Dyno Plot Question
 

Hi,

I did 3 chassis dyno pulls last night on my fresh street ported 13B. It makes peek power and starts to drop off at 7000 RPM. My last street port (different builder) pulled easily to 10K, I never dynoed it. The new engine now has 2 to 3 hours on it since the rebuild.

Here is what my setup:
- early 4 port irons
- GXL-SE rotor housings
- S5 rotors
- carbon apex seals
- 48IDA with 225 mains and 160 airs 38 mm venturies
- holly blue pump with 5 psi fuel pressure
- 1st gen inductive pickup distributor
- 2 MSD 6As and blaster coils
- 4.88 gears with a 72" circumference tire


I have attached the dyno plot. Which says it is running a bit rich. I was thinking it should make around 200-210 hp at the shaft. Given 17% driveline losses, it would only be around 180. One thing to note, it is a bitch to start after it comes up to operating temperature. I am racing this weekend so any ideas on why it is dropping off so would be appreciated.

thanks,
Ron

i'd never recommend doing a dyno pull on a cold engine, but i wonder if the builder put the seals together too tight and it's losing compression.

does it continuously lose power the hotter it gets? maybe pop in a colder thermostat and see what that does?

I am going to do a compression test tonight. Would bad compression not be throughout the whole power band though? The 3 pulls were done at 190 degree water temp. It did produce the most power on the first pull.

1st pull 0 deg advance
2nd pull 2 deg advance
3rd pull 3 deg retard

I guess lack of compression would cause it to hard start when hot. To start it when it's hot, you have to alternate between running the fuel pump on and off. Perhaps there is too much fuel pressure?

Why don't you let the thing break in a little...

The current engine's builder set that it was broken in after 1 1/2 hours. I did break the previous engine in much easier as it was first in a street car. However this is a race car that can't be driven on the street so it got it's break in doing some progressively harder lapping after an easy 1 1/2 of running.

Since I have never dynoed a rotary before, where does the power band of a street port normally drop off?

No point checking the compression. I removed all of the plugs after getting the engine up to temp and the rear housing is pumping water out the plug holes when cranking. Nice bit of water in the oil too. So actually the dyno plot was good considering the state of the thing. It's out now and back to the builder on Monday. So much for racing on the weekend.

thanks for the replies.
Ron