Limiting factor for RPMs?

[dieselgeek]

That is your opinion, others may be smarter.........

Words whose definition TC does not know:

Theory
Fact
Opinion


feel free to add to the list.

Meanwhile, I'd just like you to put up or shut up: show us a running video of a car you "built"

[dieselgeek]

Crickets chirping. I just discovered how to make Alex shut the hell up - PROOF PLEASE

[38P]

As has been repeatedly proven over the past 100 years, 4-valve engines tend to have drastically more valve curtain area and low-lift flow, relative to bore size.

`Nobody is going to deny the flow advantages of 4-valve heads or the RPM potential of OHC engines with their lighter valvetrain.
There are significant disadvantages though regarding cost ( 2-valve 5.4 engines cost $800 more at the factory level than 5.3 LS engines) complexity and overall dimensions. OHC engines were produced in the 20's or 30's so they must be vintage also. I believe in the KISS principle so if the simpler cheaper and smaller dimensionally engine does the job why change? The hated LS is so much more popular in swaps than the Mod because it is easier to fit. With the LS3's redline at 6600 you would think the 5.8 Mod would redline at 9000 being so superior and lighter in the valvetrain instead of 7100. I suppose if Ford had designed its 4-valve heads with a direct acting camshaft position over the valve instead of rocker arms with hyd. lifters it would RPM higher but that would require more maintenance via buckets with shims or some such arrangement.
According to Chevrolet advertising the ALMS Corvette engine had to be de-tuned to be accepted in its class which explains why its RPM is kept so low. Maybe the 2-valve is still viable in high performance applications

The Chevy "detuning" ad is about the supercharged ZR-1. The ALMS Corvettes are unsupercharged. In other words, advertising slight- of-hand in comparing prunes to raisins. Obviously a relatively big, slow-turning two-valve "obsolete" engine has worked sufficiently well in the intake-restricted world of ALMS. Without the competition equalizers, "Government Motors" would be a distinct disadvantage to more advanced powerplants.

Moreover, there are plenty of series in which pushrod engines are "crutched" or completely protected by the rules, from the three big NHRA pro categories (which ban overhead cams), to NASCAR, to WOO. Thus, there are legions of pro engine builders who know nothing but 2V pushrod mills.

Where DOHC and other forms of valve activation are on an equal footing (no handicaps), DOHC is virtually universal. Even when Penske and Ilmor achieved the last great "clean sheet" pushrod engine triumph (Indianapolis 500 1994) Penske's "Mercedes" had more cubes and more turbo boost than the DOHCshttp://www.nytimes.com/1994/04/18/sp...ard-blues.html

Noone wants this thread to degenerate into another pointless LeSs versus DOHC thread. Suffice it to say that there are a large number of Luddites who will go to their deaths clutching their beloved pushrods and hating on multi-valve DOHC engines. Meanwhile, the vast majority of engines in production today and for the foreseeable future will be multi-valvers. That's not by accident.

Finally, the basics of DOHC design were first penned 100 years ago (not in the the "20s and 30s") by Ernest Henry for Peugeot, who designed a long-stroke 7.6-liter four-cylinder, sixteen-valve DOHC powerplant for Grand Prix racing. Cost has always been the primary knock on DOHC 4-valvers. But in the age of CNC machining, even some of the dirt-cheapest cars in the world use overhead cams and multiple valves for maximum "power density."

[BKBridges]

Speedzzter
I saw a nice Aardema Model T 4 cyl with DOHC at El Mirage last month. The dream is alive! (this thread is kind of beat up though ) I think this is the car:

[TC]

Crickets chirping. I just discovered how to make Alex shut the hell up - PROOF PLEASE

Nope you just can't explain things to stupid people, so I just stopped posting.....

[jcharliem]

...you just can't explain things to stupid people...

Wow. A post from TC that makes some sense.

[squirrel]

In a wholly unintended way.

Sorry Alex

[OldMachinist]

The Chevy "detuning" ad is about the supercharged ZR-1. The ALMS Corvettes are unsupercharged. In other words, advertising slight- of-hand in comparing prunes to raisins. Obviously a relatively big, slow-turning two-valve "obsolete" engine has worked sufficiently well in the intake-restricted world of ALMS. Without the competition equalizers, "Government Motors" would be a distinct disadvantage to more advanced powerplants.

Moreover, there are plenty of series in which pushrod engines are "crutched" or completely protected by the rules, from the three big NHRA pro categories (which ban overhead cams), to NASCAR, to WOO. Thus, there are legions of pro engine builders who know nothing but 2V pushrod mills.

Where DOHC and other forms of valve activation are on an equal footing (no handicaps), DOHC is virtually universal. Even when Penske and Ilmor achieved the last great "clean sheet" pushrod engine triumph (Indianapolis 500 1994) Penske's "Mercedes" had more cubes and more turbo boost than the DOHCshttp://www.nytimes.com/1994/04/18/sp...ard-blues.html

Noone wants this thread to degenerate into another pointless LeSs versus DOHC thread. Suffice it to say that there are a large number of Luddites who will go to their deaths clutching their beloved pushrods and hating on multi-valve DOHC engines. Meanwhile, the vast majority of engines in production today and for the foreseeable future will be multi-valvers. That's not by accident.

Finally, the basics of DOHC design were first penned 100 years ago (not in the the "20s and 30s") by Ernest Henry for Peugeot, who designed a long-stroke 7.6-liter four-cylinder, sixteen-valve DOHC powerplant for Grand Prix racing. Cost has always been the primary knock on DOHC 4-valvers. But in the age of CNC machining, even some of the dirt-cheapest cars in the world use overhead cams and multiple valves for maximum "power density."

