Hi, i'm swapping my edelbrock performer RPM intake this weekend for the Performer, going from part 7111 to 3711. Are the bolts i'm using with my RPM intake compatible with the 3711 in terms of size and length or do i need to order a specific set. Just want to get everything lined up to do the job in one day.

 

I think they are all exactly the same.

 

[QUOTE=wcourt3010;701072]Hi, i'm swapping my edelbrock performer RPM intake this weekend for the Performer, going from part 7111 to 3711. [QUOTE]

Why?

 

Thanks, cutty.

 

[QUOTE=cutlassefi;701077][QUOTE=wcourt3010;701072]Hi, i'm swapping my edelbrock performer RPM intake this weekend for the Performer, going from part 7111 to 3711. Curious too why you are swapping, 3711 is way more restrictive. I have not bolted my 7111 on yet but it is a bit thicker than the 3711- here are some side by side pics....
https://classicoldsmobile.com/forums...ison-pics.html

 

so I finished the swap. what a difference, i got all my low end torque back and then some. for my mild application the low rise edelbrock performer intake was the way to go.

And the bolt set was compatible.

 

Please give a description of your engine/mods, rear end gears, transmission, and carb setup.

I did the swap too, but I didn't notice a drastic change. Better, but not drastic.

 

sure.

73-76 block
removed the #8 heads and put on mildly ported 7a heads
rebuilt 750 quadrajet
hooker long tube headers
flowmaster delta 50 mufflers
highway gears (2.5x or 2.73) not really sure
stock HEI distributor (at least it looks stock)


only thing i changed in this recent modification is the intake. car is peppy now when i step on the gas. very happy with it.

 

Thanks for sharing. This is interesting. There's lots of debate as to whether the RPM intake will hurt performance when it's on a "stock" to mild engine. There was a really good thread on ROP a few years back before the crash and it "proved" even if it was overkill that it was better than the low rise.

I'm assuming your engine was rebuild when the heads were changed. Stock cam? Any other improvements? Was you RPM or your straight 3711 intake divider milled? That's when the center divider between banks is cut down to allow the engine to suck air/fuel from either side of the carb.

Can you explain more so what problems you were having with the 7111 intake?

 

Hi: yes i've read all those posts and spoken with my local speed shop (Karbelt in Pickering Ontario) and spoke with Lunati and Edelbrock and the recommendation was to go with the 3711.

I'm using a mild lunati voodoo cam, 213 @.050 i believe. Hydraulic flat tappet. didn't use a degree wheel, just lined up the keys.

I have not touched the block or cylinders. It hasn't been out of the car. I have not milled the 3711 but a buddy of mine suggested we could do that. i'm reluctant to touch anything now except for some tuning to see how much I can get out of it.

the 7111 was okay at highway driving, it really came on if i stomped on the gas to pass someone, that combined with the kickdown to 2nd gear. but when it was just around town i found it sluggish pulling away from a light from a dead stop. I'm not sure what effect the headers are having on the setup. i put them on after the 7111 and they didn't seem to really do anything. they're supposed to be good for low end torque are they not? I put them on because the stock exhaust manifolds were past it.

i could squeal the tires before i put the 7111 in and couldn't afterwards no matter how hard i stomped on the gas. now i can. the car just seems snappier, more alive at low rpm.

 

Sorry to be a pain, but I've beat my head against the wall on my car and you were in the exact same situation.

So you had the Q-jet on the 7111 intake? What intake did you have in the first place, the stock one? Has the Q-jet always been on the car? How's it tuned? Who rebuilt the Q-jet, do you know what it was rebuilt to, like year of engine, etc.?

The 73-76 motors weren't anything special, neither were the 71-72. So with a mild cam if you can squeal the tires(I'm assuming you have a posi, please correct me if I'm wrong), with highway gears, there's no reason my 72 with 3.33 gears and a open leg rear end cant. The gears should make up more than the difference of the motor from a dead stop.

The only real difference I'm seeing here is you have a Q-jet, and I have an Edelbrock 1405 600cfm carb, that I've adjusted until doomsday to no real avail.

