[Tim Corcoran]

Originally Posted by HWYSTR455

It should be safe, but going to the recommended gap for N2O has no drawback and would still be cautious with any less.

Pistons I figured would be fine, wasn't particularly concerned with that.

Just checking...

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yeah I planned ahead for that. The engine will have a few thousand miles on it before I put the juice to it. The gap does open up a bit after the rings seat in too.

[HWYSTR455]

I would imagine they open up a little once seated, but is that measurable? Not really sure how much of a diff that would be, maybe someone else can chime in on that, I would be curious.

Just to say, I make it SOP to use the first stage of N2O ring gaps on every build, gives a fuzzy, you never know how the life of an engine will change paths. And in situations where you may have abnormal heat and/or combustion, you have that padding.


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[blueghoast]

I've ran n20 with stock ring gaps without any problems on a weekend racer
The sort block was factory stock that was for probly 4-5 years finally spun
a bearing later I rebuilt that and put it in my wifes 67 LaMans with tri-power.

GT

[HWYSTR455]

I think factory rings gaps are pretty wide and are like + or - .010. And that's not taking the ring material into consideration. Assembly line stuff only uses that as a 'guide', too. It can be anywhere.

Then you take piston to bore tolerances into account, and it can be pretty big by today's standards.

Not saying it can't be done, just pointing a few things out. And not saying you can get lucky or not.

But since the point has been brought up, curious what the OP's gap is, and which rings they are?


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[Tim Corcoran]

I believe they were total seal classic plasma moly 1/16 top ring. The instructions give a recommended gap based on bore size. I don't remember for certain what the gap was but let's say the recommended naturally aspirated gap was .024 and the N20 gap was .028 then I would of set it at .026 since a 150 shot is relatively on the small side. I'm confident with my rationale and the gap I selected.

[HWYSTR455]

Fair enough, thanks.

Attached is the gap sheet, and based on a 4.189 bore:

Standard -.019
Up to 150 Shot - .023
150 -300 Shot - .027

So halfway on the 'up to 150' would be .021, and if using the 150-300, would be .023 . Not a big difference. Might still want to not go a full 150 shot with the halfway of 'up to 150', just personal opinion.

You could do a 75-125 fixed shot system, and you might not have to pull timing either. That would certainly be safe. Anything else would have a minor risk.

I think the 100/125 shot systems are 1-solenoid only, no fuel solenoid, so you would have to jet-up on the secondary side, which can be a little bit of a dance (spray/no-spray tuning), but not too bad.

I used the 150-300 on my builds, never saw evidence of ring butt on teardowns.

With iron heads on a 175-225 shot I wouldn't pull any timing (small displacement type builds) and was fine going by the plugs. On 250-300 pills, I would pull 2-4 degrees. (Just personal experience).

General rule of thumb is 2 degrees per 50 shot is safe. But that never worked for me and creeped up on going no retard.

Just thought I would share, as an example. I still have graphs and charts I made as I did testing, could dig that up sometime.


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[Tim Corcoran]

Originally Posted by HWYSTR455

Fair enough, thanks.

Attached is the gap sheet, and based on a 4.189 bore:

Standard -.019
Up to 150 Shot - .023
150 -300 Shot - .027

So halfway on the 'up to 150' would be .021, and if using the 150-300, would be .023 . Not a big difference. Might still want to not go a full 150 shot with the halfway of 'up to 150', just personal opinion.

You could do a 75-125 fixed shot system, and you might not have to pull timing either. That would certainly be safe. Anything else would have a minor risk.

I think the 100/125 shot systems are 1-solenoid only, no fuel solenoid, so you would have to jet-up on the secondary side, which can be a little bit of a dance (spray/no-spray tuning), but not too bad.

I used the 150-300 on my builds, never saw evidence of ring butt on teardowns.

With iron heads on a 175-225 shot I wouldn't pull any timing (small displacement type builds) and was fine going by the plugs. On 250-300 pills, I would pull 2-4 degrees. (Just personal experience).

General rule of thumb is 2 degrees per 50 shot is safe. But that never worked for me and creeped up on going no retard.

Just thought I would share, as an example. I still have graphs and charts I made as I did testing, could dig that up sometime.


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The directions that came with the rings didn't specify any levels of N20 just N.A. N20 and forced induction turbo/supercharged. If memory serves me correct I gapped the top ring at .026. I will use two solenoids I wouldn't add N20 without additional fuel and would probably start out with 75 shot and work my way up in steps.

[chiphead]

Start with about a 100 shot, it's just enough to really feel the hit. It takes work to clean up the tune, and you'll want to step up before you get the 75 shot to run clean.

I ran a spreadbore plate system under a Q-jet for a few years. I'm sure I've got posts on it here. I do suggest an electric pusher system and a good regulator system, makes nitrous tuning so much easier. You end up needing to make small tuning changes in the fuel side of the system, and its so much easier with an electric pump. The nitrous jet sets the HP of the system and the fuel side sets the AFR. At least thats how I tuned. Less than 10:1 compression has a fairly wide tuning window, you won't hurt it unless the NA tune if off or you're careless.

[HWYSTR455]

.026 is safe, you're good.

Depending on the system, most I've seen under 150hp have been with no fuel sol but it's been years since I looked.

My last 2 systems were NX setups, really liked them, did homework before I bought. Again tho, it's been a while.

Funny thing, bought and setup the last system and never used it on my roller e-head 461, didn't need it. Sold on here, whoever bought it got a deal.


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[Tim Corcoran]

Originally Posted by Stan Weiss

What are you seeing for idle vacuum? The Voodoo;s asymmetry makes calculates a little hard, but my rough calculation is 16.7".

Stan

Stan
vacuum at idle 750 RPM is a little over 17 in hg