Exhaust gas pressure with a turbo

I am a rank newbie as regards turbocharging, but would like to "do it right," so, in that vein, I bought a pressure gauge to complement my boost pressure gauge. I plan on trying to run as much as 30 pounds of boost on this motor (it has forged pistons, rods, and crank, and the block is O-ringed, so it may not immediately blow up in my face,) but I need some good information as regards the ratio between boost and exhaust back-pressure in the system just before the turbo.

I don't have a clue as to what sort of numbers would consititute an acceptable ratio: intake system to exhaust. I have heard 2:1 is okay, but I am SO lacking in knowledge, I need help with this...

Here is the gauge: http://www.summitracing.com/parts/atm-4325/overview/

Prine?

or, anybody else with experience with one of these gauges. It's an Auto Meter (brand) with a copper tube (mechanical-actuation,) that reads from 0 to 60psi, I figured that was enough range for my application. Was I right?

Thanks for any information...

Oh, the engine is a '64 Dodge, slant six.

you should be good with that. your turbo should be a little better then 2:1.

RustyPlymouth said:

you should be good with that. your turbo should be a little better then 2:1.

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What is better than 2:1? .... 1.7:1 or 2.3:1...? Supid question, but, I'm stupid, and ignorant. So, I ask...

Ideally, you want less exhaust pressure than intake pressure. A lot of it depends on the turbo manifold design and size of the turbine wheel and housing and exh pipe size exiting the turbo.

cdavis said:

Ideally, you want less exhaust pressure than intake pressure. A lot of it depends on the turbo manifold design and size of the turbine wheel and housing and exh pipe size exiting the turbo.

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Thanks Mr. Davis!

Here is a picture of the header, and the turbo is a 66mm Turbonetics that was used on a Buick Grand National that routinely runs high tens. My engine and that one have virtually identical displacements. Maybe it will work...rayer:rayer:rayer:

less exhaust pressure then intake wouldnt work. there has to be higher pressure on the hot side to be able to drive the cold side.

the closer to 1:1 the better but no so close that it wont spool. 2:1 is common, its also the upper end of the spectrum of desirable ratios.

RustyPlymouth said:

less exhaust pressure then intake wouldnt work. there has to be higher pressure on the hot side to be able to drive the cold side.

the closer to 1:1 the better but no so close that it wont spool. 2:1 is common, its also the upper end of the spectrum of desirable ratios.

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Thanks, Jr. The gauge came by UPS, today. It's 2 1/16" in diameter. I went out to buy a hole saw that size, but could only find a 2 1/8th". Hope it works! rayer:

It is a mistake to assume that exhaust gas pressure is the sole driver of intake pressure, EGT plays a role too. The total exhaust energy, pressure and temperature both, are what drives the turbine wheel.

ntsqd said:

It is a mistake to assume that exhaust gas pressure is the sole driver of intake pressure, EGT plays a role too. The total exhaust energy, pressure and temperature both, are what drives the turbine wheel.

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The pressure drives the turbine; the part that heat plays is, in expanding the gasses so they will create the pressure that drives
the wheel. You are, indeed, right; You have to have both.:cheers:

This may look like just a DIY gas turbine engine, but what it really is (was) is a turbocharger test stand. It was used to test this turbocharger under simulated engine loadings: http://propulsiontech.com/turbo.html & http://ecomotors.com/electrically-controlled-turbocharger#


That is me starting the generic turbo with a leaf blower. Cylinder at the far end is a combustion chamber. Compressor discharge was fed into it. With a VFD on the injection pump motor we varied the diesel injection pressure between 50 and 500 psi. The resulting hot gasses drove the turbine wheel. Eventually we put a throttle on the combustion chamber inlet to better simulate different engine loadings. Without it we could only trace a curved line thru the map. With it we could explore the whole map. We also got to the point where we were blowing those silicone bulge hoses off no matter what we did. As you may expect that was right around 40 psi. I eventually replaced them with more Marmon V-band assemblies.

ntsqd said:

This may look like just a DIY gas turbine engine, but what it really is (was) is a turbocharger test stand. It was used to test this turbocharger under simulated engine loadings:

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Thanks for the unique pic! That is impressive!

It's nice to put a face with a name...

Here's mine. I'm the idiot in the "Doctor of Motors" white coat... and my ex-partner who built most of this car I now own.

