Ok So i'm not new to turbo or nitrous applications, but in reguards to using them on a 420a i am. My question is when i do a search,
I find these builds for nitrous with Low compression engines...
Why would you want to lower the compression if your not going F/I?

All that'll do is make your car a dog even more then it is stock when your not running a rediculas amount of spray.

Could be a variety of reasons why they have low comp (maybe they got a good deal on some low comp pistons or something), but you're right, it can be sluggish. On the other hand if they have low comp, it can allow you a slightly larger tuning window.

It's a give and take on either scenario:
low comp - easier to tune, slightly lower power
normal comp - in the middle
high comp - well, you get the idea

low comp is usually the novice tuners' choice. read up on it more

Originally posted by 420agreenvilleSC
Could be a variety of reasons why they have low comp (maybe they got a good deal on some low comp pistons or something), but you're right, it can be sluggish. On the other hand if they have low comp, it can allow you a slightly larger tuning window. It's a give and take on either scenario: low comp - easier to tune, slightly lower power normal comp - in the middle high comp - well, you get the idea low comp is usually the novice tuners' choice. read up on it more

very true, like most builds i see on here are low compression. Which if they're gonna throw like a direct port 200shot at it I can understand. I just wonder how much power one of those low compression motors put out n/a. probably on par with a honda civic.

I've decided if I do end up trading my motorcycle for this 96 eclipse, instead of going the turbo route, and headache. (i'm tired of wrenching on cars but I love tuning)

I'm just going to go the spray route with just a 75hp wet fogger, if i do build an engine though, it'll be done with 13:1 compression ratio and run on e85. + wet nitrous. As we all know high compression motor LOVE spray.

90% of folks going the low-comp route is because of the more forgiving nature. The more you up the compression the smaller your window for error becomes.

Also keep in mind the platform. Pretty much any 17 year old kid with a part-time job can pick up one of these cars. So, expect a good portion of community to reflect that.

The answer is simple. First you need to understand what a Nitrous motor really is. A true Nitrous motor is a motor utilizing a great deal of nitrous instead of a turbo or supercharger. A nitrous motor is not a motor with a 150hp kit bolted to it. Nitrous motors will typically run a port fogger which starts out around 250HP+.

When your going with a 300HP increase you want to drop your compression ratio just as you would a Turbo motor. I expect you know the reasons for this. One of the main reasons is the lower compression increases the CC volumn which lowers the flame front combustion heat and as you know if you get too close to the thermal capacity of a metal, it will weaken. This is what happens when you deal with pre-ignition and worse, detonation. Pre-ignition is a intake charge that ignites early on leftover heat in the cylinder. The piston will compress the igniting fuel and as a result the heat generated by the burning fuel increase exponentially and if this goes no further then you are slowly destroying your plugs and rings. If preignition gets worse it can and will lead to detonation. Detonation is different, detonation is a more violent ignition of the fuel mixture. One example is preignition leading to Detonation. As i mentioned in preignition the fuel mixture ignites early due to heat. As that is going on imagine the spark plug is getting hotter and hotter. The job of a spark plug is to disipate heat into the head, too hot of a plug will begin to glow if preignition becomes a problem. Now you have fuel buring in the cylinder as a piston compresses it making it hotter. Soon enough the spark plug will get so hot it will ignite the unburnt fuel still in the cylinder (pre-ignition doesnt burn the entire mixture evenly). That flame front is far more of a sudden lighting of the entire mixture. The expanding gasses push so hard against the piston (that is too hot already) and the metal will reach its fatique point and it will either begin to melt small portions or it will entirely cave in. Decreasing the Ratio will keep this under control.
That is only 1 example of hot Detonation occurs, there are several.

Why Cant you just lower timing? Think of Timing as fine tuning the cylinder temps during a burn cycle. Compression ratio would be your course adjustment. IF you are trying to get every tiny bit of power you can from a motor, you first want your timing and plug heat range tuned out. Once you have both of those set in stone, you tune based on heat (EGT's). Every motor will be different. Widebands are good for getting you close and you can use them but if you were to compare heat marks on the spark plugs as you go, you will see the same pattern just not in numbers.

