Turbo Tech: 7sec boost run(s) compared - draw through & blow through

[kmart356]

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The graph is a comparison of a boost vs rpm data capture for two different engines, one a draw through turbo engine and the other a blow through turbo engine.

Both of these engines have 140 heads with similar CR, 140 exhaust tubes/logs.
The draw through has an F/B turbo and the blow through has an E/B turbo.
Fuel on both is provided by carburetor, spark is controlled by programmable timing box, water-methanol starts spraying at .5psi on both engines to help manage AFR.
Wastegates have 13psi springs on both engines - neither of these boost runs was limited by the wastegate.

The data was logged using the an EBC controller (one installed on each engine). I managed to find a boost run from each engine that started at the same rpm and used that as a start point for each of the 7sec plots. RPM is scaled to fit the vertical axis. Boost is "actual" as logged by the controller.

Observations include some expected & some unexpected (to be investigated).

The E/B larger compressor leads the F/B in creating boost but the rate of increase is very close once the F/B gets going.
The blow through turbo looks to be limited after 7psi as it starts to flatten out. After hitting 8.9psi peak it falls off a bit.
The blow through continued to rev smoothly up to 5600+ RPM...the boost limitation is under investigation.
The draw through turbo RPM curve is slightly less aggressive (rate of increase) compared to the blow through RPM curve and with a little push from 4500RPM to 5500RPM the draw through should be able to hit that wastegate.

Yes, I am a bit of a geek with this data analysis stuff, I admit it.

[toms73novass]

Bit of a Geek.

Love how you can analyze the data. I stare at it and see those 3d images like from the 90's of rabbits and such.

BTW, for those reading, mine is the other engine. I do have to solve crossover to carb seal. It might involve reengineering the crossover, OH BOY!

[chris]

Geek out all you want because it's good information and I enjoy reading it!

[Nashfan]

Another geeky observation that I made- The E-flow seems to only gain .5 psi over the F at the same engine rpm. As big as the inlet inducers are on those, I wonder if the compressor housing on the E is a machined F. If it is the graph makes a lot more sense because those machined housings are the same size as the stock F, all the way to the portion where it has been machined bigger to fit the larger inducer.

[toms73novass]

I wonder if the compressor housing on the E is a machined F.

Kevin,
I am not sure, I will have the car finally out of storage next weekend and take a closer look. I know that it is not the same as the stock housing and can not find a pic right now.
Also, I will be installing my roller fan belt guide and begin to get more aggressive with it. I really did not have time to fine tune all the parameters last season due to having to handle my uncles estate.

[kmart356]

When you get a look at your compressor housing this is the Rajay E-flow compressor housing to compare.
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Rajay E-flow turbo.jpg (14.78 KiB) Viewed 212 times

[Nashfan]

If its a machined housing it will only be around 1.8" at the inlet. I had one of these and it was not a stock housing but did have a three bolt triangle flange as though it was a F housing and turbo. In fact, I ran it for a long time and thought it was a stock F. But then with the carb off and looking down the inlet I finally noticed that the inducers were way different than a stock F and then noticed the housing wasnt a stock F either!!

[Spectre]

Could the lower boost on the blow through system simply be the result of better flow through the carbs?

[Nashfan]

Could the lower boost on the blow through system simply be the result of better flow through the carbs?

Theres 3 reasons why that isnt what is happening. The first is that the draw through doesnt have any carbs where the blow through has them and is more or less flowing as a perfect round hole, so the draw through has the flow advantage at that spot in the system, and both are reading boost at the same spot so flow is "showing up" just as well in both cases. The second reason is that while mechanically driven superchargers (centrifugal or otherwise) will experience a loss of boost if the heads or rest of the inlet to the engine are modified for more flow, it doesnt work that way on turbos... any extra flow gained in the intake automatically gets turned into more exhaust, which spins the compressor ever faster, leading to more boost. Lastly, even if boost was being lost from more inlet flow like a mechanically driven supercharger does, it wouldnt hit some boost level and then flat line like is happening. Both set-ups have their waste gates set at the same boost level so should actually flat line at the same boost, even though the blow through is slightly ahead at the same rpm from a different compressor.

[KenHenry]

Interesting that the draw through F is building higher boost while the RPM is increasing at a slower rate. Different gear ratios maybe? Is the blow through running 4 carbs? And what carb is the draw through running? Ken

[toms73novass]

Interesting that the draw through F is building higher boost while the RPM is increasing at a slower rate. Different gear ratios maybe? Is the blow through running 4 carbs? And what carb is the draw through running? Ken

Ken, I believe that I have a intake boost leak after 7 psi and that is what is causing the flattening of the curve. I have to develop a better method of sealing to the top of the carbs. Yes it is 4 carbs. Ken is using a Mikuni carb.

My car has 3.55 gearing

[KenHenry]

Thanks Tom, I’m still in the mock up stage and will post more later, but I’m planning a Mikuni throttle body turbo for my car. It’s from a Suzuki TL1000 w 2 870cc injectors fitted. Hope it works!
Ken

[toms73novass]

BTW My housing is an E housing, B hot side.