White_Shadows

Oh and before it gets said I would like to avoid sequental turbo's if possible, far more work then I would like at this point in time. Parallel twins or triplets is fine though.

TrochoidMagic

ur idea sounds terrific. and a small turbo is actually an advantage in some motorsports...depending on track conditions.

turbo's having big on/off boost behaviors are usually harder to control i believe...

so supercharger route is out huh? they are expensive too...


GL on ur project, and post on ur benefits if u achieve ur goal.
and not ALL are after HP =) (or at least even huge HPs)

White_Shadows

Yeah it could just be a stab in the dark, but we shall see.

Yes boost can be rough to controll if lag is bad enough. Hennessy had some issues I believe it was last year when they were trying for top speed numbers because boost would kick in turn the car sideways and kill the transmission, but at like 200mph lol. Just nutty.
http://www.youtube.com/watch?v=g0AJLWH_p_g
http://www.youtube.com/watch?v=yqMzhvxTEyA




More Eye candy http://www.youtube.com/watch?v=rOWhtVuccMI

chris__n

i'm quite interested in this project as well. have you looked into the vw 1.8t turbos? they're always swapping those out for bigger ones and the stock ones are TINY. i'm sure you can get them for cheap.

not sure if they're ball or journal bearing though.

edit> also, were you planning on running an intercooler of sorts? with a small enough turbo at 6psi i feel you might be able to get away with a really small IC.

White_Shadows

Yeah I'll probably just look into the DSM stock intercooler. Something I can shove in the wheelwell.

I'll look at the vw turbo, I like the one Mazdamaniac put up.

chickenwafer

iTrader: (9)

I like you're idea. Sounds interesting. Keep us updated on how it works. If you go through with it post build pics!

Spoolin8

iTrader: (2)

there is one problem with this. Since the turbo will be so small you will almost always be in boost. This means at idle you might only be at 1 psi but this constant boost could severely wear down your engine so make sure you get something small but not so small that your constantly over spooling.

mysql101

you know what they say: A tiny turbo = making up for a large *****.

chickenwafer

iTrader: (9)

That doesn't make sense....he will still have a wastegate. If the w/g is open he won't be generating positive manifold pressure. He won't be in boost at idle!

Yeah he may see his peak boost by 2,000 rpm or even sooner, which is really, really, early, but if it's only 3-6psi and with such a small compressor it's not that much extra airflow.

Spoolin8

iTrader: (2)

Doesnt make any sense lol you have a boosted vehicle so you should know the wastegate wont open if he has it set for 4-5 psi and its only at 1psi at idle... I have personally helped build and been in a Lexus GS300 that had a turbo that was too small on it and it would be at 1-2psi at idle.

chickenwafer

iTrader: (9)

The car idles at 5 grams a second of air...I don't see how it can produce boost at idle. There simply isn't enough airflow and exhaust pressure to spin the compressor fast enough

05rex8

iTrader: (7)

Spoolin8

iTrader: (2)

If the turbo was too small it would create back pressure between the turbine and exhaust ports. Even though the car at idle is barely pushing air this could create the car to be in boost. Hey i could be wrong and rotary cars are also different in that aspect but it can happen on piston cars and i was simply trying to notify OP to be careful with choosing a turbo that doesnt flow enough. Was not trying to offend anyone but merely tossing in some input that i wanted to make aware of. There is no arguing the fact that if you get a turbo that is too small and restrictive it will cause alot of backpressure/heat which will quickly destroy your engine.

chickenwafer

iTrader: (9)

There is no way you can compress 5-grams a second of air to positive manifold pressure with a turbocharger....

I agree with you on the heat aspect, as in too much back pressure. But if he installs a free flowing exhaust with no cat after the turbo he should be OK

Spoolin8

iTrader: (2)

I agree with you. i Didnt realize the renesis only flowed 5grams at idle and thats why i made the statement of its possible to spool a turbo at idle because some cars flow alot even at idle.

A little off topic but has anyone looked into a anti-lag setup for the rx8? What im referring to is the "2-step" or "brake boosting" so that you launch with boost and once driving you remain in boost.

White_Shadows

Are you refering to sequential? That is how the fd is set up and probably the biggest reason it failed (cost).

As for back pressure, i'll be welding all my own piping so I don't see an issue, but that is one of the things I will be testing is the affects of back pressure. Back pressure is not always a bad thing when looking at efficiency. If it becomes an issue i'll double pipe the exhaust or something deal with that bridge when I get to it. Also the 5gsi of pressure is that if all three exhaust ports are combined or is that per port?

