compound boost

[cobaltssoverbooster]

now im still passing this around as an idea for a soltice im thinking about putting together as a all around multi sport(track, drag, drift) car and when i hear people talking about the compound setup i am hearing two ideas on controlling boost....someone who knows please help me out...

1st) no matter what the large turbo boosts the final boost is regulated by a bov after the high pressure turbo......so and to calculate total boost im being told 8 psi from the low psi turbo + 20 psi from the high psi is still 20 psi because its after the high psi turbo....

2nd) in order to controll boost i would need a bov for after both compressors and to get total boost calulation of 8psi low psi turbo + 20 psi high psi turbo= 28psi total into engine

which one of these is most correct...if not maybe something from each to make it correct??

i saw marks video for the strtfighter compounds and i will run dual wg like he has setup if i do this but i obviously need to know more first....and last thing how do i go about matching the turbos to eachother....(was thinking gt2871r + gtx42r or gtx45r)

[silverbullet08]

I have always liked this idea. never messed with it but it seems interesting. The only thing that confused me was how do you get all the air out of the motor from the big turbo if your sending the exhaust to the small turbo? I guess you would need a massive wastegate to use for flow after the bigger turbo was spooled.. You could also run that wastegate when it opens into the larger turbo exhaust housing. Well I guess that is the only way to make it work. You would only need two wastegates and one blow off valve in that case.

[shabby]

You can't add boost like that, a compound setup multiplies pressure, it gets a bit complicated especially if you want the stock ecm to control boost with its 3bar sensors. You'll be well into the 40psi+ range with a compound setup.

[Leafy]

Which compound do you want to do? Small turbo and big turbo in parallel, ends up making the boost the big turbo would and not using the small one, and having the lag of the small turbo, aka none. Or Small turbo feeds into the inlet of the big turbo and you make super high boost numbers and retarded power will small lag.

With the first setup you would run the stock boost control setup and have it go to both turbos and also put a check valve on the outlet of the small turbo, both turbos put in series in the exhaust, and the waste gate from the small one feeds back in front of the big turbo.

With the 2nd you run a standard boost controller to the first turbo, and use the computer control on the big one, remember the big one multiples boost. If your boost ratio is 2:1 and feed it 15 psi it will give you 30 psi at the output. The boost controller on the first one would be set to the peak efficiency of the small turbo. They will be in the exhaust the same as the other setup.

[cobaltssoverbooster]

i think now since ive been explained too,being that the compound is boost multipied i will not run that setup. even with a girdled block and arp studs i dont want to be running the 40+psi which is where the efficiency is lying for compounds i can however run a setup that is sequential. twins are two same size but sequential i can have a small one bolted just like a single however the exhaust out of that would go into the large and the compressor side would meet up with the small turbo just before the intercooler. i will run 1 wg around the smaller turbo so when the big one kicks in i can say at oh for giggles 22psi it will divert exhaust around and into the largethis way there is max flow to the large turbo via two paths and it happens of course wehn the large is already spooled up. and the second wg goes around the large turbo to disengage the large as a single or if both wg open then dissengage both turbos. this setup will spool sooner off the smaller turbo which should change the spool of the larger turbo to a far lower rpm and once she gets going then i can demand full flow potential from the larger turbo. for huge midrange to up top performance.....

only problem i can see (and i may be wrong because i havent touched this setup either) is once the larger turbo is going and i route exhaust around the smaller one using wg 1.....what is preventing large ammounts of air from being backflowed out the front of the smaller turbo...??
ideas and or any known devices to prevent this if i am correct......

max psi would be 30 and for the drag setup only......ok well depending on how it runs maybe 35 max but probably not trying to keep it reliable-ish

[Leafy]

only problem i can see (and i may be wrong because i havent touched this setup either) is once the larger turbo is going and i route exhaust around the smaller one using wg 1.....what is preventing large ammounts of air from being backflowed out the front of the smaller turbo...??

Thats what the check valve in the 1st setup that I mentioned does.

[cobaltssoverbooster]

ah ha making sense now.....do they make one thats in the 2-3" range that flows a sh** ton of air when in open mode?

could get crazy and steal a motorcycle tb plate and ecu controll it to shut at a 22psi mark when switched into the drag tune.

would i need one for the larger turbo as well or the oposite condition of little one flowing out the larger one?

this is what i have in mind origionally..



but apparently max efficiency range is in the 40+ psi range and i dont understand calulating the boost with the multiplier...8( explain more please?
if i did that id have to try and get my compression down even more than the 9:1 i have planned prolly 8.5 or 8:1 and then im pretty sure i cut out some initial torque not to mention i could run into crank to skirt clearance issues and could even end up with a partial oil control ring land witch i would preffer to have a full ring land if im pushing boost like im thinking.

[Leafy]

Yeah I guess you would. Have to see if they make one specific for this, else they have them at mcmaster/msc/grainger.

[cobaltssoverbooster]

i just thought of this after studying this picture.......if you open said wg 1 at say 22psi after after the big one starts spooling then technically you have eliminated the velocity to that small turbos turbine making it inactive but you still have full exhaust flow to big turbo so technically this would be blowing through a dead smaller turbo which would free wheel in the airflow not adding to the pressure .....yess?

[Leafy]

once the big turbo hit 22 psi, yes.

[cobaltssoverbooster]

ok so then this origional plan would work... 8) ---> 8D

just for poops and giggles how do i do the compound boost ratio math?

[Leafy]

The compound math. You see on your compressor map how the axis on the Y axis is actually in a ratio? Typically 2.0:1 refers to 14.7 pounds of boost. Well not in a compound, it actually means Boost = pressure in X ratio. So if you hit peak efficiency at a 2.0:1 ratio on both turbos (1st turbo wont be in peak efficiency once the big turbo spools because it will be flowing sooooo much air to try and keep up) and set the small turbo to output 15psi and set the you would set the big turbo to output 30 psi to keep it on its peak efficiency. You've got to do a bunch of research on this. I've done a bit and then have a lot of theory myself. Such as, is it a good idea to run a really big compressor on the small turbo to try and keep up with the air you would flow on the big turbo?

[cobaltssoverbooster]

tractor pullers are tellin me general sizing is twice the size of the small one is what the big one should be.

so since i can open a wastegate and make the small one not boost when the big ones kickin it i will most likely end up with gtx3071r with a gtx4508r to kick in after if not that a gtx4202r

i dont want to mess with the efr series when i know the gt series work great....and arent on backorder...

[Leafy]

Why get a gt series when then BW journal bearing turbos are just as good?

[cobaltssoverbooster]

because i dont want a journal turbo and the gtx is upgraded a little bit over the gt base turbo little better wheels to help spool some

[laser_racer]

Why not use the stock turbo to spool the bigger one? In this link this guy used the big 16g which is just a small step above our 14b turbo in dsm land. http://www.dsmtuners.com/forums/cust...bo-set-up.html

[cobaltssoverbooster]

stock has a journal and i dont want that. i dont thinks it will last very long with a huge turbo like a 45r spining it at mach omg. id feel safer with bb center.

[laser_racer]

Can't blame you just thought I would give you idea.

[cobaltssoverbooster]

no its a great idea just the journal is stopping me.....the s256et turbo would be a nice starter as well and i believe there is a smaller s series that is smaller than the s256et
but i cant find it?

[laser_racer]

They did have a 252 I thought.