I'm experiencing a slight loss low of torque, and I'm wondering if the intake is the culprit. I changed intakes and installed ti-retainers this winter. No other changes. I noticed now that my car doesn't do the rolling burnouts in 1st like it used to, although the midrange/top-end seems stronger. No bogging or anything - just doesn't break 'em loose anymore. I thought the RPM intake would give me more torque everywhere? Guess not. Maybe the GM intake was better?

I moved the jetting/accelerator nozzles around a bit, no change. Although I was getting a "tip-in" hesitation while cruising - had to go to 76's in the front to get rid of that. Maybe she wants more in the front?

I bet your timing got moved around a little during the swap. Try advancing it a little. Just my 2 cents. hope it helps. --Josh

I'm at 18/38...where its always been. Wondering if it wanst more?

I'm at 18/38...where its always been. Wondering if it wanst more?

Could be worth a shot. accel pump arms still properly set?

Ron, yea its tight, no slack. Possible that the intake wants more jet? I had a tip-in stumble that I never had before - had to jet up for that.

I suppose, how do the plugs look? Does it have a valley pan/shield?

It does have that sheild in the intake.

Plugs look fouled...I had the heads off this winter, and I oiled the sh@t out of the cylinders. Took a while for it to clear out. Car runs awesome otherwise.

Have you run any carb cleaner since? Likley you have, just checking. I am sure you already checked on throttle linkage has full travel from your pedal. Just trying to think of things that were touched during the swap...

The easy thing is to try 40°, then maybe the jets. I wonder if there is much difference in runner size between the intakes....

i am not exactly sure what intakes your talking about . i am guess the old GM highrise was a dual plane ( like my old one) ? if the new RPM intake is a single plane you will lose bottom end and gain top end .

Maybe you can try putting the jets back where you had them and increase the shooter size?

Guys, the intake was the factory dual-plane that comes with the crate motors (its a rectangular, like the old 163's(?)). I tried the stock jetting and went all the way to a size 40 shooter, still had a slight tip-in stumble at cruise. Stock shooter is 25, primaries are 72. I'm at 76 primary and the stock 25 shooter - runs crisp.
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Rectangular heads on a street car is a no-no, especially w/no gear, no compression, and a heavy car shifting at >6000. I wondering if I exasserbated a problem here. Loss of torque occurs from idle to about 2500 - then she's gone! Think I'll try new plugs and 40°

Any other suggestions?

Being realistic, the RPM does have an open plenum and is spec'd as 1500 - 6500. Most guys do report a loss of throttle response below 1500, just as advertised. My suggestion would be to limit total mechanical advance so that you can get the timing to about 22 at idle for 38 total. Or install the lightest mech advance springs you can get which keep the timing stable at idle (assuming that motor will idle at 600-650??) but allow the timing advance to start just off idle.

You have a BB, but I saw the same thing going from a GM intake to an RPM on my ZZ4, but a 4 hole spacer seemed to make it right again in my case. Can't hurt to try one.

Good suggestions guys. I must say, the powerband has definetly been shifted upwards...there is a noticeable (very) in midrange and top-end power.

Joe, you maybe onto something here w/the timing...had that stuble I never had B4. How do I go about limiting my advance w/o having to send this dizzy out, I have the lightest springs in there.

Use a bushing on the pin to limit the travel, and watch that curve. Usually the lightest springs bring it on too fast.

Nothing wrong with those old Winters intakes, imho.

Being a "rectal" kinda guy ( Joe will tell ya!) one other "trick you can use is to get the front PV at 2-3" below idle. It *might* mess up your mpg, as it does in a clutch car, but it might not. It will give the engine a slightly richer mixture to alleviate the low velocity through those ports. You will have to adjust the shooter again, likely in the 36-38 range, although I was running a 9.5 PV and 40, this with a Winters with the plenum divider replaced ( yeah, I hogged it out as a kid!) with around .600" open at the top and a 850 DP jetted 76/81 with a 4.5 PV in the rear..

Your results may vary!

Where can one get those bushings?

Do you have a vacuum secondaries carb? If so, have you tried different secondary springs? I only changed from a standard air filter to a K&N filter and had to change the secondaries spring to get it to accelerate smoothly again after the install of the K&N. The more free-flowing filter lowered the vacuum signal so a softer spring was required to get things back on track. With a more free-flowing intake, the strength of the vacuum signal might have changed, especially at lower RPMs.

I tried a lighter spring (yellow), no change.

Maybe I should try a heavier...I have a black one I could try.

I tried a lighter spring (yellow), no change.

Maybe I should try a heavier...I have a black one I could try.

With an off-idle hesitation a heavier spring would make more sense.

I like the idea of bumping the initial a bit, this is stills omething I want to try with my car.

I was assuming double pumper (for no good reason), sorry. Secondary springs are another easy try as Rich suggested.