Spark plug heat ranges are another way to tune heat but they also will affect your timing. as you get hotter on the plug, your timing will need to be retarded. I recently toyed with a car on a dyno that when increasing the heat range 1 set up, cuased the timing to be 6* to far advanced. I went from 41* total timing to 35* total. Further tuning will identigy if the heat range choice was better for the motor or stepping down will be warrented. Too rich of a fuel mixture can also make the heat range of a plug look too cool.

Why Nitrous or a Supercharger or Turbo? Becuase you will never be able to get a supercharger or Turbo setup to operate with an intake charge as cool as Nitrogen gets. Nitrous Oxide does 2 things. The Oxygen when introduced into a Flame front increases the Flames heat which is what gives the compressed fuel/air mixture a more aggressive gas expansion during the burn cycle. The Nitrogen is used purely as a cooling medium. Oxygen on its own will melt the pistons/ring before you even get past the 60' mark. Nitrogen gives the mixture some controlability in terms of heat.



A motor with a 150 shot is not considered a Nitrous motor. Thats why its called a cheater kit.

Obviously the downside with Nitrous is the increase maintenance of bottle filling and system cleaning.

Originally posted by Star Turbo Talon
The answer is simple. First you need to understand what a Nitrous motor really is. A true Nitrous motor is a motor utilizing a great deal of nitrous instead of a turbo or supercharger. A nitrous motor is not a motor with a 150hp kit bolted to it. Nitrous motors will typically run a port fogger which starts out around 250HP+. When your going with a 300HP increase you want to drop your compression ratio just as you would a Turbo motor. I expect you know the reasons for this. One of the main reasons is the lower compression increases the CC volumn which lowers the flame front combustion heat and as you know if you get too close to the thermal capacity of a metal, it will weaken. This is what happens when you deal with pre-ignition and worse, detonation. Pre-ignition is a intake charge that ignites early on leftover heat in the cylinder. The piston will compress the igniting fuel and as a result the heat generated by the burning fuel increase exponentially and if this goes no further then you are slowly destroying your plugs and rings. If preignition gets worse it can and will lead to detonation. Detonation is different, detonation is a more violent ignition of the fuel mixture. One example is preignition leading to Detonation. As i mentioned in preignition the fuel mixture ignites early due to heat. As that is going on imagine the spark plug is getting hotter and hotter. The job of a spark plug is to disipate heat into the head, too hot of a plug will begin to glow if preignition becomes a problem. Now you have fuel buring in the cylinder as a piston compresses it making it hotter. Soon enough the spark plug will get so hot it will ignite the unburnt fuel still in the cylinder (pre-ignition doesnt burn the entire mixture evenly). That flame front is far more of a sudden lighting of the entire mixture. The expanding gasses push so hard against the piston (that is too hot already) and the metal will reach its fatique point and it will either begin to melt small portions or it will entirely cave in. Decreasing the Ratio will keep this under control. That is only 1 example of hot Detonation occurs, there are several. Why Cant you just lower timing? Think of Timing as fine tuning the cylinder temps during a burn cycle. Compression ratio would be your course adjustment. IF you are trying to get every tiny bit of power you can from a motor, you first want your timing and plug heat range tuned out. Once you have both of those set in stone, you tune based on heat (EGT's). Every motor will be different. Widebands are good for getting you close and you can use them but if you were to compare heat marks on the spark plugs as you go, you will see the same pattern just not in numbers. Spark plug heat ranges are another way to tune heat but they also will affect your timing. as you get hotter on the plug, your timing will need to be retarded. I recently toyed with a car on a dyno that when increasing the heat range 1 set up, cuased the timing to be 6* to far advanced. I went from 41* total timing to 35* total. Further tuning will identigy if the heat range choice was better for the motor or stepping down will be warrented. Too rich of a fuel mixture can also make the heat range of a plug look too cool. Why Nitrous or a Supercharger or Turbo? Becuase you will never be able to get a supercharger or Turbo setup to operate with an intake charge as cool as Nitrogen gets. Nitrous Oxide does 2 things. The Oxygen when introduced into a Flame front increases the Flames heat which is what gives the compressed fuel/air mixture a more aggressive gas expansion during the burn cycle. The Nitrogen is used purely as a cooling medium. Oxygen on its own will melt the pistons/ring before you even get past the 60' mark. Nitrogen gives the mixture some controlability in terms of heat. A motor with a 150 shot is not considered a Nitrous motor. Thats why its called a cheater kit. Obviously the downside with Nitrous is the increase maintenance of bottle filling and system cleaning.

im not reading this as im not new to f/i or nitrous...
I NEVER said I was building a nitrous motor and I never said i was going to run a 150 shot. I stated it was going to be a 75shot on a stock motor.

Wait let me get this straight.......You ask a question......someone gives you a vwery comprehensive and thorough answer and your going to be some ignorant little shit faced kid and claim you already know the answer. Do the entire community a favor and get the fuck out before we make you leave. Again i take the time to post an answer that will benefit the other members as well and we are all rewarded with your ignorance.

Perhaps you should read more, you will learn a lot.

Take your 75 shot and go join a hyundai forum.

IF you were as knowledgable as you say, then you would already know there is only a 35hp difference between 9.-13.0 compression in a n/a car. Compression does not create nearly as much power by itself liek most people think. Thats been proven......go read more.

Originally posted by Star Turbo Talon
Wait let me get this straight.......You ask a question......someone gives you a vwery comprehensive and thorough answer and your going to be some ignorant little shit faced kid and claim you already know the answer. Do the entire community a favor and get the fuck out before we make you leave. Again i take the time to post an answer that will benefit the other members as well and we are all rewarded with your ignorance. Perhaps you should read more, you will learn a lot. Take your 75 shot and go join a hyundai forum.

I had already left this forum but you had to do some retarded elaborate crap. i asked a simple question...I grew up with drag racing, when I was 13 my father and i built a 1923 ford model t kit car, high compression, nitrous and propane injection. i asked why these people on this forum would build low compression engines if they're gonna run nitrous.
And i asked how much power it would produce in a low compression engine and i guessed about the same of a honda civic.

hmm 140ish - "35hp"= 115....stock civic around 115....WOWWW what do you know i was right!

Originally posted by amiturbo

Well you still came across like an ass with your reply. See ya!

Not a good way to ingratiate yourself to the community, acting like an impertinent little shit and pissing of the senior members...

Originally posted by amiturbo
hmm 140ish - "35hp"= 115....stock civic around 115....WOWWW what do you know i was right!

Actually, you are wrong. He stated that you would GAIN 35hp by increasing to 13:1 compression ratio vs. stock (9.6:1) compression. Stock compression = 140hp. 13:1 compression = 175hp. Lower than stock compression (usually 8.6:1 or 8.8:1) = 130-132hp.

Thanks for clearing that up SorryIWin. I've been staring at that post for the last few days going "I don't think he read that right."

Terry's initial response got me curious, so I spent a whole of two seconds on Google and found a ton of calculators will show you roughly how much changing compression ratios will change hp numbers at different base hp ratings.

If anyone else is curious, here is a pretty simple one and it links back to a ton of other calculators for other things.

http://www.wallaceracing.com/hp-cr-chg.php

**I don't have anything to do with wallaceracing and and don't know anything about their products/skills/reputation. I am not endorsing them in anyway. I am just sharing a resource I found.

You can see by just plugging in numbers that until you get to fairly high starting hp numbers, the difference compression makes is relatively marginal. Personally, I don't have any tuning experience, so I would rather go low compression in any build I were to start because it would give me a better chance of success, as Terry explained.

Without an experienced tuner, I don't personally think the difference in a relatively low HP build is worth the extra risk. When you're trying to push the limits with an all motor build or set some new record, I could absolutely see a high compression build being worthwhile. But for beginners, like myself, that are just looking to learn and make a fun street car, it makes more sense to go with a relatively safe build to get into something reliable that's still fun to drive. I'm sure that's the same mindset that lead others to go that route. That's just my opinion and I'm sure there are some guys running high compression that will disagree. I would be interested to see what they have to say, as I'm sure they could teach me something.

Despite the OP, I did find this thread interesting and Terry managed to clear up some of my personal confusion about tuning. Thanks to everyone who shared something.

First off an engine is an engine and they all react the same to any form of Forced induction. You are responsible for making sure the materials used in the build are up to par and that the tune is adequate.

As for the compression ratio question the answer is simple in the fact that N20 is another form of Forced Induction, meaning you are dealing with compression pressure more so then the actual ratio. Compression ratio is only useful when other factors accompany it. Compression pressure is what the engine actually sees. High compression pressure increases the tendency toward detonation, while low compression pressure reduces performance and economy there by allowing a forced induction system to make up the power loss.