6 Valve Headcylinder

[countersteer]

just to throw another FACT into the conversation....

An OHC motor is taller than a pushrod motor obviously due to the valve train on top of the cylinder head(s) vs. being buried in the block. As I understand it, that was one of the reasons given for not using the Northstar in the Vette.

An OHC motor also makes more noise than a pushrod motor for the same reason as above. That's why you see luxury cars with shrouds over the top of the motor, also adding to height.

Speaking of the Northstar. As I understand it, this motor is undersquare, that is the stroke is longer than the bore diameter. Given that the bore to displacement ratio is lower, the available bore diameter into which fit valves is lower, driving the need for multiple valves. When introduced into the IRL, the rev limit was originally set at a point where an IRL motor had a max piston speed higher than an F1 motor at that time. (and they ran it for 500 miles at near peak revs.) There was a lot of spectacular blow-ups. They eventually lowered the rev limiter, which was followed by a reduction in displacement, followed by non production parts, etc. etc.

This is the first time I've ever heard the ZR-1 motor described as a dog. If you'll think back, this motor raised the bar for US iron. They may not have pushed it as far as they could because they didn't have to.

Finally, I find it darn impressive that the NASCAR boys are now routinely spinning a pushrod motor north of 9000 rpm for 500 miles with a flat tappet cam. Holy Smokes.... Imagine if they were allowed a roller cam.

[Carlos]

The 1991 Corvette used a DOHC 4 valve without any height or packaging problems

It's a back to back comparison. Same Bore. Same Stroke. Same Type Block.Shared Many Internals. Different Horsepower. Different Price Point. The 2 valve reflects a base engine and the 4 valve a performance optional engine that cost considerably more. But still, not a bad comparison. Interesting talking points for discussion.

EDIT - An Entertaining Comparison Between 2 1991 V8's of 5.7 Liters
Back to Back Comparison 2 valve/4 valve.
Feature Standard Engine (RPO L98) ZR-1 Engine (RPO LT5)
Type V-8, 90-degree Overhead valve V-8, 2 valves, cam in block, pushrods, 90-degree Overhead valve with 4 valves per cylinder and 4 overhead camshafts
Block Cast iron block and aluminum cylinder head Cast iron block and cylinder head
Displacement 350 cid (5.7 liters) 350 cid (5.7 liters)
Bore & Stroke 4.00" x 3.48" 4.00" x 3.48"
Compression ratio 10.0:1 11.0:1
Brake horsepower 245 @ 4000 (250-hp for hatchbacks using 3.07:1 rear axle due to use of low-restriction mufflers with this option combination only) 375 @ 5800 rpm
Torque 340 lb-ft @ 3200 370 lb-ft @ 5600
Main bearing five five
Valve lifters hydraulic hydraulic
Fuel supply Tuned-port induction (TPI) system Tuned-port induction (TPI) system

On the subject of the Northstar V8. There was Never an Undersquare version.

The Northstar V8 engine family is all OVERSQUARE. A V6 vaguely related is UNDERSQUARE and generally known as a Shortstar.

The Northstar and Shortstar engines are almost completely different engines, using different castings but they share a design blueprint - DOHC 4 valves.

A "Shortstar" LX5 inside an Intrigue's engine bayThe LX5 V6 is a DOHC engine from Oldsmobile, introduced in 1999 with the Oldsmobile Intrigue. It was produced by the Premium engine group at GM and was thus called the Premium V6, or PV6, while it was being developed. It is based on the L47 Aurora V8, which is itself based on the Northstar engine, so engineers called it the Short North, though Oldsmobile fans have taken to calling it the Shortstar.

It is not a simple cut-down V8. Although it has a 90° vee-angle like the Northstar and Aurora, the engine block was engineered from scratch, so bore centers are different. It has chain-driven dual overhead cams and 4 valves per cylinder, but is an even-firing design with a split-pin crankshaft similar to the modern GM 3800 engines. The LX5 displaced 3.5 L (3473 cc) and produced 215 hp (160 kW) and 230 ft·lbf (312 N·m). Bore is 89.5 mm and stroke is 92 mm.

