[BERN]

OK HEAR GOES. GM 330 HRS. 350. TURNS 5200 RPMS.
32 DEGREES TOTAL TIMING. SINGLE PLANE SUPER VORTEC VICTOR. I KNOW OVERKILL RIGHT. 750 CLASSIC DOUBLE PUMPER. GREAT RESPONSE, NO HESITATION. LARGE SQUIRTERS. FAT JETS.
RUNS GREAT. CERAMIC COATED HEADER TUBE ON #5 HOLE GLOWS 2" OFF HEAD. FROM 2800 RPMS UP. UNDER 2800 IS OK. #6 GLOWS JUST A LITTLE. ALL OTHER HOLES DONT. PLUGS LOOK GOOD. WATER TEMP 150. MSD. LARGE AIR CLEANER. 10:1 COMPRESSION. 93-GAS. WHATS THE DEAL WITH THIS THING. LIKE I SAID IT RUNS GREAT IT JUST BUGS ME A FEW PISTONS MAY BE GETTING HOT. WAITING ON THE PISTON SLAP. THANKS FOR ANY HELP. BERN

[4 Jaw Chuck]

Sounds normal to me, is this at night?

[BERN]

YES THIS IS AT NIGHT. I SHOULD JUST LEAVE IT ALONE THEN? THANKS FOR YOUR TIME. BERN

[KULTULZ]

Doesn't it sound as though those two cylinders are running lean at speed 4 JAW?

[colaus]

sure does to me...

[deuce_454]

it sounds like you have a lean condition propably from poor distribution at the low runner airspeed (big intake on relatively small motor, below the rpm range for the intake)

mabe try and add an exhaust crossover to help get the same exhaust back pressure at all the exhaust strokes on all the cylinders, intake wise i am not sure at all, perhaps a carb spacer will help by adding some plenum volume and allow more equal filling of the cylinders

if you look at the manifold from above and follow the fireing order it would seem like the #6 cylinder is being denied fuel bu the intake stroke if #3, almost dirrectly accross from it and 90 degrees ahead in combustion cycle. and then again #5 is being starved by #6´s intake stroke.

i think the best fix is propably a dualplane manifold, or mabe some plenum devider like the offenhauser singleplane manifolds, try and fabricate a devider hanging about one inch down from a carb spacer. I think it will calm things down in your plenum and cure your rpm dependent lean condition.

anyway, lots of assumptions, but right now its the best my 0.02$ are worth

ps. what does the plugd read... white, brown, black, black cracked electrodes.. etc. its the best way of figureing whats going on in your engine

[KULTULZ]

That's exactly what it sounds like, improper fuel distribution. The only way to verify this is to make a hard run, shut her down and read the plugs.

<a href="http://www.centuryperformance.com/spark2.htm" target="_blank">-Reading Spark Plugs-</a>

Those two should show lean. If the others don't show an overly rich condition, you might want to fatten the fuel until the glowing stops.

Running a single plane on the street is a pain. I know one NASCAR engine builder (tech article) that was experimenting with higher ratio rocker arms on certain cylinders to increase flow on the overly rich cylinders (short track).

[willys36@aol.com]

Classic case of bigger not being better. You will be much happier on the street and occasional bracket race w/ a Performer+ and 650cfm vac secondary carb. However, if you like to heads- up race for pink slips, by all means keep the 750 and Victor 'cause top end is important in that case. Engines are nothing but a bunch of compromises.

PS; With a few properly placed mirrors, you could use those header pipes as map lights.

[4 Jaw Chuck]

Looking at glowing exhaust pipes to determine jetting is a misleading way to tune an engine. Where and how much a pipe will glow is affected by too many things such as restriction in the pipe, proximity to other tubes, inaccuracies in fuel/air distribution at idle etc.etc.

You want to tune by color? Pull the pipes off and run the engine without headers, tune to get a nice 2 inch long blue within blue flame at the port. Many radial engines were tuned this way before EGT recording devices were common. On a dyno loaded up is the only way to do this properly.

One thing for sure is your sparkplugs are the key to tuning your engine, if the plugs are all nicely colored and the engine runs well with no hesitation or misfire/pinging then don't worry about the pipe glow. At least you know that cylinder is firing and with an open plane intake meant for circle track race cars what did you expect? These intakes are enormous compromises meant to perform well at high flows/rpm.

There are other more street oriented open plane intakes that also work well at lower engine speeds, the Street Dominator line comes to mind (not sure if they still make them?). Exhaust crossover is one of those things best left functional for the street, if your intake has blocked heat risers or doesn't have the crossover then low speed mixing will suffer. Vaporizing fuel at low speed in a large open plane intake takes heat or the fuel just falls out of suspension.

[BERN]

ok thanks everyone for your time. dont mean to be a pain or anything but these headers glew with a dual plane and 650 carb as well. i met someone the other day who bought the same motor and he said he could never get them to stop either. maybe its just a votec thing. anyway i did notice tonight fire comes out when i open the throttle about 4-5 inches. if this is normal im just gonna have fun with it. oh its on an airboat. thanks again im learning lots.

[bullheimer]

4-jaw. gee i hate 4 t'question such a big giant engine brain but when i read your post thought for sure you ment pull the pipes off and run open headers. then you made reference to a blue flame coming out of the port. surely you jest! and if not, pleasse to explain how to keep valves from warping.

[4 Jaw Chuck]

Bullheimer, yes I did say to tune without any pipes at all. At one time almost all radial aircraft engines were tuned this way right from the factory. Of course these engines basically ran this way in the aircraft but many truisms remain that apply to any engine.

Proper mixture in the chamber will generate a flame at the port that is unique to that engine. If you know what that is it is easy to tune to it.

Individual differences at different rpms will be easily seen from the flame shape, length and color. Purple coloring in the flame indicates oil in the mixture.

Of course if you tune without pipes the engine will need completely different jetting with pipes. This is why you will not warp valves if the jetting is right without pipes. What it does do is give you a good baseline with which to tune from. Ideally you would want to tune the engine on the dyno with a complete exhaust system installed to get a setup that works in your chassis, not likely is it.

What you have noticed is that all final tuning should be done with the engine in the car and doing plug chops to determine final jetting etc. In todays age doing this makes no sense at all since every dyno I know of has banks of pyrometers to determine exhaust temps, a small hole drilled into your ports head pipe will allow you to insert a probe and you can check temps to your hearts content...for each cylinder individually.

Thats how I do it, shoot for 1250-1400 degrees F two inches from the port exit at full throttle and your done. The part throttle driveability part is the difficult one and may cause you to go back to square one.

Good luck.

[Jay396]

Hey man, the reason that I have heard that you see visual indications of excessive heat on headers is actually due to the fact that you are runnin' to rich, and the unspent gases are burning on the way out. You would think that it is a lean condition, but it's not. take those jets down a bit and see if that solves the problem. <img src="graemlins/pimp.gif" border="0" alt="[pimp]" />