hi guys need turbo expert opinions on this one Assuming u have say some t04b or something that can flow 55lbs (550hp) for example... how will the output change if u have a real small ar like .48 or .50 or so as far as the turbos potential?? i understand it will spool up quick but its never clearly explained to what extent the smaller ratio will kill the turbos top end, does that mean it'll turn into a 400hp turbo or what? Some original photos have not been recovered yet.

essentially, yes. the smaller a/r will limit exhaust flow through the turbine, especially at extremely high gas velocities in the upper band of the rev range. it will spool early, but exhaust back pressure will go through the roof and you will make less top-end power. this is where you have to compromise, do you want a solid band of power through the midrange with a bit of top-end compromised, or do you want a big surging power hit that comes on late in the rev band but has huge top-end potential?

Quote: Originally Posted by StockyMcStock essentially, yes. the smaller a/r will limit exhaust flow through the turbine, especially at extremely high gas velocities in the upper band of the rev range. it will spool early, but exhaust back pressure will go through the roof and you will make less top-end power. this is where you have to compromise, do you want a solid band of power through the midrange with a bit of top-end compromised, or do you want a big surging power hit that comes on late in the rev band but has huge top-end potential? i prefer option a would rather a killer midrange and decent top end rather than just an all top end setup anyday, i cant stand turbo lag.. to me its a turbos biggest downfall but if u can set it up like i want to with the small housings and still support the power u require then u should in theory have the best of both worlds Some original photos have not been recovered yet.

Get a GT3040 with the 0.86 rear. It'll spool up similar to the stock t03 but will still flow 65lbs

serious? does that mean it'll be putting through the same amount of air in the end? cause how quick it spools depends on how much air it'll take to spool. i agree totally with what stocky said, smaller a/r = less potential power out of more boost

Juzi, not really sure what you're asking. But yea, this turbo can flow 65lbs of air max and it is rated at 550hp. The main reason it spins up so quick is the ball bearing centre and I'm tipping wheel designs have improved substatially since 1986. Here are the specs of the GT3040 i bought from MTQ Engine Systems (Garrett's australian distributers)...... Part no. SB8006A CHRA 700177-0014 Compressor: 0.70 A/R 64 trim GT40 wheel Wheel diam. 2.41/3.22" 550hp, 65lbs flow Turbine: 0.82 A/R 84 trim 2.16/2.36" wheel

i was really talking about running a pair of these Forget my plan for now, whatabout you vlt guys.. surely u guys would benefit from 2 smaller turbos say 2 hi flowed t3s with small turbine housings running off the side of your rb30 than say a t66 or something? Assuming both the t66 can flow about 650hp or so, and the two t3s can make 330hp each, they both should in theory make the same power but the twins should do it with better power delivery, yes? Some original photos have not been recovered yet.

no hahah na i dunno im just being a smart ass.. i see wat ur gettin at tho..

geoff, if the twins are sized to directly compare to the t66, then response and delivery will be verry similar. i'd lean to the t66 being a better thing, cause 2x .64 AR isnt exactly small for a 3L. there are lots of guys i nthe states with 5L running twin t3 with .64 ar exh and they find full boost around 2500-3000 i believe. i have a feeling that on most rb30's (not heavily worked) they wouldnt spool up till rediculously late

Quote: Originally Posted by MADDNEZ geoff, if the twins are sized to directly compare to the t66, then response and delivery will be verry similar. i'd lean to the t66 being a better thing, cause 2x .64 AR isnt exactly small for a 3L. there are lots of guys i nthe states with 5L running twin t3 with .64 ar exh and they find full boost around 2500-3000 i believe. i have a feeling that on most rb30's (not heavily worked) they wouldnt spool up till rediculously late nice danny, im liking full boost @ 2500 that means she'd be spooling in the late 1000's ud imagine liking it Some original photos have not been recovered yet.

if you're interested, when you get the motor running and if you have lag problems, i could possibly do you up a blower kit similar to what i have. all you would need is a few new pipes made up (one from turbo to blower inlet, and one from blower outlet to the intercooler) and i'm tipping you pretty well wouldn't have any noticeable lag. the car wouldn't be doughy off boost at all either, because there would be no such thing as "off boost". this is what i'm doing eventually with mine, just gathering parts at the moment. you can run massive exhaust housings with very little lag, best of both worlds. only problem is, nobody's ever done it before so i'm pioneering a bit Some original photos have not been recovered yet.

