HeavyMetl

iTrader: (2)

I'm basically building a street toy with my 1970 C10 truck.



I'm hoping for something that spools quickly and is overall a blast to drive. From the research I've been doing, a 2.5 crossover is fine, but big enough to make north of 1000hp. I've even seen 1 5/8 crossovers reportedly making 1500hp (crank), so obviously getting that heat energy to the turbine is primary.

Anybody see a downside to a flipped truck manifold, 1.75" crossover?

Also, FWIW:
2004 LM7
PT7675CEA, Precision Intercooler
Ching-chang head studs
Used 02 LS6 cam
LS1 intake
LS9 Head gaskets
PAC 1218's
4L80E w/Transgo HD2
Holley Dominator EFI/Trans/etc/etc (Seriously this thing is awesome)
Holley Dominator Fuel Pump
E85 (2 stations 3 miles from my place! Score!)
Ford 9" 3.25 gears

I know the Precision stuff is overkill given the used/junkyard nature of the other parts, but I got a deal and it's already sitting in the shop.

I'd like to see 600+ to the tire on E85 and maintain daily-driver type manners.

geoff17

I'm not sure if 1.75 would be a restriction but why that small? That turbo will spool plenty fast for you for a street car if thats what your after, especially since its an auto. I run that same turbo with my lq4 (I know slightly bigger motor) with a 2.5 crossover and it spools instantly, there really is like zero lag to it. I'd at least step up to 2 inch for the crossover.

2muchboostNY

iTrader: (8)

Same suggestion here....2" or 2.25" crossover. I am building a 7675 LM7 setup myself and going with 2"

HeavyMetl

iTrader: (2)

Ok, thanks for the feedback.

I guess I will stay "in the box" with my thinking and go ahead with the usual size crossover. It does seem like a lot of builds run larger than needed crossover pipes from what I've been reading and researching.

2muchboostNY

iTrader: (8)

Agreed. For some reason 2.5" became the norm and may be adequate for some builds but I remember a calculation showing that 2.5" was capable of over like 1500rwhp. I am also running T4 turbo setup so I think the 2" should be right at home. Plus 2" plumbing is easy to find.

pwrtrip75

iTrader: (8)

What size hole does it get reduced down to (driving turbine)? or even divide the T4 flange in half and what is the volume of that opening and why exceed it by so much? Increasing the pipe size above the size of its smallest opening only decreases initial velocity.

Suggestions based on only the that it "is the norm" is kind of worthless info, anyone can guess. I don't know the exact dimensions of the inside of the turbo, but that is where I'd start. Also, each elbow in the crossover will add X amount of resistance, so if you had a crazy routed setup with a ton of elbows that would be a reason to step up to the next size piping above what your minimum orifice would be.
There are sites like engineeringtoolbox.com that you can find formulas for flow on pipe distances and bends if you wanted to get precise about it, but using like one elbow in a distance less than 2 ft I wouldn't worry about it.

TurboMonte

I am running 2.5" piping on my 5.3 with LS9 cam. The turbo is an older Master Power T70 with the supposedly poor performing .68 A/R turbine housing.

This is running through a 4L80E with the HD2 shift kit into a 2002 Mustang GT rear end and all in an 86 Monte Carlo SS.

Running through a little baby intercooler and with meth injection the car is an ANIMAL.

I currently am only running 6-7 lbs of boost but did go out this afternon and turned the boost controller up to 14 lbs. WOW!

Boost comes on like a light switch as soon as you stab the gas. The car is just awesome, and to be honest terrifying.

At only 7 lbs of boost is will easily bark the tires pretty hard on a 2-3 shift at 75 mph. On 14 lbs of boost it lights them up at those speeds and will keep them smoking almost as long as I want!

I don't know if it would spool faster with smaller primary piping but in my application the 2.5" works really well. It may be due in part to the small turbine housing, I'm not sure. But damn is it ever fun on the street!

Awesome looking truck by the way, can't wait to see more of your project as it progresses. I have a feeling 2" would work just as well for you and be a bit easier to package also.

Forcefed86

iTrader: (4)

I love these... "I think i read" ... "I thought I heard"... threads.

