A flathead (valve in block) tends to have an awfull lot of surface area in the combustion chamber. Surface area = Heat loss = more cooling system capacity required, less efficient, poorer fuel economy.
Maybe flame travel issues, detonation issues?
OTOH, you'd certainly blow the media's minds...

Jay Maechtlen

There's no way that you would be able to run a 30 psi boost . . .

unless you started with a extraordinarily low compression ratio, like 3:1 . . .

or you used a special high-octane fuel. You might be able to do it on natural gas.

Haven't told me anything I don't already know. Don't agree with the 3:1 CR estimate, though. There's a fellow in Missouri running 250 (two hundred fifty) psi manifold with a 414 cube International tractor engine and 3 stages of turbos. I believe pump gas could be used at 30 psi max, even with a flathead, and the compression ratio would still be high enough to provide reasonable performance at low boost. Would want to avoid the cost of an intercooler, of course. I've seen the torque curve for the BRM 1.5 litre centrifugally supercharged Formula One engine and it was surprisingly flat, considering the high peak power and rpms.

Uh, that 414 ci engine is a diesel engine. With diesel's there is not a problem with high boost pressures, like there is with spark ignition engines.

If you can get a gas engine to run with 30 psi boost without an intercooler, you will be accorded the honor of turbocharger/supercharger supreme wizard. The typical gas engine can tolerate up to seven or eight psi of boost without problems, but runs into real problems at 15 psi. The 30 psi ranges has always been in the range of alcohol fuel engines, such as indy engines.

Good luck!!!

Okay, I might have gone a bit overboard on boost pressure. That really has nothing to do with my suggestion. You can rephrase it as an "acceptable" boost pressure, if you like.
My question remains: Can this be done to provide adequate performance, low maintenance and production costs, and still provide an attractive package for the consumer.

I might not have made it clear, also, that this is NOT an engine for a high performance car. This would be an econobox standard engine. Although, an added benefit, for the buyer, would be the "prestige" of a turbo badge on his economy car.

Well before I address the topic at hand, I have to set the record straight about boost.

Docengineheat said:

The typical gas engine can tolerate up to seven or eight psi of boost without problems, but runs into real problems at 15 psi. The 30 psi ranges has always been in the range of alcohol fuel engines, such as indy engines.

This is not entirely true. There are many factors that will dictate the maximum boost attainable with a fuel of a given octane rating. Combustion chamber design, spark plug location, spark plug heat range, intercooling, cam timing, valve material, ignition timing, port design... the list goes on and on.

Another thing to bear in mind is that manifold boost is nothing more than residual pressure. It is not a direct indication of the amount of air/fuel flowing through the engine. An engine with a poor flowing head/intake combination will register a higher boost pressure for a given amount of air flow.

And finally, I personally have piloted a vehicle that was running 34 lbs of boost using VP Fuel's 103 octane race gas. Though the octane rating is far greater than pump gas, this fuel is a street legal unleaded gasoline, and clearly not alcohol. Also Formula One cars once ran up to 45 lbs of boost on gasoline. Alcohol fuel is not allowed in F1 competition by the FIA.

As far as making a turbo flat head goes, what would be the goal? The flat head design has some very poor flow characteristics that make it unsuitable for either an ultra-high performance or high efficiency application. Granted, using some form of forced induction in a Miller-cycle type fashion, may improve matters some. Though there are still a good number of flat head enthusiasts out there, I do not see the design ever making a comeback.

Regards,
Bryan Carter

Bryan, thanks for your comments on boost pressure. I was given a ride in a street rod that was running about 25 psi on pump fuel, but I didn't want to get sidetracked into a discussion of boost pressure/octane limits.

And, I'm not a flathead enthusiast (though I'm certainly old enough). But, we all can appreciate the economies of production and maintenance associated with the flathead design. I'm just wondering if we could start with a displacement small enough to overcome the high BSFC values for the flathead and gain the necessary performance with a turbocharger. This is not a trivial question. It would require a detailed cost analysis to answer and I'm not certain a qualified engine designer would want to even tackle it without financial compensation.

This is slightly off the subject, but this reminds me of a similar question posed to engine designers at Chrysler in the forties. Specifically, should the old flathead six be fitted with a dual overhead cam head or should a new pushrod V-8 be designed? This was not considered a trivial question, for I ran across pictures of the six cylinder overhead cam engine. Another one for you history buffs: In the same file cabinet, I ran across a picture of a 24 cylinder radial engine, using 4 Chrysler flatheads. This was a WW II tank engine which, I was told, was a stopgap until GM could tool up with their engine. Don't know if any made their way into tanks or not.

