n20 compression

[427belair]

ive never used nitrous and i want to add a plate system to the 496 bbc im building for my 74 nova. I want to know if its better to run low compression 9 to 1 or higher 13 to 1

[MOKANRACER]

ive never used nitrous and i want to add a plate system to the 496 bbc im building for my 74 nova. I want to know if its better to run low compression 9 to 1 or higher 13 to 1

Most that I have spoken to ,say More compression,the better?? A lot of cars running way high ratios are running with major shots of N20. My mtr is 14.8 and runs ok with a 150 shot,tunning now for a 175,than a 210 shot.Its a sbc. John prob will be able to shed some light on this.

[sc racing]

Nitrous increases cylinder pressure but its main purpose is to let you bring more fuel into the engine thats where the extra power comes from, so if you have the right parts and the right N2o set up I dont think compression is an issue, you can probably run anything you want. I would guess that a normaly aspirated engine would benifiet from higher compression or what I mean is it would make more power off the bottle with higher comp.Ive only played with N2o motors with 12.5 and lower comp and smaal kits (less than 300 HP )so I might be way off but just my .02

[John_Heard]

I don't think I would use 17:1, but something lower, say 15:1 would be nice. Problem is with the big blocks is getting the right piston. 13:1 or slightly higher is probably all your going to get with lower cost pistons and open chamber heads. You'll have to angle mill/turn the heads and get custom fit pistons to bump it up a lot more than that. I wouldn't want to go less than 13:1 for a race motor.

Moose you're the expert on big compression ratios... How much is too much huh?

[Mike Peters]

I don't think I would use 17:1, but something lower, say 15:1 would be nice. Problem is with the big blocks is getting the right piston. 13:1 or slightly higher is probably all your going to get with lower cost pistons and open chamber heads. You'll have to angle mill/turn the heads and get custom fit pistons to bump it up a lot more than that. I wouldn't want to go less than 13:1 for a race motor.

Moose you're the expert on big compression ratios... How much is too much huh?

You're asking a guy who says he runs over 16.5:1 what is too much? I don't think Moose knows the meaning of "too much". LOL!!!

[John_Heard]

ehehehe

[MOOSE]

GEEEEEZZZ guy's so early in the morning. In my humble opinion and that of my engine builder is that whatever you can do to make the most of what you got than do it. Do not leave anything on the table. So, with that being said, whatever compression is best suited for your situation than use it. The higher compression you use with nitrous the less timing you will be able to use. Compression in a nitrous motor is not linear, there is a point of no return. Meaning, it is not going do anygood to put anymore compression in a motor because your gains have stopped. John, is right though. Don't get so extreme that your intake, heads and other stuff become one due to the alterations done to get the higher ratios. In other words, don't make it to where you can't sell your heads without the intake manifold cuzz one out of the box won't even come close to working.

I would think that about 14.5.1 would be a good all around ration that would seem to be the upper limits of off the shelf stuff. Just use good fuel and really watch your plugs and timing.


MOOSE

[John_Heard]

Good post Moose

[Mike Peters]

Good post Moose

I thought it was a crappy post!!!! I was waiting for him to turn loose some of those PK Racing Engines secrets!!! LOL!

Someone do me a favor this Saturday and put a whuppin' on Mike G-Whiz if he actually has the cojones to drop down into R/S. PLEASE!!!!!

[ytnova]

The way I look at it is this: if you are going to run a low compression motor with alot of nitrous, then you are going to run race fuel. If you are already running race fuel, then why not put as much compression in as you can. I agree with not going over board with the heads and intake, it really sucks to not be able to sell your current stuff to go to the next level. Odds are you will always be wanting to go just a little faster.

[427belair]

thanks for the advice everyone, im on a fair buget for this motor/car. next year is going to be my first real year of racing, for the last few weeks ive been racing our 55 chevy which has dipped into the high 11's pretty good for a street car here in montana,but next year in the nova i want to run 10's. for the nova im pretty much set on a 496 i already have the block and scat forged crank and im want to build it to take a 200 or so shot any advice on rods and pistons..im thinking about 12-12.5 compression also user friendly/ dummy proof plate set ups. my dad/finacial backer buddy is selling his fogger set up off his top comp car but i want to start slow

[sverbus]

THis is a good thread for me as well because I'm thinknig of a plate setup for the nova next year and it's a 15.5 ratio car. Some good advice in here :)

[aitch o]

my small block was somewhat forgiving at 12:1 or so on the plate system up to 400 as long as timing was watched closely.
as the compression increased it became more picky. the fogger also got considerably more picky, even staying in the 400 range.
to be specific, i would pull 1.5* timing out for each 50 horse of spray. 2* retard per 50 on my combination turned it into a turtle, 1* per 50 and it ran great for just 1 second however it would melt the pistons.

also, there is a big difference between $5 per gallon race gas and $12 per gallon race gas. $5 gas is fine for 150 shot and moderate 12:1 compression. $12 gas would be a waste. however, over 250 shot and 13:1 to 15:1, $5 gas just won't cut it. VPC16 (118) or VPNOS is a must. sonoco 118 is ok.