Posted By: blownEFI
Cylinders 8 and 6 run leaner, hotter, more prone to det - 06/03/12 12:59 AM
Question for engine builders. On a Chrysler RB engine do cylinders 8 and 6 run leaner or hotter than the others? I have experienced problems with a few of my engines where these cylinders seemed to get heat/detonation damaged but the other six cylinders were fine. Just wondering.
Posted By: HemiRick
Re: Cylinders 8 and 6 run leaner, hotter, more prone to det - 06/03/12 01:08 AM
They definitely run hotter as they get the poorest cooling. In any V engine the rear cylinders always run hotter IMHO.
Posted By: Cab_Burge
Re: Cylinders 8 and 6 run leaner, hotter, more prone to det - 06/03/12 03:26 AM
Usually number seven detonates first, not six or eight
Posted By: FastmOp
Re: Cylinders 8 and 6 run leaner, hotter, more prone to det - 06/03/12 09:31 PM
If you have the individual cylinder controll on the EFI. You can pull timing out.
Posted By: Cab_Burge
Re: Cylinders 8 and 6 run leaner, hotter, more prone to det - 06/04/12 02:29 AM
Is this on a roots blown motor?If so maybe it is the intake manifold distribution
I seem to remember that the roots blown motors do that, load up the rear cylinders on the passneger side bank
Posted By: Cab_Burge
Re: Cylinders 8 and 6 run leaner, hotter, more prone to det - 06/04/12 06:13 AM
Let us know what you find
Posted By: FastmOp
Re: Cylinders 8 and 6 run leaner, hotter, more prone to det - 06/04/12 04:17 PM
I would not trim fuel at first. It's prolly lean now. Unless the plug shows otherwise, just pull some timing. I'd pull four degrees and sneek back up on it.
It's an air distribution problem. You have a pic of the intake plumbed up?
Posted By: wegner426
Re: Cylinders 8 and 6 run leaner, hotter, more prone to det - 06/05/12 05:44 AM
Just a thought, but what is the fuel plumbing situation? I can't tell allot from the pics you posted, but it looks like 6 and 8 are the farthest away from the regulator. How much pressure? I can't see but assume you have a crossover in the back? How much is the pressure rising with boost?
Posted By: Cab_Burge
Re: Cylinders 8 and 6 run leaner, hotter, more prone to det - 06/05/12 08:16 AM
I would definetly have those two injectors look at, maybe have all eight flowed by the same company
Posted By: TRENDZ
Re: Cylinders 8 and 6 run leaner, hotter, more prone to det - 06/06/12 01:43 AM
Is this a siamese bore block? If so, was the deck/gasket/head drilled for steam bleed off?
Ringland issues can be caused by a few different things. Blown/ turbo motors with ringland issues are almost always to rich. Liquid fuel gets into the space (usually close to the intake valve) and burns or breaks the piston. Nitrous motors will do this to, but oil control is usually involved.
I would suggest making sure the deck area is drilled as I mentioned before, knock your A/F ratios back into the mid to high 12s and keep your timing in a realistic zone. To much breaks things, not enough melts things.
Another poster asked about sparkplugs. Use the coldest plug you can get away with. Trim back the electrode strap. The shorter the strap the cooler the strap will be. Keep your plug gaps tight(.020- .025). If you blow out the spark under boost, fuel will puddle in the lower portion of the piston and the ringlands will be damaged at the 6:00 position of the piston.
Posted By: wegner426
Re: Cylinders 8 and 6 run leaner, hotter, more prone to det - 06/06/12 02:09 AM
Prior to the damage, what have past plug readings had to say about the mixture? Do they look leaner than the others? Does the ECU you are using have individual cylinder fuel trims?
Posted By: Cab_Burge
Re: Cylinders 8 and 6 run leaner, hotter, more prone to det - 06/06/12 06:47 AM
One way to get cylinder damages in a good cylinder is for pieces from the bad cylinder to be blown back into the intake and be sucked into a good cylinder
I've seen it way more than once, especially broken valves
Posted By: TRENDZ
Re: Cylinders 8 and 6 run leaner, hotter, more prone to det - 06/06/12 09:53 PM
There are no bleeder holes in the deck for the lower water jacket. I've never had a KB block, so I could be steering you wrong. I would suggest calling the manufacturer and asking them about using that block in a "continuous duty" situation versus racing duty. In the olden days people would use 400 inch small block chevys(siamese bores) in race apps without the holes in the heads to let the air escape. Worked fine in a drag car, but melted down in street apps. All it takes is a small hole at the highest spot of the waterjacket on the deck to get water where it needs to be.
I agree with cab about broken parts floating into different cylinders.
Posted By: instigator
Re: Cylinders 8 and 6 run leaner, hotter, more prone to det - 06/06/12 10:20 PM
How in the world does water get into the heads?.....
Posted By: TRENDZ
Re: Cylinders 8 and 6 run leaner, hotter, more prone to det - 06/07/12 03:06 AM
Actually, thats not right. A big block has two waterpump holes at each side of the block(r&l). Water does flow into the block from the lower hole, around the cylinders,(and normally thru holes in the deck to the heads in small quantities) to the back of the block, where it enters the head and than flows back to the front water passage, into the front of the block. The front water passage in the block is separate/divided from the inlet waterflow. Remember, a big block has the t-stat housing on the pump, not the intake.
The picure shows the upper small holes in the deck, but on a siamese block, air gets trapped in the hourglass shape on the lower deck because the air cant escape between the cylinder bores. Your gaskets will have holes in them, and my guess would be that your heads have holes there also. It may be as simple as drilling a few 1/4"holes in the deck to get rid of this problem.
The timing you report seems awfully low. Do you have a real small cam?
Posted By: TRENDZ
Re: Cylinders 8 and 6 run leaner, hotter, more prone to det - 06/07/12 05:07 AM
I'm not being critical of your tuning approach, it's sound. With a cam that small I can understand the timing sensitivity. I do wonder about cylinder pressures on this thing though... A good flowing head with cooled boost and no overlap to speak of is much more dangerous and sensitive to tuning than something that is allowed to exhale some cylinder pressure.