@ZZKKER

iTrader: (1)

i am building a twin turbo 383 and am curious which brand ( afr, trick flow, brodix, pro top line, ect.) would be the best to use. i am useing turbonetics t series t70 Qtrim turbos with custom stainless headers. the boost will be a a variable 5 - 25 psi boost, the lower for economy and the later for all out power.

i would like suggestions on which ones deck can handle the boost pressurs because i dont want to be changing head gaskets every 2 weeks, due to premature failure.

i also would like suggestions on the what size heads to run( intake cc's), i will be using an converted lt1 intake with these heads. i know i have to run a low compresion like 8.0 to 1 or 8.5 to 1, so the combution chamber size is not as imprtant because i will adjust what i need with the type of pistions.


thanks
anthony

89ProchargedROC

Few things:

1) who helped you decide on your turbo selection? A pair of 70s is a lot of turbo and there shouldn't be a reason why you are using q-trims on the exhaust. P-trims would be ideal imo

2) look at the compressor map for the 70 compressor wheel. Running that low of pressure (5) puts it in the surge part of the map, not good

3) due to the above surge problem means that you would have to run more pressure to keep the compressor efficient and i dont see that happening with a small cube SBC and q-trim wheels very often at all. You'd be on motor most of the time

4) Any of the heads you suggested can handle the deck pressures. I prefer brodix stuff. But as long as the deck hasn't been milled, pick your poison. A note on head gasket failures: most failures are due to fuel/detonation issures more so than deck issues. I know of a few sets of aluminum heads that were pretty far from flat and holding up due to good a/f ratio

5) combustion chamber size is GOING to be IMPORTANT. with a 383 you are limited with the amount of dish you can run. So you are going to have to figure out your compression you want and pick the piston prior and then get the head that can get you the combustion chamber cc's to match it

6) I'd choose a head with intake cc's in the 200-220 range

7) lastly, imo the LT1 intake cannot be ported properly to support a) the amount of airflow the 70s can put out and b) it can't be ported to the point of fitting a big cc head

kfoley

I'd got with AFR 227's CNC ported, or Dart Pro 1's CNC'd they're nice, I saw some on display at the U.S. Nationals today (too bad it got rained out ) and I was impressed. Brodix also makes good stuff. Like said above, pick your poison...

@ZZKKER

iTrader: (1)

1. the tech rep, but he said q trim wouldnt be needed for the particular motor i am building, so i figured why the hell not, i only want to buy the turbos once, so i dont have to drop 4 more grand if i upgrade at a later time. so in your opinion would a t 70 (not q trim) still be to big for my twin setup. i am lookin for a max hp of around 1000. but i want to be able to drive it on the street regularly (good weather) so that was why i was wanting to run low boost for cruising. also in your opinion, what would be the lowest boost pressure a t70 non Q trim could maintain? they are the ball bearing by the way.

2. kinda tied in with 1, but could you explain the chart, i dont know everything to know about the compressor maps, that is why i ask questions and call the tech lines when deciding what to buy, hence this thread.

3.do you mean on motor all time with boost down to 5 psi due to no spool, or on motor all the time no matter the boost seting do to not enough air flow over the turbine to spool the compressor?

4. i had heard of heads "warping" under high pressure from forced induction and did not want to drop 2 grand on junk heads. thanks for answering this question.

5.i am aiming for in between 8to 1 and 8.5 to 1 compression and was aiming for 76cc chambers, so i guess i worded the earlier statement wrong. but since were here, do you think that would be the proper size combustion chamber for the projected compression?

6. that is what i was thinking, but i wanted to make sure.

7. i talked to john milican (sp) and he said "Felpro 1205 gasket, maybe a 1206 but I never tried that one." i am going to take the intake to the zone tomorrow (if they are open) and compare the gaskets to the intake and should tell us. if a 1206 fits i should be able to run about any size runner i want to. i will definantly report back on this because i am sure this question has come up more than once.

again, thanks for the replies, and sorry if i sound like a retard, but that is why i ask so many questions, so i can be not as stupid


anthony

kfoley

Unfortunately I can't help with the tubo stuff, I don't know much about them. Any of the heads listed above can handle lots of boost. The block is definitely going to have to be o-ringed to hold that much boost or you'll be blowing head gaskets left and right. For low compression you'll want a 76cc chamber. With 76cc chambers, 4.03" bore, 3.75" stroke, .041" gasket and zero deck you'll need a -27cc dish piston for 8:1, -20cc dished for 8.5:1. No problem helping you out... These are good questions, not retarded at all. You should see some other threads, this is nothing compared some of them...

AutoRoc

iTrader: (1)

Twin 70mm turbo's @ 25 PSi with some giant heads on a 383....

HAHAHAHAHAHAAH sounds cool. I hope a good shop is doing the buildup for ya. Goodluck man I can't wait to see the results.

B4Ctom1

as far as I know AFR's have a deck made for boost (thicker)

PETE

iTrader: (1)

The afr's if i remember correctly have a .030 thicker deck. Good for forced induction. The benefit to the classic sbc is 5 bolt holes around the cylinder there is ample coverage there for boost(just stud the deck and be secure). 70's are frickin huge. You mentioned boost but what about power. It's nice to claim a certain boost but power and what you want it to do along with what intake you'll run is more important. I ran 28 psi in mine(although different than a sbc it's a good reference). Not for long since the #3 piston is vacationing currently.

