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Discussion Starter #1
I was told I might want to open up the ring gap a bit on my top ring because I'm running nitrous. I'll be assembling my stock crank and rods 306 in the next couple weeks and this was one of the steps I was told would be beneficial with the new motor.

I know I'll be running at least a 150 dry shot, maybe as much as a 200 dry shot if I pick up and inline pump.

What sort of ring gap should I go with?

Is it just the top ring I should open up a bit? Why is this beneficial, won't I lose compression?

TIA,
Chris
 

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Typical ring gaps:

Alcohol, .003 to .005 x bore dia= gap
N/A gas .004 to .006 x bore dia= gap
Forced induction, N2O etc .005 to .007 x bore = gap

For an N2O application on your engine, with the LOW RPM the typical stock rodded engine is built around I would run a .024 top gap, with a .022 second ring gap.

Higher RPM engines, run more gap, and I actually run a larger gap on the second ring than the top ring. I dont want any gas pressure building between the rings. It only unseats the top ring (Causes ring flutter) My Engine runs a .035 top ring gap and a .038 second ring gap. 4.625 bore though, and itll see mid 8000RPM pulls.


Childs and Albert did some stuff and found engines turning in excess of 10,000 RPM showed no difference in blow by or HP loss when run WITHOUT compression rings.

Another group had done a test and noticed no loss in HP with a ring gap that started at a conventional .018 and went all the way up to .035, above .035 to .050 they had 3 to 4 hp loss. I dont remember what RPM window they were testing in. The slower the speed of the piston (lower RPM) the more critical the ring end gap. The higher the RPM the less affect you see with a larger gap. But, larger is always better than too small. The top of the piston comming off because of end gap butting sucks!
 

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Discussion Starter #3 (Edited)
Max rpm on this motor should be 6500 or less. This is a street/strip car. I plan on running on motor and on nitrous and I'm not expecting to make more than 320rwhp on motor: 306 with Edel. 6032 heads, TFS Stage 1 cam, RPM intake, 70mm tb, 76mm maf, 24# inj., LT's, o/r H, 6AL ign. with the basic bolt ons and a TKO. Edit: Also planning to pick up a JMS or Fordchip.

So with a 4.030 bore x .005 /.007 = .020/.028 gap

or should I go to a .030 gap to be conservative.
 

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For an N2O application on your engine, with the LOW RPM the typical stock rodded engine is built around I would run a .024 top gap, with a .022 second ring gap
 

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Discussion Starter #5
Thanks Kim, it usually helps to say things to me several times, helps penetrate my thick skull.:p

So I won't lose any power running those gaps n/a right? Or was the loss of power only calculated with the power adder? Sorry if these are foolish questions, I just want to do it right the first time.
 

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Maybe 1hp, have to compromise a little otherwise bad things can happen. The higher the operating RPM of the engine, the less loss noticed, the lower and slower the more.
 
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