Im running a holley 3310-s carb. I checked the vaccum and it pulled 17.5". I have a 6.5 and a 8.5 power valve. Which should I use? Or should I go to a 10.5?

I did a check and the holley site says 2" lower than called for. You devide the vaccum # and then subtract 2 or add 2? The 8.5 would be half. I am using the 8.5 right now with the stock 92 L98 cam. I think I am leaning out at WOT.

Is it not opening early enough?

thanks for any advice guys.

 

is that 17.5 in drive?

 

You didn't read far enough on the Holley site. 17.5" at idle means you have a mild street performance cam. Ignore the idle reading and get the cruise readings it suggests in the next paragraph. Most likely the 6.5 will be enough, but if you get a little dead spot coming off idle, go for a higher number.

If you're leaning at WOT, you either are running out of fuel (supply problem), or the secondaries are too lean.

 

Yes, in drive. With the stock L98 cam.

 

Right now, I am running a 8.5 pv with 72 main jets and 76 rear jets. I changed over to a rear metering block instead of plate. Should I step up to maybe 80 in the rear?

I am still running the stock L98 cam at about 10-12* timing.

 

Why do you think your leaning out? 72-76 jets + a power valve sounds like plenty of fuel to me for N/A 350 or even a 383...what exactly is happening at the top of the band...Bog? spark knock? loss of acceleration? I`d probably stick with the 6.5 power valve regardless of what the upper rpm problem is

 

At WOT when the motor gets to about 3500 rpm the motor shutters. If I let up on the gas just a little it quits doing it. If I stay in the throttle, it will clear up also. It just does it for a few seconds. Maybe im running out of timming? I might need to recurve my dist?

I check the plugs after a WOT pass and they look like new. No black or red. Just clean and white. Maybe slight tan.

 

You have a problem SOMEHEWHERE, but it's definitely not in your carb. Carb problems don't act that way (in a certain RPM range, otherwise fine).

Might be running out of fuel pressure under hard acceleration or it might be an ignition issue but you can pretty much rule out any internal carburetor problem right from the get-go.

 

BTW- the power valve's "number" only relates to WHEN it opens, not how much more fuel it adds. Low numbers open closer to WOT. Higher numbers open with less throttle opening. You've got penty of manifold vacuum that you shouldn't have to worry about it much. A 6.5 or 8.5 should work just fine- won't make much difference.

The AMOUNT of fuel that is added when the power valve is open depends on the metering block's PVCR (Power Valve Channel Restriction). In MOST Holley-type carbs the power valve opening has an equivalent effect to going up 8-10 jet sizes. That's why you don't want to cruise around town with it opening- it would run far too rich, waste gas and eventually cause damage to the rings.

 

Well for fuel delivery, I have the stock TPI intank pump with a mallory 3-port return style afpr.

The power valve was just something I wanted to rule out. Maybe I dont have my total timming comming in soon enough?

I run about 6.5 psi on the fuel pressure. Im between 10-12* timing. Everything in the dist is new except for th module. Im running an accel supercoil, new plugs and wires.

Maybe I need to remove the intank pump and put a pickup in. Then use a inline holley pump?

 

Iunno...it doesn`t sound like fuel supply, especially if you let up a bit and it goes away, I`m thinking you`d have a bog or a surge if your supply wasn`t there, Plus holley have such large fuel bowls it would take a little longer than 3500 in first to run them dry. If you look at anything on the carb look at the secondary side...the opening rate of the rear butterfly`s mostly. I`d also look at the timming, make sure your total is no more than forty.

 

Yeah, I need to put a timing tape on the balancer to check total timing. Just not sure what size.

I need to have all my timing in by 3500 dont I? I have medium springs on it right now. May need to go to a lighter spring also.

I have a Quick fuels adjustable secondarys. No springs to change, just a screw. I am still learning how to adjust it. Might be some of my prolems. Im not getting any bog when I take off.

 

Ah, the QF adjustable secondary housing.

Try opening up the valve a little, like a quarter turn at a time, and see if the "shuttering" occurs at a lower RPM. Basically, get the secondaries opening at a lower speed to see if it is indeed the secondaries opening that causes the shutter, or something else.

If 72's are right for the primaries, 76 sounds too lean for the secondaries to me.

 

I need to do more testing with the QF. Im not sure if it is set right.

I had though about trying some 80 jets in the rear and see how that works.

Funny thing is, It dosnt do it at the track from a dead stop. If I go WOT off the line it does fine. If I am out on the road and just driving normal, then kick it down. When it gets to 3500 it starts shuttering.

Should have mentioned this in the beginning post.
What do you guys suggest?

 

Maybe all you have is a hot fuel situation, then. That would be a lean situation, and momentary until cool fuel gets into the mix.

 

Well the header and pipe does come close to the fuel lines back in the trans tunnel. How close is too close?

Maybe I can put some heat sleave on the fuel line?