Cylinders running too hot

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bhthomas83

bhthomas83

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I have a 408 stroker with an Indy mod man intake with the 3x2 carb plate on it. Bored .30 over with scat forged crank and Keith black flat top pistons. Mopar purple cam with .508/.508 lift. Edelbrock rpm performer heads with Hughes engines bigmouth porting. Center carb has 68 jets outboard carbs have promax carb billet jet plates with 88 jets in them. Anybody have any idea why cylinders 3 and 4 are running at 500 degrees on the header? Here are my header temps at idle after 2 or 3 minutes. Cylinder with temp.
1 200+deg
2 200+ deg
3 500 deg
4 500 deg
5 400 deg
6 400 deg
7 200+ deg
8 200+ deg
Anybody have any idea why the center cylinders are running so hot?
 
Maybe a high flow water pump, or a smaller pulley is needed.
It sounds like a coolant flow issue being the center cylinders.

Are you using a temp gun on the tubes to see this?
The reason I ask is because the 4 center cylinders exhaust ports are next to each other and the outer cylinders have an intake port between them.
 
bhthomas83 said:
I have a 408 stroker with an Indy mod man intake with the 3x2 carb plate on it. Bored .30 over with scat forged crank and Keith black flat top pistons. Mopar purple cam with .508/.508 lift. Edelbrock rpm performer heads with Hughes engines bigmouth porting. Center carb has 68 jets outboard carbs have promax carb billet jet plates with 88 jets in them. Anybody have any idea why cylinders 3 and 4 are running at 500 degrees on the header? Here are my header temps at idle after 2 or 3 minutes. Cylinder with temp.
1 200+deg
2 200+ deg
3 500 deg
4 500 deg
5 400 deg
6 400 deg
7 200+ deg
8 200+ deg
Anybody have any idea why the center cylinders are running so hot?
Click to expand...


When they are that far off at an idle it's usually an intake manifold issue. Most times it gets amplified with RPM but I have seen some stuff that had wacky distribution at idle that cleaned up as RPM went up.

If you are going to really sort it out it should go on the dyno.

Also, I could be nuttier than a jar of goobers and it could just be a tuning issue.

I've been wrong before.
 
Yea using a good temp gun on the bend of the headers has a hi flow mopar performance water pump.
 
yellow rose said:
When they are that far off at an idle it's usually an intake manifold issue. Most times it gets amplified with RPM but I have seen some stuff that had wacky distribution at idle that cleaned up as RPM went up.

If you are going to really sort it out it should go on the dyno.

Also, I could be nuttier than a jar of goobers and it could just be a tuning issue.

I've been wrong before.
Click to expand...
yea my fear is its an intake issue that's the way im leaning towards
 
TrailBeast said:
Why is that?
Is there some sort of running issue?
Have you looked at all the plugs comparatively yet?
Click to expand...
Plugs all look the same. Think that the fuel doesn't atomize all the way before its sucked into the center runners.
 
boy, could be a lot of things. My first guess would be the interior cylinders are running very rich, or very lean.
Another possibility is valve face/seat leakage, but that's kinda remote, because what are the odds it would just be the interior cylinders? I guess you could pull the rocker shafts and do a leak down check to eliminate that possibility.
 
bhthomas83 said:
Plugs all look the same. Think that the fuel doesn't atomize all the way before its sucked into the center runners.
Click to expand...

OH, I missed where this is a 6 pack.
I would have to side with Yellow Rose then on it being a tuning issue (exept all the plugs apparently look the same.)
If it was a tuning issue you would think the four centers would be whiter than the outers.
So you don't think it's possible that the 4 center cylinders having their exhaust ports right beside each other compounding each others heat might have anything to do with it?

The plugs apparently say the cylinders are burning at about the same temps.
 
