How far could a pt67/76 dbb get me?

[20psiofevil]

I would shift it higher but you are limited with the 63 housing and may see a lot of back pressure at your level. You might be able to get 5800 rpm out of it. I think a larger turbine would help also.

 

[BEATAV8]

I was thinking same. Shift at a higher RPM. If you are running a BRF valve body in the trans you could look into an olds KC valve body.

 

[bison]

John Crawford ran 9.8x with this turbo years ago and the mph was close to 140mph iirc. 70-72lbs/min is plenty to run high 9's in a 3600lb car. This turbo will do it. Fwiw my car ran best shifting at 5500rpm with a 76 trim T04 when at 70lbs/min when I ran it with an MFS 62 compressor.


Sent from my iPhone using Tapatalk

 

[evil666]

John Crawford ran 9.8x with this turbo years ago and the mph was close to 140mph iirc. 70-72lbs/min is plenty to run high 9's in a 3600lb car. This turbo will do it. Fwiw my car ran best shifting at 5500rpm with a 76 trim T04 when at 70lbs/min when I ran it with an MFS 62 compressor.


Sent from my iPhone using Tapatalk

Hi Bison
I know John Crawford a little, he is from up here in Canada, maybe 2 hours away from me. He is a really nice guy but I haven't seen him for a while, or heard of him, I think he has taken a break from racing for a while. I don't know how much his car weighed, I know he had a small 206/206 roller cam and if I am not mistaken a front mount intercooler and GN1 heads which are probably better than my M&A heads. He did run very well with his pump gas and alky set up. I sent my Fast XFI files from 2 of my runs to Dusty to look at to see if there is something up with the convertor and I am thinking of getting my tranny built by David Hussek. When I get all of this worked out I will try to go back to the track next season and try to shift my car manually at a higher shift point and see where this brings me.
Bison, do you feel like looking at my files as well? I would really appreciate to hear what you think of my files as well.
Thanks,
Marco

 

[bison]

You can email me your files and I'll take a look. Based on what you've posted so far the converter isn't an issue. It's likely John was all in or close to it to run those numbers with that turbo. Heads likely aren't a limiting factor on yours or his engines. Chances are his 206/206 is an extreme energy lobe. I wouldn't call any of them small. Moderate aggressive lobes. The cam matters little when the turbo is close to all in or all in.


Sent from my iPhone using Tapatalk

 

[Ttype6]

Doesn't mph determine how hard you're being on parts? I would think an engine running at 140mph with turbo A @ 28psi would be just as hard as turbo B running 35psi at the same mph. As long as it's knock free, cylinder pressure should be the same.

This is so true. MPH is the result of horsepower. If two turbocharged V6 engines produce the same power at the same RPM with different amounts of boost,the pistons of each engine will be exposed to the same amount of downward force.

 

[Mr.Spool]

The car is not that far from the nines and this is with a flaring tranny on my second to 3rd shift and a convertor that I am not to sure is doing it's job wel

getting the trans fixed and some good air on a good track should put you into the 9's without major changes.you are going 10.15 right now

 

[Mr.Spool]

But to get 140 mph with this turbo, what should I change in my set? Maybe if I go to a bigger front mount intercooler instead of a stock location, roller cam set up and more boost

more boost and taking some weight out of the car.

 

[BEATAV8]

This is so true. MPH is the result of horsepower. If two turbocharged V6 engines produce the same power at the same RPM with different amounts of boost,the pistons of each engine will be exposed to the same amount of downward force.

Think about that for a bit....
Doesn't the engine with lower boost and lower back at that RPM also have lower peak cylinder pressure? Isn't it putting much less work effort into the turbocharger?

 

[bison]

There's a lot of things going on in a cylinder in a turbocharged engine. It's possible to pick up hp without increasing manifold pressure. I've even seen hp go up and fuel consumption stay the same or even regress by dropping exhaust pressure. There's pumping losses on the exhaust stroke that hurt the power. It doesn't necessarily have anything to do with the manifold pressure.


Sent from my iPhone using Tapatalk

 

[BEATAV8]

There's a lot of things going on in a cylinder in a turbocharged engine. It's possible to pick up hp without increasing manifold pressure. I've even seen hp go up and fuel consumption stay the same or even regress by dropping exhaust pressure. There's pumping losses on the exhaust stroke that hurt the power. It doesn't necessarily have anything to do with the manifold pressure.


Sent from my iPhone using Tapatalk

These examples sound like changes in overall engine efficiency.

 

[bison]

These examples sound like changes in overall engine efficiency.

Yes and the force exerted on the pistons and crank will vary. It's possible to make more power with less strain. I always take into account the exhaust pressure. If an engine is making 800hp and has 50psi ex pressure and another engine with the same power has 30psi the one with 30psi is likely an "easier" 800hp.


Sent from my iPhone using Tapatalk

 

[Ttype6]

Doesn't the engine with lower boost and lower back at that RPM also have lower peak cylinder pressure?

