Don Terrill’s Speed-Talk

I read that Chevy is doing an engine for some road racing venue that requires production of 300 street units. It will have a flat plane crank 5.5 liter v8. Is there some benefit of using flat plane cranks in road racing? I am ignorant of higher end race engines, but I'm pretty sure that if flat plane cranks made more peak horsepower, serious drag engines would be using them

Far as I know, the only benefit is that the exhaust tuning can be better.

The downside is vibration/shake.

I don't know about balance factors, and how they may or may not make life easier on the main bearings/main saddles.

Yes, the new factory Corvette C8R has a 5.5l flat plane crank. It was pretty clear when the car started up when it was unveiled. It will be at the Petit LeMans at Road Atlanta this weekend, and demo laps to be done before the race Saturday morning.

Remember, these application are heavily restricted with sonic choked restrictors being used to keep it at 500hp NA. These are also endurance applications, which anymore are just 12-24hr long sprint races, so it will absolutely be reliable. The 12hrs of Sebring, 24hrs of Daytona, and 24hrs of LeMans should ring a bell.

Likely, the flat plane crank will likely smooth things out in the air box (which is sealed and split into banks) and exhaust side, which should help with the restrictors they use. Also being mid engine, they likely don’t have have enough length to have a crossover or combine the banks into a single pipe, so the engine now is basically two I-4s with a shared crank.


The engine also has DOHCs.

Lastly, being a factory effort, this is the real deal, factory resource, kind of development program.

A flat-plane crankshaft makes complete sense in an application like this. It will spread out the pull on the restrictors. Thought they are ultimately limited to a certain horsepower value, it should reduce cycle-to-cycle variation and be easier to tune as well as boost the area under the curve.

Note: The exhaust collector. Who thinks there is some anti-reversion stuff going on inside of there? I do. MadBill built an exhaust like that where the tailpipe slips over the actual collector exit.

hoffman900 wrote: ↑Thu Oct 10, 2019 9:26 pm...Note: The exhaust collector. Who thinks there is some anti-reversion stuff going on inside of there? I do. MadBill built an exhaust like that where the tailpipe slips over the actual collector exit.

Wow, you must have cranked the Wayback Machine up to eleven to come up with that Bob!

Hopefully they didn't do that ^V^V crank layout that Ford did.

I have yet to hear a good explanation for it.

MadBill wrote: ↑Fri Oct 11, 2019 12:39 am

hoffman900 wrote: ↑Thu Oct 10, 2019 9:26 pm...Note: The exhaust collector. Who thinks there is some anti-reversion stuff going on inside of there? I do. MadBill built an exhaust like that where the tailpipe slips over the actual collector exit.

Wow, you must have cranked the Wayback Machine up to eleven to come up with that Bob!

I just remember it being a good idea and have seen it done here and there since.

Schurkey wrote: ↑Thu Oct 10, 2019 6:40 pm Far as I know, the only benefit is that the exhaust tuning can be better.

You can do a little better with the intake tuning too.

Got to see he C8R do a demo lap today. Sounds nothing like the previous generations. I understand progress, but

Here is how it sounds:


Same displacement as this:

hoffman900 wrote: ↑Thu Oct 10, 2019 7:23 pmbeing a factory effort, this is the real deal, factory resource, kind of development program.

That's what GM claimed with the Vega, and the Citation. And the V8-6-4. And the HT4100.

mk e wrote: ↑Sat Oct 12, 2019 7:03 pm

Schurkey wrote: ↑Thu Oct 10, 2019 6:40 pm Far as I know, the only benefit is that the exhaust tuning can be better.

You can do a little better with the intake tuning too.

Makes sense. Thanks.

The advantage is that the exhaust pulses never overlap.

Think of it as cars merging onto the freeway. With a flat plane the cars merge smoothly.......left right left right.....

With a normal crank the pulses collide twice a cycle.....so it looks like the 101/405 interchange at 5:30.

SchmidtMotorWorks wrote: ↑Fri Oct 11, 2019 1:06 am Hopefully they didn't do that ^V^V crank layout that Ford did.

I have yet to hear a good explanation for it.

That engine sounds nothing like Fords attempt and everything like a Ferrari flat plane crank engine.

To me that says they did it the right way. But I'm no sound engineer so I could be completely wrong about that.

Schurkey wrote: ↑Sat Oct 12, 2019 10:36 pm

hoffman900 wrote: ↑Thu Oct 10, 2019 7:23 pmbeing a factory effort, this is the real deal, factory resource, kind of development program.

That's what GM claimed with the Vega, and the Citation. And the V8-6-4. And the HT4100.

If you were born when all that happened, you would be 40+ years old now. Half the population of the US wasn’t even born yet. Seems like a silly argument...

hoffman900 wrote: ↑Sun Oct 13, 2019 10:25 am

Schurkey wrote: ↑Sat Oct 12, 2019 10:36 pm

hoffman900 wrote: ↑Thu Oct 10, 2019 7:23 pmbeing a factory effort, this is the real deal, factory resource, kind of development program.

That's what GM claimed with the Vega, and the Citation. And the V8-6-4. And the HT4100.

If you were born when all that happened, you would be 40+ years old now. Half the population of the US wasn’t even born yet. Seems like a silly argument...

https://www.caranddriver.com/news/a2743 ... -problems/