RedBaron

iTrader: (2)

For a street motor that uses primarily pump gas (93 oct.) would you be able to make more power with a low compression motor with more nitrous, or with a higher compression motor and less nitrous? The reason I ask is because on a FI motor people seem to make more power with less compression and more boost for a given octane. So would this apply to nitrous as well? Thanks

tuff

iTrader: (15)

More compression the better.Your not pumping air into a cylinder like a turbo or supercharger.

777

iTrader: (21)

n20 is oxygen rich (which is why it makes power) The fuel is not really what burns. It's the mixture of oxygen with the fuel that makes it combust. Anyhow, to answer your question. A nitrous motor is built with high compression, where as a turbo/supercharger motor is built with low compression. Nitrous adds more oxygen, turbo/supercharger adds more air (which increases compression by itself)

Somebody09

Excellent question... now what about people who want to use Nitrous and FI? (Like me in the next year or so). I don't plan on boosting more than 12-15psi with ATI's S/C. I'm guessing I should search in the FI forum and that my answer will be "low compression."

-somebody

brad8266

iTrader: (23)

With FI go low compression even with nitrous. A good rule for building a motor that plans to see nitrous is to build it for how you want it to perform without the nitrous. Hence is you want FI and nitrous, then build for FI, which is low compression, if you want a great DD with not needing high octane gas than go stock compression with the nitrous, for a race NA motor, go high compression and then spray it.

Red Dawg

iTrader: (1)

But if you run lower compression shouldn't you be able to spray more before you run into detonation(sp?)? Enough to make up for the difference in compression? I don't think he means an all out race motor, just something limited to pump gas...

So how would you go about making the most power on pump gas. A 8.5-9:1 motor with a 300 shot, or a 11.5-12:1 compression motor with a 150 shot?

brad8266

iTrader: (23)

Yeah you could spray more, but you will lose power from the compression drop alone and then have to make up for it with a larger shot anyway, like I said build for what the motor will be like without the spray. In my opinion it would be kinda dumb to lower your compression just to spray a larger shot. A 200 shot with a tune and decent fuel system(pump, injectors) at a 10.5 compression can be handled by a stock bottom end ls1.

383LQ4SS

iTrader: (33)

but if your goal is maximum power on pump gas...lower compression is better. It seems to me it has to do with pressure drop during piston travel and peak pressures. Yes your going to have to spray more to make up for the lower compression...but you will be less detonation prone. Hell...most '"race only" nitrous motors are 13 to 1 +. Your not even going to be able to run that on pump gas NA let alone any significant shot.

MadBill

I'm with Red and 383. It will take a ton more nitrous, making a ton more power, to reach the 'failure zone' on a moderate vs. high CR engine, especially if the cam and exhaust are built for the juice.
Going from 11:1 to say 13:1 CR will gain you what, 30 HP max? The lower CR will allow enough extra nitrous before meltdown to pick up at least another 100 HP, maybe 150.

brad8266

iTrader: (23)

My main point was to build the motor for what you want when you are NOT SPRAYIN! Dropping the compression will net you less power during normal driving. Yeah you may be able to squeez more power out of dropping the CR so you can get a bigger shot, but that could also be done by pulling a little timing, I personally would rather keep my stock compression rather than go low just to spray more. How much power you plan onb making anyway? There is a pump gas ls1 here that ran a 9's with a stock block H/C/N2O, so I dont see any reason to drop CR to allow more nitrous. Just my opinion, would be nice to see some results from a low CR N2O ls1 though.

Red Dawg

iTrader: (1)

The main reason why I would want to drop the compression in order to run a larger shot on pump gas is because I am a big fan of dry setups. With a wet shot you can run a high compression motor with pump gas and have a dedicated fuel cell for the nitrous's fuel. Which won't cost you a lot in race fuel. But for the dry setup running around on race fuel gets expensive. As for driving around with a lower compression motor.... it's not all that bad... at all. Whenever I really want to get on it all I have to do is crack open the bottle.

How much RWHP do you think it's possible to make with a pump gas 346" 9:1 motor and a 12:1 motor. If both are sprayed just to the point of detonation? All other things being equal except compression...

brad8266

iTrader: (23)

A 12.1 motor is most likely not built to run on pump gas, it is probably meant to run on race fuel. A 346 with heads/cam can make 400RWHP, add a 250 direct port shot and you have around 650RWHP, and i am sure plenty more can be had as long as you have a strong bottom end. I make close to 500RWHP with my light boltons and 150 shot.
People that have FI setups have lower compression and are still pulling timing to prevent detonation, so just dropping compression will not make the detonation problem go away. I would rather keep my compression and pull a few degrees than drop my compression and maybe still have to pull a bit of timing.