No. Boost pressure is a measurement of the pressure inside the intake manifold. It's a measurement of the air pressure that has not entered the cylinders. If we do things to remove the restrictions that limit the amount of air entering the combustion chambers (bigger cam,bigger valves,bigger ports,more cubic inches,),the engine becomes less of a restriction and it is easier for any given amount of air to enter the cylinders. If more air enters the cylinders easier the turbo's compressor doesn't have to work so hard to force it in. The result will be better cylinder filling with less pressure inside the intake manifold.

 

[BEATAV8]

No. Boost pressure is a measurement of the pressure inside the intake manifold. It's a measurement of the air pressure that has not entered the cylinders. If we do things to remove the restrictions that limit the amount of air entering the combustion chambers (bigger cam,bigger valves,bigger ports,more cubic inches,),the engine becomes less of a restriction and it is easier for any given amount of air to enter the cylinders. If more air enters the cylinders easier the turbo's compressor doesn't have to work so hard to force it in. The result will be better cylinder filling with less pressure inside the intake manifold.

I don't disagree with anything you're saying here about boost.

Think about the back pressure specifically, keeping in mind we're not changing the engine at all from one example to the next (just the turbo is different). Citing Bison's 800HP example... If an exhaust stroke has to pump against 50psi exhaust manifold pressure, it will require more work than it would if it had to pump against 30psi exhaust manifold pressure. The work to drive that pumping stroke comes from inertia (mass and RPM) and from the power stroke of the next firing cylinder. Since the engine mass, the RPM are all the same for the given case, then the only place that extra pumping work can come from is the next firing cylinder. That firing cylinder has to work harder to pump the exhaust out against the higher back pressure, meaning it needed additional air, fuel, timing, cylinder pressure that ended up loading the power cylinder more than the 30psi case. None of that extra work goes into the power output of the engine, it's just wasted as pumping work.

translating this back to the intake manifold: since the firing cylinder did not work as hard to pump the gasses, it did not require as much fill and therefore required less boost to generate/contribute to the 800HP output of the engine.

In the end, the newer more modern turbo will generate an "easier" 800HP than the older less efficient turbo that ran with higher back pressure.

 

[Ttype6]

In the end, the newer more modern turbo will generate an "easier" 800HP than the older less efficient turbo that ran with higher back pressure.

My writings are in response to the statement that we4Mateo made. He basically said that the pistons,of two different turbocharged V6 engines propelling two identical weight cars to the same MPH with different amounts of boost,will experience the same amount of downward force. My comments aren't about two different turbos although the same thing is true if the two engines have different turbos,cubic inches,cams,heads,etc. It takes X amount of downward force on the pistons to produce X amount of MPH with x amount of weight. The turbo might be working less,but the reciprocating assemble will be subject to the same amount of force generally speaking.
Boost numbers aren't the be all end all information. This is why I don't like the way piston ring manufacturers will recommend different end gaps for different boost numbers. This shouldn't be the only determining factor. If it were,I would run tighter ring gaps on my new bigger cam,bigger cubic inched,bigger valve engine because it will be making the same power I was making but I will be making it with less boost because the air will enter the cylinders easier. The thing that will remain the same is the downward force on my rings and pistons. It would be foolish to tighten my ring gaps based on their boost level recommendations. Their recommendations should be based on cylinder pressure/HP. we4Mateo has made a simple observation that too may people don't make.
Don't brag to me about how much boost you are able to run. You have to because your engine is so restrictive. In the mean time,I will brag about how little boost I run to get the same job done.

 

[20psiofevil]

An engine making 500 peak hp at 5400rpm has x amount of cylinder pressure. A similar motor making 500 peak hp at 6200 rpm is the cylinder pressure the same as the first? To me shifting the power to the right makes the combo more efficient at making power.

 

[we4Mateo]

Bottom line is not enough are looking at the pressure side of the equation on the exhaust side of things. The talk is always about boost. Makes sense that lower exhaust pressure makes more power at any given boost level vs a higher exhaust pressure. But how many measure the exhaust pressure like they do boost? The higher exhaust pressure setup is probably nice on the street

 

[Mr.Spool]

Makes sense that lower exhaust pressure makes more power at any given boost level vs a higher exhaust pressure

you can lower the backpressure to a point where the comp doesn't move enough air and the car slows down.actually all the faster cars I have seen run better with the correct amount of boost and a healthy amount of backpressure.the turbine and comp wheel must work with the ex gases volume in order to make the power.

 

[Mr.Spool]

An engine making 500 peak hp at 5400rpm has x amount of cylinder pressure. A similar motor making 500 peak hp at 6200 rpm is the cylinder pressure the same as the first? To me shifting the power to the right makes the combo more efficient at making power.

waiting 800 rpm to get the same power slows the car down.efficiency or not.

 

[Mr.Spool]

It's possible to make more power with less strain

is that measurable?are you referring to egt temps/intake charge temps on a 125 hp per hole combo?