Turbine Backpressure

Turbo1dr

Dual Fuel Injected
Judging from this screenshot of my data log, what would be the things to check to reduce pre-turbo exhaust manifold backpressure? At 26psi of boost I'm seeing 40-43lbs before the turbo and at 30psi of boost I'm seeing 53-55psi of backpressure.

The turbo is a PT70-GTQ DBB with a .85 exh housing. It's physically good with no bent fins and it's not rubbing the walls of the housing. I don't see actual data in the Buick community about people checking their backpressure. I hate to buy another turbo and get the same results.

The engine is a stroker 249cid with Champion aluminum R heads, Champion GN1 intake. The compression ratio figures out to be 9.3. Camshaft is a 212-212 with .570 lift at the valve with 113* lobe separation. Springs check at 200 seat pressure & 500 on the nose of the cam. Cam is set up straight up without advance or retard. Intercooler is doing its job with minimal to no differential backpressure. ATR headers with 3.5" downpipe into single 3" exhaust with about 1.5lbs of backpressure taken at the bottom of the downpipe. The air filter is clean too.

Anyone with BP numbers with a similar combo to compare to? Am I out of turbo? Cam too big? Cam too small? Opinions? Educated guesses?

Exhaust-BP.png
 

Mr.Spool

Well-Known Member
When Your almost 2 to 1 the turbo gurus say it's time to change the turbo.
You have plenty of data showing this.
When you turn the boost from 26 to 30 is it using more fuel?
The new turbos are light years ahead of the old cast stuff and old turbine wheels.
You have a nice motor combo with good compression and springs and flow it would love a new turbo.
 

Haulz A

Active Member
Turbo1 dr- I can understand your concerns pertaining to BP but the ? I have:

What type of turbine housing is on the turbo ( three bolt, V-band or 4 bolt housing). There a distinct difference as to the characteristic of each turbine housing. The three bolt turbine housing seems to be the most restricted of the three turbine housings.

I agree with Mr spools comment; turn up the boost and calculate the fuel migration increasing- once the injector duty stop increasing- then your out of compressor wheel. Dyno the car and you will find its limitations/BP based on the amount of boost required.
 

Haulz A

Active Member
Personally I think your camshaft (212/212) duration is too small for that turbo- a larger duration camshaft (218-224 ) range with an aggressive ramp rate (such as Compcams XFI/QXI lobe profiles) would be more suitable for 70 mm turbo. I like the cylinder head valve spring seat pressure which is good for high boost and protect against valve float.

Also those PT-70 GTQ turbo's are known for having high BP issue- those are older style turbos which the turbine wheel design is not as efficient as the newer GEN2 turbine/compressor wheels. I would opt for a GEN2 style turbo such as 6870 with Vband or four bolt turbine housing- definitely would solve your BP issue. If your cars exhaust system is a Vband set up- you will have a numerous amount turbo options to choose from such as Borg Warner, Garrett, Precision, Works Turbo, Zona turbos etc.
 

boostingbuick

Going to be buried in this.
BP has always been an issue. The boards normally talk about performance street cars, most see little track time. High back pressure will be with most of these cars, and most have no idea about it. When the exhaust wheel becomes larger that the compressor wheels, the BP is more manageable. But then the car is not as much fun on the street. The 76/75 T4 on my car on the street is so much fun. Spools really fast and most cars can't touch me on the street. But........ at the track the BP is so high I can't use it on E85. So I am the crazy guy that has an extra pass header and an 88/103 v-band that I run at the track. Lower BP at the same boost, but I just don't like it on the street. I hope this helps, but IMO you need more turbine.
 

Turbo1dr

Dual Fuel Injected
Turbo1 dr- I can understand your concerns pertaining to BP but the ? I have:

What type of turbine housing is on the turbo ( three bolt, V-band or 4 bolt housing). There a distinct difference as to the characteristic of each turbine housing. The three bolt turbine housing seems to be the most restricted of the three turbine housings.

I agree with Mr spools comment; turn up the boost and calculate the fuel migration increasing- once the injector duty stop increasing- then your out of compressor wheel. Dyno the car and you will find its limitations/BP based on the amount of boost required.
The injector duty cycle does increase with boost pressure. Around 60% at 21psi of boost, 69% at 26psi & 80% at 30psi.

The turbo housing is the typical 3 Bolt Buick.
 

Haulz A

Active Member
The injector duty cycle does increase with boost pressure. Around 60% at 21psi of boost, 69% at 26psi & 80% at 30psi.

The turbo housing is the typical 3 Bolt Buick.
I don't know what size your injectors are but based on the info you provided- you should have enough injector to run up to around 35 lbs of boost with an injector duty cycle of approximately 90% which is the limit on those injectors. Once BP reach closer to 2:1- the gain in HP made reduces - how much has to be measured on a dyno. The newer Gen2 turbo's seem to continue making power even when the BP reaches closer to 2:1 mainly due to the new turbine/compressor wheel design.
 

Turbo1dr

Dual Fuel Injected
Personally I think your camshaft (212/212) duration is too small for that turbo- a larger duration camshaft (218-224 ) range with an aggressive ramp rate (such as Compcams XFI/QXI lobe profiles) would be more suitable for 70 mm turbo. I like the cylinder head valve spring seat pressure which is good for high boost and protect against valve float.

Also those PT-70 GTQ turbo's are known for having high BP issue- those are older style turbos which the turbine wheel design is not as efficient as the newer GEN2 turbine/compressor wheels. I would opt for a GEN2 style turbo such as 6870 with Vband or four bolt turbine housing- definitely would solve your BP issue. If your cars exhaust system is a Vband set up- you will have a numerous amount turbo options to choose from such as Borg Warner, Garrett, Precision, Works Turbo, Zona turbos etc.
My two changes I was thinking before posting a question was to try a slightly larger cam or a newer turbo. My converter is a 17 blade PTC non-lock. The Gen2 6870 seems to an old turbo that was released a decade ago. Has the aftermarket gave up on the Turbo Buick?
 

Haulz A

Active Member
My two changes I was thinking before posting a question was to try a slightly larger cam or a newer turbo. My converter is a 17 blade PTC non-lock. The Gen2 6870 seems to an old turbo that was released a decade ago. Has the aftermarket gave up on the Turbo Buick?
Precision Turbo's gives us a limited amount of turbo choices when it comes to three bolt turbo's but they have the latest turbine/compressor wheel design available in a small frame three bolt turbo. Like I said earlier- with a Vband style exhaust system there many options available for different turbo manufacturers which offer similar Gen2 versions of the compressor/turbine wheels.

I had Reed @ Works turbo's build my Gen2 style 6766 water cooled BB turbo which works really good. I race my car and also street drive it as well- the water cool dual ball bearing seem to handle street driving duty because it primarily use coolant to keep the turbo cool instead of oil- oil is used primarily to lube the ball bearing.

My engine build is similar to yours but with a larger camshaft, compression is similar as well, CNC/race ported Champion Aluminum heads. Give Reed @ Works turbos a call (205-874-6608)- he has several different turbo combinations that will work for your car. Also go to my youtube channel @ Watts Performance Buick- we just posted a video Sunday where I was testing my car. Its a THS legal car (3680 lbs) which has a stock style waste gate- no electronic boost controller. It currently hold the fastest THS pass in history. If you go to BG to the GS nationals in May feel free to come by our tent @ Watts Performance Solutions.


Darrow Watts
Haulz A
 

Mr.Spool

Well-Known Member
BP has always been an issue. The boards normally talk about performance street cars, most see little track time. High back pressure will be with most of these cars, and most have no idea about it. When the exhaust wheel becomes larger that the compressor wheels, the BP is more manageable. But then the car is not as much fun on the street. The 76/75 T4 on my car on the street is so much fun. Spools really fast and most cars can't touch me on the street. But........ at the track the BP is so high I can't use it on E85. So I am the crazy guy that has an extra pass header and an 88/103 v-band that I run at the track. Lower BP at the same boost, but I just don't like it on the street. I hope this helps, but IMO you need more turbine.
Could you explain this further?
How fast are you going to run out a 7675 4bolt?
I know of several cars that run this turbo even on stage motors and they aren't hitting the bp wall.
 

RUQWKNF

KEEPER OF SECRETS
Staff member
Howdy guys. Very interesting subject we have going here.
Mind if I chime in a bit?

What's been said by the others is correct.
The older GTQ turbine wheel equipped turbos with our .85 3-bolt turbine housing, was decent technology back in the early 2000's when we first released it. It was superseded by the HPQ turbine wheel, which lead to our previous generation CEA 68 turbine wheel and now the GEN 2 CEA 70 turbine wheel.
Just so everyone knows, I'm working on a new turbo comparison chart in my spare time, that will show the lineage and what we currently offer today for the true bolt on 3-bolt Buick applications.

Our Precision 3-bolt turbine housings have performed very well over the years with the technology that we had to work with. Many racers have set records using our products, all the while utilizing our off the shelf Precision 3-bolt Buick turbine housings. When the original Precision housings were first introduced, we saw significant flow increases over the original Garrett .63 and .82 offerings from the mid to late 80's. There always came a point, where the back pressure becomes an issue, especially when the boost is set to orbital insertion levels. The newer turbine wheel designs have drastically increased in efficiency, as well as raised the back pressure threshold across the entire board of turbocharged applications. IE: side by sides to Pro Mods. Power levels are literally reaching insane levels in the highest classes of racing.
As of now, we offer two 3-bolt turbine housing equipped turbos that would be a direct replacement for this stroker motor combo that would displace any GTQ / HPQ equipped turbo.


GEN 2 PT6870 BB HP Compressor Cover W/ Buick 3-bolt inlet .85 A/R turbine housing. Available with and without a HD wastegate actuator.
The official part numbers are:
21607215579 GEN 2 PT6870 BB HP CC w/ Buick 3-bolt .85 turbine housing and HD wastegate actuator.
21607215799 GEN 2 PT6870 BB HP CC w/ Buick 3-bolt .85 turbine housing and no wastegate actuator.

GEN 2 PT7270 BB HP Compressor Cover w/ Buick 3-bolt inlet .85 A/R turbine housing. Also available with and without a HD wastegate.
The official part numbers are:
21907215578 GEN 2 PT7270 BB HP CC w/ Buick 3-bolt .85 A/R turbine housing and HD wastegate actuator.
21907215579 GEN 2 PT7270 BB HP CC w/ Buick 3-bolt .85 A/R turbine housing and no wastegate actuator.

Now the next question will be this... How much HP can they support?
Answer? TBD... As more and more of them show up on these specific Buick 3-bolt combos and start blowing the heads off the engines, we will find out.
:LOL:

In all seriousness though, the GEN 2 6870 is technically listed as capable of supporting 1100 flywheel hp. And the GEN 2 7270 fwhp rating has not been published yet. Not very many vendors know or have tried it yet with the 3-bolt housing. Or if they have, they've kept the numbers close to the chest. We do have many other applications running this turbo with out T4 .81 and T4 .96 single inlet, tangential turbine housings with great results. I will say this though... It makes serious power.

With regards to the other models we offer with our Stainless all v-band turbine housings, all I can say right now is yes! We have a ton of options available from 1000 hp up to insanity hp levels. Our Sportsman chassis turbos, are the next upgrade in size compared to the standard T3/T4 chassis turbos that all of our Buick 3-bolt turbos have been based around. Everyone has seen this over the years in the various heads up Buick classes. And most of the serious racers know, that the ultimate limitations have always been the 3-bolt housing and the current level of technology available at the time with regards to turbine wheels and compressor wheels. We even developed the famous Cantaloupe 3-bolt turbine housing, to work with our PT88 turbo for a short time until it was banned from the class. It made some serious steam for what it was and helped prove to the racers that there was power to be made by stepping up the chassis and turbine housing sizes.

Turbocharger technology development has been on a constant upward trend over the past 10 years. Almost as drastic as computer technology development. IE: Bigger better more efficient.