[SZ]

An OHC motor is taller than a pushrod motor obviously due to the valve train on top of the cylinder head(s) vs. being buried in the block. As I understand it, that was one of the reasons given for not using the Northstar in the Vette.

no, it's not. the vette needs to be powered by a small block to be marketable. that means a two valve head, that means a lot of torque low down and a certain exhaust note - the torque requirements put displacement, bore and stroke into a certain range (as do marketing aims), the exhaust note arguably is the only thing LS1 screwed up on release.

An OHC motor also makes more noise than a pushrod motor for the same reason as above. That's why you see luxury cars with shrouds over the top of the motor, also adding to height.

no, it makes different noise to a pushrod motor, with more high frequency noise. unless you're running a geared valvetrain, valvetrain related noise is a small part of engine acoustics regardless.

Speaking of the Northstar. As I understand it, this motor is undersquare, that is the stroke is longer than the bore diameter. Given that the bore to displacement ratio is lower, the available bore diameter into which fit valves is lower, driving the need for multiple valves. When introduced into the IRL, the rev limit was originally set at a point where an IRL motor had a max piston speed higher than an F1 motor at that time. (and they ran it for 500 miles at near peak revs.) There was a lot of spectacular blow-ups. They eventually lowered the rev limiter, which was followed by a reduction in displacement, followed by non production parts, etc. etc.

the relevance to the whole two/four/multi valve argument is?

his is the first time I've ever heard the ZR-1 motor described as a dog. If you'll think back, this motor raised the bar for US iron. They may not have pushed it as far as they could because they didn't have to.

this is the first time i've head the zr1 motor referred to as a dog. it's clealy not.

two valve heads as a technology isn't ---. it just has it's limits as does any other.

Finally, I find it darn impressive that the NASCAR boys are now routinely spinning a pushrod motor north of 9000 rpm for 500 miles with a flat tappet cam. Holy Smokes.... Imagine if they were allowed a roller cam.

NASCAR is more impressive in that it offers a high degree of entertainment and relevace for the fans, a high degree of competitiveness for those involved all at a moderate cost to go racing.

doesn't really matter what's restricted or used under the bonnet so long as everyone's in with a relative shot on race day and the fans know it.

the engines involved are dinosaurs by modern standards but the racing can teach more technologically evolved racing formulas a hell of a lot.

[countersteer]

I stand corrected on my comments related to the Northstar being "undersquare". That's what I get for going off of memory rather than spending the time to google.

As for the other responses...

The 1991 Vette (C4?) had a larger engine compartment than the current generation (height) (C6). I wasn't discussing marketing. Obviously, if they had chosen to make the Northstar fit, they would have.

I was quoting Ray who referred to the ZR-1 as a dog... I clearly did not think that was the case given the time. That being said, he is entitled to his opinion. Compared to recent offerings, after 16 years of development, it is down on horsepower per cubic inch. At the time, it was a screamer.

Sorry if you didn't appreciate the comments related to the IRL's use of the Northstar (actually the Olds Aurora V-8). I do find it relevant to the 2/4/6 valve discussion as a longer stroke motor would require more valve area per bore area at a given rpm to make good power.

I stand by my comments on engine noise. Try to sell a Beemer or a Merc when you can hear the clicking and ticking of the valvetrain ...

ALL racing series are technology limited by the rules. Even our beloved F1. Part of the beauty of it is what creative things can be done within these constraints. (Ferrari's spring loaded brake balance bar comes to mind). Yes, the architecture on NASCAR engines is 50 years old. That being said, the ability to spin these things to 9000+ rpm for 500 miles within the constraints of a flat tappet cam/pushrod/rocker arm valvetrain is very impressive in my book. In fact, ifrom a pure physics point of view, it ranks up there with the 20k target that F1 had before the rev limiter.

[Carlos]

I'd have to agree that it all contributes to an interesting discussion, and we are handling a lot 2>4>6 valves, so many variables as the thread has brought out. For instance, 2 valve head development is not confined to modifying stock heads for racing, Dan Gurney's work with Westlake, the English firm resulted in totally custom 2 valve racing heads. 0n a 289 or 302 CID horsepower was about 460>500 and the 289 heads were used on the GT40. There are also custom 4 valve heads for American V8 blocks of 500+CID that are 4 valve.