CORRECTION: That was 30 cylinders and 5 flathead six engines. (30 is such an "odd" number of cylinders for an engine that my brain found it difficult to accept this memory.)

Considering the costs involved with a turbo, and the critical lube and cooling needs, the old pushrod ohv motor seems pretty good. Can go with much more displacement, get off-idle torque, decent peak torque and horsepower, and pretty good fuel economy. Engine life is long, and much harder to damage by stupid startup-shutdown habits.
(turbo needs a moment to get oil at startup, right? And they don't like to be shut down from hard use without a cooldown?)

But- certainly room for a  fun project? Maybe pick an inline six (flathead) with known strong bottom end, and conduct some experiments?
regards

Jay

Jay Maechtlen

Billyshoppe and Retracnic:

Okay, maybe I'll award you guys the coveted supercharger/turbocharger supreme wizard title.

You're making it sound like it's no problem at all to run gas engines with 34 pounds of boost (albeit 103 octane gas was used) and 45 pounds of boost.

Would you care to share some of your secrets? Are you using intercoolers? Are you using water injection? Are you talking about Miller cycle engines? Were the engines specially designed for turbochargers by using a markedly decreased compression ratio -- like perhaps 5:1? Are the engines running on natural gas, which has an octane rating of about 130? Are they using 130 octane aviation gas? Are they using racing fuel that costs $3.00 a gallon?

I will concede that it's probably possible to have a street engine with 34 pounds of boost if you 1) use an engine with a 5:1 compression ratio, 2) use an intercooler, 3) use water injection, 4) adjust the ignition system appropriately, and 5) use very high octane fuel. And of course, it will help if you have a crummy intake air system.

If you're trying to save money by equipping a flat-heat six with a turbocharger you're probably fighting a losing battle, though.  

So why do you suppose the typical gas engine has so much trouble if you get much over 10 pounds of boost?

Docengineheat,

I wouldn't say that it's "no problem" to run high boost on gasoline, but it can be done with some careful planning. The particular engine that I referred to running 34 lbs of boost was a Honda B16A1 1.6 liter 4 cylinder. The compression ratio had been reduced from the stock 10.2:1 down to approximately 9.0:1. The engine received extensive head work including combustion chamber reshaping. The engine made use of forged pistons and rods, and a stock polished Honda crankshaft. Add in a bucket of money and a rather large intercooler and you have 34 lbs of boost. BTW, I am not a fan of water injection as a viable solution. I have my reasons, but that is another thread, as they say.

With the advent of more efficient inducer/exducer design, improved efficiency intercoolers, and better electronic management, the boundary of streetable boost is constantly being raised. As an example, the current generation of SAAB Vegan sports a staggering 21 lbs of boost straight from the factory!

If you'd like to get into more depth about turbochargers and such, I'd suggest starting a new topic.

BillyShope,

As far as the original topic goes, I've been playing with a few numbers, and it just doesn't look good. Flathead and L-head engines simply have some horrible characteristics. Sure there’s cheap to build, but that's about all they have going for them. The VE numbers are just terrible, and with that combustion chamber (or lack there of) it seems it would not take much boost before becoming the undisputed King of Detonation. But I'm still researching, I'll keep you posted if anything good comes up.

Good Luck
Bryan Carter

I see a number of problems with side valve engines.

The only one that a turbo will help is their poor inherent VE. Due to the poor VE, higher than normal manifold boost might be sustainable, as this will not result in such high cylinder pressures.

Other problems like very poor thermal efficiency, high demand on the cooling system, and possible downstream detrimental effect on aerodynamics, very long flame paths, potential for detonation and high weight, are not helped by turbocharging.

Regards
pat

Further to my previous post
I hope it doesn't sound negative, as good ideas come from throwing radical or crazy ideas around and analyzing and thinking.

Regards
pat

This is not the first time I have heard this suggestion recently. Sidevalve engines are much simpler and cheaper to build than modern OHC engines. They are also much more compact so can give lower engine bays and more design flexibility. Materials and fuels have come a long way since sidevalves were last designed and I think Billy's suggestion is worth thinking about.