On the highway now, when you punch it and it kicks down into second, is there a substantial difference from when the RPM intake was on the car?

 

didn;t have the Q-jet on my 7111 as it would have required an adapter and i probably would have had clearance issues so i didn't even bother. INstead I was using a edelbrock performer carb, 650 cfm i think. my Q-jet is 750 so there probably would have been a bit of a difference there if it was on the 7111.

before the 7111 i had the stock one on there. i put the performer rpm cam in with the 7111 but hated it, ran horrible except at highway speeds. the highplane intake and matching cam was the wrong way to go for me so i've backed away from that.

Q-jet was rebuilt by a carb rebuilder up here in ontario. that's probably bringing something to the table too, i might put my 650 edelbrock carb back on to see what happens.

had the car out on the highway this past weekend and i'm very happy with the overall performance.

 

It'd be very interested in what you find going back to the 650 cfm carb. I don't see a 650 listed on their site. Mine was an Edelbrock 1405 carb, which is only 600cfm. I've pretty much tuned it through the whole spectrum without finding a good tune. I don't have the rpm cam or anything, but I don't want to spend $200 to have a qjet rebuilt to find it's the same.

Did you swap out the lunati cam for the rpm or visa versa? (or are those the same, sorry for the dumb question). What Q-jet are you running? Like number on it? Was it rebuilt to stock specs for that carb?

I've gotten conflicting information on the Q-Jet, specifically the 7042250, it's possible it's a 750(not that a stock 350 ever needs 750cfm but the potential is there).

 

Manifolds and carbs need to be matched to the engine and intended rpm use. It's all about getting the right vacuum signal to the venturis at the right time. A larger runner and open plenum responds differently than smaller runner. I had a hell of a time getting my 330 with 3711 and Holley 670 set up correctly. Do some reading on carb and manifold theory by David Vizard, he explains better than I. I added a 1 inch 4 hole spacer to my setup and it really helped.
Tim

 

I agree with you 100%. My 7111 intake wasn't matched to a stock 72 350. So I changed it to the 3711. Right now I'm torn between trying to mill the 3711 intake divider, or trying a larger carb, which I would be going to the stock Q-jet.

What'd you end up doing with your Holley 670? I'm just curious.

 

If you're running a stock 350, 600 cfm should be plenty. I'm curious as to the issues you're having. I had poor idle, lousy fuel economy and a flat spot the size of New Jesey on wide open throttle..

Both the 3711 and 7111 are dual plane manifolds. The intake runners draw each cylinder 180 degrees apart. This tends to even out the air being drawn into each cylinder as it starts its intake stroke. It helps make the vaccum at the plenum under carb more even, and less 'spikey'. For a mild cam engine this is a better arrangement. Iwould save milling the plenum divider for last, you may fine it makes it worse, not better.

I took my Holley off, and set the throttle blades at the recommended opening. I set the floats to the correct level. I used a vacuum guage to set the idle adjust screws. I also have an exhaust gas analyzer and confirmed idle mixture was at about 14:1

My real issues were poor vacuum signal to the venturis and a wacked out accelerator pump. The original spacer was an open plenum type, and it allowed the intake pulses to bleed together to the point where the transition from idle to main fuel circuit was slow and unreliable. I put a four hole spacer in, which isolated each barrel from each other and let the dual plane manifold work as intended. The spacer increases the velocity of the air fuel charge enough to get the transition to mains much better.

The accelerator pump didn't even start to work until almost 10 degerees of throttle rotation. Ihad to buy a Holley cam kit to get the pump lever to move instantly with the throttle. That helped, but I also ended up upsizing my squirter nozzles from the factory 31 to a 37. I can explain in greater detail, but I'll stop now so no one passes out from reading this long reply.