Six packs can have whacky distribution issues. I think that and the exhaust ports are siamese on the center cylinders are the issue. What ignition? MSD can hide rich cylinders at idle. Keeps the plugs cleaner. I know a bunch of six pack guys who run it just because it keeps the plugs clean while running around the pits. Not sure of the design of the indy intake, but it f its a base you can add different tops to it can be a compromise situation. The base is a jack of all trades master of none thing.
 
1st off your running a modman intake and it's just one big open plenum.
2nd did you ever think that the center tubes are right next to each other and are just hotter for that reason.
3rd what coating is on the headers, you know that a heat gun will give you a false reading on shiny surfaces, and 200*F is not hot for a header tube so I think it's a false reading.
 
yellow rose said:
When they are that far off at an idle it's usually an intake manifold issue. Most times it gets amplified with RPM but I have seen some stuff that had wacky distribution at idle that cleaned up as RPM went up.

If you are going to really sort it out it should go on the dyno.

Also, I could be nuttier than a jar of goobers and it could just be a tuning issue.

I've been wrong before.
Click to expand...
I don't think you are nutty. A lot of times with older dual planes you can get all four corners looking just right but the center four cylinders all end up looking bone white. It's a distribution issue that usually pushes you to having the the outer Four Corners a hair fat to get 4,6,3,5 looking decent.

Intake work could be in his future.

But to be blunt I don't not sure why he's worrying about 500 Degrees, I usually tune the idle as to not stink to the best of my ability and so I usually run my idol just 'fat enough', as in 'on the lean side' and end up with temps around 400 and 500. I think it's when it reaches over 600 that you got some tuning that will hurt you over some time. I wouldn't worry about those higher temps he has @ idle as i would wonder about the lower being too fat at idle. Remember it's not under any load.
See what it does under load @ RPM like 4000-6500
 
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That mod man intake has the reputation of being the worst intake made, one big plenum?
 
yellow rose said:
When they are that far off at an idle it's usually an intake manifold issue. Most times it gets amplified with RPM but I have seen some stuff that had wacky distribution at idle that cleaned up as RPM went up.

If you are going to really sort it out it should go on the dyno.

Also, I could be nuttier than a jar of goobers and it could just be a tuning issue.

I've been wrong before.
Click to expand...

That "at idle" statement has me thinking about that from last night.
It seems that intake may very well have an erratic dispersal at low RPM's that could clear up at higher RPM's
I have never seen that, but I never dealt with large plenum intakes either.



Wyrmrider said:
exhaust ports are not siamese
THis is not an Olds or Pontiac or Cad or flathead
Click to expand...

I think he meant like this with no cooling between them, and is also why I thought it might be higher temps in the center pipes.

normal_102_0296.jpg
 
the inner two exhausts do run hotter
recall the HD valves for the Industrial/ truck/ Motorhome/ Marine -3 motor
but that's not the problem here
where it is you need to cut down on overlap- see the overlap thread
and keep the valves on the seats as long as possible
most heat transfer is through the seat not the stem
 
Jets mean nothing at idle. You need to adjust the outboards' idle mixture screws. And if you really want viable readings get it on an engine dyno.
 
That cam (292/508FTH) wanted a fair bit of idle bypass air on my 367, and a bit of idle timing. I was at 11.3Scr. And I was using the AirGap with a 750DP and TTIs.
Your throttles may be too far up on the transfers and so idling pretty fat. Then the charge may not finish burning in the chambers, but may continue burning in the pipes.
In my case the solution was to reduce the T-port exposure, introduce bypass air elsewhere, and bump the timing up to start the fire a little earlier. And I brought the Vcan in fast and hard.
I drilled the throttle-valves between the idle-holes and T-ports;about half way from the shaft to the leading edge. I started with 1/16"holes and ended with a 3/32" in each. IIRC 1/8ths were too big and I had to fill them in. This was in addition to the PCV.
My exhaust temps were not as high as yours, nor as far apart to start with; but they evened up pretty good. I found tho, that placement of the laser dot was pretty critical. Just a few millimeters could change the reading a lot. That's what led me to the still-burning theory.
Happy HotRodding
 
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