ptuomov

I am allowing for less than perfectly matched transmissions, rear differentials, unexpected events, etc. that prevent shifting at exactly the optimal point. Building in a bit of flexibility. Plus 1.5 is a nice round number, I can do the math in my head! ;-)

Do you have a better SIMPLE approximation in mind?

By the way, is there some simple and reasonably accurate approximation for the time spent at each rpm level? Is it something (just guessing) like inversely proportional to torque at that rpm level? Being lazy here, not thinking it thru.

mark kibort

actually, im like you . I like nice round numbers, so I use the .72% number because the nice round numbers are 4500 rpm to 6400rpm. (close enough)
Then, just take into account the shapes of the HP curve to determine if the time spent up top in a higher range is an advantage. in most cases, its only a 5% advantage, in a curve that is quite a bit different.

averaging is probably just fine, and as we know, its a simple integration of the curve with a pretty accurate result.

mk

ptuomov

Couldn't resist coming back to this thread and seeing where our first tuning day landed us. I am eyeballing about 540 average whp for the 4333-6500 range from my graph. I may have optimistic eyeballs, perhaps I am like one of those parents judging their figure skating daughters performance...

IcemanG17

540whp average from 4300rpm or so (once it crosses 500whp) seems about right....since its probably 530whp when you shut it down at 6500rpm....

Do you have any dyno runs on this engine BEFORE the TT? Now that would be REALLY interesting!!

mark kibort

looks like 540 to me and thats using an average, which is a simple intergration anyway.

IcemanG17

Alright MK its time to TT your stroker!!!!!!!!!!!!!!!!!!!!!!!!!!! Hmm 572whp out of 5L is 114HP/L....or about 740whp from your stroker!!!! I wonder how much that would improve lap times???

Hilton

Bah, forget TTing it.. Sharktuning it would be a good start

ptuomov

Another entry:

https://rennlist.com/forums/928-foru...le-report.html

Carl's race car appers to be making about 640 rwhp average between 4500 and 6750 rpm.

It's a 6.5 liter engine so it's about 100 average rwhp per liter, with a centrifugal supercharger. There seems to be a lot of head room to make more power with the engine. It needs more rpm, much like the other very high power centrifugal engine in this thread.

Mike Simard

Thanks! I do like the idea of a simple engine. Just your basic big healthy engine that's simple, strong, doesn't overheat or detonate and is always there for you..Ahh

Tuomo, there is something specific to my 928 engine and another that I did with big individual throttles. They both have a 'camel hump' torque curve with a dip at midrange. You can't tell from the dyno chart you posted, there were some funky fueling issues during that pull, but driving the car it's very noticable.
At low rpms it's very strong, like a low rpm American muscle car and presumebly dips around 3k or so. At 4k it then feels like something big kicking in and stays that way. I don't know why the dyno chart doesn't show that but you can really feel it as acceleration. The car will run away from everything on track once it gets over 4k.
BTW, I actually don't think that camel hump is purely ITBs, on the other engine it was present even with a normal intake but same exhasut and cam. It's a bit of a mystery to me but not a problem. Being strong both off idle and up high is nice and you never know there was a hump until it kicks in over 4k, it's engine 'character'!

I expect to see 1000+ HP out of Todd's garage any day now...

ptuomov

If one doesn't use any sort of dual mode resonance intake and instead just has constant length intake runners, the short port + runner length will based on my sims create two resonant frequencies. For example, one at 3000 rpm and another at 6000 rpm. Then, if the engine gets "on" the cam at 4000 rpm, one should get valley between 3000 and 4000 rpm. Noob speculations, for what it's worth.

For a turbo engine with a good controller, one only has to worry about what happens before the turbos spool. For example, for my car, the stock intake manifold isn't horrible because it does give a good low-end torque and then to an extent I can turn up the boost after 5500 rpm where the stock intake manifold falls flat on its face.

1000 rwhp x-1.5x rpm average with pump gas and 5.0L would deserve a serious hat tip. One would have to use some revs as well as boost and build the whole engine from get go navigating around the octane constraint. I am having hard time trying to figure out how to get much above where I am now with my car with 93 pump gas and I am only about half way from that 1000 rwhp average. With race gas a turbo car can do almost anything, but with pump gas it's a difficult balancing act.

blown 87

The best speeds while doing a 1/4 mile seem to use a lot of this.

928mac

Hmmm yes, liquid dynamite

ptuomov

When I was a kid, my father run an engine at 30,000 rpm in -15C weather using 25% nitromethane, 60% methanol, and 15% oil.

It was a model airplane engine, Rossi I think. But still, we had nitromethane and methanol in the garage, imagine the number of permits needed for that.

with hindsight, I should've tried that cocktail in my 50cc Suzuki PV moped (actually 73cc but who's counting).

RKD in OKC

When I was into R/C planes a typical .5 cuin engine would produce about 1 hp on nitro methane. You put a big enough propeller on it so it maxes out at about 15K rpm, you don't really want the tips of the propeller going supersonic. I ran my model plane nitro methane in my old worn out weed eater that wouldn't even start on gasoline any more. Kinda expensive even back then at $11 a gallon.

ptuomov

The bring your own oxygen parties are the best kind! Before thinking it thru and seeing it in practice, I had no concept of how much more power nitromethane makes than anything that doesn't carry its own oxygen.

The Rossis did do about 30k rpm. This was almost thrity years ago so maybe my memory has been incrementing the rpm count. It may have been a single blade propeller with a counterweight. There were so many, the first four stroke R/C plane engines I remember, those started so reliably it was incredible compared to the two strokers which basically run whenever they felt like it (or encouraged with nitro).

The original rpm number, whatever it was, was measured with home brewed tachometers. The old man built a tachometer that measured the pulse from sound waves. He did another one which was optical signal from the propeller.