done a little more research I guess. What about milling the dividing wall down a bit like the Air Gap is? Saw a video about that & they were able to get just about the same hp & torque from the Performer as the Air Gap. Or just add a 1" spacer? You guys are right about the ram air, more of a cool factor than anything. Should probably use the money for a posi unit instead.

Was this the video? They tested on a Chevy but I think the results should have the same characteristics in your motor though HP numbers would be lower as they were using a more modified motor. They milled the center plate on the performer to match the numbers that the Air Gap had.

 

[jpaz]

Yes this is the one. I thought it was pretty cool. Was thinking about doing the same. Not sure how much to take out or just try a 1" open spacer.

 

[jpaz]

Got my new 770 Aluminum Street Avenger carb yesterday. Very nice looking...but the throttle lever is hitting the intake runner. I just set the carb on the intake here in the house to check it out. I don't have heat in my garage yet. Anyway, 4vforever your right, I have to put a spacer on it. I'm gonna put a 1" one on like you did & see how it works.

 

[4Vforever]

Thought you'd have to run a spacer, every cleveland I've put a performer on (2V or 4V) have needed one for that exact reason. Anyway a RPM air gap is a great intake if you intend to drive it hard most of the time, but I tell you for a near stock 4V O/C headed Cleveland, this one is more than adequate for general driving duties and will pull well to around the 5000 rpm mark. Realistically though I would not rev a stock cleveland much past this for any great periods of time, maybe 5500 and a flash at 6000, but that's probably all that's in a stock 4V O/C Cleveland anyway, good luck with it all and you'll definitely notice the difference using this intake, especially down low.

 

[jpaz]

Thank's 4v, can't wait to try it out. I was so sick of the stock carb & it looks like its starting to leak, so its time for a change. Most of my driving it is cruising around town going to car shows & an occasional road trip. This should work good. Gonna be awhile though, its the middle of winter here.

 

[4Vforever]

No worries you'll definitely notice the difference first time out too. You're over there in winter and we're over here in summer, today it's nealy 40 degrees centigrade and humidity is in the high 80's, fun, fun, fun. Trying to get the car ready for a club run tonight and can't stop sweating and you guys over there are freezing, be nice if it was just a happy medium.

 

[jpaz]

Hey I'd take the heat and sweat, then I could drive my Mach. Got 4" of snow on the ground & it's 25 degrees F here. Oh well gives me time to figure out everything I need to do this intake & carb change. Been awhile since I've done any wrenching. Have fun cruising 4vforever!