anyone ever run a slightly larger ptw in one cylinder compared to another, ie larger in the #3 due to its increased heat? im not talking like 2 thousands more, but maybe like .0038 when the others are at .0035???

how bad would this be to do

 

i have heard that as well but from a dumbass that cant keep a motor from flying apart to save his life. so i wouldnt.

 

Forgive my ignorance, but why would cylinder #3 be hotter then the others?

 

I've never really understood the apparant logic behind this.

Apparantly, it's because of firing order. Cylinder three goes off and then 4 and 2 which are right next to it, so it gets no time to cool down. Problem I see...

1-3-4-2-1-3-4-2-1-3-4-2 ...

2 gets the same treatment if you extend the firing order through a few cycles...

So, if someone wants to explain to me the reason or if it's just another myth I'd love to hear it.

As far as the original question. I wouldn't bother. I didn't, and that small of a change I don't even think you're getting outside of Honda's original tolerance lol.

 

Agreed, #2 should be as hot as #3. But no dont mess with p2w clearance to compensate, that is stupid the difference is not that significant. Use your fuel trims to add 1% in the middle cylinders.

 

2 shouldn't get as hot as 3. 4 fires, then 2, then 1. the fact that nothing next to it fires before it gives it an extra cooling stroke, so to speak... that is, when 2 fires, theres no immediate combustion event next to it.

while minimal, it still wont get as hot as 3.

and as to the op's question... dont mess with p2w clearance to compensate... use fuel trims to do that... of course you could always go stupid and run 4 egt's and use individual injector trims if you're that concerned about it

 

This doesn't make sense to me. I agree with Sovxietday.
After a short amount of time, the effect should be the same on cylinders 2 and 3.
the order 4,2,1,3 should have the same effect on cyl. 2 as 1,3,4,2 has on cyl. 3, over time. Maybe I am missing something. I definitely have heard that more stress is put on cyl. 3 thank the others, why is this?

 

oh, i see now. i had a dyslexic moment lol. too many numbers

 

I would love to see someone do this on stock-ish motors to see really how much they vary from the factory. The flow balancing of the injectors (since most people are likely 0,0,0,0 in the individual compensation tables) likely has more effect in the EGT/cyl temp differences than the difference in firing order. I'm just thinking aloud. I'd love to see some concrete numbers.
Then again, I wonder if Honda engineers already thought of this and flow extra fuel to the middle cylinders by default. To know this I suppose we'd need Calvin Baanks input or someone else who has experience reverse engineering the ECU code.

 

Some V8 guys do this. Its not so much the firing order, but the cooling system that causes the cylinder-to-cylinder variation in temperature. Those cylinders closer to the water pump may be getting cooler water than the rear most cylinders.

Its not stupid at all, its smart. You may machine all the bores to have .0038" clearance, but if one cylinder is hotter than the others, obviously it will expand more. Its the same line of thinking that produced torque plate honing with a heated block, as well as F1 engines that will seize unless everything is at operating temp.

 

i was using the cyl fuel trims with more fuel added to #3. this all came into my mind after i had piston to wall contact on the dyno saturday in the #3 cyl. afr was between 10.9 and 11.2 and there was no detonation on the plug. coolant and oil were between 180 and 190 and my iat was 118. 17 psi 412hp on 93 pump gas. the skirts on my other 3 pistons show only normal wear, so i wouldnt honestly want to run that much more ptw there, but i know the #3 made contact so it needs to go bigger.

 

ok, how would running a sleeved block influence this? i was thinking the other day that since ive got an iron sleeve and aluminum pistons the pistons will expand at a faster rate, possible requiring more ptw???

all you guys with sleeved blocks, what ptw did you come up with?

 

sleeving a block shouldnt change ptw, your stock sleeves are iron...

all aluminum pistons expand, its the alloy that determines how much expansion and how much ptw you need to run