Is it gonna be a track car,street car,endurance,top speed,etc.) With the 227's you'll have the ability to flow enough air for high horsepower. With a 383 being the smaller bore you only have so much room in the cylinders combined with a 3.75 stroke you'll make very good low end tourqe(street car). 70's would most likely be a waste of money. If you are set on a 383 and a twin setup I'd call cotton performance and order to cpt 63's at most 66's and would go with a slightly smaller head. You don't need to rev the snot outta the engine to make the go power so build on that attribute and build for tourqe.

From the info you gave about your proposed setup one t-76 would do fine for you in any of those boost ranges. It would cut down on the cost of two turbos and two headers, headache of packaging the kit in the engine bay and the cost of an excellent intercooler to cool off the air charge from those two huge compressors. Ask yourself what power you want, what power you'll be able to use,how much you wanna spend and what will the car be driven for.

HTH

Guido

Jimmy (procharged) covered everything perfectly.

@ZZKKER

iTrader: (1)

1st off, could someone please explain how to read the flow chart that procharger posted?

second, i am not going to a single setup, because i already have the custom stainless turbo headers made, they are not hack jobs either, they are equal length with 1 5/8 primary.

the reason i did not post my power expectations is because i wanted this to be a serious thread, and i knew that it would turn into a flame. but since you asked, i will post it. this is real, not someone conning up a story.

i am shooting for around a 1000 HP. this motor will use the best of everything. i am not building it for drag racing, but for road course type racing. this is why i need the boost to be variable, so i can controll my power output, which is also nice on the street because i plan to drive it regularly on the road.

the reason i want such big turbos is as you know i dont want to buy another set if i go to a bigger motor. after all, these things are 2022 a peice. that is a lot of cash to have to spend that much more in the future.


now, with all of that in mind, if i went with the normal bb t 70's, what would be the ideal heads to get, the 220, or the 227? i am going to stay with the lt1 intake because i checked to see how big it could be ported and it can be prted to a 1206 with no problem. now that means that i can run about any size head i want to, correct.

now since my headers are well built, and the intake and heads will flow some serious air, would you still think that 2 t70's would be to big. i dont, but i would like you to give me expanations of why you think they would or would not be to big (ie. lag, to much air flow even with boost turned down, ext.). then tell me what size you would suggest and why.

about the small head and turbo combination, wont the amount of air that the bigger turbo puts out compnsate for the bigger head size, so i would have to rev to 8 grand for power? i want my redline to be around 7000.

i am very openminded, and i admit i dont know everything about forced induction, and i am still learning about it. any help would be appreciated.

thanks
anthony

@ZZKKER

iTrader: (1)

what no more comments?

i would still like to know how to read that flow chart above.

thanks
anthony

uh oh, my 666 th post. must be a bad sign

83 Crossfire TA

iTrader: (2)

OK, since nobody else is saying it (probably too polite, that’s never stopped me), I will… what have you been smoking? To be blunt, if you are going to have any success in this, if you’re asking these questions you should probably be talking about just writing someone a check to build this thing for you.

I’ll start with Procharged’s comments:
Who cares what trim turbines he’s using, the turbos are way too big. ONE T70 would top out somewhere in the mid 900hp range. At 25# boost and 1000hp, 2 wouldn’t even be past their surge line. In simpler terms, at 25# boost the LEAST amount of air that those turbos will be able to move will be more then what is needed to make 1000hp.

Running a lower pressure at the same airflow will take you OUT of surge, not put you in it. Turbos move less air at lower pressures and the surge line moves to the left, allowing them to move less air before you have surge. In a nutshell, you need a LARGER turbo to move the same amount of air at a lower pressure.

In the above example, if he lowered the boost that he made 1000hp to 22 psi it would put him right on the surge line, and if you got it down to around 15-18psi it would put the compressors in their maximum efficiency island.

realistically, you’re not worried about holding boost but BMEP needed to generate 1000hp. The fact is that I’d be looking for heads capable of supporting the airflow needed to make the power, and I could virtually guarantee that heads that can will be strong enough.

FWIW, to make 1000hp at any reasonable boost, especially with a 383 (which will be difficult to build with low enough compression to run really big boost on), you have to figure that you’re building an engine capable of making something in the range of 500hp NA (which will be difficult considering that you cannot count on any scavenging effects from the exhaust since they will not be available with the turbos). In the interest of keeping compression down you’ll end up having to find heads that will flow the air and still use a 23* valve angle and large chambers (you can ignore some of this if you’re going to run it on race gas all the time, ie, you’re rich)

1000hp? Choose whatever flows enough. I seriously doubt that you’ll find a head that has too big an intake runner for the application which will still support that low compression. I’d probably be looking at some of the bigger AFR’s like the 220’s or 227’s.

I will agree that there would be better choices for the amount of air that 2 t70’s will move, but it will be fine for 1000hp.

Porting the head side of an LT1 will not buy you anything unless you weld up the top of the runners and relocate the injectors, otherwise you’ll just be widening the point where they attach to the head and screwing up the runner taper and shape.

To start with, I’d consider changing your mind and going with either a larger single, or choose a smaller turbos, something more in the T60-T66 range.