Thought that would get you fired up! Ford took 2 DOE low interest loans to develop more fuel efficient cars in 2009 it was 5.9 billion
and in 2010 1.8 billion. Of course this wasn't called a "bailout" loan so it doesn't make them another Gov't Motors. Works if your definition of a gov't loan is narrowly defined.

The mod motors redline at 7000 which is 400 more than the current hi-performance pushrod engine so yes the pushrod is slower but debatable as to slow-turning.

Pushrod engines are "crutched" for one thing to keep costs somewhat lower. OHC engines are more costly to produce plus the development costs would be high. My goodness racing needs to lower costs not increase them.

OHC engines certainly have the advantage in performance and since fuel economy has become such a big deal most cars today are 4cyls. especially if you include the whole world and not just the U.S. in the mix. Without a doubt an OHC head is needed to get adequate performance and fortunately there are half the valvetrain parts in these engines which helps keep costs down. Also the inline 4 has much less packaging problems than a V-8.

I didn't feel the need to be so specific but since you called me on it the first Grand Prix DOHC engine was produced by Fiat in 1912 with Peugeot following in 1913. The first production DOHC was introduced by Sunbeam in 1925 with Alfa Romeo following in 1928.
These were long stroke undersquare engines like the 5.8 mod is undersquare.

I'm sure the machining time is similar to both designs with guides and seats machined on "gang" machining centers. The additional cost is parts which are double in regard to guides, seats, valves, springs, retainers, locks lifters and rocker arms. Then you have 4X the number of camshafts and gears and additional idlers, chain guides and tensioners and an extremely long timing chain or additional chains depending on design. Also the casting is more complex with more potential for scrappage.

You make it sound like the pushrod V-8 engine is stone age when in truth it is still a viable design in the right application and the external dimensions certainly make it easier to install in a smaller space.

The thing I have against the Ford mod is it could have been so much better than it is. The short bore centers limits the cubic inch available and small bores limits flow capabilities. In an attempt to gain size Ford coats the aluminum bores with some type of flame spray as there is not enough room for sleeves in the 5.8. This means no repairs to cyls. for wear or damage-block will have to be scrapped which again has the potential for additional cost to the end user. At least they didn't try to run rings against silicone aluminum like the Vega although Porsche had success with this process. Also Ford can't take advantage of one of the real advantages of the lighter valvetrain for RPM because they use hydraulic lifters and rocker arms.

Maybe you should consider another manufacturer who has a better designed engine to worship at the alter of. The reason you grate on me and others is your attitude that Ford is perfect and all else is junk. Sorry that is not the case or Ford would have run all other manufacturers out of business by now.

[Ron Ward]

[38P]

DOHC Conversions and Speedy's insanity

Speedzzter
I saw a nice Aardema Model T 4 cyl with DOHC at El Mirage last month. The dream is alive! (this thread is kind of beat up though ) I think this is the car:

Bitchin!

If I was slightly more insane (and deep pocketed), I'd love to tweak the "350/350" fiberglass catalog car street rodders and the hidebound, rust-loving neo-traditionalists with a speedster-style T (not a T-bucket) powered by a Megasquirt-injected, turbocharged, intercooled (maybe even a brass charge air cooler . . . .), Model T engine with a rare DOHC conversion head.

Sure, such a mishmash wouldn't do anything well, would be crazy-dangerous on the road and track, and would probably blow up almost instantly (3 main bearings and a T-planetary gearbox aren't the hot set-up for a turbo car). But it'd be a real hot rod.

http://www.mtfca.com/discus/messages/29/4198.jpg

[squirrel]

Yeah, you should do that. The flathead A motor is just two low of performance.

[38P]

@Oldmachinst

Not. Taking. The. Bait.

But, Boss 302 redlines at 7,500 r.p.m. with a full warranty. Competition DOHC Fords are turning even harder.

If the Feds are mandating that OEMs develop products for which there is insufficient market demand, why shouldn't they bear some of the costs. I suppose that every Bangshifter with an FHA or VA Mortgage is living in a "government house."

The difference between "Government Motors" and Ford is that a low-interest loan isn't the same thing as: (a) taking an ownership interest and giving one to the unions; (b) trashing the bondholders and stockholders in a quickie, sham bankruptcy that disregarded the law on how such reorganizations are normally done; (c) pouring in billions of tax dollars to cover losses (not loans that must be repaid); (d) having a goverment "czar" say who's in charge.

[38P]

@Squirrel
I've thought about a turbo "Banger" in an A-based speedster . . . .

[JeffMcKC]

@Oldmachinst

Not. Taking. The. Bait.

But, Boss 302 redlines at 7,500 r.p.m. with a full warranty. Competition DOHC Fords are turning even harder.

If the Feds are mandating that OEMs develop products for which there is insufficient market demand, why shouldn't they bear some of the costs. I suppose that every Bangshifter with an FHA or VA Mortgage is living in a "government house."

The difference between "Government Motors" and Ford is that a low-interest loan isn't the same thing as: (a) taking an ownership interest and giving one to the unions; (b) trashing the bondholders and stockholders in a quickie, sham bankruptcy that disregarded the law on how such reorganizations are normally done; (c) pouring in billions of tax dollars to cover losses (not loans that must be repaid); (d) having a goverment "czar" say who's in charge.

What does any of your posts have to do with the OPs question ?????

[squirrel]

But, Boss 302 redlines at 7,500 r.p.m. with a full warranty.

Chevy was selling a 454 over the counter 40 years ago that would spin that fast. No warranty.

I still don't see where there's any big advantage to the OHC and 4 valve thing, unless you are racing in a class that gives it an advantage. Out in the real world, GM seems to do ok with the archaic technology. And Ford and others do ok with the modern technology. It's almost like it's just a matter of taste.