Cost Benefit Ratio

[Loren]

I was leafing through an old Hop Up magazine from December 1952 and I came across an advertisement placed by Barney Navarro.

Navarro knew what he was talking about as he made the best cylinder heads for the Ford V8 and was a pioneer in the use of the GM 6-71 blower on gasoline engines.

What he was saying is universal for all gasoline engines, COMPRESSION is what makes horse power.

Not Cams, not Carburetors, not Ignitions.

One of his good friends (and mentors) was the great Ed Winfield who was a manufacturer of carburetors and the guy who taught most of the successful cam grinders how to grind cams. He could not have gotten away with saying this if it wasn't true (in fact this issue of Hop Up has an article he penned entitled "The truth about Cams" which Winfield approved). Anyway, Cams, Carburetors and Ignitions all work in support of the almighty Compression Ratio. You can if you want add them to a stock engine but nothing makes one come alive like Compression.

Barney's ad used this logic to sell his cylinder heads and he made the case that adding Compression was a really economical way to get more power.

 

So....

Think about it.

When you go to make some big modification to your stock/original Plymouth, what is the cost benefit ratio?

More importantly what does that mod do for your car and is it worth doing?

Changing a rear axle won't add 1 horse power. (changing the ratio might bring up your highway speed but you can do that with an Overdrive or a ratio change, which is much easier with the stock axle)

Changing to Disc Brakes can actually take away horse power through drag. (you do know those pads are always in close contact with the rotors and if they weren't you would be pumping the brakes every time you stop)

Just sayn'

 

[Sniper]

Years ago, back in the 80's, there was an aftermarket cylinder manufacturer that used to buy full page ads in the various hot rod magazines touting the huge by large improvement their heads made on a SBC 350.  When you read the tiny fine print at the bottom you found out they were comparing it to a 350 with 305 heads on it.

 

no kidding it was an improvement.

 

So any ad that puts forth unsubstantiated claims, such as the one you posted, is worthless to me.

 

I'm not going to argue your other points, not because you are right, or wrong, but because they are strawman arguments in regards to making HP.  But if you were really serious about making HP at the rear wheels I have an even better cost benefit analysis.  Ditch the stock fan, it eats HP and that is free or close enough.  Many ways to skin a cat and making more efficient use of your existing HP is part an parcel, just like adding in a more efficient, and safer, braking system to control those available horses.

 

[Plymouthy Adams]

given a flathead is 100HP  (rounded)  and the above ad shows 164% increase...we would have 265hp......(BS alarms going off everywhere) lets spitball this a bit...as we add all that up in dollars...

 

heads...22% is 22hp @ 6.16 =135.52

exhaust...15% is 15hp @ 9.66 = 144.90

s-charger...127% is 127hp @ = 880.11

 

total 1160.53  anyone care to convert this to today's dollar......

 

I say nothing on improved handling braking or overall reliability 

[Bryan]

23 minutes ago, Plymouthy Adams said:

given a flathead is 100HP  (rounded)  and the above ad shows 164% increase...we would have 265hp......(BS alarms going off everywhere) lets spitball this a bit...as we add all that up in dollars...

 

heads...22% is 22hp @ 6.16 =135.52

exhaust...15% is 15hp @ 9.66 = 144.90

s-charger...127% is 127hp @ = 880.11

 

total 1160.53  anyone care to convert this to today's dollar......

 

I say nothing on improved handling braking or overall reliability 

$12,585.00  ->  Inflation Calculator | Find US Dollar's Value from 1913-2022 (usinflationcalculator.com)

[FarmerJon]

Barney Navarro was certainly one of the greats. He seemed to have a good grasp of the physics, and a healthy ability to think outside the box. I have read his column a few times in various early hot rod rags. 

However it strikes me how little those type of publication have changed over the years. 75% of the content is with the aim of getting guys to spend $. 

Given the common aftermarket flathead combustion chamber shape in the early 1950s, I would bet that a late model Mopar iron head, milled to equal compression, would perform as well or better than his $74 one, for significantly lower cost.

 

Interestingly, George Asche has the same opinion about dual points distributors, no gain.

 

Another thing to keep in mind is that dynos were even less common, and even OEM numbers were VERY generous. I would suspect many companies based gains off of improved track times, or timed laps around their shop parking lot. Does that invalidate their claims? No, but just something to keep in mind. I believe it was the late '60s before OEM companies started rating engines with a full exhaust, water pumps and alternator being driven by the crank...if you look at a model before and after, same engine, same trim car, will usually have a good bit less power than the year before.

 

But,if we look at the factory HP rating, we can see that as they needed more power, they added more compression. There were changes to cam, chamber design (flow) and carb (56 power pack) but compression was a major factor in raising power 30+% (with only a 14.3% increase in compression) while not causing problems with the drivability, reliability or fuel consumption.

If a person had a stock 100hp F*Rd (target hot rod audience) with 6.7-1 compression, and aftermarket heads brought it up to 8.5-1, expecting 122hp total would not be out of line. Adding a dual exhaust for a 15% gain would give another 18 HP, bringing total to 140. Seems about right for what guys get with warm flathead V8s. This was one of the main reasons WHY hotrod flatheads were SO popular thru the '50s: a few cheap mods give a huge percentage gain. But once you got the low hanging fruit, you get into smaller and smaller gains with every $. Even full house, naturally aspirated, $12000 stroker flathead V8s rarely break 200hp, usually 175-180 max for anything that can live on the street. 

Now superchargers do change that, with 250-300 realistic.

 

So, he is right in a lot of ways, even if he wants you to buy his stuff. For a mostly stock car from the late '40s early '50s, raising compression is likely to be a reasonably economical first step in improving performance, in a way that you can feel. Many other modifications, like cam and intake are dependent on adequate compression to give the desired results. 

 

 

[TodFitch]

34 minutes ago, FarmerJon said:

. . . However it strikes me how little those type of publication have changed over the years. 75% of the content is with the aim of getting guys to spend $. . .

Very true of lots of magazines. Ones on investing are probably even worse in that regard.

 

An automotive internal combustion engine is basically a Carnot cycle heat engine. The efficiency (amount of usable mechanical power out from the heat energy in) is determined by the the expansion ratio of the gases. On an Otto cycle the expansion ratio and compression ratio are identical and everyone is used to talking about compression ratios. So, yes, compression is king with respect to getting power out of a gas engine.

 

But if there is back pressure on the exhaust you are not delivering all all the power possible based on the compression ratio. Ditto for restrictions on the intake. Or insufficient or incorrectly timed spark. Etc. And the power you get could be sapped away by fans, pumps, generators, friction in all sorts of places including brakes, fluid couplings, etc.

 

The limit on compression ratio (assuming a strong enough mechanical assembly) is pre-ignition of the fuel-air mixture. So higher compression needs higher octane fuel. And there are some effects based on shape of combustion chamber, timing of the ignition, etc. that might allow you to achieve a little higher compression without pre-ignition than if they were not optimized.

 

Compression ratio is also the reason Diesel engines generally get better mileage (more efficient conversion of chemical heat to mechanical power). They can go to higher compression ratios without worrying about pre-ignition as the charge is simply air.

 

As to the actual horsepower claims, I have insufficient data and experience to say how optimistic they are. But generally the highest compression ratio you can achieve without pre-ignition will give you the highest power out.

[allbizz49]

Weird, because one of the most successful, low budget backyard fuel teams secret to success was low compression. Wasn't their only secret but was a big factor of their success. 

[Loren]

Barney Navarro was also the guy who built the Rambler 6 that qualified for the Indy 500 many years ago.

How many times have you heard Rambler and Indy 500 mentioned in the same sentence?

Ed Winfield was famous for out running Arthur Chevrolet’s 16 valve DOHC Frontenac Model T, with a flathead Model T. Chevrolet made the comment, “I see it but I don’t believe it!” Timed speed 122 mph on a board track. The secret was the “Two up, two down” crankshaft which made the intake pulses 180 degrees apart and his “Hooker” roller cam. Tommy Thickstun, the designer of Plymouth manifold we like so much, was a student of Winfield’s 180 degree theories regarding manifolds.

 

If we look at compression ratios over the last 100 years, the trend has been upwards until the 1970s when smog regulations forced a temporary drop.

World War ll brought high octane fuel into popular usage and compression ratios followed. The L head engines were not made for good high octane fuel and could not take advantage of it. In fact there is a limit to how much compression you can get from a flathead. At a certain point they can’t breathe because you’ve made the combustion chamber too small. Navarro had an answer for that. The 6-71 supercharger. One of the guys who worked with Barney on it was Tom Beatty. I knew Tom much better than I knew Navarro. He had one of the early P 38 drop tank Lakesters with a blown flathead V8. That lasted until he started putting so much boost to it that he pushed the crankshaft out the bottom!
Anyway, with electronic engine controls and turbocharging compression ratios are unheard of high now. Engines have grown smaller, more powerful and economical because of compression ratios. Supercharging or turbocharging used to mean you had to have lower compression to control detonation. No longer. Direct injection (like a diesel) keeps detonation under control and it makes for a denser charge. (The fuel doesn’t displace air in the intake charge) knock sensors assist and offer an extra layer of protection.

I suspect we have reached the high water mark of gasoline engines. Electric cars seem to be gaining the edge. Still there is something about the sound of an engine that gets the blood pumping.