I feel a big rush of power around 7250rpm. Maybe it's just a coincidence?

Perhaps it's different on a SC setup ??? I have mucked around with it a lot and eventually decided it was better for the powerband that it didn't open when it does . Might be an advantage to leave it open rather than closed ...haven't tried that .

Did a test to check boost pressure drop over the intercooler and pipework . Looks like around 2psi total at peak rpm (7500) and close to zero at 4000rpm .
Boost at manifold :

https://cimg1.ibsrv.net/gimg/www.rx8...ee2c75290e.png



Boost at turbo:
https://cimg8.ibsrv.net/gimg/www.rx8...dd508136da.png


From this and other previous tests I believe I have the following pressure losses (at 14.5psi) in the system at this point:

Intercooler pipework turbo to intake mani. : 2.5 psi
Muffler system : 2.5psi
Intake system : 1.5 psi

None of the above is huge but you can see they all add up and each has an effect on turbine back-pressure.The task to get turbine back-pressure down further from here is very difficult and expensive. I can now see how it would be a crap load easier to get the best WHP from a top mount system.

Paging Slash. Slash please report to the thread....

Great analysis Brett, thanks for sharing your findings.

Edit: Would be good to compare this with losses on a Greddy setup, being the most common turbo setup. For those that want to tweak their Greddy setups for more efficiency.

I hate to think what those are on a stock Greddy ! Wasn't yours over 30psi turbine backpressure at only 10psi and 7000rpm ? And your setup would be much better than a stock Greddy .

That's right, with my best Greddy setup at 7krpm and 10psi the exhaust manifold backpressure was 33psi, giving a BPR (back pressure ratio) of 3.3:1 - pretty inefficient and unhealthy for a turbo setup. I'm hoping my new setup with Greddy manifold and external wastegate will give a lower ratio (will update my thread after this weekend).

Have any of you guys measured temps at the compressor outlet? I doubt it but thought I would ask.

I haven't. My IAT sensor is located after IC before TB. Once I installed it I found that it was a bit laggy with the readings, not showing instantaneous temp. Would only produce useful results in a prolonged pull at fixed load/rpm/boost. Why are you asking, IC sizing?

I just know some high HP turbo drag guys use the temperature at the compressor outlet to determine if the backpressure is too high. But you need an IAT sensor that will read to like 400F or so.

Not sure why they wouldn't just look at the backpressure if they want to determine the backpressure?
Reminded of a quote from Corky Bells'Book re turbo systems ... "everything depends on everything else"

Easier to tap a compressor housing than a manifold is my guess.

Here is my latest dyno . Taking into consideration that this dyno reads conservatively (akin to a Mustang in the US) I think the results are pretty good . Best peak number I've made so far and far and away the best torque at 302lb/ft .


https://cimg3.ibsrv.net/gimg/www.rx8...f04ef478db.jpg


The difference between this and my earlier 411whp dyno is that the engine was comfortable at this power level . The dropoff of boost at the end of the run is due to where I set the wastegate to open.

For anyone that doubts the effectiveness of virtual dyno (when used properly) check this actual dyno vs the VD on the previous page . Within 1% on both power and torque !

How are you judging the engines comfort level? Is it just back pressure? Is there any other signs like exhaust temp?

Can you run more boost or rpm?

I'm checking the rise in boost against the extra power from that rise . Up to 14-15psi I get a pretty steady 14-15 whp per psi of boost . After 15 it drops away to less than 10. Also the boost is starting to fluctuate a lot ...although the smoothing on the dyno log doesn't show that , I can seee it on my aem logs .

Really didn't want to take it higher given the idicators .

Thanks for sharing.
Those indicators sound like they indicate limitations in the turbine and plumbing?
What about combustion pressure, how do you judge that?

Yes , that would seem to be the case . Although I do suspect that the porting work I did as part of the patent has actually hindered high end power while improving low end and mid range torque . While this makes the car awesome to drive ..... it doesn't help the peak power which everyone judges it by .

Combustion pressure ....no idea ....

I suppose I'm getting back to your comments in this post https://www.rx8club.com/showpost.php?p=4826030&postcount=1339
where you think the exhaust ports are overwhelmed rasing combustion pressure.
I would like to know if you think you could run to 9k and higher boost without the backpressure of the turbine?

Ah got ya now .
Short answer ...no . SC or turbo ...backpressure or not .
I've changed my thinking a little since then - I think past a certain engine flow /chamber pressure - it's the siamese port sleeve that becomes the overriding issue, not the exhaust ports themselves.

but that flow rate would have be influenced by rpm, boost and backpressure and a whole lot of other related factors. Do you find a definate limiting point and how do you spot it?

Yes absolutely "everything effects everything else" so the limiting point must be affected by those things . However, in my experiences plus looking at what others have done , it appears this particular issue raises it's ugly head at a certain point no matter what setup you have.
As far as spotting it ... diminishing returns from boost , even though you think you have everything in place to minimise backpressure.

Sorry if I've missed it( I haven't read all 63 pages)... What happens in the higher RPMS if you don't drop the wastegate duty cycle? Do you have the virtual dyno sheets of this?

Well in the past ...engine destroying detonation ...not sure if this particular engine will be the same but I'd rather errr on the side of caution!


Yep ... see page 62 ...results are amazingly close !

Congratulations Brett! 381hp at 13psi is a fantastic result, I'd say. It means that a boost that does not reduce life expectancy of engine drastically, can actually deliver very impressive numbers. On top of that torque is nice and flat, not just a big lump.

:bowdown:

Thanks man .... It's actually at the point I can say it's a genuine 400whp daily now as the power/boost doesn't start dropping away till over 15psi so I know the engine is happy there.

Just did this comparison so you can see what I mean :

Assuming the base for an NA engine is 190whp

up to 14.3psi I get 14.6 whp for every psi of boost

from 14.3 to 15.9psi I only get 7.5 whp for each additional psi .

So the return from the extra boost is HALVED after 14.3psi !

BTW :we did another run at 14.3psi which netted 405whp