I will close by saying this. We have some Wicked turbos coming out very soon in the Sportsman chassis and Pro Mod chassis class of turbos. We are also actively building a new website so stay tuned for that. In the meantime, everyone can check out the original website located at www.precisionturbo.net and we also have our slightly newer shop.precisionturbo.net website. It has some of our latest turbocharger offerings, our boost control products as well as the swag.
Let's keep this thread alive guys. Maybe some of the real world users will let loose with some valuable intel.


Patrick Rubio

Precision Turbo & Engine

Technical Sales Representative
patrick.rubio@Wabtech.com

855-996-7832

NEW ADDRESS:
Precision Turbo & Engine
9401 Georgia Street
Suite 2
Crown Point, IN 46307

P.S. Pics for attention and lols...
:ROFLMAO:

GEN2 PT6870 CEA.png
 

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Mr.Spool

Well-Known Member
And the GEN 2 7270 fwhp rating has not been published yet
It will do around 1200 even in a 3 bolt.
That's combo specific.
The 3 bolts will do that.
I have pushed the 3 bolt with porting and custom wheels that's there as well.
From my experience the rpm range must be kept in check.
My 4 bolt car can make the same power and more with more rpm.
 

forcefed3.8's

Buckeye Bullet
7270 3 bolt FTW. It spools slightly slower than the 6870, but has less backpressure. Wastegate strategy helps with backpressure as well. You can bleed of backpressure once the turbo is spinning. I havent seen much of a rise in backpressure with rpm. My old TSM engine with a 7270 3 bolt went 8.19@166 on 34psi. Backpressure was over 72psi. Boost in the mid 20s backpressure was in the high 30s. Peak hp was at 6200 274" engine and a 224/224 xfi lobe cam with solid lifters tight lashed. I am a huge fan of the 3 bolt housing and 70 turbine. Great street set up.
 

Haulz A

Active Member
Howdy guys. Very interesting subject we have going here.
Mind if I chime in a bit?

What's been said by the others is correct.
The older GTQ turbine wheel equipped turbos with our .85 3-bolt turbine housing, was decent technology back in the early 2000's when we first released it. It was superseded by the HPQ turbine wheel, which lead to our previous generation CEA 68 turbine wheel and now the GEN 2 CEA 70 turbine wheel.
Just so everyone knows, I'm working on a new turbo comparison chart in my spare time, that will show the lineage and what we currently offer today for the true bolt on 3-bolt Buick applications.

Our Precision 3-bolt turbine housings have performed very well over the years with the technology that we had to work with. Many racers have set records using our products, all the while utilizing our off the shelf Precision 3-bolt Buick turbine housings. When the original Precision housings were first introduced, we saw significant flow increases over the original Garrett .63 and .82 offerings from the mid to late 80's. There always came a point, where the back pressure becomes an issue, especially when the boost is set to orbital insertion levels. The newer turbine wheel designs have drastically increased in efficiency, as well as raised the back pressure threshold across the entire board of turbocharged applications. IE: side by sides to Pro Mods. Power levels are literally reaching insane levels in the highest classes of racing.
As of now, we offer two 3-bolt turbine housing equipped turbos that would be a direct replacement for this stroker motor combo that would displace any GTQ / HPQ equipped turbo.


GEN 2 PT6870 BB HP Compressor Cover W/ Buick 3-bolt inlet .85 A/R turbine housing. Available with and without a HD wastegate actuator.
The official part numbers are:
21607215579 GEN 2 PT6870 BB HP CC w/ Buick 3-bolt .85 turbine housing and HD wastegate actuator.
21607215799 GEN 2 PT6870 BB HP CC w/ Buick 3-bolt .85 turbine housing and no wastegate actuator.

GEN 2 PT7270 BB HP Compressor Cover w/ Buick 3-bolt inlet .85 A/R turbine housing. Also available with and without a HD wastegate.
The official part numbers are:
21907215578 GEN 2 PT7270 BB HP CC w/ Buick 3-bolt .85 A/R turbine housing and HD wastegate actuator.
21907215579 GEN 2 PT7270 BB HP CC w/ Buick 3-bolt .85 A/R turbine housing and no wastegate actuator.

