6.1 High Compression Head

[wkvasnicka]

What would be the horse power increase by installing a 6.1 high compression head to an otherwise stock engine?

[Purdy Swoft]

I would think that you might gain 12 to 14 horsepower

[BRENT in 10-uh-C]

Purdy may be correct in his numbers but the Model-B engine only saw a 10 Hp increase in horsepower with a slight compression increase however it also had nearly a 6% bigger camshaft and about 25% increase in induction airflow. If everything else was stock Model-A, I would think less that 10 horsepower.

[Benson]

I installed a Model A Police Head 5.2 on a worn out stock Model A engine more than 50 years ago..

This is the "head with the large B" which is 5.2 vs the another common head of the time the "Head with the large C" which is only 4.6.

The difference is very noticeable

Low end torque is much better which makes climbing hills a delight.

Over all the engine just runs better...

THe 6.0 should be better than the "Large B" head.

We never put the engine on the Dyno BUT the "seat of the pants" Dyno says it runs better.

That same head is now installed on a rebuilt (1989) Model B engine... it really wakes up this engine!

[Benson]

About the Model B engine mentioned above.

I should say that the biggest mistake that I made was to change the rear end from 4.11 to 3.54.

3.54 is WAY too tall for this setup.

I have since then installed 3.78s and Mitchell 26%

I also found out that regrind camshafts do not run very well as they reduce low end torque, Just the opposite of what is needed to run 3.54 or 3.27 gears.

The same with overdrives to use an overdrive you need low end toque!

My next change is to install a Stipe IB330 camshaft … (NOT a regrind cam there is a BIG difference!) I have driven IB330 and it really runs well and is well worth the extra $300!

[BRENT in 10-uh-C]

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Originally Posted by Benson

I installed a Model A Police Head 5.2 on a worn out stock Model A engine more than 50 years ago..

This is the "head with the large B" which is 5.2 vs the another common head of the time the "Head with the large C" which is only 4.6.

The difference is very noticeable

Low end torque is much better which makes climbing hills a delight.

Over all the engine just runs better...

THe 6.0 should be better than the "Large B" head.

We never put the engine on the Dyno BUT the "seat of the pants" Dyno says it runs better.

That same head is now installed on a rebuilt (1989) Model B engine... it really wakes up this engine!

Yes, you are correct and I probably should have expounded in more detail in my answer however the O/P only asked about Hp gain and not performance. Aagain, you are correct, there is a definite difference by adding compression over stock CR.

The bigger change IMO comes from better breathing. While a higher compression ratio is definitely a help, a larger camshaft and improved airflow thru increased size of valves, manifold, and carburetion is what makes the most performance gain. Volumetric loading of the cylinders is basically the same whether you have 4¾:1 or 6:1 compression. By creating the ability to load more air & fuel into the cylinders will allow the 6:1 head to perform to its maximum potential.

[Benson]

If you pull a trailer …

5.5 or 6.0 head is a good thing along with a Stipe IB330.

4.11 and 26% Mitchell would be even better.

This is just from my 60 years of driving Model As!

[alexiskai]

Here is a website that answers this question in detail:
http://www.rarecarrelics.com/tests-t...ord-engine.php

You'd want to look at dyno run #1 versus #8.
Correction: dyno 2 vs 8

[Benson]

Originally Posted by alexiskai

Here is a website that answers this question in detail:
http://www.rarecarrelics.com/tests-t...ord-engine.php

You'd want to look at dyno run #1 versus #8.

Only 77 Ft lbs !



Something is wrong with test #1!
55 years ago Bill Kenz told me that stock Model A


gets max torque at 1200 rpm at 128 foot pounds


AND MAX HORSEPOWER at 2000 rpm at 40 HP.


Piranio's test done in 2006 agrees with these numbers.


129Ft lbs


41HP



click here to see tests:


http://www.modelaparts.net/dynosheets.htm/dyno1.htm


Notice Also Mr P's tests are corrected for altitude and barometric pressure. Where other site does not seem to have used correction.

[alexiskai]

Upon inspection, it looks like dyno 1 is without the timing adjusted. Dyno 2 shows numbers that are closer to the Piranio numbers, though still lower.

I feel like there's enough unknowns about how the dynos are set up and calibrated that these tests are mostly useful for comparisons of different setups on the same dyno, rather than different dynos to each other.

[katy]

I also found out that regrind camshafts do not run very well as they reduce low end torque, Just the opposite of what is needed to run 3.54 or 3.27 gears.

I would say that it depends on the grind put on the camshaft.

[Jim Brierley]

I ran my tudor years back at the Auburn hill climb, with A carb, manifild and exhaust on a "C" engine. A few months later I ran it with a 6:1 Winfield, it went up the hill a full second quicker. That same day I installed a downdraft Stromberg 81, gained almost another second. A year later I put a 97 on and gained .3 of a second. The moral is, compression and a bigger carb are the fastest and easiest way to increase HP. Look at https://www.modelaparts.net/ for many dyno runs.

[alexiskai]

Originally Posted by Jim Brierley

The moral is, compression and a bigger carb are the fastest and easiest way to increase HP.

Maybe better phrased as "compression and airflow" – after all, when you switched to the downdraft carbs I'm guessing you installed a new intake manifold.

Compression alone will improve performance at low RPM, but airflow is key to unlocking performance at high RPM.

[don3527]

https://www.snydersantiqueauto.com/R...lease-8780.pdf

Here is a link from our web site to show you the actual dyno results when we contracted with Bill Stipe to design our 6:1 combustion chamber.

[Synchro909]

From the above posts, there is not much love here for reground camshafts but that is what I have used. One of those Stipe cams would cost about $900 by the time I got one here.The timing of the one I use is very similar to the B 330 but lift is less.
I subscribe to the 3 Cs in engine performance. Carb, Cam & Compression. A little on each will yield big results with a Model A engine. Getting radiacal on one without touching the others is a waste of time, IMO.
That is the approach I have taken with a 5.5 head, one of those cams and a downdraught Stromberg from an early Holden. On one engine, I have the same head and cam but a Zenith carb with bored out A manifold. It is not far behind the others!
The most disappointing engine I have is a B engine (counterweighted crankshaft) with 5.5 head, the same downdraught carburettor but standard B camshaft. The downside for that car is its 3.54 differential and when I engage the 26% O/D, it struggles with the resulting effective 2.81 ratio.
My dilemma is do I change to 3.78 or 4.11? The effective ratios for those with O/D are 3.0 and 3.26 resp.
Adding to my dilemma is if I change the camshaft (do I need to), how much better is a B330 than the B cam? How much better is the one I have used in the other cars, assuming both are better.
So many unknowns, only one answer!

[updraught]

>> My dilemma is do I change to 3.78 or 4.11?

Put a taco on it and find the power band. My guess is you want it sitting in the sweet spot of the power band.

[Y-Blockhead]

Originally Posted by updraught

>> My dilemma is do I change to 3.78 or 4.11?

Put a taco on it and find the power band. My guess is you want it sitting in the sweet spot of the power band.

Why you puttin' a taco on it? I eat my tacos. Do they even have tacos in Australia>

[Y-Blockhead]

...

[alexiskai]

I think he might have meant to write "tach," as in tachometer, and it autocorrected to taco.

[Y-Blockhead]

Originally Posted by alexiskai

I think he might have meant to write "tach," as in tachometer, and it autocorrected to taco.

Ya think??