Volumetric Eff. Question

[Anonymous]

I'm trying to find some info on figuring the V.E. for my engine. I got a 69 M code head with a 300 carter YF. The valves have been enlarged to the late model size. I worked the head and ports a some. Not totally ported and polished but way better than stock.

Anyone had this test done. I havn't seen anyone post what VE's they have gotten from their heads. It would be cool to see if anyone did and what they got.

Later,
Paul

 

[CZLN6]

Howdy Paul:

My guess, with your setup, properly tuned, would be somewhere between 80 and 85 % of VE a@ WOT @ Max HP rpm.

The shortcoming with your setup would likely be the large one barrel. While it is likely most efficient at higher rpm, it still lack the capacity, fuel mixing capability and fuel distribution to maximize your engine package.

Note the VE changes with engine demands. Idling may extract a VE of only 30 - 40 % VE. VE is a reflection of what percent of the total cylinder capacity is being used. Engines are most efficient at filling the cylinder at there max HP rating rpm.

It is a rare street engine that achieves 90% VE- unless it is turbo/super/NOS aided. Then it is possible to exceed 100% VE- but only for a short time!

I hope that helps you.

Adios, David

 

[Anonymous]

I'd have to disagree a little bit and say its not too hard to hit 90 with the 8s, maybe you were referring to only the 6's?

A mild 302/351, 350 hits 90% VE pretty easy and you I have seen a very streetable 351 that hit around 104 VE naturally aspirated... If you take race engines, they can approach 120 naturally aspirated..

 

[Anonymous]

Thanks for the input. I talked to one of my professors in my engines class and we looked over the numbers and came up with about 80-85 percent VE at WOT too! How much would a 2 bbl directly mounted to the log be? Another 2-5% or so?

After learning about the dynamics of engines, I've been trying to apply the information I've learned in the classroom to my own car. I'm trying to get a ballpark BHP for the engine. I think in a month or two I might squeeze out the cash and get it dyno'd. Then I got to figure out how much HP I'm loosing due to the drivetrain. Stock rear, new T5 and such shouldn't loose too much. What is the rule of thumb...15-25% on a manual trans?

Thanks for the info!

Paul

 

[CZLN6]

Howdy Back:

Mav72- You don't have to disagree. I said it's "rare" to find a street engine that achieves 90% VE, I didn't say there weren't exceptions to that generality. I guess I should have qualified it farther by saying carbureted engines. And , Yes, these exceptions would likely be V8s of the 302/350/351 type as they have been flogged to the enth degree. But still, my contentions is that these are rare exceptions. One out of one thousand street vehicles? One in ten thousand? think of all the vehicles going down the road and the state of tune they are in.

I have yet to read of quantifiable documentation of a naturally aspirated carburated engine achieving 120 VE. Please enlighten me.

Modern electronic and computerized engine management systems are coming closer and closer to a NA 90% VE in a daily driver by the moment. That's not our beloved sixes though.

Paul- Only a dyno can tell empirically. Everything else is just guessing. My guess is that your next step up is a two barrel mounted directly to the log, in the 300 cfm range and well tuned to your system for a 3 - 5% increase in VE.

I don't recall hearing your CR in the mix of variables. Did I miss it?

Adios, David

 

[Lazy JW]

Hmmm... I have been under the impression that maximum VE occurs at the max torque level rather than the max HP level When the cylinder is filled as much as it can get, it will exert the max push on the piston, thereby delivering max torque. This can, (and I believe does) occur at lower rpm than does max hp. More HP is typically developed at higher rpm because there are more power pulses per time unit even though the VE is lower. Or maybe I'm all wet
Joe

 

[StrangeRanger]

The VE curve looks almost exactly like the torque curve.

Torque is a function of displacement and BMEP. For any given engine, BMEP is determined primarily by VE

 

[Anonymous]

my compression ratio is around 9.0:1 to 9.5:1.

Thanks,
Paul

 

[Anonymous]

Mike (StrangeRanger) is correct...and furthermore, that's only at WOT. In any case, I would be astonished if any log-head engine, especially an early one, could reach a max VE of 80%. Bigger valves and pocket porting can certainly help (as has been documented many times), but given the very low hp per cubic inch and barely acceptable torque of the early log-head engines, I just don't see it.

I've been wrong before, though...