Now the next question will be this... How much HP can they support?
Answer? TBD... As more and more of them show up on these specific Buick 3-bolt combos and start blowing the heads off the engines, we will find out.
:LOL:

In all seriousness though, the GEN 2 6870 is technically listed as capable of supporting 1100 flywheel hp. And the GEN 2 7270 fwhp rating has not been published yet. Not very many vendors know or have tried it yet with the 3-bolt housing. Or if they have, they've kept the numbers close to the chest. We do have many other applications running this turbo with out T4 .81 and T4 .96 single inlet, tangential turbine housings with great results. I will say this though... It makes serious power.

With regards to the other models we offer with our Stainless all v-band turbine housings, all I can say right now is yes! We have a ton of options available from 1000 hp up to insanity hp levels. Our Sportsman chassis turbos, are the next upgrade in size compared to the standard T3/T4 chassis turbos that all of our Buick 3-bolt turbos have been based around. Everyone has seen this over the years in the various heads up Buick classes. And most of the serious racers know, that the ultimate limitations have always been the 3-bolt housing and the current level of technology available at the time with regards to turbine wheels and compressor wheels. We even developed the famous Cantaloupe 3-bolt turbine housing, to work with our PT88 turbo for a short time until it was banned from the class. It made some serious steam for what it was and helped prove to the racers that there was power to be made by stepping up the chassis and turbine housing sizes.

Turbocharger technology development has been on a constant upward trend over the past 10 years. Almost as drastic as computer technology development. IE: Bigger better more efficient.

I will close by saying this. We have some Wicked turbos coming out very soon in the Sportsman chassis and Pro Mod chassis class of turbos. We are also actively building a new website so stay tuned for that. In the meantime, everyone can check out the original website located at www.precisionturbo.net and we also have our slightly newer shop.precisionturbo.net website. It has some of our latest turbocharger offerings, our boost control products as well as the swag.
Let's keep this thread alive guys. Maybe some of the real world users will let loose with some valuable intel.


Patrick Rubio

Precision Turbo & Engine

Technical Sales Representative
patrick.rubio@Wabtech.com

855-996-7832

NEW ADDRESS:
Precision Turbo & Engine
9401 Georgia Street
Suite 2
Crown Point, IN 46307

P.S. Pics for attention and lols...
:ROFLMAO:

View attachment 354932
Rubio I talked to one of your colleagues @ the sweet16 radial race last week- we discussed some strategy’s on over coming three bolt turbo BP issues and the restrictive 3X2 compressor cover that I have to run in THS legal class. If you all can design a better and less restrictive turbine/compressor housing cover to compliment the current Gen2 wheels- we would probably gain about 20% or more efficiency in the compressor map with the current wheel design. Then our cars will make every bit of the advertised FWHP ratings on our Buick’s without twisting the engines rpm to the moon. Again thanks for everything you do @ Precision Turbo that helps our old cars be competitive to the newer cars of today.

Haulz. A
 

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Turbo1dr

Dual Fuel Injected
Here's a follow up on exhaust system back pressure instead of pre-turbine backpressure. I wanted to see how much my exhaust actually has.

I installed a pressure sensor on the downpipe about 1 foot after the turbo. At 30psi of boost, it has 8psi of exhaust back pressure. That's pretty high IMO. The 3.5" downpipe goes into a 3.5" flex joint and then tapers down to an ATR 3" single exhaust. In front of the axle, I've installed a 3" straight through SUMMIT RACING muffler. After that, I'm still using the ATR twin outlet crossflow muffler with tail pipes. Back in the late 90's, I owned an 89 Turbo Trans Am with a single Flowmaster crossflow muffler. It was already on the car when I bought it. I checked the backpressure and it had 7 psi on it. The car was running 7.50's in the 8th mile and when I removed it the car ran 7.30's on the next outing using a Flo-Pro muffler with 1.5psi of backpressure. That was a decent increase in power with no other changes. I have an automatic exhaust cut-out on my car but I've not been using it. I'll have to go do another sprint on the highway to see if opening it actually reduces the pressure.
 
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