89fbrestor

guys I'm really not trying to sound like an idiot or ask an very stupid question but honestly just trying to understand this stuff thoroughly as I'm to the point of purchasing the higher dollar items for my build and just want to be smart(lol ya me and pertaining to smart shouldn't be in the same sentence lol ) about the turbo stuff.

why is compression so important with forced induction?
couldn't you build it with higher compression and just lower the amount of boost?
would it get the same results?

Off the top of my head i would think because its going to break stuff once it starts forcing the air in. I'm typing this shaking my head cuz i feel like this is as dumb of a question as it gets lol but anyone who's talked to me knows i got into wrenching a little late in life and just trying to catch up I've been a reading fool these last few months but finding the answers to the obvious questions is harder then you'd think lol

i will be starting my build thread soon so hope I'm not being a bother with these quick question threads.

thank guys and happy holidays... i love this time of year. new baby(well kinda new, 1yr old) and a loving wife... life is good this year
Brian

DIGGLER

iTrader: (1)

you could add compression and lower boost, but it wouldnt make as much power.

89fbrestor

thanks diggler. "not as much power" are we talking a lot less? my set up should get me a solid 450hp with out the nitrous and turbo. 100hp shot of nitrous plus what ever the turbo adds on. i like to get to the 600hp range.

Guest

compression = force


(something like that....i.e like lifting heads....-force-)

We'reNotWorthy

IT would be a good bit less. Forced induction is not just slapping on a turbo adding some fuel and saying go. There is alot more that goes into it to keep the motor healthy for a long time. The enemy of a boosted motor is heat. This why a a good intercooler is a must for big f/i numbers. From my understanding a higher compression motor will cause way more heat inside the cylinder than a low compression which is one of the main reasons you see low compression with big boost numbers. This heat will cause knock and that will inturn cause you to pull timing which in turn will rob hp.......If this is wrong feel free to correct me this just what I have understood from what i am learning as I know own a turbo car.

89fbrestor

"Forced induction is not just slapping on a turbo adding some fuel and saying go."

ya i'm not by any means trying to do this i was just curious the reason behind it and if it was a necessity or not. thanks for chiming in i appreciate the input.

We'reNotWorthy

It's not necessary but if you plan on putting a turbo on it anyways why not build it to maximize the turbo. I would highly recommended talking to a professional engine build about what you want out your build. They will be able to help you tremendously and point you towards parts. It sounds like you want a ton of power but can't decide which way to achieve it. It sounds like you are building a na motor that you then want to throw nitrous and boost at. This is really not the best idea. Nitrous in a turbo situation isn't alot and normally only off the line to spool the turbo. I think the combo of a na built motor with nitrous and a turbo thrown in is a recipe for disaster. A 100 shot on top of a na motor would be fine and I have friends who run that setup with great results. I also know people who run low boost on na motor with good success but I just don't see both nitrous and boost lasting very long together on a motor not built for it. Wasn't trying to come off as a dick and I'm sorry if I did in my first post I was just trying to make sure you knew the complexity of boosting a motor.

89fbrestor

worthy no i didn't take it that way, your fine. i have most my parts already.about the only thing i have not bought yet is the pistons and the turbo. I'm still undecided on if i want to go single with a gt45 or twin with gt35's. the green car on the left is the camaro i just finished over the summer. that one is about 550hp with the nitrous and i love it lol it was the first solo build i did. so i just thought a little nitrous on top of the turbo would be fun as well. my parts list as of now is

standard bore 350 4 bolt main,2pc rear seal.
summit steel crank
eagle forged I beam rods
camel hump 2.02/1.65 port matched polished and bowl blended heads
vitor jr single plane intake.
holly 850 cfm carb

still need to get my trans(4l80e)
and i was thinking meth would be a safe thing to have as well.

i have a ways to go before i start assembling and i can change things up as i get more and more advice. anyway just thought this was an interesting question and asked

thanks
brian

89fbrestor

oh ya, my goal is a solid 600hp to wheels. which from what I've read shouldn't be that hard.... I'm a newbie .. be nice lolol

sailtexas186548

iTrader: (2)

Ok I'm gonna give this a shot, if I'm wrong someone who KNOWS, can correct me please do, but I think I've got a decent idea how this works

high compression, low boost is not as effective as low comp high boost becasue it's all about volume. This is a pretty basic explanation, but the way I understand it is you want as much oxygen in the combustion chamber at top dead center as possible, so you can add maximum fuel (correct ratio), resulting in max power. The thing is there is also a maximum pressure for a given head, block, or fuel/air mix can take before your reach detonation (all depends on dynamic compression, head/piston shape, hot spots, fuel, IAT's, etc..) but the point is that there is a max pressure for your 93oct and air mix in a given combustion chamber before you have problems. Now remember it's about volume.

for a high comp low boost motor at TDC there is this much [ ] space between the piston top and head, so at the max pre-ignition pressure there is [ ] compressed air and its at its max fuel capactiy for a given air/fuel ratio, so you have this [::]

now for a low compression high boost motor, you have this much space [ ] and with fuel you have [:::::]

so when you compare [::] to [:::::] and consider that they are at the same pressure, which one is gonna give you a bigger bang = more power?