New plugs can never hurt. If the squirter/jet change did not help, I am thinking timing might. g/l

Now that I think about it, its not the secondaries...when I jetted up the off-idle hesitation dissappeared.

When I get home today, I'm gonna bump-up the initial to ~22 for testing purposes and see what happens. I wont do and WOT blasts cause that will push my total to 42.

Being realistic, the RPM does have an open plenum and is spec'd as 1500 - 6500.

Open Plenum? Mine is not open, the divider is notched slightly, but far from being an open plenum.

I have a reworked 750 vac Holley that had a stumble the shop had me max idle vacume with the idle screws and then give it 1/2 turn more. Something about the idle transfer slots not geting enough signal becouse the blades had been tweeked for the bigger cam. Definatly made an improvement and not hard to try.Good luck

Guess I assumed the RPM was open. My AirGap has a minimal divider, would think the RPM is the same.

RPM divider is cut down about 1/4" from the top.

Now that I think about it, its not the secondaries...when I jetted up the off-idle hesitation dissappeared.


That's a pretty good indication that your power valve is wrong and you've now overcompensated with larger jets.

Are your float levels high enough?

Bottom line, the manifold change can explain some of the loss of low end torque but you still shouldn't have to struggle to get it moving from a stop at low RPMs unless you have a really wild cam in there. Those aluminum GM manifolds are usually pretty good pieces so the difference really shouldn't be dramatic. I'm still convinced you have some adjustments to make on the carb or timing or both which will clear up most of the "problems".

What Rich says is important , ALWAYS set the float level before you do any tuning, it is a key variable. Mr. Gasket must sell those bushings in their spring kit.

Float height is good, I have those clear plugs in at the moment.

There isn't any "problems", it takes off good and carburates clean, just a SLIGHT hesitation while say, going around a corner and lightly accelerating. This is pretty much just off idle, around 1500-2000. You almost can't notice it, but I'm a little wacky and pay attention to this stuff.

As far as the low-end..still working on that. Again, she takes off strong and good w/no hesitations at all. Just doesn't bust 'em loose like she used to. But I like the new top-end charge.

I can't understand how an intake manifold made such a difference. My carb was setup PERFECTLY before, now thing have changed.

I bet the humidity and recent crappy weather is a possible culprit..

I bet the humidity and recent crappy weather is a possible culprit..

Just might be...its pretty nasty out (humid).

Just to let everybody know, I set my dizzy to 38* at idle and disconnected my vac line to simulate locked out timing and reved it up a bit a couple of times and I must say...felt pretty good. We won't go there just yet though ;)

Naw, you wont need to. What you have, methinks is a squirter that is slightly off. Sounds like it's so subtle so as to be the cam profile. Might be a bit too "front loaded" actually. What color cam, blue or orange I would bet? try white..or do what I;ve done, contour it yourself.

You are still running off of the idle circuit at low speed and at tip in time at least that is how it was explained to me. Also may have less signal with the new manifold at lower rpm.

Again, the higher rated power valve will likely cover it too.

When the tip-in stumble happens, I'm pulling around 18"- 20" of vacuum, no PV will be opening at this point. Again, I moved shootersa round from teh stock 25 all the way to 40 - no change. Theres the green cam in there.

But the stumble is gone anyway.

Alright everybody...I have to admit the truth.

Its all my fault :o !

When I 1st got the car running this summer, I opening up the secondaries a little more so I could close the front a bit. We'll, it created a bunch of slack, which I thought there wasn't any (the pump arm did touch the lever, but there was space bewteen the lever and diaphram). Ajusted the slack out, went back to my prior jetting/nozzle, and she's ripping again. She has more midrange and top-end than b4, and bottom-end is still there. I'm gonna tinker a little more here and there to see if I can get anymore out of it. 110+mph here I come!
Moral of the story - check your accelerator pump ANYTIME you touch the idle screw

Awesome to see that you fixed it. Just back to the basics tuning....

What a man!

I spoke too soon...

I'm afraid there really is a loss in low-end. I've driven the car a whole bunch, and w/o a doubt, a little torque is lost. I guage this by the fact that my car doesn't really do the "rolling" burnouts in 1st gear anymore. EVERYTHING else is the same (timing, jetting, etc.). The RPM intake just exaserbates the inherient low-end (lack of) w/rectangular heads I guess. But, in exchange, theres a definite inprovement in midrange and top-end power.

Exactly what the intake is advertised to do.

How can I get the low-end back short of putting the OE intake on - the Voodoo 60211 maybe?

I bet if you'd try a little more advance you'd be smiling. G-night

I bet if you'd try a little more advance you'd be smiling. G-night

I did...alot more, no diff :(

I'm gonna try one last thing tommorrow then I'll give up.

Sorry man, I wish it woulda helped you out. Later--Josh