Here is a good article on int/exh pressure ratios. Under the sub heading "Turbo cam basics"

http://www.hotrod.com/how-to/engine/ctrp-1106-turbo-camshaft-guide/

cdavis said:

Here is a good article on int/exh pressure ratios. Under the sub heading "Turbo cam basics"

http://www.hotrod.com/how-to/engine/ctrp-1106-turbo-camshaft-guide/

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All good information and an interesting "read," I think. One thing wasn't addressed, though, because the article, probably, was written for a V-8 audience that has access to aftermarket heads that have increased flow capabilities "to the moon." The slant six head, (the only one available,) can be ported, and can use bigger valves to give somewhat increased flow, but the limiting factor here is not something that can be changed; small bores, which limit valve sizes to some pretty restrictive "breathing" numbers. It is unusual to see where anyone has achieved flow numbers on the intake side, exceeding 220 cfm which seems downright pitiful, when compared with the 302 small-block Chevy that can utilize aftermarket heads that can be worked to flow over 300 cfm, on the same size cylinder as a 225 motor (39 cubic inches.)

So, we do the best we can, which usually involves tapping the slant six's "ace in the hole:" the ability to withstand really large amounts of boost with no damage, if the engine was built with the right parts. That includes forged pistons, forged rods, O-rings, ARP 220.000psi cylinder-head studs, and a coppper head gasket. I am sure there are other factors and parts that could be used to increase the longivity of a high-boost, high-output 225 slant six, but this technology regarding the slant six in in its infancy with regard to using forced induction, even though the engine design dates back to 1960.

The utilization of supercharging or turbocharging on slant sixes is a relatively new phenomenon, and has a scarcity of information available because this is just not something people DID with these motors for decades... unaware of how much power was available through the magic of blowing the mixture in... They, instead, tried using conventional methods of getting more power, with results that were always less-than-spectacular, because of that strangulated head design. It was built for the 170 motor, and they increased the displacement to 225 and ignored the head... What could they do; the bores are so small there's no room for decent-size valves (the 302 Chevy has 2.02" intakes, stock, on the same size cylinder)

Turboing one of these motors is not particularly cheap, nor is it easy... (tuning the carb seems to be the hard part,) but the rewards are great for the folks who have the wherewithall and patience to endure the frustration and steep learning-curve long enough to make it work. Well-over 500 horsepower at only 5,500 rpm is available for those who have the tenacity and persistence to stick it out to the end, and that amount of power will move an A body into the tens... a result that will put a smile on almost anybody's face.:burnout:

I have a question? can you get 30psi of boost on gasoline or are you using alcohol?

bOb shingler said:

I have a question? can you get 30psi of boost on gasoline or are you using alcohol?

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Bob, my car is new, and I have not yet seen over 10 pounds of boost (waste gate set at 10 pounds,) but the two other cars I am familar with that run 28 pounds (and one, up to 37 pounds,) do it all on gasoline.

It might be easier on alcohol; I don't know.

Since my car is so new (I've on;y had it to the strip once, so far,) I wanted to get the chassis sorted out before trying to run more boost, but I surely will, shortly.

Stay tuned. I run race gas.

Just a note of caution, at around the 37-40 psi point you can't keep those Purosil hoses clamped down. No matter what kind of tube bead is under there they will blow off. If you go that high you'll need to go to either Wiggins couplings or Marmon V-bands. On the HGTS above we went to V-Bands because it was the easiest for us to customize and make custom flanges or adapters.

ntsqd said:

Just a note of caution, at around the 37-40 psi point you can't keep those Purosil hoses clamped down. No matter what kind of tube bead is under there they will blow off. If you go that high you'll need to go to either Wiggins couplings or Marmon V-bands. On the HGTS above we went to V-Bands because it was the easiest for us to customize and make custom flanges or adapters.

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Thom,
I read your entine '65 Valiant build thread on the .org forum. It was very interesting.

I have three questions for you, and please don't take this wrong; everyone has his own ideas about how to do things; Mine are coming from an old brain that has probably seen better days... and is apparently incapable of "thinking outside the box." I guess I am just set in my ways and too old to change, at 76.:banghead:

But, I was wondering: With all the knowledge you obviously possess about forced induction, and your deep involvement and experience with /6s, how is it that your super-cool '65 Valiant is going to have to go through life naturally-aspirated? It deserves better! An A body powered by a slant six without a turbocharger (or, supercharger,) is like a rhinocerus without a tusk. That original head is SO restrictive, the only way around that strangulated chunk of cast iron is forced induction of some sort (or, nitrous.) Even a super-mild 10 pounds of boost can put that car into the mid 13's, a full second ahead of a stock 340 Duster. It will turn a ho-hum slant six into an exciting, fun-to-drive, muscle-car beater. And, you don't need fuel injection to achieve this. The potential for an easy 300 horsepower is tanalizing. That would drop that BEAUTIFUL '65 sedan, into the good 12's... The lack of enthusiasm on your part for this route had me puzzled, so, I had to ask, nosy old bastard that I am...