Read this... (not saying any of it's correct)

https://ls1tech.com/forums/forced-in...over-pipe.html

They suggest a 2.5" crossover will support 2300hp. 2" supports around 900.


I say stick to your guns! A 1.75" crossover should support 600hp on a 5.3.

kelsey_canard

iTrader: (6)

Should be a nice build!

HeavyMetl

iTrader: (2)

Thanks for your experience monte. I've been around some wicked fast N/A cars but this is my first foray into the turbo scene. Looks like 2" is easier to work with so that'll likely be my choice. I'll be sure to update my build progress.

yenkomike

iTrader: (2)

I don't think your 1.75 will hurt you as much as what your going to have to do to neck it down that far. I whould measure the id of the exaust manifold at the point where you are welding the vbands on and spend more time making nice smooth transitions into and out of the manifolds and use nice flowing mandrel bends. a 2" crossover might be a better transition .

2muchboostNY

iTrader: (8)

Ahaha....thanks FORCE that's is the thread I was referring to and couldn't find. When I said 2.5" would support 1500+rwhp I was only under estimating by 45% lol.

Forcefed86

iTrader: (4)

Lots of mixed thoughts on piping size with turbo stuff. I know and respect several people that believe bigger is better too.

I’d like to see some smaller piping used on these lowish HP builds though. Aside from packaging… to see the most performance gain with smaller piping you need to run larger housings and wheels on the turbo itself. In theory smaller piping should allow you to maintain the “small turbo” spool time with a larger turbo housing and less overall back pressure. Lower back pressure makes more power and allows a more aggressive cam choice.

I really think the $640 S475 with the 1.32AR t6 would be the way to go with a small bore LS. Then choose your hotside piping based on your HP goal… 1 7/8 to each side of the t6 scroll with the piping protruding into the turbine housing would be my pick for the OP. 1.75” would be a cool experiment though!

Good luck!

THADD

iTrader: (12)

Take this for what it's worth.......I am running a 76mm t6 on a 347 with 2.25 in hotside piping. I have a 8 psi gate spring and I am having to put 50 psi of co2 on it to make 27 lbs of boost. Back pressure is to high. I am in the process of building a new hotside and going to 2.50 in. I am almost positive stepping it up in size will pick the car up without changing anything else

HeavyMetl

iTrader: (2)

Thadd, thanks for the info. That's a lot of co2 for boost control. Interesting.

Forcefed86

iTrader: (4)

Not comparing like motors IMO. How large is your turbine wheel and AR housing? How much power would you say your motor is making NA? In boost? Head flow? You’re running a more cubes and I’d guess pretty high rpm as well?

Do you have actual backpressure readings? I wouldn't think the amount of pressure applied to the WG port is a good indication of actual back pressure. The larger the gate valve face, the more pressure will be needed to keep it closed. A 60mm WG will require more pressure to stay shut than a 40mm WG etc.. WG pressure chamber size would also come into play I'd think.

Again I’m not taking any sides, it depends on the setup as a whole IMO.

THADD

iTrader: (12)

Yes it is. Of course cam plays into that as well but I am doing the hotside first then a cam after if I am not satisfied with the results

Forcefed86

iTrader: (4)

Why would changing your crossover size have any effect on the systems total back pressure? If the turbo is the restriction (bottleneck) in the system… you could run a 4” cross over and your drive pressure will remain the same as it was with a 2.25” crossover. The amount of pressure needed to control your WG would also remain the same.

static low 92

iTrader: (2)

So far, I'm liking this thread. I'm in exactly same position as OP.

I have an 84 C-10 LH6 5.3 with ls6 cam. One3 76mm build.

Recently rode in a buddys Camaro 5.7 big N/A cam, hogged out 243s with same turbo and 2.5 hot side and it definitely has some lag unless you do some brake boosting... Really wanting a much more responsive boost curve than that. I'm not particularly looking at a high hp goal because I think truck will get unmanageable at limits of this turbo.

Looking like 1.75/or 2" is going to be best option

FirebirdSS

iTrader: (7)

I am scratching my head on this one as well...