Lots of road and racing engines run 2 to 2.5 bar (30-37psi.) of boost. With a properly designed cam, correct ignition timing, good cooling and forged pistons it is not as hard as you might think.

cheers, derek

Derekwhite,

I agree, in part, with what you have to say. Yet better fuel and materials quality can only take you so far. I use this phrase guardedly, but side-valve engines are simply an inherently poor design. There are a whole host of issues that cannot be solved by better material and fuel. Granted, SI engine technology has come a long way since the flathead left the drafting table. I am quite sure vast improvements could be made if the latest in CAD, machining, and materials were applied to the problem. I just don't feel the finished product would be worth it. You would have a highly engineered flathead, constructed from the finest in unobtainium, which was only marginally competitive with the most basic OHV design.

The real truth of the matter is that simplicity of design is not the only means of determining a how cheaply an engine can be manufactured. Raw numbers go a long way towards driving down costs. Make 3 million of the same engine and you start to learn how to make that engine cheaply. When Honda first debuted VTEC, I heard a many an auto engineer say "There's no way you're going to see that on their regular production cars. Too complex, to hard to build, and way too costly. No way." I think we know what happened in that case.

When this topic first sprang up, I must admit, the words "silk purse" and "sow's ear" sprang irresistibly to mind.

Regards,

Bryan Carter

Bryan, it's amazing to consider that which has become acceptable in the way of production engine design. I'm reminded of a little "bull session," back in the fifties, which took place in the Engine Lab department of Chrysler. Don't remember who all was involved, but Trant Jarman [Jarmann?] and, I'm pretty certain, Tom Hoover were there. Somebody brought up the idea of an overhead cam and immediately another rejected the idea, saying that production costs were too high. Trant then said something like the following:"I've got an idea! Let's put a slug of metal on the cam, which we'll locate a foot or so below the valves. Then, we could use a long, skinny piece of tubing to get up on the other side of the valves. Of course, we'd have to reverse the motion, so we need some kind of sheet metal or cast rocker arm, which we'll have to mount some way on the top of the head...." By this time, we were all laughing very hard. We all appreciated Trant's sense of humor.

BillyShope
Ask around if any old timers remember the Ardun heads for ford flatheads, made them look like Chrysler hemis. I think originally they were made for cooling reasons, but hot rodders liked them too. Ford passed the exhaust through the block. The old timers may also recall the word "Relieved", now mainly heard when exiting the beer recycling room. Most flatheads had very restrictive valve shrouding and the gap between the valves and the cylinder was also a restriction. The flathead design my seem simple but adjusting the valves was an all day job, even with the special wrenches. BTW Ardun was also the designer of the famous Duntov cam for Chevrolet. I think the name was Arkus Zora Duntov but the spelling may be incorrect.
Pancholin.

"Old timers"? I resemble that remark! You have the spelling of his name correct, but you've jumbled things a bit. It's Zora Arkus Duntov. He was employed, for many years, by GM, where he was obviously a rebel. He wore Hawaiian shirts to work, while everyone else was wearing white shirts and ties. (I didn't own anything but white shirts until I left the automotive industry.)

The Ardun head was intended, first and foremost, for performance applications. Cooling benefits were concomitant, of course.

You mention adjustment of the tappets (never heard them called "lifters" in a flathead) by a special wrench. These were aftermarket items. Stock adjustment was the same as in an Offy (i.e., you grind the tip of the valve, meaning, if the gap's too large, you must add weld metal and then grind). Don't know if anyone ever supplied hardened disks (as used in the Jaguars). This is, admittedly, second hand knowledge. My teen friends drove Fords. I favored GM.

So, while valve adjustment was a chore, the flathead V-8 design certainly offered a slick way to cheat. I know of at least one circle track car that was stock under one head and "full race" under the other. As long as the protestor didn't insist on choice of head for removal, he was safe. Difficult to hide that sort of thing when the intake is off.

If the side valve was redesigned with a modern design, it would surely have hydraulic tappets.

Regards
pat

BillyShope:
Ardun heads were originally designed for the trucking industry, to get more power out of the flathead engine.  They indeed worked well and quickly found their way to the performance crowd.

When I was apprenticing to the auto repair industry in the mid 60's, I was introduced to the world of flathead Ford engines.  We indeed adjusted valves by grinding from the stem end, and there was rarely too much clearance since the valve seat was cut too.  We had a jig that calculated the amount of seat cut then cut the stem the same amount.  If I got too crazy on stem cutting we just ground the seat a little deeper.  I still have some of the keeper removal tools and what we still call "tappet wrenches".
Franz