Assuming that you actually put a hairdryer on that lightweight A body, you could install a plenty-strong, 8.25" Duster or Aspen/Volare rear with minimal modifications, and utlilze the OEM 2.76:1 gears to advantage. It would enable you to forget about an overdrive, as the turbo slants seem to perform their best with axle-ratios in the "twos." They don't seem to need ratios in the 4's to run their best in drag contests. Weird, but true; Both Tom Wolfe and Ryan Peterson's slant-powered cars (500+ horsepower, each,) have been tested both ways and the 2.76 rears out-performed higher-numerical ratios, running faster and quicker.;.

THIS would allow you to run a 904, insted of a manual/overdrive box for highway cruising.

Tubos and automatics seem to go together exceedingly well.


That '65 is YOUR car to be built the way YOU want it, and I am sure that is what will happen, and SHOULD happen. I just thought I'd suggest some alternative ideas for it...
Ideas that seem to make sense to me, but, that's just ME.... YMMV!

This was my 340-powerewd '64 V-100. :wack:

I wouldn't say that I've got extensive or in-depth knowledge of turbo engines, only in the testing of turbo's on that stand. And of that, I built the stand, I only have testing experience from helping those doing the actual testing as part of my responsibilities to developing the stand.

The car came to me with the turbo off of a 3.0L Audi in the trunk. I need to build an exhaust manifold for it that doesn't have the massive heat riser hole in the top of it. The plan for that manifold is to locate the appropriate place for the turbo to sit, terminate it in a turbo flange, and then build a head pipe with a matching turbo flange. I've already sourced both flanges and have surface ground them to be truly flat. I know that welding and use will warp them a little, but at least they're starting out really flat instead of just a piece of plate cut out to the right shape. If/when it gets the turbo I'll just build a new head pipe.

I want EFI, the over-all plan is for this car to be a DD and "date night" car. I've messed with carbs long enough, I want something different. Having driven both, the best tuned carb can only compete with EFI in drivability for a short while. Then you have to tune/tweak again because the seasons changed or you drove out of the tuned-for altitude or........ I want a driver, not an on-going project. I have of the latter in this: http://www.gofastbroncos.com/forum/viewtopic.php?f=34&t=2252&sid=a84b87d81ce16f96976698649089ca69

Current engine is a 170 and that will not change. Lots of people have tried to talk me into a 225. They're wasting their breath, and some seem bent on continuing to do so. Current engine has a very large oil leak that is somewhere around the oil pump. Which pretty much means that the engine has to come out to get to it. If I'm going to pull it I'm going fix everything else wrong with it too, so my other 170 is waiting it's turn in line at my local favored engine builder.
IF I can't get the moderate mileage and performance goals out of the / it will get an engine swap, but not to a 225 or a V8. It will get an OM-617 or a an OM-603 Merc turbo-diesel.

I like the manual. This isn't a drag car. If anything it's to be a very occasional auto-x car, but mostly a curvy roads & DD car.

ntsqd said:

I wouldn't say that I've got extensive or in-depth knowledge of turbo engines, only in the testing of turbo's on that stand. And of that, I built the stand, I only have testing experience from helping those doing the actual testing as part of my responsibilities to developing the stand.

The car came to me with the turbo off of a 3.0L Audi in the trunk. I need to build an exhaust manifold for it that doesn't have the massive heat riser hole in the top of it. The plan for that manifold is to locate the appropriate place for the turbo to sit, terminate it in a turbo flange, and then build a head pipe with a matching turbo flange. I've already sourced both flanges and have surface ground them to be truly flat. I know that welding and use will warp them a little, but at least they're starting out really flat instead of just a piece of plate cut out to the right shape. If/when it gets the turbo I'll just build a new head pipe.

I want EFI, the over-all plan is for this car to be a DD and "date night" car. I've messed with carbs long enough, I want something different. Having driven both, the best tuned carb can only compete with EFI in drivability for a short while. Then you have to tune/tweak again because the seasons changed or you drove out of the tuned-for altitude or........ I want a driver, not an on-going project. I have of the latter in this: http://www.gofastbroncos.com/forum/viewtopic.php?f=34&t=2252&sid=a84b87d81ce16f96976698649089ca69

Current engine is a 170 and that will not change. Lots of people have tried to talk me into a 225. They're wasting their breath, and some seem bent on continuing to do so. Current engine has a very large oil leak that is somewhere around the oil pump. Which pretty much means that the engine has to come out to get to it. If I'm going to pull it I'm going fix everything else wrong with it too, so my other 170 is waiting it's turn in line at my local favored engine builder.
IF I can't get the moderate mileage and performance goals out of the / it will get an engine swap, but not to a 225 or a V8. It will get an OM-617 or a an OM-603 Merc turbo-diesel.

I like the manual. This isn't a drag car. If anything it's to be a very occasional auto-x car, but mostly a curvy roads & DD car.

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Thank you for your timely, complete, and well-reasoned response. The 170 has its upside, and I promise you, I won't try to talk you out of it; you obviously know what you want.

I appreciate the time you took to write that! Have fun with your projects!

Different strokes for different folks...:cheers: