how much hp to turn impeller?

[LVjetboy]

21Rayson, 71.4 mph...nice jet. ZZ4 crate "rated" power not the same as impeller "required" power at the lake. Rated power most likely at different conditions than your lake test...so you see less power absorbed by the impeller at lower rpm's.
So also follows the 1.2 hp/cuin. This power-to-cubic-inches based on corrected or measured? Based on race fuel or dock gas compression? As info posted, rated at what rpm? These things not unknowable or mysterious, just need accounting for to compare oranges to oranges.
jer

[Duke]

Originally posted by Jet City Rebel
Looks like 338hp to me. It would take 430hp @ 5417rpm for that same boat to see 80mph (I was curious).
Blown 472, sorry about the bunk numbers, I based off berk imp.
that mean 100 shot of n2 will take you to 80...

[Infomaniac]

10.5 compression is a bit beyond pump gas. It can be done but the engine has to be very cool and the timing backed WAY off.
1.2 HP/CID is my standard for pump gas carb n/a engines. 9.6:1 at the most running at normal Mercruiser type RPM's. Typical boat engine.
You can get more from one of these engines with a big solid cam and a lot more RPM's, but would not be able to use those RPM's in the boat. Could claim the HP numbers though.

[HOSS]

I have 10.25 comp in my 350. Iron heads. Combustion chamber shape plays a big role. Run pump with 36 total.

[Infomaniac]

Originally posted by HOSS
I have 10.25 comp in my 350. Iron heads. Combustion chamber shape plays a big role. Run pump with 36 total.
Are you positive about the exact compression ratio?

[HOSS]

Yes. I have Dart 2 Sportsmans. 72cc, .060, want to say 15 off the deck but could be 25, .028 compressed composite gasket

[HOSS]

Sorry, flat tops. 2 valve reliefs. TRW`s forged.

[Infomaniac]

pretty close
10.11 pistons .005 in the hole less if more in the hole
10.236 zero deck.
only allowing 2cc for valve reliefs. less if 4cc reliefs.

[Jet City]

Originally posted by LVjetboy
21Rayson, 71.4 mph...nice jet. ZZ4 crate "rated" power not the same as impeller "required" power at the lake. Rated power most likely at different conditions than your lake test...so you see less power absorbed by the impeller at lower rpm's.
So also follows the 1.2 hp/cuin. This power-to-cubic-inches based on corrected or measured? Based on race fuel or dock gas compression? As info posted, rated at what rpm? These things not unknowable or mysterious, just need accounting for to compare oranges to oranges.
jer
I had a similar thought, lots of variables between the GM dyno run that determined that HP rating and a lake speed run. The biggest one in my mind is engine temp, many of these boats run far cooler than what is best for peak power output. On a side note, I think 71.4 mph out of a glass lake hull/ZZ4 crate engine kick's ass!

[DogHouse]

Originally posted by Infomaniac
10.5 compression is a bit beyond pump gas. It can be done but the engine has to be very cool and the timing backed WAY off.
1.2 HP/CID is my standard for pump gas carb n/a engines. 9.6:1 at the most running at normal Mercruiser type RPM's. Typical boat engine.
You can get more from one of these engines with a big solid cam and a lot more RPM's, but would not be able to use those RPM's in the boat. Could claim the HP numbers though.
Well I hate to be argumentative, ok not really, but here are the hp/ci numbers we made, also posted in another thread:
With n/a EFI, 91 oct, we made 1.22 @5000, 1.32 @5500, 1.34 at 6000, 1.36 @6500, corrected of course because that's the only way to provide meaningful comparisons of engines tested on different days under different conditions. Yes, in the boat on a normal blazing hot day they will be lower. My boat regularly sees over 6k rpm. This motor also idles between 800-900 rpm and carries over 700 ft-lbs torque from 3100-6000 rpm. No exotic parts here, just a solid roller, coatings, 10.8:1, 36 deg timing, coolant temp while on the dyno in the 150-160 range, no detonation, EFI with knock sensor just in case. Tested on Larry Peto's "fudge factory" dyno. Anyone who doubts the validity of Larry's work or his dyno, just go to Havasu for a poker run and see who everyone is chasing at 165 mph. Ok, this last poker run not withstanding (blown freeze plug, oops, everyone has a bad day now and then). I think that the 1.2 number is a good target for a mellow low maintenance motor (i.e. hydraulic roller valve trane) that can also be tolerant of lessor grade fuels, but it is not the cutting edge of pump gas any more.