Alright, don't bash I'm not new to vehicles and worked on a million sbf but never torn into one of my own. Here's what I have, it's a chp 331 shortblock that bought with a car. It has -14.2cc dish pistons in it with a set of gt40x heads. The heads have 64cc chambers. (Not against going with diff heads but trying to stay cost effective for the time being) it also have a f cam in it from what I'm told as I've not checked yet. It's gonna come out for a more suitable cam anyway. It's got 1.6 rockers blah blah blah. Question is, is this motor gonna have too low of compression to make any significant power on the bottle before it scatters itself. I'm not trying to set land speed records but would like a reliableish 400whp when on the bottle. I'm aware that I'll prob have to gap the rings to better suit the nitrous etc and am thinking of building a stand alone fuel system for nitrous and run 118 oct in that through a 4150 plate. How wrong am I if I am point me in the right direction
Need A Little Help With My 331
- Thread starter Brandon Palmer
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Using a CR calculator shows me a 8.75:1 CR for your combination.
Ideally, more compression is desirable in a high output, purpose built nitrous engine,...but a 100-150 shot of nitrous is far from that. MOF, that 100-150 hp shot is w/i the confines of what can be safely dumped into a engine sporting near stock internals.
Big nitrous use requires that you pay attention to three things specifically.
Spark timing, fuel octane, and what your plugs look like. (and you gotta know what to look for)
The timing thing is easy, and there are several recommendations from different mfg's out there to serve as a guideline for that. Typically, you remove 2 degrees timing for every 50 HP of nitrous injected as a starting point.
So,...if you are running stock timing curves and total advance of say......32-36 degrees total,.....you'd remove 4-6 degrees from that to compensate. If you don't want to continually get under the hood w/ a timing light, Several MFG's make timing retard boxes that will allow you to run stock timing right up to the instant that the n2o is activated, then retard the timing to your desired setback.
The fuel thing is a catch 22. Use a fuel with enough octane to cover detonation and keep it in check, but not so much as to slow the burn down to where it starts causing the engine to make less power.
That said, there's no way in hell I'd use 118 in a low CR/low nitrous injected engine. I'm thinking that you should call somebody at VP or Rocket to be sure, but I'd bet they'd cap you at 100-110 instead.
The plug reading is a direct indication of whether you are safe at your chosen HP level. The plug color will be a tell tale of that. Now that I think about it, you're gonna have to know what kind of alloy the pistons that are in the engine are made of.
A true forged piston will be more tolerant of abuse, however the industry has put out a bunch of confusing info about what the word "forged" means, and it doesn't automatically mean that you have a good piston that will tolerate getting rattled if you have something go wrong.
A 2618 alloy is a true forged piston, using the best aluminum that can be used in high HP applications.
It is more "soft" and less brittle and consequently can absorb more abuse. The negative to a 2618 piston is that they are noisy in the engine,..and you can hear them rocking as the engine runs. They grow w/ heat, so the engine has to be finished honed w/ more sidewall clearance to allow for that.
A 4032 alloy forged piston is made w/ a higher silicone content, and as a byproduct expands way less than a 2618 piston does. The engine builder can run tighter clearances because of that, and that nets a quieter running engine that typically lasts longer, and has better ring seal. But,...
The piston is more brittle because of the higher silicone content, and less tolerant of detonation.
A hyper-eutectic piston, typical of what KB uses is the least tolerant of the three, and is considered a cast piston. They transfer alot of heat to the rings, and the ring end gap has to be set huge because of that. They are NOT suited for a power adder, and should only be considered in a N/A application.
Ideally, more compression is desirable in a high output, purpose built nitrous engine,...but a 100-150 shot of nitrous is far from that. MOF, that 100-150 hp shot is w/i the confines of what can be safely dumped into a engine sporting near stock internals.
Big nitrous use requires that you pay attention to three things specifically.
Spark timing, fuel octane, and what your plugs look like. (and you gotta know what to look for)
The timing thing is easy, and there are several recommendations from different mfg's out there to serve as a guideline for that. Typically, you remove 2 degrees timing for every 50 HP of nitrous injected as a starting point.
So,...if you are running stock timing curves and total advance of say......32-36 degrees total,.....you'd remove 4-6 degrees from that to compensate. If you don't want to continually get under the hood w/ a timing light, Several MFG's make timing retard boxes that will allow you to run stock timing right up to the instant that the n2o is activated, then retard the timing to your desired setback.
The fuel thing is a catch 22. Use a fuel with enough octane to cover detonation and keep it in check, but not so much as to slow the burn down to where it starts causing the engine to make less power.
That said, there's no way in hell I'd use 118 in a low CR/low nitrous injected engine. I'm thinking that you should call somebody at VP or Rocket to be sure, but I'd bet they'd cap you at 100-110 instead.
