Is there anyway to fig out the VE of an eng...
Would a stock eng be @ 80% VE and if so how much would it go up with intake/heads/cam/header and so on (LT1)

thx

 

http://www.grapeaperacing.com/GrapeA...ccompratio.cfm

It gets into VE a little bit there, too bad we cant hit 100%..haha.

If I were to guess id say less than 80%, an LS1 is maybe around 80%, only people above are probably germans and italians.

 

cool thx ...but how would you take into acount we have a tb not a carb (58mm 1000cfm) and diff intake how would that fig in....


Volumetric Efficiency

The only way a 10:1 engine will have 10:1 dynamic compression, is if it completely fills the cylinders, a hard thing to. If a 350 cubic inch engine inhales 350 cubic inches of air in one complete cycle (720 crankshaft degrees) it has a 100% VE. The VE of the engine has the greatest effect on actual (dynamic) compression ratio while the engine is running. Most stock engines are in the 75-80% VE range, high performance street motors can get as high as 90% with good intake tuning (most fall in the 80-85% area), and all out race motors can exceed 100% with well designed intake systems that take advantage of induction wave tuning (see Tuned Port Basics). Getting over 100% VE is hard, the motor will have to rev pretty high and it will only happen in a narrow rpm range, but with careful gearing, it can be put in the range needed. Figuring out VE without a dyno is hard, but can be done with a good vacuum gage and a carb with a known CFM rating. If it's a Holley Four barrel, it is rated at 1.5 inches of vacuum, so if your engine is pulling 1.5 inches with a Holley 650, it is flowing 650 CFM. This does not work well on air valve carbs like Quadrajets and Carters because you don't know how far the secondaries are open. If you know that the carb is fully open and you have a good vacuum gauge that will measure in tenths on an inch of vacuum, you can fine the actual airflow through the carb. Since most performance engines pull less than 1.5 inches of vacuum at WOT you'll need a formula to convert to different pressure drops. The formula to convert airflows to different vacuum ratings is:

Square root of (measured vacuum ÷ rated vacuum) × rated flow = Actual Flow

So if you have a Holley 750 ,which flows 750 CFM at 1.5 inches, and you're only pulling .75 inches of vacuum, the formula will look like this:

Square root of (.75 ÷ 1.5) × 750 = 530.3 CFM

So a 750 Holley is only flowing 530.3 CFM at .75 inches of vacuum. The last thing you need to know is the theoretical airflow of your engine. The formula to figure air flow is:

Air Capacity (in CFM) = (rpm × cubic inch displacement) ÷ 3456

On a 350 engine turning 6000 rpm this would equal 607.6 CFM. Now we have every thing we need to figure out the volumetric efficiency

VE% = (actual CFM ÷ theoretical CFM) × 100

After you plug the numbers in from our 350 example, the formula looks like this:

VE% = (530.3 ÷ 607.6) × 100

Our 350 would have an impressive 87.32% volumetric efficiency at 6000 rpm, not to bad.



thx

 

****tttt...dont ask me .....BRET

 

A number of NA engines get over 100% VE due to intake and exhaust tuning. Intake tuning can cause a positive pressure of several psi about the time the intake valve is closing if everything is done correctly. Obviously cam timing is critical.

NASCAR 358 cube engines have risen from the 650 hp to the 800+ hp range over the last 10-15 years by increasing the VE and rpm simultaneously.

The engine will pull as hard as it can thru the intake restriction it is given. A good NA engine may be below 1 in Hg in an unrestricted for, but may be WAY over 1.5 in Hg if it is restricted.
NASCAR modifieds use a 390 cfm rated carb to get over 600 hp on a good day. That's much more than 600 cfm.

To answer the original question, good engine simulation programs come pretty close to giving good VE numbers if they have good input data.

