1bdbrd

iTrader: (12)

now let me say that im still learning as much as i can about the turbo world. i dont know it all nor do i claim to but something i have noticed is this. theres LOTS of turbo ls1s running on this site but most of them are running huge turbos and big cubic inch engines. why? most dont even run their turbo into its efficiency range. not to attack a single person but ive seen several running a gt42 at less than 20-30 psi. is head lift still a concern as to keep you from running a smaller turbo at a higher boost level? ive seen t76 turbos running 15 psi or less. to me thats an inefficeint setup that would create some good numbers but at a cost of a broader powerband.

then you have people running HUGE engines and solid roller cams with ultra expensive heads and intake combos. why that either? why not let the compressed air do its job? most here look for a decent street strip car. as a strip car with huge slicks and a stalled th350/400 or a powerglide i could see something like a twin turbo 408 or 427 or even bigger. but as a street car? i dont think again thats a very effective combination.

again this is something ive seen and would like maybe a little clearification on this because im very curious (mayber theres something im missing here ). also let me say that i know boost pressure is just that. but it does come in to play somewhat.

Race-Prep

Well I am nearly finished with a setup that will certainly be wringing the most from the turbo. My gt76 will be pushed as far as it will go on my 382 foundation, I am trying for 1KRWHP but it remains to be seen if it will go that far....we will see. If not I will go bigger!

-Bryan

ABeasst

iTrader: (5)

the larger the heads and intake the better flow you get so you dont have to push as much boost to make the same amount of HP. Therefore causing less stress on the engine. Thats the reason most people run free flowing heads and so on.

JZ 97 SS 1500

iTrader: (2)

We have customers with LS1's going 25+ psi with custom turbo units. Most standard 76's won't support a sustained 20psi on a built LS1.

JZ

NA$TY-TA

iTrader: (21)

Yep Yep.......

to 1bdbrd

Were are you getting your idea's and info????? Imports...?????????

Just asking because alot what you sounds like you know nothing about Turbo charging V8's............. to me allot of the big cubes and T76 make for a real Efficient set-up......................

1bdbrd

iTrader: (12)

i do hang around alot of import sites yes. but thats not what drove this post as i still am an fbody guy and will continue to be one.

however, a big cube t76 car IMO isnt a good setup. im not a huge drag racing person though so maybe thats why i say that. i know that kind of setup works great for straight line racing on a prepped track. i guess i should have been a little more clear though as i see a lot of mostly street driven cars here with that kind of setup. it might make big numbers at a relatively low boost amount but at the cost of powerband. im not huge into street racing but i do it and know that a car making 600rwhp from 4500-redline is going to lose to a car making even 550rwhp from 3k-3500 till redline. plus the latter car with the smaller turbo will have better response before the turbo is spooled.

*EDIT*JZ im curious as to what you mean? 20psi on an fbody is the same as 20 psi on any other given engine. unless you mean for airflow sake? even then why would it be ok for that boost level over a shorter time vs. a longer time period?

again, i like these style posts as i learn quite a bit from them so im not trying to step on toes or anything.

TransAm

Jose this is Geoff, long time buddy. I have to come in an disagree with this comment, and its shocking coming from you because I know you know better, was this just a typo?


this is a compressor map of a t76 i dont know what a/r it is but as you can see it flows 93 lbs a minute with 78% effciency, thats pretty cool air for that many lbs per minute. assuming its around 112 degrees thats 1322 cfm. 1322 x0.070318(112 degrees) = 93 lbs /min with a max speed of 93k Rpms. but its peak effciency is at 30.8psi and max rpms is at 35psi so how can it not sustain 20psi which is about 50k rpms and 40+ lbs per min?

parish8

iTrader: (6)

you guys are missing something. these motors will flow a ton of air at low boost numbers. look at that chart above and imagin more like 80lbs of air at at 2.0pr and you might be able to see why that turbo wont hold boost at a 3.0pr. it just wont be able to flow enough air to hold that presure. it just gets too far off on the right side of that map and looses all efficiency. your not likly to get to the 93lbs of air that turbo is rated on on a motor this large. you will need more compresor if you want to hold 20+psi.

i had a t76 on a camed 6.0 and it would only goto about 14psi. i pushed it to 16psi once but didn't gain much if any hp and would not go any higher. i swaped my motor out for a 408 and actualy lost a little peak hp.

the coments on wide power band seem to be all backwards. a t76 on a 5.7+ will boost prety quick and have a wide power band. a t76 isn't large at all for these motors.

TransAm

Parish I agree with you, and honest truth was I considered that after I posted but didnt feel like editing it. yes on the compressor map it does show at 1.4 bar it can reach compressor surge pretty fast, I would think on a viper 8 litre it would surge at 20psi in a matter of seconds. I admit I was wrong and this has everything to do with the fact that I mostly deal with 1.x litre engines as of late and not too active in the v8 community any more. airflow volume is something that needs to be factored in.

1bdbrd

iTrader: (12)

100% of what i was looking for. i knew there was something i was missing. i never even considered air flow through the motor. i guess i kinda missed the most important part here.

*EDIT* cuz im an f'in retard.

parish8

iTrader: (6)

surge is on the left side of the map and would be more likly on a small motor with a large compresor. a v10 with a t76 wont surge but it will run out of turbo even more quickly than an ls1 motor. i would bet a v10 will flow 80lbs of air at a 1.8pr or even lower. you can see where it is right off the map.

going off the right side of the map that fast means you will be way out of the eff range of the turbo. the air will get hot fast. a 8.0L will probably see less peak hp than a 6.0 just because of the turbo running out.

all of this talk doesn't even take the turbine side into acount. a t4 (t76) would probably be prety restrictive on the exhaust side for a v10.

i didnt really understand why i was maxing out at a little over 600rwhp with a t76 but when you look at the map it makes sence. i have been told smaller motors with the exact same turbo have seen 900+rhwp.

NA$TY-TA

iTrader: (21)

Thank You Parish........ very good explanation......

White.Lightning

iTrader: (53)

So just a general question......

Forged motor + 6.0L heads + Precision 76gts

Edit: add 346"
370"
383"
or 408"

for max "efficiency and power" ???

Edit: Yes, I read the above posts. Just getting a general concensus

Andy

JZ 97 SS 1500

iTrader: (2)

Go 370 with a 76GTS out of those 3 engine combo's. A 346 would work even better.

Jose

ddnspider

iTrader: (26)

370 even though im not a huge fan of it...but it is more efficient.Im doing a 383 with the T76GTS and i plotted out the same stuff at 1.82 and 2.02 PR on that map and im hanging on the edge.Now the graph will shift about 10#'s to the right from what ive been told by Jose because it flows more than a normal T76. It wont be totally efficient but its not a race car,its a M6 street car so i want full boost much earlier.Doing out the math and using a program V8 DSM V8 showed me at 15#'s on my motor i should see full boost by ~3k which i think is right where it should be for a street car.600rwhp is my goal which is less than if it were a smaller cubed motor,but i wasnt shooting for 8-900rwhp,i was shooting for earlier boost while still make decent numbers.just my $.02

White.Lightning

iTrader: (53)

I was intending on forging my stock motor originally, then swayed towards a 408" motor, now after reading this I will most likely forge my 346" motor

Haha

Andy

parish8

iTrader: (6)

they are all good combos depending on what you are looking for.

for me a heavy street driven truck the 408 makes the most sence. i can use the massive tq it is going to build and quick spool.

for a car the insane tq at low rpms will not be a great thing so a 408 might be a waste but is sure would be fun. a 370 is really cheap and durable as hell.

347 will have a little lag, not as much tq but it will have the highest peek hp potential.

you would be happy with any of those motors i bet.

DeltaT

iTrader: (5)

Except trucks are so light in the rear - how do you get around that?

Jim

Frost

iTrader: (45)

That is a HUGE assumption that I would not be comfortable making.... What if the first car in the above was running a stall that flashed flashed 4500-4900, which is just part of a matched setup?

hellbents10

iTrader: (10)

Cal-tracs!