 

I agree that 600 cfm should be plenty. But it doesn't seem to be. My idle is a little erratic, but it's something you really have to listen to and watch the motor to notice. I don't have a flat spot persay, but the acceleration isn't 'snappy'. If I go WOT from a stand still or 5mph the car goes, but it's not like bam the car comes to life. Like the power isn't immediately there. I can't really put it into words. On the highway it's a little sluggish if I nail it from 60-70. Again it's just not snappy. Either like it's momentarily flooding, or momentarily running lean. With the 1406 it would do the same thing, but like stumble for a split second, the 1405 the stumble is gone but still not snappy.

And, the biggest problem, If I'm on the highway or doing 50+ and I left off to coast or slow down, I smell gas. For 5-6 seconds, and it's strong enough to smell like a leak. But I've checked, nothing's leaking. Edelbrock tells me it's not a closed system and sometimes you'll smell gas. I call bs on this, something wrong. When coasting at 65mpg I've gotta be somewhere around 2500rpms, not sure what the vacuum would be there, but something not right. Maybe it's E-Brocks metering rods/springs staying open too much, but I needed to bump those up to get enough of a shot for WOT. To have had to calibrate the carb this much, I'm starting to think it's not the right carb.

The stock 7042250 Q-Jet would flow up to 750cfm, so even if my motor only needed at max 675 or 700 during high load, I'm starting to debate whether the e-brock is just a poor choice. Especially after wcourt's experience,with very similar components.

What are you using for the exhaust gas analyzer? That was my next though, somehow install a gauge and take not of the a/f ratio during a thorough drive. But that seems excessive on a street car, it should not be this complicated.

 

First off I'm curious as to your idle vacuum reading. Second, the idle timing advance and the all in advance (2500RPM'ish).
I have an old Heathkit analyzer. It was still $150, but less expensive than a new unit. JEGS and Summit have gauges that mount in the car like any other aftermarket guage, but you need a wide band O2 sensor in the exhaust for it to work. When my car was running rich, I had plenty of black soot in the tailpipes, so no analyzer was needed.
The first thing to figure out is if the jetting/rods or accel pump are the cause for poor power on WOT. Vizard says with engine at temp and basic idle and timing adjusted with no known vacuum leaks, slowly open the throttle from idle to WOT. If opened slowly enough, the accel pump bypass circuit will bleed off the pump shot, to prevent a false result. The engine should increase revs smoothly with no bucking or stalling.
If that is OK, that indicates the jetting is pretty close and the accelerator enrichment is likey the fault. Turns out you need to add fuel for acceleration not just because of engine load, but because as the vacuum drops rapidly from high to low as the throttle is rapidly opened, the atomized fuel coming from the idle circuit tends to fall out of suspension, collecting in droplets on the sides of the manifold runners. This causes a lean run condition, and if lean enough the engine will stall. The accelerator pump adds the missing fuel back into the mixture, preventing stumbles and poor performance. Too many times guys jet up, rather than fixing the real cause, which is accelerator pump volume or timing. I would try adjusting the accelerator pump to come in a bit earlier with one discharge nozzle larger.

Also, if the mixture gets lean enough, it won't burn at all, giving a heavy smell of unburned gas just as you describe. One last thought, the fuel enrichment circuits between Holleys and Edelbrocks is a bit different, and I have far more experience with Holleys, FYI.

Tim

 

Thanks for the help. My idle vacuum reading is about 18". So I'm using the 8" springs from Edelbrock. The timing is kind of a 'hairy' situation. It's another problem I have to explore and I have a very old thread on here discussing it, and I have to follow up. I've checked it with two timing lights and it appears the balancer and timing mark may be off, in the sense that TDC is reading 18* on the timing tab, and all in reads 55*.
Thanks for all the advice. I did bump up the accelerator nozzle sizes 1 step to no real change. From edelbrocks 28 to 31. I don't have a complete calibration kit for the 1405 yet, but I did change the rods to up the power mode, and it seems better. I may just need a little more rich on the cruise mode to be all set.

I fear rebuilding the q-jet and then having all the same problems. At least with the E-brock I know what I have and I have a lot of parts to try and make it work. If the Q-Jet is too lean after rebuilding, then i'm off buying all new parts all over again.