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I have a 68 327 on which I installed a offenhauser low profile dual quad intake with 2 edelbrock 600 cfm carbs.
Primary is brand new and second is recent re-build. Cylinders 5& 6 are running cherry red hot. Suggested solution is high rise manifold to improve air flow thru manifold and get proper fuel flow.
Car is a GM drag car which sat for 30 years. Previous owner removed racing carb/intake. Installed cast iron intake and 4 barrel holley .
Would appreciate any insight/help on this problem.
Thanx
Last edited by geryjw68; Jan 22, 2019 at 07:01 AM.
Does it have a progressive linkage setup? If so.....throw it in the trash. Look at where 5 and 6 are relative to the back carbs primary blades. Also......are the back carbs idle passages and metering pistons functioning properly? On a 327 with two carbs.....each carb idle screw should be 1 1/4 turns out from stop.....this is a good baseline.
Why ditch the progressive linkage? Distribution.......that low manifold is awful flowing anyway......the back carb pulls the primaries first followed by the front carb.......
I have had luck with Edelbrocks progressive linkage on a Performer Dual Quad RPM manifold but it only allowed the back carb to pull enough to move around town, stop and go.....it was adjusted to be all in right after that.......
I do recommend the RPM Dual Quad......it works well. I would put a stock intake and single four on a vintage engine before I ran any low profile dual quad intake......especially the woeful C36 Edelbrock.....not even worth the extra carb for looks.
Ten years ago I "enhanced" a 32 Ford 3 window coupe that had a 320 horse Edelbrock Crate engine with 2x4 setup.......the owner wanted me to put a cam that "slobbered" in it....I said no way unless you go to the high rise intake and throw out the $90 block hugger headers and $50 exhaust.......I went throught he engine with cam, intake, Speed and Performance 3" outlet block huggers and a 3" exhaust all the way out.......with a 3000 stall it was a beast........he asked me what he could do with the old C36 and I said "garage art". The owner just looked me strange....he could not understand what was wrong with his vintage "dual quad" manifold......
Point is that those old intakes do not flow.......but if you are stuck keeping it......use some 1/2" or 1" open spacer under the carbs.......it helps.
Edelbrock carbs can be wonderful if you understand them. The manual is poorly written and the graphs of rod and jet changes are in big percentage changes
so I sat down with an online area calculator. Jets and rods have a diameter. Which corresponds to area. The area of the jet is total possible fuel flow. The two diameters of the stepped rods are causing how rich the air fuel ratio is during cruise high vacuum and low vacuum wide open throttle. The jet area minus the rod area is the total fuel flow area. So you can figure out what they are doing in the manual for air fuel ratio changes. So you can make your own tiny percentage adjustments by doing the math
so you can buy rods with just a tiny bit larger diameter to lean out the carb and cure the glowing 5&6 cylinders
the idea of under carb spacers increases the distance before the air and fuel mix has to make a 90 degree turn towards the cylinders. So you get less fuel droplets forming. Low rise manifolds have poor fuel distribution. They are more for show than go my 61 vette came with two four barrels and only a solid cammed 283 ci from the factory. I spent years sorting it out
If you are stuck with an aftermarket low rise use a good one...imo weiand is better than most of what guys choose.
Avoid the cheap chinese ones, they arent always the same internally.
Thank you for the detailed information. I have shared with my friend/mechanic and hope we can get it to work.
A mid to high rise looks like it might be part of the answer.
Its possible its a fuel issue,,,but, Glowing exhaust usually means retarded timing.. you obviously removed the distributer to change manifolds, you may have your ignition timing too late.. The combustion finishes as it goes out the exhaust valve ..headers glow.. and yes the middle gets hotter faster .. Check your timing before you go any further. .....When you hear hoofbeats.,. think horses.......not zebras
Not sure how a dual quad intake could cause that problem, agree on tuning.
Youre probably a twist or two away from the problem going away...keep the intake.
Glowing pipes means usually, rich, late timing, or a serious vacuum leak.
I ran one of these years ago with 625 Carters on a decent 350, raising the float drop tangs helped alot and lighter springs for the metering rods. I think the engine only made 10 inches of vacuum or so.
If you really lower the float level you can get away with 6psi but I had best luck with 4-5 and pretty level float settings, again with sort of a stingy drop setting.
To make the engine correct, it may require 2 fours. If the engine has high enough compression it will do fine.
My dad still runs 2 fours on his mild 396 with a stock mechanical pump and a regulator.
I like electric pumps so if one of the needles stick you can cut the pump off until it clears out. This also unpins any debris that might be caught in the needle.
with a mechanical pump, its pop the hood and start tapping on the carb(s) with the butt end of a screwdriver. no thanks.
I have seen some period correct vehicles using electric pumps that route the fuel line through a dummy mechanical pump.
From: At my Bar drinking and wrenching in Lafayette Colorado
Originally Posted by fishslayer143
Glowing exhaust usually means retarded timing.. you obviously removed the distributer to change manifolds, you may have your ignition timing too late.. The combustion finishes as it goes out the exhaust valve ..headers glow.. and yes the middle gets hotter faster .. Check your timing before you go any further. .....When you hear hoofbeats.,. think horses.......not zebras
Biggest cause of glowing red exhaust on an engine like that is retarded timing. I assume it has a "race-type" distributor in it with no vacuum advance. The initial timing needs to be up in the low- to mid-20 range, with total timing set up for whatever heads you're running (36 is probably a good number). This means you need a very short advance curve in the distributor (only about 12 degrees long). If the distributor has locked-out centrifugal advance, initial timing will need to be 36.
Air flow problem with low profile intake?
