Let's talk turbo back pressure!

[Deespeed99]

Ok now that i have base line numbers for the Hellion kit I want to go ahead and make changes to test and provide more information on what exactly is the design flaw with the kit. I planned on starting with the turbo but after speaking with Precision yesterday I don't know that it's really the issue.

They said it's a 6775 .96 a/r and should flow well above 6000 before running outta steam. So that's leading me to believe it's a piping issue. A T4 inlet is 3" x 2" so I'm thinking the inlet pipe to the turbo being 3" would be fine but would changing the driver side pipe from 2-1/8" to 2.5" to match the passenger side really make that much of a difference? Or should I change the piping off the header to 2.75" or 3" then neck it down to 3" at the crossover? Also could a change in the cross over make a difference? Meaning if it was designed different or moved up close to the turbo. Also should I shoot for 1:1/1.5:1 or would 2:1 be alright?

Open to ideas before I start cutting and changing things up! BTW I'll get a back pressure testing kit before I make any changes and measure before and after :beer:

 

[Fabbed5.0]

Measure the pack pressure first. it will only get worse the more boost you add. so if its already at 2:1 now then i would start making changes. Personally the 67mm turbo are too small for these cars minimum i would do is a 72mm and up.

 

[Deespeed99]

Measure the pack pressure first. it will only get worse the more boost you add. so if its already at 2:1 now then i would start making changes. Personally the 67mm turbo are too small for these cars minimum i would do is a 72mm and up.

Even with the 75mm turbine wheel? You think the 67 compressor wheel is choking it out?

 

[ModMotorMadMan]

..

I just tuned a turbo coyote and saw the same issue.. Its definitely back pressure related.. I dropped the mufflers off the car and cleaned up the air fuel and power and rpm came up.. Rpm only slightly though.. I feel that the turbos are to small for sure.. I can't see the piping causing the issue but I've spoken to people that are saying they believe thats what it is..
Honestly I'm a comp dealer and feel like these things would really love something like a 78/79 and I bet with the ball bearing arrangement it would spool it with no problems and operate with cooler charge temps epper:

I'm interested to see what you find out messing with yours.. Kit I tuned was the original style with the 64mm turbonetics..

 

[slamdcoop0428]

With my hellion twin kit, just to show you a for instance on back pressure being an issue. I ran my kit with a restrictive catback and on 5.5 psi it made 525whp then I put a less restrictive cat back on and with no changes other then cat back I made 586whp. So turbo cars hate back pressure. Sometimes I think of just running straight x pipe with clamp on dumps at the end lol.

 

[D.T.R]

With my hellion twin kit, just to show you a for instance on back pressure being an issue. I ran my kit with a restrictive catback and on 5.5 psi it made 525whp then I put a less restrictive cat back on and with no changes other then cat back I made 586whp. So turbo cars hate back pressure. Sometimes I think of just running straight x pipe with clamp on dumps at the end lol.

What cat back was the one robbing you all that power?
I'm wondering what these turbo 5.0s would sound like with open H or X pipe

 

[StevenStarke]

Ok now that i have base line numbers for the Hellion kit I want to go ahead and make changes to test and provide more information on what exactly is the design flaw with the kit. I planned on starting with the turbo but after speaking with Precision yesterday I don't know that it's really the issue.

They said it's a 6775 .96 a/r and should flow well above 6000 before running outta steam. So that's leading me to believe it's a piping issue. A T4 inlet is 3" x 2" so I'm thinking the inlet pipe to the turbo being 3" would be fine but would changing the driver side pipe from 2-1/8" to 2.5" to match the passenger side really make that much of a difference? Or should I change the piping off the header to 2.75" or 3" then neck it down to 3" at the crossover? Also could a change in the cross over make a difference? Meaning if it was designed different or moved up close to the turbo. Also should I shoot for 1:1/1.5:1 or would 2:1 be alright?

Open to ideas before I start cutting and changing things up! BTW I'll get a back pressure testing kit before I make any changes and measure before and after :beer:

The inlet to the turbo is not the issue. If you're running a single 0.96 housing (precision?) on a 5.0L coyote, that's your problem right there. You really need an 85mm turbine on that thing.

Unfortunately the hellion single kit kind of sucks. I would have went with CPR or JPC for a single.

