DaveP
Active member
Re: Engine issues
I agree it has nothing to do with fuel pressure distribution in the rails.
I disagree that it is uneven intake air distribution in the intake manifold. While I understand this explanation is widely held and believed on .net, I think for the most part, it's BS. Here's why:
I agree it has nothing to do with fuel pressure distribution in the rails.
I disagree that it is uneven intake air distribution in the intake manifold. While I understand this explanation is widely held and believed on .net, I think for the most part, it's BS. Here's why:
- We'll assume the fuel at each injector is the same amount. Therefore for #3-4 to be "lean" they would have to be receiving MORE air than the other 4 cyls. This seems unlikely, as airflow against the end walls will 'stack up' against the walls and tend to flow into the end cyls. This will make the center cyls richer as they would receive less air.
- Air under pressure will flow fairly evenly around obstructions, and deformations in it's path. No so for NA engines, which is well documented in cyl head and air-flow studies. SyTys are under pressure. So airflow is fairly even under boost. Which is where it matters.
- 15 years of reading SyTy spark plugs has revealed mixture distribution to be fairly uniform.
Now. I feel it's a temperature issue. Specifically chamber temperature. The center cyls run hotter due to block and cyl head design. Hotter chambers detonate sooner than cooler chambers given other pertinent conditions are the same.
- Coolant flow is minimal between the cyls. So the center cyls are cooled on each side, but not so much where coolant flows between the cyl walls.. The end cyls each have an additional 90º exposed to coolant flow. Particularly the fronts exposed to the water pump. There are large coolant transfer holes at the REAR of the block that transfer the flow up into the rear of the head, then forward to the thermostat passage where it exits the head. So there is also good flow around the rear of the rear cyls. Thus the end cyls have 270º of good exposure to flow. The center cyls only get 180º of comparable exposure.
- #3 and 5, and #2 and 4 have adjacent exhaust ports. In small block V8's the center pair of chambers on each bank is known to run hotter because of this configuration. I posit that the same situation exists in a V6. That the exhaust-paired chambers run hotter. EXCEPT that the coolant flow through the head is different [in each of the paired cyls] because of the above coolant flow distribution.
Conclusion: The center cyls in a SyTy run hotter than the other four because of coolant flow, and cyl head exhaust port design. And therefore the center two cyls detonate first, causing the damage. It's not a "mixture problem". It's a temperature problem.
Discuss.
DaveP - Coolant flow is minimal between the cyls. So the center cyls are cooled on each side, but not so much where coolant flows between the cyl walls.. The end cyls each have an additional 90º exposed to coolant flow. Particularly the fronts exposed to the water pump. There are large coolant transfer holes at the REAR of the block that transfer the flow up into the rear of the head, then forward to the thermostat passage where it exits the head. So there is also good flow around the rear of the rear cyls. Thus the end cyls have 270º of good exposure to flow. The center cyls only get 180º of comparable exposure.
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