 

on my SuperFlow SF-901 dyno , there is included with it an Air Turbine you fit over carb that accurately measures Volumetric Efficiency PerCent %..along with the Carb's Air Intake temperature, BSAC, Carb CFM , etc


when dyno testing i also hookup manifold vacuum to check actual CFM of carbs..


so its easy to measure Ve% , and on good engines , Ve % usually
100+ Ve easily

There are 2 kinds of VE

Measured raw Ve = actual amount of air being inhaled at any moment

Trapped Ve= Measured_Ve - ( Ring_BlowBy_CFM + Overlap_Period_CFM_Loss)

its the Trapped_Ve that counts

Example=> i've had one NHRA Chrysler Super Stock Hemi engine on my dyno that was showing + 140.0 PerCent Ve

but its was false Ve ...most of actual mixture was going right out of exhaust ports during overlap period , falsely increasing measured Ve % ...its easy to see this effect on SF-901 , then all yopu do is look at BSAC ...and if Ve is suspicious, look at BSAC , if BSAC is also looking too high, its overscavenging .
and measured Ve are false

the cam use in that example was experimental, and way off for the cylinder heads that happened to too good of low-lift flow

so it produced a BAD combination

2 weeks later , same engine with different cam timing/cam..picked up 30+ HP with 120.0 % percent Ve -vs- 140+ as before
new cam stopped a tremendous amount of overscavenging

Hemi chamber has special problem ..valves are directly opposed, and during overlap, its easy to overscavenge

 

All very cool but i am talking about an LT1 .....58mm/1000cfm LT1 intake,heads,cam,headers LT ......6500rpm....will this still work

thx

 

I you have ALL the engine data, including head and manifold flow, all exhaust system specs, cam specs, etc. an engine simulator will predict VE.

Why is it you want to know VE?

 

Do you have an eng simulator, if so can i give you all the data to fig this out...Why i ask is in tunercat you have the VE table i would like to set this to what my eng's VE is.....i know everyone will say it dose nothing wast of time and so on well it is there so why not...it can't hurt anthing and by some crazy chance it dose well.. i have the right number in there for WOT....

thx

 

Am I so far out to lunch on this there is no point

 

Well, I don't see your point. That doesn't make you wrong.

I'm not sure where you are going with this. VE is different at every rpm. Obviously it varies with throttle opening, but we are talking wide open throttle (WOT) and full load. Unless there is some specific tuning for a given rpm, WOT VE curve pretty much follows the torque curve. That's one of the reasons the torque curve is shaped like it is.

My $.02

 

I'm looking at the dyno sheets right now for one of our RMRE 555's. The printout only shows the dyno run from 5100-7200rpm, but through that range VE stays above 100% the entire run. VE peaks at 6700rpm, with 110.1%. At the same rpm BSFC is .462 lb/hph, HP is 907 and TRQ is 710ft/lbs. BSFC is the highest at the same RPM as max TRQ (736ft/bs@5900rpm, .476lb/hph BSFC), but VE is *only* 104.4% at the TRQ peak...so the real question is what does all this tell me? SStrokers, please enlighten me!

 

My take is that your intake tuning is maximized around 6700. I suspect you might be seeing 5 psi or so just as the valve closes. Hard to measure, but not too difficult to simulate. IMO, your intake, heads, valve timing and probably exhaust are working together. I suppose if we had all the engine particulars we would see about the same thing on the simulator. If it is 555 cube engine, that's 1.63 hp/in^3 or that would be 580hp in a 355. With torque peak only 1200 rpm lower than power point, and the very flat torque curve (within about 3%) in that area, your tuning spreads out over that band. You said VE stayed over 100% until 7200.

It tells me this NA engine is doing a pretty good job! I'm guessing 4.555 x 4.25. What rpm band does it run in? What's it's use? Drag car , boat, (fast) tow truck??

My $.02

 

hahha........thats one bad tow truck.

 

Just for my peace of mind...... if i no the VE of my eng i put it into the wot part in tunercat and just go from there if it helps great if no o well......... can't anyone fig out the ve of the lt1.....