The plug reading is a direct indication of whether you are safe at your chosen HP level. The plug color will be a tell tale of that. Now that I think about it, you're gonna have to know what kind of alloy the pistons that are in the engine are made of.
A true forged piston will be more tolerant of abuse, however the industry has put out a bunch of confusing info about what the word "forged" means, and it doesn't automatically mean that you have a good piston that will tolerate getting rattled if you have something go wrong.
A 2618 alloy is a true forged piston, using the best aluminum that can be used in high HP applications.
It is more "soft" and less brittle and consequently can absorb more abuse. The negative to a 2618 piston is that they are noisy in the engine,..and you can hear them rocking as the engine runs. They grow w/ heat, so the engine has to be finished honed w/ more sidewall clearance to allow for that.
A 4032 alloy forged piston is made w/ a higher silicone content, and as a byproduct expands way less than a 2618 piston does. The engine builder can run tighter clearances because of that, and that nets a quieter running engine that typically lasts longer, and has better ring seal. But,...
The piston is more brittle because of the higher silicone content, and less tolerant of detonation.
A hyper-eutectic piston, typical of what KB uses is the least tolerant of the three, and is considered a cast piston. They transfer alot of heat to the rings, and the ring end gap has to be set huge because of that. They are NOT suited for a power adder, and should only be considered in a N/A application.
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Good stuff there.
I will only add this:
I am getting ready to spray my 331 and have been reading tons of stuff trying to make sure I have an idea of what I am doing. In the course of this, I have read a few guys claiming that running pump gas then using a stand alone with race fuel for the nitrous is not a good idea. For the life of me I cannot remember the reason why they did not prefer it, so please do not take that as gospel, as I cannot back it up. I only mention it so you can ask the question of the fuel manufacturer, as Mike suggested, or your nitrous manufacturer.
Good luck with it and keep us posted.
Joe
Thanks for the info guys, fuel idea was simply a thought to keep it safe. We've done it on other motors and they've lived a long life but they're high comp also. The pistons are 2618 probe dished pistons. Which from what I can find seems to be a good company etc. so should I change heads and cam around or leave it like it is and just throw a 100-150 on it? Should I gap the rings etc?
Thanks for the info guys, fuel idea was simply a thought to keep it safe. We've done it on other motors and they've lived a long life but they're high comp also. The pistons are 2618 probe dished pistons. Which from what I can find seems to be a good company etc. so should I change heads and cam around or leave it like it is and just throw a 100-150 on it? Should I gap the rings etc?
Throw 100-150 at it. You'll make more than 400 and be within safe parameters(as long as the timing is correct,enough fuel,proper spark plugs etc etc).
If it has a girdle it is probably a stock block. If you keep your tune safe you will probably be okay with that amount. I am 10.7 compression on a stock block and plan on spraying a hundred pretty regularly. Hopefully it stays together. Probe Pistons are good piston, but they went out of business the end of last year.
You will not know without checking, but I would bet your ring gaps are probably pretty good considering it was built for a boosted application. The cam would also probably work okay, maybe not optimal, but probably okay.
For what it is worth my rings are gapped for a naturally aspirated combination and my cam was also cut for that combination. I talked with Ed Curtis about this and he said I would be fine with a 125 to 150 shot.
Joe
You will not know without checking, but I would bet your ring gaps are probably pretty good considering it was built for a boosted application. The cam would also probably work okay, maybe not optimal, but probably okay.
For what it is worth my rings are gapped for a naturally aspirated combination and my cam was also cut for that combination. I talked with Ed Curtis about this and he said I would be fine with a 125 to 150 shot.
Joe
anytime a power adder is being used the ring gaps are made larger regardless of the method. The additional heat from the "supercharging", whether that come from forced induction, or because of the effect nitrous has on the burn cycle requires a wider ring end gap either way.
Again, that would've been a question asked of the piston mfg to be sure,..But in lieu of the fact that Probe is no more,.the next phone call would go to the ring mfg.
Your ring gap will be fine at that nitrous level. You're not going to be creating the cylinder pressures or temperatures to justify a ring change.
If you have any more questions pertaining to your piston and ring gap, the former owner of Probe and CHP can be found over on the corral under his name, Mark O'Neal. He has always been helpful.
Joe
Joe
Ok, I'm a painter, so my main view is your mustang is beautiful
!I hope it goes well for you with the nitrous. I'm kind of interested in seeing how it does at the track. Post a slip when you try it out.
Thanks bud, it's got some iffy spots in the paint because of painter error but it's a solid 5 footer lol. And I will for sure. It'll be a stick car forever. It's got a cage, built rear tubular front and rear everything yada yada yada. I'm hoping for it to be atleast lower 7s range in the 1/8th.Ok, I'm a painter, so my main view is your mustang is beautiful
I hope it goes well for you with the nitrous. I'm kind of interested in seeing how it does at the track. Post a slip when you try it out.
