2017 engine build

[Cobra #3170]

Here is a photo of the new Sonny Bryant short stroke small bearing crank. Note center throw counter weight. 9300 rpm can't be far away!

[/url]

[1795]

Pretty impressive! Looks nice.

[Dwight]

very interesting

Tell us more


Dwight

[Cobra #3170]

Originally Posted by Dwight

very interesting

Tell us more


Dwight

They have not finished the heads yet so no flow numbers but I think it will be down on HP vs last year probably around 800 or a little less. We are about 4 weeks from dyno runs. Changing to FAST XFI injection and a different data acquisition system with predictive lap timing so that he will know where he is as he runs vs a target lap. RED Yellow Green lights on cowl. Scott is good enough to read stuff like that and push harder if needed.

[Blue66]

Wow !! It's great your working the FE. I am still stuck in 1970

[olddog]

Originally Posted by Cobra #3170

Here is a photo of the new Sonny Bryant short stroke small bearing crank. Note center throw counter weight. 9300 rpm can't be far away!

[/url]

Out of curiosity, what was the bore and stroke in the old engine and what will the new engine be?

[Cobra #3170]

Originally Posted by olddog

Out of curiosity, what was the bore and stroke in the old engine and what will the new engine be?

Old engine bore = 4.32 stroke = 4.25

New engine bore = 4.32 stroke = 3.75

[olddog]

By my old rule of thumb you are likely giving up 75 ft-lb of torque, but if you spin it to 9300 you should make the same Hp as the bigger motor made at 8200. Since you changed the ramps on the cam, you should pick up a bit more power.

I'm not sure that you are going to gain anything in the usable power range, in terms of MPH of the car, assuming that the gear ratio change has you running the same speed at maximum rpm of both engines. At least in theory you would need ~13% more rpm to put the same Hp to the wheels at the lower torque output. Wherever the torque dropped off (on the low rpm side of the torque curve) happen on the long stroke, it should happen on the short stroke at 13% higher rpm. So the usable torque range of both engines should give the same speed range, even though the rpm range of the short stroke is a bit longer.

That said, theorys don't always hold water. Since you said you already had too much torque to start with, I would bet this is going to help you out a bit. You may have to play with the rear end ratio a bit. I'm thinking you do not want to drop the ratio as much as the stroke ratio was changed. Maybe half way.

Keep us informed, I find this quite interesting.

[1795]

I think what 3170 is trying to gain with the higher rpm range is the ability to shift at a later point, or not shift at all in certain situations, on the courses that he will be racing on. The lower torque will not bother him that much, and even if there was a cost to the lower torus it would be more than offset by the ability to avoid several shifts during the course. Upshifting, and especially downshifting adds to the total time on a race course. Whether it be in a solo event or on a road course.