 

[slamdcoop0428]

What cat back was the one robbing you all that power?
I'm wondering what these turbo 5.0s would sound like with open H or X pipe

It was the stainless works retro chamber cat back. The original cat back like I had necked down to almost 2 1/4 in those chambered mufflers. It was fine for when I was NA but with turbos, NOPE! Lol so I sold. But BBR has worked with stainless works and had them basically make a replacement type chambered straight through muffler but its basically straight 3 inch pipe lol. So there is no power loss. But for now I've been running the stock OTA pipes with the resonators cut out with 3 inch pipe in its place. Then added a 3 inch axle back.

Trust me the car sounds wicked with just open x pipe lol pure turbo whistle. I'm going to talk to Chris tomorrow about an option for some type of cutout or something. I'm still sure my cat back that I have currently is holding me back some.

 

[D.T.R]

It was the stainless works retro chamber cat back. The original cat back like I had necked down to almost 2 1/4 in those chambered mufflers. It was fine for when I was NA but with turbos, NOPE! Lol so I sold. But BBR has worked with stainless works and had them basically make a replacement type chambered straight through muffler but its basically straight 3 inch pipe lol. So there is no power loss. But for now I've been running the stock OTA pipes with the resonators cut out with 3 inch pipe in its place. Then added a 3 inch axle back.

Trust me the car sounds wicked with just open x pipe lol pure turbo whistle. I'm going to talk to Chris tomorrow about an option for some type of cutout or something. I'm still sure my cat back that I have currently is holding me back some.

Noice. I think i'm going to remove everything after the mid pipe lol... and run it like that :rolling:

 

[Deespeed99]

I just tuned a turbo coyote and saw the same issue.. Its definitely back pressure related.. I dropped the mufflers off the car and cleaned up the air fuel and power and rpm came up.. Rpm only slightly though.. I feel that the turbos are to small for sure.. I can't see the piping causing the issue but I've spoken to people that are saying they believe thats what it is..
Honestly I'm a comp dealer and feel like these things would really love something like a 78/79 and I bet with the ball bearing arrangement it would spool it with no problems and operate with cooler charge temps epper:

I'm interested to see what you find out messing with yours.. Kit I tuned was the original style with the 64mm turbonetics..

I'll definitely post up results once I have them. Everyone is saying the turbos are too small but the 7675 has the same turbine wheel and uses a T4 as well so that's where I'm trying to get clarification because I'm pretty sure a lot of the other kits that are successful are using 75mm turbine wheels as well. I could see if it was the 6768 or smaller.

With my hellion twin kit, just to show you a for instance on back pressure being an issue. I ran my kit with a restrictive catback and on 5.5 psi it made 525whp then I put a less restrictive cat back on and with no changes other then cat back I made 586whp. So turbo cars hate back pressure. Sometimes I think of just running straight x pipe with clamp on dumps at the end lol.

I have a cutout and on low boost it made almost no difference which is why we believed the pre-turbo exhaust/back pressure is the issue. A few supra guys have used that turbo and it spooled up to 6500+ fine for them.

The inlet to the turbo is not the issue. If you're running a single 0.96 housing (precision?) on a 5.0L coyote, that's your problem right there. You really need an 85mm turbine on that thing.

Unfortunately the hellion single kit kind of sucks. I would have went with CPR or JPC for a single.

How come other manufactures are running 75mm turbines with no issues though? The Hellion kit doesn't suck (check out my review) it just wasn't designed well IMO. I also bought it because I got it used for a great price, it was more then worth it for the numbers Adam got outta the kit. I'm trying to pin-point and fix the flaws so others can have the right information and maybe they will even consider re-designing or fixing it.

 

[slamdcoop0428]

Noice. I think i'm going to remove everything after the mid pipe lol... and run it like that :rolling:

Trust me I'm thinking about just getting something done like that. Maybe go to an exhaust shop have some clamp on turn downs put on the end of the x pipe and add a hanger to the x pipe and have them bolt it to the trans mount just so nothing is welded to the car lol. I can change it if it gets old then I can put the cat back back on lol.

 

[CPRsm]

It's a combination of things. In the magazine artical w the single kit it had no filter, atmo dump on the gate, 1-2ft of down pipe and a 1.15 ar. It still didn't pull rpm. So all you're left with is the hotside and turbo itself. It's odd PTE said it was Ok. When I talked to them they said it was too small, and the 85mm was a better fit. Usually a small turbine will spool fast and make more down low and lose it up top. Fwiw our 82mm turbine spools fast enough to make more down low than anything I've seen on the market, including twins.