You can cram more air/fuel into a low compression motor with boost that a high comp motor, it the bottom line AFAIK.

89fbrestor

good explanation .. i think i understood it lol thanks. so needless to say i need to make sure i buy dished pistons for my build

Street Lethal

iTrader: (16)

Identify the free radical that causes detonation in gasoline. Contemplate how alternative fuels allow you to run more compression and more timing w/out having to worry about detonation. Then you will understand why less compression will yield better results and more power with pump gas fuel...

We'reNotWorthy

This is a great explanation its a pure volume thing.

89fbrestor

yup thanks easy to understand

Street Lethal

iTrader: (16)

Is it really a pure volume thing? If that were the case, then a naturally aspirated engine will make more power with less static compression too, no? The reason why lowering your compression will yield more power in a pump gas turbo application has to do with ECR, Effective Compression Ratio, and the only reason for that is because we are forced to pull timing and boost pressure to avoid detonation at higher compression levels with gasoline. It isn't a volume thing because you can cram just as much air in an engine with 11:1 as you can with an engine having 9:1 compression, however, you run into limitations when running higher static compression when using pump gas though, which is when ECR comes into play. Run E85 in it's place, then test your theory again...

89fbrestor

huh lol i just got that deer in the head light look on my face now lol

Street Lethal

iTrader: (16)

Detonation from gasoline (caused by the hydrogen radical) hinders our ability to run high boost pressure with higher static compression levels, so we are forced to pull timing and boost pressure using regular pump gas gasoline. When you eliminate the detonation factor, you will always make more power with higher static compression levels. But because the majority runs pump gas, you lose the benefit of running higher static compression levels because of the timing and boost pressure limitation...

89fbrestor

makes since. if i'm grasping this correctly (forgive me if i'm not .. i'm trying) kinda goes along with meth injection as far as lowering temps to be able to adjust timing more.... is that an accurate correlation?

Street Lethal

iTrader: (16)

Bingo, which is why most guys will run 10:1 compression w/alky injection, they try to utilize the best of both worlds. It is detonation because of the fuel we're using that causes the problem, it holds most people back, as even cast parts will laugh at 30-psi so long as detonation is eliminated from the equation. Those who run E85 know what I mean...

89fbrestor

gotcha. well i have camel hump heads i'm going to be using and with dished pistons i'm going to be around 9:4 i think for compression but i plan on using meth as well so i should be ok right ? i hope thats a big yes cuz that would really ease my fears lolol

Street Lethal

iTrader: (16)

You will be fine running methanol. Here is Don's high compression 224 cubed V6 running methanol and nitrous, the car has been 8.76 @ 158-mph, with only 1.83"/1.50" intake and exhaust valves, making your camel hump heads even more desirable...

http://www.youtube.com/watch?v=KZ4phJOP13Q

http://www.youtube.com/watch?v=oHD5zRjnep8

89fbrestor

life is good and i'm happy lol

Orr89RocZ

iTrader: (20)

yep, detonation and pre-ignition stuff is a problem. Your compression ratio and boost level are dependent on the fuel you use and the intake temps you have among other things like engine temps/piston temps/valve temps and ofcourse ignition advance. You got to get heat out of the chamber if you want to run more and more boost with a set fuel. If you eliminate detonation/pre-ignition, you should beable to run whatever compression you want at whatever boost you want. Only catch is heat. At some point, its heat that melts the motor, regardless of what fuel you run and regardless of how much timing you pull.
Nitrous motors are much more sensitive to this. Turbo cars are much more forgiving. Its all about pressure rise in the chamber. If you burn the compressed charge too fast too soon, too much heat is made. Then again, if you burn too much fuel/air at one time regardless of how soon you do it or how late you do it, still have too much heat produced. Compression makes more compressed air/fuel charge so you generate more heat when you combust it. In addition to that, your squish zone caused by the flat portion of the piston and the flat portion of the head deck surface induces tumble/swirl to the mixture allowing it to burn faster and more effectively. This can be bad since faster burn means more pressure rise rate, and that can lead to too much heat You can design pistons and head chambers to minimize those effects and get more boost and or compression out of a setup on a set fuel you use.

So you gotta find a balance.

89fbrestor

good info as usually orr89 thanks for chiming in. the last few months iv tried to be wise about the parts i'm aquiring for this build and it seems like every time i learn something new i have to change my set up around and get some different parts lol. a few thousand $ later .... I'm getting close to start putting all this together lol I'm holding off on the turbo till last but right now i pretty much just need to get the car cleaned up as i have it stripped down. clean it up and start putting everything back together and build the motor. thanks guys third gen as been a tremendous help for someone like me who started a little late in life on wrenching.