Nitrous - Clearance

[PC Rat]

Talked to an engine builder today. We got on a discussion of adding piston to wall clearance for nitrous use. He said that he doesn't add clearance for a nitrous application because if the tune up is right (which you want it to be anyway) you shouldn't be adding heat, just more power.
Thoughts?
Brian

[Fiat48]

Heat is horsepower. Add more clearance. Treat it like a blown motor.
Take a look at suggested ring end gaps. Just some food for thought.
Ring End Gap Recommendation Guide
top
Speed Pro Top Rings
(Ductile Iron & HF479)
4.000" Bore Example
Min. Gap Factor
Moderate Performance .016 - .018 (.004 per inch of bore diameter)
Drag Racing, Oval Track .018 - .020 (.0045 per inch of bore diameter)
Nitrous Oxide – Street .020 - .022 (.005 per inch of bore diameter)
Nitrous Oxide – Drag .028 - .030 (.007 per inch of bore diameter)
Supercharged .024 - .026 (.006 per inch of bore diameter)
Speed Pro 2nd Rings
(cast iron)
4.000" Bore Example
Min. Gap Factor
Moderate Performance .020 - .022 (.005 per inch of bore diameter)
Drag Racing, Oval Track .022 - .024 (.0055 per inch of bore diameter)
Nitrous Oxide – Street .024 - .026 (.006 per inch of bore diameter)
Nitrous Oxide – Drag .028 - .030 (.007 per inch of bore diameter)
Supercharged .024 - .026 (.006 per inch of bore diameter)

[Norseman]

Talked to an engine builder today. We got on a discussion of adding piston to wall clearance for nitrous use. He said that he doesn't add clearance for a nitrous application because if the tune up is right (which you want it to be anyway) you shouldn't be adding heat, just more power.
Thoughts?
Brian
If your making more power your increasing the heat in the cylinder, the power has to come from something. More power means a bigger burn = more heat!!! :idea:
I think you would be better off talking to another engine builder. This time one that knows what he's doing. :boxingguy :boxingguy

[PC Rat]

Say I order a set of pistons and the manufacturers recommendation on the card is for 0.005 piston to wall clearance, they don't know if I'm building a 300hp engine or a 900hp engine. If horsepower is heat, then how much difference in combustion chamber temp is there between the two engines and why don't they spec the clearances different?
Brian

[Slyder]

Call the piston manufacturer and make sure you let them know that it is a marine application and at what water temp. you keep the engine. Bore size will be critical, and be honest with how much spray you will be injecting.
On our car, 4.560 bore, we are running .008 clearance with CP pistons. We also are running the end gaps .040 top and .042 second rings. We have two foggers on the engine and with a tighter gap - .003 - we were seeing signs of butting.
Good luck. Just my .02.
Paul

[sanger rat]

I thought we was having a Nitrous sale here! LOL :D

[PC Rat]

If your making more power your increasing the heat in the cylinder, the power has to come from something. More power means a bigger burn = more heat!!! :idea:
I think you would be better off talking to another engine builder. This time one that knows what he's doing. :boxingguy :boxingguy
I talked to another engine builder today, he told me the same thing - he would not increase piston to wall clearance, but would slightly increase ring gap.
Brian

[Norseman]

I talked to another engine builder today, he told me the same thing - he would not increase piston to wall clearance, but would slightly increase ring gap.
Brian
Brian;
If it were me building the engine, I would definitly increase ring gap. I would also talk to who ever your buying the pistons from and explain exactly what you intend to do. Then take the manufacturers recommendation.
I've run Arias in a blown 354 Hemi, and JE in a blown SBC and in both cases the manufacturer recommended more clearance. The engine builder that did the machine work agreed with both recommendations.
YMMV :D

[SmokinLowriderSS]

I'd be mostly concerned about piston slap with increased piston to cyl. clearance and the slap could break skirts. I'd agree with the ring end gaps though, makes sence.
I've run probably over 100 pounds N2O through a mid-perf 330HP Mk-4 454 since dad bought the boat new in '78. Winter that year he put the Nitrous on, under the carb. We ran enough to approach 450HP for all those years without a single problem on his/now my Taylor SS jet.

[DeputyDawg]

I know a lot of the guys who run BIG shots of nitrous also set the pistons down in the hole some instaed of even with the deck. Does anyone know why they do this?

[UBFJ #454]

Our nitrous piston (lower top ring) tops are essentially even with the block deck, no zero gap rings and the piston to wall clearance initially was nom. 0.003, now after refresh nom. 0.007 (cost savings as didn't want to get new pistons right now) ... Next refresh, new, larger pistons. Our heads combustion chambers are about 1/2 half the size of what most of you'all are running and our static CR is 15 +:1.

[PC Rat]

I want to use a fuel pressure and oil pressure safety switch in my electrical system. There has to be a supplier that has them cheaper than the $35 name brand ones, anyone know who?
Brian

[HP350SC]

Like these?..........http://content.honeywell.com/sensing/hss/hobbsparts/products/pressureSwitches.asp

[CARLSON-JET]

PC-Rat last year I went looking through napas oil pressure safety switches and found one that opens @ 2-8 psi, shuts down at 11 psi. part # op 6626.. seemed better then the 5 lbs switches. I used a 20 amp relay in conjunction with it to the electric fuel pump. switch was about 8-10 bucks. put alot of hours on it works great. R.B.

[Jeremy1Kanobe]

I design pistons for a living and in my experience the use of nitrous demands more piston to bore clearance to keep the part happy. If possible the top ring should be dropped to get a bit more material between the valve relief and the top ring groove. It is not only the bore clearance which is modified but also the cam shape of the skirt. This will put the clearance in the place it is needed and provide stability for the ring stack. Nitrous is great! I could call it "job security".

[UBFJ #454]

I could call it "job security".
Yep you sure can ... especially if you have large piston to bore clearances in serious nitrous motors ..... the tighter the fit, the less hot ignited vapor can get down along side the top of the piston and burn it off .......