Also about the 1-2 psi at idle. I don't see the issue even if that comes up? Adjust the idle down and/or close off the throttle a bit. Air is air . I won't be able to do this project without adjusting fuel and air mixtures.
I am certain I will become very comfortable with rebuilding this motor many many times when I get around to this (don't expect it tomorrow, doing the research now will be some time before I get to welding away) You have to assume I will be pushing the starving limits of the motor rather often.

Keep the turbo options flowing.

Spoolin8

iTrader: (2)

I dont mean sequential. i was referring to anti-lag in boosted cars that have the engine management setup to send fuel through the engine without ignition. This unburnt fuel hits the extremely hot exhaust manifold and combusts which cause the turbo to spool and allow you to launch the car in boost.

In the video below the evo driver floors it while holding the clutch in and it begins building boosts and when the clutch is dropped the car launches in boost and even when he shifts his foot remains on full gas the entire time but his management system is setup so when the clutch is engaged timing is pulled and spark is stopped which allows him to remain in boost while shifting.

http://www.youtube.com/watch?v=mXfUbFR-x7g

pieter3d

iTrader: (7)

Why don't you have a seat right over here.

White_Shadows

umm... Sounds like a horrible waste of fuel...Why would you send fuel through? I saw your manifold is hot blah blah, but you do realize to make power it requires compression right? Just lighting atomized fuel in a tube would have very very very low pressure. If anything wouldn't it create a suction effect as the air is burnt? (refering to the egg in a bottle trick) Are you sure its not just keeping the revs above 4,000 rpm?

Yeah did research, thought you sounded funny sir. Here read this....
http://www.rallycars.com/Cars/bangbang.html
This would not work with a rotary sorry. We do not have valves.

Shijin-Kun

iTrader: (1)

interesting subscribed.

White_Shadows

Turbokits.com has them for $900-$1000

Curiosity question. Now what makes a turbo limited to horsepower? Is that rating the amount of air in and out of the engine must be "said horsepower"?
If that is so then a set of 250hp turbo's on different exhaust ports should be able to support 500hp?

Next question. If you achieve more than "said horsepower" will the wastegate save the turbo, or will the turbo just be compromised. Or better yet will it just kill boost at lower rpm's then redline?

Loki

iTrader: (1)

^

Yep, it's down to airflow. A given turbo can only pass so much air per unit time, and its cfm that makes you power, not psi. You can put a turbo on each exhaust port, if the plumbing makes sense... this is what twin turbo is. On the TT Supra, for example, there are 2 fairly small turbos good for about 200hp each, plumbed into 3 cylinders each (1.5L of displacement).

You can't actually achieve more than the rated horsepower, it's not possible. You can overboost it, but usually that will take out the engine before the turbo. If you try (like set your boost too high, outside the turbo's efficiency envelope), after a certain point the turbo will be compressing against itself (the additional power needed to produce more momentum on the turbine, to produce more boost and give the engine more air, is greater than the power produced by the increase in boost). Or, in some setups, like Legacy GT, the turbo can't keep up with the engine's demands (compressor side is too small), so at high rpm it can't maintain max boost..

If neither of those conditions occurs, the turbo can be destroyed internally by the torque produced on the connecting shaft, but normally they try to build turbos such that the shaft is stronger than the turbos thermodymanical limits. I had a turbo blow up on me, but it appeared to be the result of a bad rebuild, as it shook itself apart within regular operating ranges.

White_Shadows

I thought the supra was sequential? Wouldn't that mean only 3 of the cylinders would be under boost while the other three are not? Also I'd like to avoid having to figure out seperate throttle bodies. (deal with that if I run into pressure issues)
{Looked this over. Yes the turbo's work off of seperate cylinders, but are plumbed back into the motor through one manifold.}

I dissagree with PSI not creating power as it all boils down to what amount of air and fuel you have compressed in the combustion chamber. Amount of air per minute is just how much air the wheel is pushing.

If you are correct though I should be able to use a set of gt25's one on the rear exhaust port and one on the front and plumb everything together and by the middle joined port for scaveging ish effect. I donno if I have that kind of room which is the main reason wanting small itty bitty turbos.

Also wanting to see what it would take to make an external oiling system for the turbos. Much like how the jackson racing rotrex superchargers are doing it.

shaunv74

i think you're asking the wrong questions in terms of turbo size. You should be asking which turbo is the most EFFICIENT for the RX8. A small turbo doesn't necessarily mean it's going to be efficient. You should figure out which will create the least amount of loss vs. theoretical maximum at cruise and at full load. That will lead you to which turbo will give you the best gas mileage.

bhop

Well, seems like you are on the right track to some extent. Judging by the limited space we are granted, you could probably get away with those turbo sizes but I would not know how effecient those are for the RX8. I have not thought of a build like this but I will def follow closely if your plan actually gets put to use.

Good Luck