yeh, the only prob i can think of stocky is if the supercharger will end up limiting the airflow at high revs, and also the pressure on the supercharger at low revs cause of the backpressure the turbo would have. You would have to run sum high boost from the supercharger to not limit high end but then you might have belt problems from teh pressure built up between turbo and blower, know wot i mean? or maybe not, lol

http://www.honeywell.com/sites/ts/t...ts_VNTworks.htm (http://www.honeywell.com/sites/ts/tt/turbofactsbenifits_VNTworks.htm) check out this link, sounds like a good thing to reduce lag

the theory behind twin turbo's spooling faster is to do with tha smaller mass of the wheels and shaft. they are smaller and lighter,so a given amount of exhaust gas flow will spin the 2 smaller turbo's capable of x lbs of airflow faster than it will spin 1 large turbo that is capable of the same lb of airflow hope that makes sense!

the blower can not really limit airflow as such, it's an air compressor not an air "mover". as inlet pressure on the blower increases, so does its adiabatic efficiency. this means you get a greater total boost increase across the blower as inlet pressures get above atmospheric. so with the blower alone, you might get 4psi. with a turbo pushing 6 psi into it, you might have 12 psi overall boost. compressed air filling the vanes is much more efficient than the vanes struggling to gulp a portion of air which is in vacuum as it usually is on a standalone setup. so long as your drive isn't slipping on the blower, there's no real reason it wouldn't continue to produce very high boost levels, i'm sure there would be a point at which the bearings/vanes would start to become compromised though, and that's what i'm hoping to find. exhaust back pressure increases with exhaust flow, and boost produced from the turbocharger. at low revs, and low load, there is very little back pressure, similar to an atmo engine.

Quote: Originally Posted by StockyMcStock exhaust back pressure increases with exhaust flow, Hmmmmm, I went from a 1.25" runner on my exhaust manifold to a 1" pipe with perfect 6-1 collector, With the same turbo (TO4 P trim front .6, and .84 V trim rear), it used to spool at 3000rpm, and boost by 4500rpm. Now it spools at 1500rpm, and is on full boost by 2500rpm. Top end is better than ever as well. I'll be trying to squeeze a 3.5" stainless system under mine, with one of those magic 4" cats, should reduce backpressure considerably.

So did the inner diameter of the pipe change? if both pipes had an inner diameter larger than or equal to the exhaust outlets in the head then that wouldn't have mattered. the better flow you noticed was almost certainly due to the better design of the manifold and better angle of attack of the exhaust gases on the turbine. that's where custom manifolds come into their own, it's all about directional flow at the turbine inlet and keeping all 6 cylinders separate as long as possible for laminar flow. the standard VLT exhaust manifold is particularly bad, which is why everyone loves custom manifolds. huge gains are there to be had!

Yes inside diameter of 1", smaller than the exhaust valves.. The new manifold uses a long runner style which works very well at getting the turbo to spool quickly.. It's all about getting the exhaust pulses intact and undisturbed to the turbo wheel. Eg: If you push a pinwheel with your hand, it will spin but not fast or hard, but if you flick it hard then it will keep spinning for longer.. Same with exhaust gas pulses... My collector actually mounts inside the turbo's housing and blows full force on to the turbo wheel, making sure all gas goes to making it spin. That also why the wastegate is mounted off the housing, no point in letting them go till thay have done their job!. Some original photos have not been recovered yet.

Quote: Originally Posted by StockyMcStock the blower can not really limit airflow as such, it's an air compressor not an air "mover".. but the blower will always be spinning a certain amount compared to the engine revs, the turbo spins slower compared at low revs and spins a lot faster compared to engine revs at high speeds, what i meant by the blower limiting at high revs is that the turbo will wanna spin faster at high revs but if the blower isnt moving enough air at high revs the turbo wont be able to spool up as much. and i know you said a blower isnt an air mover but to me it is, and to me it'll pretty much always move the same amount of air turbo or no turbo.

ah, not true at all! a blower takes a fixed amount of air, and compresses it, then discharges it at the outlet. so if you force more air into it with a turbocharger or some other compressor, it will take MORE air particles (at a greater pressure) and compress them even more, before discharging them at the outlet. the delta across the blower gets marginally better, but that's not really the issue. the turbo will only have to produce say 10 psi for my intended 15 at the plenum, the other 5 is gained at the blower. exhaust back pressure is substantially lower than inlet pressure, which is the main thing the setup hopes to achieve. (along with good spool times and off-turbo response of course) anyway if you can't visualise it i understand, it's pretty complex and it took me ages just to figure out how a dodgy little roots blower works after looking at a whole heap of boundary-layer sims on a fluid dynamics machine at uni in the mech labs. i guess i'm keen to find out just how well it will work, which is why i'm going to do it. nobody else has in an RB30 before to my knowledge so it's all a matter of time till it's up and running. the results will be interesting to say the least i should think. morgo: seen some pics of that mani before, looks very tight. bet you get heaps of people going "oh why are the runners so long i bet it sucks ass!" and you just smile and laugh Some original photos have not been recovered yet.