hybrid motor idea-criticism

[Diamond Star Werks]

There are several good points on this thread about how to get higher RPMs. But not a post about how to get more air through the valves. The absolute limit of horsepower for any version of the 4GXX engine is sonic air flow through the valves. The valves will reach sonic flow at the same CFM regardless of the RPM.

Race engines have over square engines where the rules limit the displacement. For any displacement, the bigger the bore the more room there is for valves. Longer strokes for the same displacement means smaller valves.

If you need higher RPMs for higher trap speeds or just to enjoy hearing the Eagle scream then longer rod ratios and lighter reciprocating parts are the way to go. But this olde phart chose more stroke for more street friendly torque. Your mileage may vary.

What is an over square engine? Lol

and at which point would larger valves be benefit? With a stroker or destroker?
& I like torque too soo its an up in the air thing of high revv or big stroke high compression. I love to "hear the eagle scream" aswell .

I'm running towards road coursing though so torque would be a better friend? Or hp?

 

[LandSpeed-DSM]

Over-square = bore > stroke

Gearing, Tire, Course type, driver preference determine the answer to the rest of the post.

Stepping up to a larger valve hat is also a contextual decision. But bowl blending, back-cuts and de-shrouding are always beneficial.

 

[TunaTalon]

Thank you for addressing the effect of air flow, all true for any RPM. That's my point. Flow through the valves in CFM is the limit regardless of the RPM.

Bigger valves, more flow is true. I put 1mm oversize valves in my Talon along with some port work for more clearance around the valves. The 2.3L stroker will be limited by air flow at a lower RPM than the de-stroked versions of the 4G63.

Bigger valves will help some until they get too close to the combustion chamber wall. Port work will allow more flow for any displacement or stroke. But sonic velocity is not affected by stroke or bore. Temperature yes, but not RPM or pressure.

More boost pressure does allow more pounds/min of air for any CFM, but again that's true for any RPM.

Edit - This was in response to Land Speed's post 25 but two other posts came in while I was drafting.

 

[LandSpeed-DSM]

Thank you for addressing the effect of air flow, all true for any RPM. That's my point. Flow through the valves in CFM is the limit regardless of the RPM.

Bigger valves, more flow is true. I put 1mm oversize valves in my Talon along with some port work for more clearance around the valves. The 2.3L stroker will be limited by air flow at a lower RPM than the de-stroked versions of the 4G63.

Bigger valves will help some until they get too close to the combustion chamber wall. Port work will allow more flow for any displacement or stroke. But sonic velocity is not affected by stroke or bore. Temperature yes, but not RPM or pressure.

More boost pressure does allow more pounds/min of air for any CFM, but again that's true for any RPM.

I agree with the majority of this.

Velocity, in this case "port velocity" .. is determined by charge density, port shape/angle and cross section. But it's pulsed, not like stokes flow or laminar flow. Harmonics of several orders come into play, and so yes RPM is a factor.

Temperature is going to determine charge density.. which affects mass flow per CFM. So Temperature is also a factor. It's why a more efficient compressor (at the same operating point for the sake of discussion X PR/turbine shaft RPM and Y Volume Flow) when compared to equal wheel dimension and flow capability can make more power. Less heat is added to the charge by compression, leaving it denser.

Then when it passes through the intercooler the temperature drop is even greater, and again so when injectables are introduced..