Intake manifold problem

[MOTORHEAD]

I've been having problems with my FE 452 shelby block based engine since shortly after it was installed about 10 mo's ago. Induction was a used set of webers purchased from a CC member. The carbs were in fine shape, and are the Bologna units. It ran well initially, but developed a intermittent missing at cruise which was traced to oil fouled plugs on the left bank only. Valve seals were changed with no inprovement. Put UV dye in oil and found oil comming past the int gasket on the left side only. Pulled intake and installed different gasket set-up , but still had oil fouled plugs. Decided it must be the manifold, even though I had checked it before installation.
Not having another weber manifold to try, I installed the BT 4bbl manifold that was originally on the engine along with a Demon 750 DP carb I had laying around.
WOW ! what a difference ! No plug fouling, engine will idle for a long time w/out fouling plugs, very stable operation, BUT----- it feels like It's down about 100 hp !!!!
However it did confirm that the weber intake was the problem all along. Don't think it's worth salvaging because it was ported and milled before I got it, and there's not enough mat'l around the ports to ensure a good seal, so the hunt is on for a good used manifold ( or smokin' good deal on a new one) is on.
While the 4 bbl is on, I'll get the car on a dyno, and then again after the webers are back on.
The engine is cammed for webers, so it's not optimal for the 4bbl, also initial timing is at 22 deg, wondering if thats ok for 4bbl, or should it be lower ?

[ERA Chas]

I ran 18 with 2 x 4's and 10.33:1 compression. Dial back to 18 and test. Make sure total is no more than 38.

[MOTORHEAD]

Thanks Chas, I'll do that>

[Anthony]

Had a similar problem with a Hi-Riser single 4 intake. Tried doubling up the gaskets, still no better. Bought a new NOS intake, never been ported, milled, or anything. Problem solved.

At this point, bite the bullet and buy a new intake.

[Mdman352]

22 initial seems high. I use 39 total at 3000 rpm.

[MOTORHEAD]

Anthony: yeah,I've got one located, the guy is out of town, waiting for him to get back.

Mdman: webers like advanced timing, still at 38 total.

[blykins]

Check the total as the initial doesn't matter when it comes to making horsepower. As soon as the weights start slinging outward it's not at 22 anymore....and that generally happens pretty quick.

If the starter will roll it over, the curve is right, and the total is right, then you're good.

That 4bbl intake and carb should not be down to a set of webers, if the carb is right and the intake ports match up well.

[PANAVIA]

Have you looked at the timing curve from 22 to the total >? ( where does it kick in >? ) 22 would be a biatch to start cold...

of course this all depends on where the cam was indexed , either using a timing chain gear modifier ( multiple key-ways) to advance and or retard the cam , or is it "Straight Up" . Even if it is straight up , was the cam ground with "advance-Built-In" --

I would chart all your info down and that way we can plan for tuning success.
(maybe a call to Shelby Engines is in order )

---Steve

[blykins]

Steve, you're mixing up cam timing and ignition timing buddy....

[MOTORHEAD]

Brent: the weber manifold I have had been ported to the point I needed 428 int gaskets and trim them to fit, and I matched the head ports to the manifold. The BT4bbl intake has not been ported to match the heads, so they are much smaller, so the flow is from smaller to larger, while not ideal, is better than the other way around larger into smaller, but I'm probably loosing some power there.
I forgot to mention another benefit of the change, and that is no more BACKFIRING OUT THE EXHAUST !!!!!!!!!!!!! A big problem with the webers, I tried every solution on this website except welding on flanges. I even borrowed a tubing beader and put a slight bead 1/2" in from the end of the head pipes, all to no avail, and my slip joints are now EXTREMELY TIGHT. Didn't even slow the popping down ! mixture lean or rich made no difference! Now with the 4bbl, no popping/backfire when backing off throttle ! Nothing like imitating the 4th of July to attract the fuzz and P.O. the neighbors !! I'm enjoying the QUIET!

Steve: the 22 deg was no problem w/webers, the 4 bbl doesn't like it, bogs down coming up on compression, but then catches and starts. I'm running MSD don't remember the springs and bushing at the moment, but all in @ 2400rpm. This intake swap was intended to be a temporary change to eliminate the possibilities of the intake causing the original oil fouled plug problems.

Thanks all , for your input.
Ted

[Barry_R]

With a Weber intake you should be able to stick a flashlight into the ports and see where it was leaking - pretty clear trail to view. Have not seen an intake yet that we could not fix - but some of them have been pretty challenging.

The backfiring is a tuning issue - probably too rich and loading the pipes when the throttle got closed.

Timing - 22 initial should be easy to light and crank - hot or cold. Now, when you go to locked out at 36 it can be another story

The 2x4 should be pretty strong upstairs compared to Webers, but the Webers can be really tough with big torque through the midrange - probably why it felt so strong in normal driving. In this case the track clocks might disagree with your "butt-o-meter", but most of us spend much more time tuning with the latter.

[MOTORHEAD]

Barry:
I did a lot of looking down the ports with carbs on and off,all looked very clean, no visable oil. It wasn't until I added UV dye to the oil that I could see the tracks. I think part of the problem may have been that I used the permatex "ultra gray" sealer around the ports and just noticed after I took the manifold off that the gray sealer is marked " not recommened for parts in contact with gasoline" ! Used T-31 when installing the 4 bbl.
Also it's a single 4 bbl, not 2x4.
Ted

ps: the manifold sinks below the heads, lines up using .090" shims. We used the double BT gaskets initially, but they squeezed out the bottom on the left side because of the port face angle being off (although I checked head and intake angles and every thing was 45 deg.) or the int could be warped slighty, and the seal area around the ports was very small due to the porting done on the manifold before I bought it. I think it would need additional mat'l welded on around the ports and then milled. Does that sound feasible?

[Anthony]

I'd buy a new intake and sell the old one. if you are going to fix, ie weld and mill the old one, make sure you have somebody who has done it before. maybe barry r can give an idea of the cost.

I'm guessing the popping was from a too lean mixture, when you backed off the throttle, closing the throttle butterfly, running high vacuum, and air leaking into the cylinder.