Deep you can't compare the same turbo on different engines. The back pressure ratio will be different, and some just have more exh energy. A smaller engine will make more HP on a smaller engine in almost every case.

 

[Deespeed99]

It's a combination of things. In the magazine artical w the single kit it had no filter, atmo dump on the gate, 1-2ft of down pipe and a 1.15 ar. It still didn't pull rpm. So all you're left with is the hotside and turbo itself. It's odd PTE said it was Ok. When I talked to them they said it was too small, and the 85mm was a better fit. Usually a small turbine will spool fast and make more down low and lose it up top. Fwiw our 82mm turbine spools fast enough to make more down low than anything I've seen on the market, including twins.

Deep you can't compare the same turbo on different engines. The back pressure ratio will be different, and some just have more exh energy. A smaller engine will make more HP on a smaller engine in almost every case.

I agree it was odd because I figured that the turbo would be the primary cause especially after I spent hours on yellow bullet reading about piping and see that the diameter might not be such an issue. With that being said is it even worth messing with the piping or just swapping turbos? I would check back pressure before the swap and after of course. Also would the PTE 7675 be a waste of time? I definitely agree about the difference in engines, my turbo busa made 650 with a small GT40R lol!

 

[D.T.R]

I agree it was odd because I figured that the turbo would be the primary cause especially after I spent hours on yellow bullet reading about piping and see that the diameter might not be such an issue. With that being said is it even worth messing with the piping or just swapping turbos? I would check back pressure before the swap and after of course. Also would the PTE 7675 be a waste of time? I definitely agree about the difference in engines, my turbo busa made 650 with a small GT40R lol!

650whp on a bike? good god lol
a GT40R iirc can make well over 700whp.

 

[D.T.R]

It's a combination of things. In the magazine artical w the single kit it had no filter, atmo dump on the gate, 1-2ft of down pipe and a 1.15 ar. It still didn't pull rpm. So all you're left with is the hotside and turbo itself. It's odd PTE said it was Ok. When I talked to them they said it was too small, and the 85mm was a better fit. Usually a small turbine will spool fast and make more down low and lose it up top. Fwiw our 82mm turbine spools fast enough to make more down low than anything I've seen on the market, including twins.

Deep you can't compare the same turbo on different engines. The back pressure ratio will be different, and some just have more exh energy. A smaller engine will make more HP on a smaller engine in almost every case.

what turbo comes in your kit standard again? is it an 82 or an 88?
so you're saying that you wouldn't even go with anything smaller than an 80mm? that just blows my mind haha... it's insane how good these motors must breath...

 

[kingnut]

For the price of the hellion kits you would think it was the cream of the crop.

 

[slamdcoop0428]

For the price of the hellion kits you would think it was the cream of the crop.

Twin kit pretty much is epper:

 

[CPRsm]

^^We'll see. Track will tell all.

It's a 74/82. Could go smaller. Back pressure is pretty low. But 500ft/lbs at 3300 is already hard on poor ole street tires lol.

Speed, (got ur name right this time lol)
The 76 might make a little more power. But not much since it's a back pressure problem. Multiple pressure ports to test pressure in different spots will let you narrow it down. Before the turbo you're going to be about 2-1 at 9-10 psi. That's what we saw. Who knows what would fix it. The people pushing the kit saying it was fine are pushing a different kit now and never shown a dyno graph that I know of. You're on your own there it looks like.

 

[slamdcoop0428]

^^We'll see. Track will tell all.

It's a 74/82. Could go smaller. Back pressure is pretty low. But 500ft/lbs at 3300 is already hard on poor ole street tires lol.

Speed, (got ur name right this time lol)
The 76 might make a little more power. But not much since it's a back pressure problem. Multiple pressure ports to test pressure in different spots will let you narrow it down. Before the turbo you're going to be about 2-1 at 9-10 psi. That's what we saw. Who knows what would fix it. The people pushing the kit saying it was fine are pushing a different kit now and never shown a dyno graph that I know of. You're on your own there it looks like.

Lol people have already gone in the 9's with the hellion TT kit so I'd say its working pretty well.

Also I can't remember but what did you make hp and TQ on a stock gt motor?

 

[D.T.R]

For the price of the hellion kits you would think it was the cream of the crop.

most single kits are pretty close to the price of the hellion TT :shrug: