AbeFM

iTrader: (3)

I was thinking exactly that when I wrote it, but assumed it would be sexist to mention the elephant in the room.

Er, where I said reduce flow till you're at 50 hp? Yeah. My point was high manifold pressure has very very little to do with power output. Small enough valves and all that pressure won't go anywhere.


talking to Bell and FM is the best advice so far, except all the people saying build a second motor.

Alta_Racer

iTrader: (4)

I wonder how many of the posters in this thread, that have given negatives on turbos and high compression, actually have experience to back up their negatives. The whole thread here seems to bring enjoyment in bashing the OP and not bringing wisdom to an area of unknown to majority of the group.

I for one will encourage the OP to research the positives. Look at cam profiles, there is a lot that can be archived by controlling cylinder pressures, with camshafts. To all remember that as you retard timing you will probably increase torque (seems to me the first post was asking for that) Water/meth injection can certainly be a player in a program such as this.

Yes this concept will see the need for major tuning, but since the OP is IRTB experienced already, I would bet he has done some of that.

This project is out of the box thinking, and I wish good luck to the OP. Everyone told me that 13:1 compression and a ton of nitrous on my bigblock chevy would lead to disaster, funny how none of the non believers could keep up to me.

Perhaps some positive responses other than drop the compression or build a new program?


Ron

mikef85

iTrader: (7)

^+1 Agree

akaryrye

iTrader: (5)

Ron, I am just going to assume you did not do that on regular fuel right? Anyway, we love to talk about this stuff, but I hate having to be the one doing all the research ... or rather, I should say the OP could have looked into it more.

AbeFM

iTrader: (3)

The OP doesn't seem to have the right idea about what to ask, how to ask it, a goal, or any proven experience tuning. You can buy IRTB's on chinabay for $300 and have a car slower than stock. He at least had an aftermarket EMU.

It's why I, perhaps without sugar, cream, and a cherry on top, have asked for a dynosheet on his car.

If he hasn't done that before, then it IS too big a task for him. If he asks 3 sensible questions, I'd be in full support.

Savington

iTrader: (31)

Can you explain this?

AbeFM

iTrader: (3)

I'd like to see something good there, too. I know it's true, certianly it helps spool - so much so I couldn't keep my system under 18 psi till I advanced the timing, now I can hold ~12.

I think the idea is that there are still burning elements, or at least less time for the charge to cool in the cylender, by the time you exhaust. Higher EGTs, more spooling energy.

But I'd like to hear it anyway. Learn me something.

hustler

iTrader: (6)

+1

I also want to know how combustion behind LPP increases torque. If you're talking about stove-piping a turbine, then have fun for the two track days it lasts. We build cars to last 100k miles, not 2-hours on a racetrack.

N3v

I like this guy. My general consensus from this thread is that its doable, but the majority of people think its a retarded idea because its not the way they did it.

Oh, and the guy who wanted a dyno sheet, I would love to dyno my setup, so if you can recommend me a good dyno place that knows megasquirt within 300 miles of nashville, TN, I would appreciate it. I've yet to find one.

Toddcod

iTrader: (8)

How far are you from DIYautotune?

N3v

i talked to them, they said there's no dyno time available, they said they have one 'mostly for R&D purposes.'

Savington

iTrader: (31)

No, we think it's a retarded idea because we all have more experience than you do with turbos and we understand the physics behind WHY it's a retarded idea. You should either go back to ClubRoadster and fellate the ITB crowd some more, or shut your yap and try to understand WHY it's a dumb idea.

Compressing an intake charge 11 times increases pressure. PV = NRT. Increase the pressure, maintain volume, and temperature skyrockets. In case you skipped Turbo 101, big temp = big knock = big boom. This is true whether you compress the air in the cylinder or in the compressor of a turbo.

The difference is that when you compress it in a turbo, you have a couple of good ways to remove heat from that charge. Intercoolers are 90-95% efficient, and water injection is 100%+ efficient. This means that no matter how hard you compress the air, whether it's 2:1 (14psi) or more, you have the ability to remove that temperature increase from the intake charge, down from the 250+ degrees to around 80 at the throttle body with a decent intercooler, or 40-50 with water injection.

At the end of the day, the cylinder will only tolerate so much pressure for a given volume at a given temperature. Because you are essentially unable to remove the heat that occurs during compression, turbo owners generally reduce compression and increase the pressure elsewhere (in the turbo). Yes, you can run 11:1 and a turbo at 10, 12, 13psi. It's doable. Will you make a lot of power? Mabye, with a huge turbo. Will it be an easy car to drive? No. The turbos that are kicking hard at 13psi produce WAY too much heat to be stuffed into an 11:1 motor, and the turbos that will keep the heat out at 13psi aren't kicking hard until 20+.

You also have to worry about EGTs. You're going to have to back the timing off so far with 11:1 pistons that you may not be able to even obtain 13psi before the EGTs are so high you're melting pistons.

You WANT your 11:1 motor to be able to handle boost because you don't want to build it again and admit your mistakes. We are not going to coddle you into thinking that you didn't make those mistakes. Boosting 11:1 motors is doable, but not intelligent.

N3v

Savington, you usually know your **** and I respect you, and I think you're right with everything else you said, but as far as this stuff ^^, that sounds like an awful lot of speculation. Also, all the other stuff you mentioned is true, yet only one side of the story. There are also upsides from running high CR. I could sit here and say that the engine will probably have better x characteristics under y circumstance than a regular engine, but that would be speculation as well. I need to do more research and see if anyone has ever actually done this before, and get some actual information, rather than opinions. I was hoping some people would be able to pipe up with info like that from this thread.

Even if I didn't have my block done, I think I'm still gonna run the 11:1 N/A for one season, then slap a turbo on and see what happens. if its impossible to tune and get running right, then I'll either sell the turbo or the engine. End thread. I'm sick of arguing about it. I'll just note that some MT guys think its stupid, and one party will be telling the other 'i told you so' if it turns out to be awesome, or is a pain and blows up.

hustler

iTrader: (6)

tell that to the engineers at toyota, nissan, subaru, mitsu, vw, and chevy to stop lowering static compression in their turbo cars. I'm pretty sure they'd like to save millions in development adjusting the NA motors to lower-compression "FI-motors."

Pretty much everyone on earth understands the relationship between static compression, spark, and charge density...its just the math involved in engineering that scares most end-users away.

Apparently you firmly believe that you're right, and everyone who's done this before, including engineers, is incorrect. Show us how ******* brilliant you are, we're waiting. Now please excuse me, I have to smoke the tires in 3rd gear of my 8.6:1 compression slug.

AbeFM

iTrader: (3)

I smoked your mom. In third.

sixshooter

iTrader: (12)

It only sounds like speculation to you because you don't have a ******* clue what you are doing!

Most of these bastards on here have read a ******* book or two on turbos and preparation of engines to accept them. Why don't you give it a try?

Why don't you go look it up, Hyper Jr.?
Instead of telling everyone who has studied this crap for years why they don't know what they know.

Yeah, you're the only smart one and the whole world is lying to you just to **** with you.

patsmx5

iTrader: (16)

You want to keep peak cylinder pressure around 14* ATDC. At some absolute temperature around 1250K, gasoline will spontaneously ignite in the presence of oxygen. BMEP is important.

These are facts. Here's some more

For maximum efficiency, you want to stay below 1250K and maintain peak cylinder pressure around 14* ATDC. This doesn't change NO MATTER WHAT!

You take in air that has some absolute temperature. Then you compress it. During compression the air is heated from the change in pressure (PV=nRT for ideal gases) as well as the turbo's adiabatic efficiency. Then you cool it using an intercooler (aftercooler), where the intercooler will reject a certain percentage of heat, bring the charge temp down closer to ambient.

The intake valve opens and the piston begins to descend, creating a vacuum. A delta P. This creates a void and the charge flows in. As the piston reaches BDC, the charge is still flowing in, but the piston reverses and begins to ascend. However the charge entering the cylinder has a mass and a velocity, therefore it has an inertia and will continue to fill the cylinder. The intake valve closes at 47* ABDC on your motor IIRC and now compression begins. Granted all the while the charge is being heated as the piston, cylinder, and combustion chamber are hotter than the charge.

So you compress it however much the actual compression ratio is after the valve event. It gets even hotter. Of course the fuel evaporates and this phase change removes some heat from the charge depending on the mass and heat of vaporization of the fuel. And of course heat is still being transfered from the surroundings to the charge until it's compressed to a point where it's hotter than the surroundings, then the heat transfer process reverses.

You send a spark to ignite the mixture to begin combustion in such a way as to:

Have peak cylinder pressure ~14* ATDC
Not light the mixture too soon as to cause knock or create peak pressure before 14*ATDC as this induces more negative torque than positive.
Not have the mixture light too late as to cause peak pressures to be after 14* ATDC.

YOUR PROBLEM: You put the compression to high and there's too much heat in the charge. So when you try to light it at the required advance to maintain peak pressures around 14* ATDC, you get knock, forcing you to retard to maintain safety at the expense of performance. Guess what? This is the point of diminishing returns with high compression. The point where you can not advance enough to maintain peak pressures at 14* ATDC. Now you retard timing and loose a lot of power.

Doing so is not ideal. Increases EGTs, reduces efficiency, causes more heat to be rejected into the cooling system, etc. And less HP.

So if any of this is new to you , consider "accepting the norm" and continuing your research on high comp, low boost engines.

Disclaimer: the above is a very broad, general description. It's in no way complete.

SKMetalworks

iTrader: (7)

that is what we call physics

hustler

iTrader: (6)

you guys are wrong. High compression turbocharged engines are faster with retard spark.

viperormiata

iTrader: (24)

This is insane. What is the point of asking for our opnions if you already made your mind up before posting!

Just blow your motor man.