Hello, decided to upgrade and switched to forced inductions billet S372 75 .88 turbo and now having very slow spool issues. Starts to spool after 4000 and i might see 9psi by 6000 this is in 3or4 th gear. bearly anything 1or2nd gear.
its an 02 mustang 4.6 2v has the on3 kit, dynod 420rwhp with their on3 70mm turbo @9psi was very fun and would hit full boost by 4000.
The car still has the old tune, not sure if that would make a huge difference. Checked for boost leaks and seems all good. Im wondering if the turbo sizing is somehow wrong? as this turbo seems to be intended for diesels?
Thanks!

 

Is the new turbo 72 cold 75 hot? I do not mean trim. If not what is it.

 

FORCED INDUCTIONS GEN3 Race Series S372 75 TW .88 A/R T4 Housing
Compressor Wheel: 72mm Billet Compressor Wheel
Turbine Wheel: S300 75 TW
Exhaust Housing: .88 A/R T4

 

75 turbine is too big diameter. Also .88 ar is too small for single turbo. If you have no hotside exhaust leak the problem is 75 turbine dimension is to big.

edit: also if your motor is not built it sucks because you are stuck at 10psi max boost. If it is fully built and forged once you figure out the turbo thing turn up the boost to make max power based on build with a proper dyno tune.

 

The motor is built now as the stock rods bent around 11psi

I know it needs a tune… just dont think its the actual issue.

This is the original turbo specs, are they that different?

Cold Side

• Compressor Wheel 61mm
• .70 a/r
• 4” Inlet and 2.5” Compressor Outlet
• Inducer- 70mm
• Exducer- 99mm

Exhaust Side

• Exhaust Housing: T4 inlet
• . 68 or .96 ar Exhaust Housing – Specify When Ordering
• 3.0″ Vband outlet
• Inducer- 74.5mm
• Exducer- 65mm

 

What turbo was on it before the swap? Have you pressure tested the hot side piping? You may have a leak.

 

Are you using electronic boost control? Keeping the gate closed will help spool some.

I am controlling a 4 port Mac value with with term X. I went from commanding a duty cycle to targeting boost. It's spools faster when it's under target it puts 100% on top and 0 on the bottom.

 

That turbo is big for the engine output. You can retard the timing a little to get boost in earlier (it won't drive as nicely off boost), you can also try running E85 if it is available and your fuel system will take it. Otherwise you need to increase the output of the engine, cylinder heads, bigger cam etc.

Something like an s362 would be a better fit for that engine, with overhead if you ever built the bottom end. It would likely fit on the exhaust side as well since you already have the s300 exhaust housing. You could go even smaller if all you are looking for is ≈400hp the stock bottom end will take.

 

The stock rods bent around 11psi so the motor is built now should be good to 900

I know it needs a tune… just dont think its the actual issue.

This is the original turbo specs, are they that different? I only went up 2mm on the wheel size

hot and cold side piping is tight, bypassed mbc and just run a spring to eliminate that for now

cold side
.70 a/r
70mm inducer
99mm exducer

hot side
.96 a/r
74.5mm inducer
65mm exducer

 

Yes they are different now you have a .88 a/r hot side single turbo. Maybe the additional back pressure is causing the wastegates to bounce open and closed non-stop. How do you have your wastegates vacuum lines hooked up?

 

They seem very similar to me. .88 a/r should only help spool imo. Youd think going from a no name china on3 turbo to quality billet wheel would only help. The mbc is bypassed for now just wg spring pressure

 

They are not similar. You are trying to put x through something that is to small to except x while also having an oversized hotside turbine wheel. Essentially you are creating a choke of a/r before a large area of 75 turbine wheel space. I hope you have a ball bearing. If it is not setup to work accordingly you will cause a non stop hiccup in the ability for the wastegates to function properly. How do you have your wastegates vaccum line hooked up because you said now spring only no manual boost controller, so it makes me ask this question.

 

Did you ask at Forced Inductions for there recommendations? What efi, trans and gear? Somebody should do a match bot and see what the deal is.

 

What is your power goal?

What modifications have you made to the engine?

 

How did it perform with the old turbo? Turbine size doesn't seem too far out of line. Did you just pick this off their website or did you get them to help your selection?

 

I picked the turbo myself after looking at a lot of compressor maps using turbo calcs reading up on turbo basics and seeing what people run on these engines
Hellion kits run 62-76mm
On3 70-78mm
Ive seen a few with s369 running 550whp+
I thought 72mm would be a nice compromise, lookking for 600-800whp
its 5spd stock rear end
Engine is stock comp, heads, cams with forged bottom end and 130lb btr valve springs
This should be the new turbo map
#ad

https://shop.forcedinductions.com/fis-gen3-race-series-s37275

 

its not bb but the old 70mm wasn't either
the waste gate was hooked up to mbc just like in all their instructions. Turbo nipple>mbc>wasgate lower port, top is vta and seemed to work fine.

 

You could try no reference line to the bottom of the gate. Maybe keep it 50% throttle at first (this could over boost it so buyer be ware). If it likes it get an electric boost controller. If there are no other leaks and the turbo is healthy, my guess is waste gate.

I assume my junk if far from optimized. Stock push rod 5.0 T5 4.10 eBay 7875 .96 housing. First gear half throttle I don't get any boost. 2nd gear it will rise from vacuum to 10 psi at right before the shift with 50-60 TPS. Same in third.

I normally leave off the 2-step at 5k+ with 2-3psi. It's spools pretty good in first like this. This is my first build so I wanted something a little soft/laggy down low. I was more worried about getting full boost at peak torque and breaking it than slow spool.

I and think about putting more timing on the 2-step. I bet 5-7psi on the hot would help my 60' if it stays together.

 

This is how im running it right now, wastegate ports just vta, kindof what i meant by bypassing mbc earlier
Its still slow spool and slight overboost over set wastegate spring

 

You are looking at the cold side not the hot side.