This week I decided to swap the RPM Air Gap intake with the original Weiand Xcelerator intake that came on the car. The intake ports on the dual plane Air Gap are WAY smaller than those on the single plane Weiand. I'm thinking that's where some of my high RPM issues are.
I have the intake installed but just need to reinstall the carb and drive. You can see from the pictures how much bigger the ports are on the single plane. These are still slightly smaller than the heads, but pretty close.
When I did this swap, I also put a 50cc accelerator pump on the primary side of the carburetor. I've always had a small, low RPM bog and I figured this update would cure the issue. Yesterday I finished putting this all together and although the weather has been less than cooperative for driving, I can tell that the low end bog is gone. It idles great and has great throttle response. But short of brake torqueing in the garage and revving the motor, I won't know until I get it on the road if the manifold has helped or hurt the top end.
The weather for this week looks pretty uncooperative, but if it's nice on Wed, I plan to head out to the track.
Last night it was dry enough to take the car out for a spin. To me and my behind, everything feels better. It idles great, has absolutely no hesitation, and pulls stronger right up to the point where it did before, just about 5400, and it lays over really badly. It really seemed to me last night like it was almost coming back through the carb a little when this was happening. To me, that's valve float. I plan to go to the track this Wed and shift at 5200 like last time to confirm that this combination is better than before.
I also sent an email to my contact at Crane Cams to see if he recommends a set of stock replacement valve springs that will work well with the cam I'm running. As strong as it pulls, it feels like it should go to at least 5800RPMs without too much trouble.
So last night's trip to the track yielded pass number one - 13.22, and pass number two - 13.15 @ 103. So I went home. The single plane intake has slowed the car down. Oh well. I'll shelf it until I get a bigger cam, or sell the car.
Tonight I ordered new valve springs and tomorrow I'll order another valley pan gasket set. It's only about $25 and I like the way it fits better than the super thick gaskets that Edelbrock wants you to use. I also plan to do some port work on the RPM Air Gap. I'm not going to gasket match, but I'll get closer than it is now. OR, I might just put it on there, try the new springs, and see what happens... I'll see how I feel tomorrow.
The single plane should help the car at higher RPMs which you are not reaching right now. It is odd that the off throttle response improved when the single plane went on because the dual plane is typically better for that.
If the cam is aggressive enough then the right valve springs are going to want that single plane back on the car.
[quote="Basement Paul"]Is that a mint rocketship on the hood?? :shock:
-BP[/quote]
I think I'm confusing the throttle response with my addition of the 50cc primary pump. There was always a flat spot off idle or any time you got on the gas initially, and now it's gone. My 60' was off, but only barely. I think I'm losing the power up to about 4400-4500. After the drag strip passes, where I can feel it pull through the RPM range, the car has a small surge around the 4500 rpm mark, which I'm attributing to the intake. I'm only running a .505 / .516 cam, and even with the good duration that it has, I'm not convinced it's big enough for a single plane.
I might do the spring swap first, and leave the manifold alone, just to see how it feels. Depending on how bad those springs are, it might help across the RPM range.
There's also the remote possibility that the springs that are on there are just binding at higher RPM. Remember that someone has already shimmed them. Either way, I'll the have right ones on there shortly, to eliminate it as an issue. If that same issue is still there after that, maybe something in the distributor? I'll worry about it then...
I ran single plane with single pattern .480 with 228 duration @ .050" lift on the 350. I don't understand the difference between Ford and Chevy intake tracts but in my book that is plenty of cam for a single plane.
Good news is now you're working on getting faster not getting running.
[quote="Basement Paul"]Is that a mint rocketship on the hood?? :shock:
-BP[/quote]
Did you ever compare the single and dual planes on that motor with the same cam configuration? So far, I'm 0 for 2 in switching to a single plane. I did it on the Trans Am with the 455 and the same thing happened. I lost about a tenth and a half and about 1mph. It had low compression and about a .490 cam.
I got the valve springs yesterday, so I'm going to try to get those on today or tomorrow. Then I'll think about either running Wed again, or just swapping the manifold.
IIRC somewhere back in the 305 or 327 days I went from dual to single plane and yes it was faster. Gear ratios 4.10 or 4.56. Never went back after that.
A .490 cam on a 455 is quite mild as far as I know. And a 455 is not designed to wind up - the lower RPM range is a factor.
[quote="Basement Paul"]Is that a mint rocketship on the hood?? :shock:
-BP[/quote]
FWIW: I'm betting on the valve springs being the "missing link". Granted, I have zero experience with Ford 351s....but I think that a cam that big should rev a lot higher. Aren't those the springs that came on the car when BP purchased it? Not only do we not know the spring specs, but we have no idea how many miles are on them or if they were installed correctly.
Back when I was doing "how to build a 350 research", I went over tons of dyno results/session in magazines and online trying to see what combos worked great together. In order for a Single Plane intake to outperform a Dual Plane/RPM type intake, you usually had to spin the motor more than 6500 RPM....+/- depending on engine particulars.
The picture above shows the old, shorter valve springs VS the new valve springs. I even included the shim that was under the old ones. I've only replaced one spring so far, so I'm not sure about the performance yet. All I know is the old spring seems a little stiffer, but even with the shim under it, seems pretty short for the application. I'm not going to venture as to what all that means, I'm just going to finish installing them and find out what happens. Hopefully tonight I'll get close.
I got the driver's side done completely, and took the valve cover off the passenger's side. Then Friday after work my back gave out on me and I'll be away from the car for at least a week I'm guessing.
My back bothers me when leaning over the fender. It helps to raise the car so you don't have to bend as much. Don't know if that's what caused your back pain but it will ease the strain when you get back at it.