Volumetric Efficiency of Model T engine (L head) ?

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Volumetric Efficiency of Model T engine (L head) ?

Post by henryford2 » Wed Oct 11, 2023 5:33 pm

Saw a chart years ago that listed an average volumetric efficiency of different engine types (L head, crossflow, flathead, overhead, etc) can't locate it again. Obviously wanting to know the VE for the T engine. Thanks


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Re: Volumetric Efficiency of Model T engine (L head) ?

Post by TXGOAT2 » Wed Oct 11, 2023 9:57 pm

Volumetric efficiency of a particular engine depends on a great many factors. Generally speaking, L head engines have lower volumetric efficiency than OHV types. Model Ts have very low volumetric efficiency due to their restrictive manifolding, small valves, mild cam profiles and very large combustion chambers. The T head type engine may be the lowest, but so many design and operating factors affect VE that there is no one type that is consistently superior.


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Re: Volumetric Efficiency of Model T engine (L head) ?

Post by TXGOAT2 » Wed Oct 11, 2023 10:03 pm

VE will vary with throttle position, engine speed, elevation, and more. The 177 CID T engine is rated at 20 HP, which is indicative of a very low volumetric efficiency, with highest VE ocurring at the lower end of the RPM range. Low end torque is good, though.


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Re: Volumetric Efficiency of Model T engine (L head) ?

Post by TXGOAT2 » Wed Oct 11, 2023 10:07 pm

A 4-valve OHV crossflow engine with high RPM capability would likely be high on the VE scale. Such an engine might exceed 100% VE at certain speed ranges.


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Re: Volumetric Efficiency of Model T engine (L head) ?

Post by Norman Kling » Wed Oct 11, 2023 10:24 pm

The early fuels were must lower octane than our modern fuels which caused detonation or pre combustion. Also with the lower torque engine only two speed transmissions were needed for the driving conditions at the time. The high head was made during the first world war and that is also very likely why the brass trim was eliminated because brass contains copper which was in demand for bullet shells.
Also the steel for the crankshaft was not quite as strong as today's steel. It wasn't until later that the "high speed" engine was developed which had shorter stroke and higher compression, but lugged the engine at low speeds so they had 3, 4, or 5 speed transmissions and faster running engines.
Norm


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Re: Volumetric Efficiency of Model T engine (L head) ?

Post by Erik Barrett » Wed Oct 11, 2023 11:04 pm

This one has pretty good V.E.
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Re: Volumetric Efficiency of Model T engine (L head) ?

Post by TXGOAT2 » Thu Oct 12, 2023 8:08 am

Air and fuel in; POWER out.

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Re: Volumetric Efficiency of Model T engine (L head) ?

Post by henryford2 » Fri Oct 13, 2023 8:50 am

Sorry, I may not have been clear in what I was asking. The attached is a comparison chart of relatively new engines (assuming overhead valve). The information I'm looking for specifically is a comparison of engine construction types, L head, F head, Overhead valve, etc. specifically the Model T engine. I've found a VE of approx. 57% for the "flathead" Ford, and for a lack of any better information I'm going to use that number. Thanks
C3320664-41C7-419E-B271-06D90EAC7814_4_5005_c.jpeg
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Re: Volumetric Efficiency of Model T engine (L head) ?

Post by TXGOAT2 » Fri Oct 13, 2023 9:43 am

A T engine would be lower on the VE scale than a Ford flathead V8. Performance modifications will improve VE. As a type, the L-head or flathead engine is at the lower end of the VE scale. VE is affected by a wide range of design factors as well as operating conditions.

Some idea of an engine's VE can be deduced by comparing horsepower and torque curves to an engine's displacement and operating speed range.

For instance, a 177 cubic inch Model T engine is rated at 20 HP at about 1800 RPM. The very similar 200 cubic inch Model A engine is rated at 40 HP at about 2300 RPM. The Model A design obviously has substantially higher VE, mostly due to improved manifolding and cam profile.

A 1938 flat head Ford V8 of 221 cubic inches is rated at 85 HP at about 3400 RPM. Improved VE plays a large part in the improvement.

Many modern day naturally aspirated engines develop well over 1 HP per cubic inch of displacement. These are typically 4 valve, high compression engines that operate at comparatively high RPM.

Most any engine's VE can be dramatically improved by selective modification or by forced induction.


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Re: Volumetric Efficiency of Model T engine (L head) ?

Post by TXGOAT2 » Fri Oct 13, 2023 10:02 am

The peak operating VE for a stock model T engine would occur at or near the torque peak. Exactly whatVE would be I cannot say, but I'm sure it would be less than the later model flat head 8 at its torque peak. You could look up the specs and do the math and get a fair idea.
VE varies widely among individual designs within the several general engine types. Some OHV engines operate at a lower VE than some flat head engines.
Hot rodding is the art of increasing VE without destroying drive-ability or the engine itself.

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Re: Volumetric Efficiency of Model T engine (L head) ?

Post by BRENT in 10-uh-C » Fri Oct 13, 2023 10:57 am

henryford2 wrote:
Fri Oct 13, 2023 8:50 am
Sorry, I may not have been clear in what I was asking. The attached is a comparison chart of relatively new engines (assuming overhead valve). The information I'm looking for specifically is a comparison of engine construction types, L head, F head, Overhead valve, etc. specifically the Model T engine. I've found a VE of approx. 57% for the "flathead" Ford, and for a lack of any better information I'm going to use that number. Thanks
C3320664-41C7-419E-B271-06D90EAC7814_4_5005_c.jpeg
Yeah Joe, you were mostly getting answers from people who are not performance engine rebuilders.

From my experiences of building racing Model-A powered vintage race cars, -and now 700hp SBC powered dirt cars, is that any published chart that you will find is very likely going to be incorrect. The RPM variances between idle, off-idle, and mid-throttle will change VE drastically. Computer sims are not going to hit this anywhere near accurate. Think about what engine they used to simulate the flow. Was it an L head engine with individual (dedicated) ports, or siamesed ports? Does the intake port area have a plenum area large enough to fully support the trailing cylinder?? The piston dwell time at BTC also affects VE. Naturally an early T manifold is going to flow better than the later cast iron manifold. Next, the CFM ability of the carb is going to factor. And finally whose camshaft and its' specs greatly affects VE. So not sure how valuable this chart is going to be for you. Think about a syringe sucking water out of a cup. You can pull the plunger back as fast as you like however you are going to draw only as much water as can get thru the end of the syringe. FWIW, typically it has been said that whenever the max torque output is found, that is where VE will be at its highest.
I'm not sure any of this is going to help you, but my advise is move on and just figure proven ways to increase efficiency on airflow pre-cylinder.

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Re: Volumetric Efficiency of Model T engine (L head) ?

Post by henryford2 » Fri Oct 13, 2023 2:26 pm

Thanks Brent, let me explain what I'm doing and my interest in Volumetric Efficiency (VE). I trying to pick a carb based on VE for an engine that I have. It's 204 CI Model T, stock bore, Model B crank with a stroke of 4 5/8", larger intake valves, ported intakes, high compression custom Ross pistons, cam lift of .280", model B exhaust with an aftermarket downdraft manifold (hint, hint). Assume this increases the power range by 25% over the stock T that developed it's max HP @ 1,600 RPM, so now I'm at 2,000 RPM. Doing the math 2,000 RPM x 204 C.I./3,450=a theoretical airflow capacity at 2,000 rpm of 118 cfm. Unfortunately, airflow is not airflow, engines generally operate below maximum capacity. The VE being the ratio between the actual airflow and the theoretical. An L head engine is pretty low on that ratio, maybe as low as 55%. Assume the changes I made increases the VE another 20% to 69%. 118 cfm x a VE of 69% would indicate I need a carburetor that will flow at a minimum of 81 cfm. A Stromberg 81 flows 125 cfm making it an option to use. A 97 or 48 would be too large of a carb? I may have this all wrong and would sincerely love to hear your opinion since you have considerably more experience at this than me. Thanks!


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Re: Volumetric Efficiency of Model T engine (L head) ?

Post by TXGOAT2 » Fri Oct 13, 2023 3:21 pm

You're on the right track. You might make your best informed guess as to carburetor CFM, then run the engine and get it broken in and experiment with timing, jetting, etc. A manifold vacuum gauge might be useful. You want very low manifold vacuum (high manifold pressure) at torque peak and you want to keep it low at HP peak. If you have much of any indicated manifold vacuum at the HP peak, a larger carb might be beneficial. When you build an engine for high performance from antique parts, you necessarily become your own engineer. Exhaust tuning will affect VE.

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Re: Volumetric Efficiency of Model T engine (L head) ?

Post by BRENT in 10-uh-C » Fri Oct 13, 2023 4:26 pm

henryford2 wrote:
Fri Oct 13, 2023 2:26 pm
Thanks Brent, let me explain what I'm doing and my interest in Volumetric Efficiency (VE). I trying to pick a carb based on VE for an engine that I have. It's 204 CI Model T, stock bore, Model B crank with a stroke of 4 5/8", larger intake valves, ported intakes, high compression custom Ross pistons, cam lift of .280", model B exhaust with an aftermarket downdraft manifold (hint, hint). Assume this increases the power range by 25% over the stock T that developed it's max HP @ 1,600 RPM, so now I'm at 2,000 RPM. Doing the math 2,000 RPM x 204 C.I./3,450=a theoretical airflow capacity at 2,000 rpm of 118 cfm. Unfortunately, airflow is not airflow, engines generally operate below maximum capacity. The VE being the ratio between the actual airflow and the theoretical. An L head engine is pretty low on that ratio, maybe as low as 55%. Assume the changes I made increases the VE another 20% to 69%. 118 cfm x a VE of 69% would indicate I need a carburetor that will flow at a minimum of 81 cfm. A Stromberg 81 flows 125 cfm making it an option to use. A 97 or 48 would be too large of a carb? I may have this all wrong and would sincerely love to hear your opinion since you have considerably more experience at this than me. Thanks!


Yeah, as you are eluding to, now you are entering a zone where theories do not cross over. Most Stromberg carburetor numbers you read about are numbers that the factory gave for sizing air flow in CFMs, ...however not fuel & air flow. In other words, they could flow air & fuel in an economy environment, but could not keep up in the higher RPMs. To elaborate on this point, a Stromberg 97 has a theoretical air flow of around 150 CFMs and were sized by Stromberg for the new Model 40 & 48 Ford V8s with 221 cubic inches. So theoretically the 201ci Model-A/B engine which was about 10% less displacement but had a more lift & duration than the 33-36 V8s, should have been a happy camper with one Stromberg 97. The reason so many dual carb intakes were offered in the day was that one carb could not provide enough fuel & air in 3,000 - 3,500 RPM range.

FWIW, back when I was vintage car racing, I had several speedsters and a big car that two 'built' 94s could not keep up, -and my track roadster with an OHV needed three 97s to keep up. Therefore, depending on what you are building and how you plan to drive it will likely see yourself needing a larger carburetor. One other thought to ponder, a stock T is around 176 cubic inches. A small block Chevrolet 350 engine is about twice the cubic displacement, ...and the factory shipped most of those engines with a Rochester Quadrajet, which in its' smallest CFM model is about 750. Granted the VE is much greater on these engines, however due to spread-bore design, the engine could utilize it. So even if you divided the 350 displacement by ½, -and divided the VE of the V8 numbers in ½ to more closely resemble real-world with your T engine, ...you still have a CFM number exceeding what the 97 or 94s were capable of flowing. IMO, the 94 would be a better choice for beginning with since the venturi size of them is a tad smaller than the 97 (-think throttle response), they have a tuneable accelerator pump circuit, they have a power valve circuit, and Speedway sells adjustable jets for them so you can tune fuel flow. Anyway, this probably WAY more than you wanted to know, so I'll leave a you a few pix of some of my old racing junk, and wish you good luck on your venture.

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Re: Volumetric Efficiency of Model T engine (L head) ?

Post by henryford2 » Fri Oct 13, 2023 7:30 pm

Brent, Pat great help, one last question any opinion on a Winfield S-BB on this engine. Have one on the shelf, but Winfield manifolds are hard to come by, although I do have an stromberg to winfield adapter. Thanks again


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Re: Volumetric Efficiency of Model T engine (L head) ?

Post by TXGOAT2 » Fri Oct 13, 2023 9:22 pm

VE is primarily a wide open throttle consideration. VE will fall off very quickly with less than WOT.

Longer, smaller ID intake runners usually favor low end torque, and larger ID, shorter intake runners are usually best for high HP at high RPM. Most everything up to and including the phases of the moon can have an effect. RPM and cam profile affects both intake and exhaust flow behavior.


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Re: Volumetric Efficiency of Model T engine (L head) ?

Post by Kevin Pharis » Sat Oct 14, 2023 12:41 am

henryford2 wrote:
Fri Oct 13, 2023 7:30 pm
one last question any opinion on a Winfield S-BB on this engine. Have one on the shelf, but Winfield manifolds are hard to come by, although I do have an stromberg to winfield adapter. Thanks again
For reference, I calculate a BB at about 185 cfm using the “standard” 3” h2o depression. This was the largest of 3 sizes offered in the Winfield catalog for Model A engines. I currently run a S-B on a warmed up flathead in my touring car and used to run a SR-C on an arguably hot flathead in my speedster
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Re: Volumetric Efficiency of Model T engine (L head) ?

Post by henryford2 » Sat Oct 14, 2023 6:40 am

Thanks Kevin! I run the S-BB on my BB Rajo and like the ease in setting it up.

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