Interestingly the Gurney heads, All American or Anglo American depending on which side of the Atlantic they are sold ... are still made and by an English firm that bought the molds and tooling, as recently as 2003 you could still get them off a dusty back shelf from California, though the tooling was sold years before. If I have time I'll post details later on. A little OT but interesting in our discussion. I Also have a page of engineering "justifications" for the Maserati 6 valve I'll have to summarize.

The ZR-1 certainly was impressive, at it's introduction almost 18 years ago, the Aurora V added to IRL but was not a large force and didn't exactly dominate the series. I never imagined so many people would be interested in this thread.

[SZ]

countersteer unfortunately you can't not discuss marketing rationale in the design of any mass market product. no market, no sales. it's arguably the biggest force shaping a product's engineering criteria. arguably many that strive to work in engineering in prototype race series do so as to focus on more "pure" engineering solution, those comparatively unencumbered by market considerations. i mean, what do marketing considerations do to affect ferrari's F1 car? they paint it red. period. the rest of the engineering effort is dedicated to having it go around a race track as quickly as possible. you can't think like that in road vehicle product design.

so much has advanced in powertrain design and development since the ZR1 that to compare it with LS1 and more recent 2 valve designs and to then pass it off on power/displacement data is laughable, or at best a good use of selective perspective. so much has changed.

valvetrains in shape don't click and tick. try sell any luxury car that's out of it. hard luck there. all valvetrains emit noise, overhead valvetrains do so at higher frequencies, but there are far louder noises on the go than valvetrain noise. thre's also a lot of work on modern cars in acoustic tuning - if you can hear the valvetrain and it's unpleasant it's manufacturers' clearly can't design properly to this end of the systems in place to form a more pleasing aural sensation are not functional.

given the forces and other factors involved, whilst a 9k flat tappet v8 is impressive, f1 eats it for breakfast re how impressive the application of technology remains.

that said there's a lot nascar can teach f1 re keeping it's fans happy and the racing competitive.

[Carlos]

Custom 4 valve heads for 500+ CID Chevy V8's
http://www.araoengineering.com/Chevy/chevybb.htm

Links to Custom Gurney Westlake 2 valve heads for small block Ford V8's
http://www.knightracingservices.co.uk/guernyweslake.htm
http://lists.twistedpair.ca/pipermail/c ... 33090.html

Article, Pictures, Technical Illustrations on Maserati 6 Valve
http://www.maserati-alfieri.co.uk/alfieri26.htm
Why 6 Valves? -Maserati's explanation

[SZ]

wow, arao is still around and doing ford/chev 32 valve heads.

see they've got a four valve LS2/LS7 package now too.

[Carlos]

Valve activation is so clever, 2 valves opposite each other, one rocker riding a cam on a pushrod, levering open the other opposite rocker to open the second valve, such simplicity. Anyone interested in engines should really take a look. Engineering brillance, I admire it more than Maserati's 6 valve... if that's possible. Well worth a few minutes to go through the site, excellent pictures:
http://www.araoengineering.com/Chevy/chevybb.htm

[mx_tifoso]

I was reading an article over the C6.R in RaceTech magazine earlier today, and one of the corvette engineers pretty much summed up the "advantages" 2valve engines have; which are, cheaper to manufacture, lower center of gravity, and more fuel efficient. And that the LS7.R in their race car did well even though it didn't achieve such high revs as other teams but instead delived more power lower in the power curve, which also increased drivability according to him.

He also mentioned something like, if Aston Martin think a 2valve setup is so good, then why don't they design their engines as such. Which I would believe it involves AM actually saying that 2valve setups are "so good".

All of the above is pretty much exact, but not verbatum.

The 7.0-liter engine combination allows us to run relatively low rpm to maximize fuel economy and reliability while producing extremely high torque numbers that make the cars very ‘driver-friendly' on a road course," explained GM Racing engineer John Rice.

http://www.corvetteracing.com/cars/c6r/engine.shtml

Buenas noches a todos....

[Powerslide]

well if six isnt enough

[J.A.W.]

Here's an interesting 800hp 6V mill, from about a century ago:
https://oldmachinepress.com/2015/04/14/ ... ft-engines

[Zynerji]

My little Audi TT has 5v in a 1.8l i4.

[J.A.W.]

Re: the kerfuffle over 2V VS 4V heads - per earlier posts in this thread..
..some may find the following article link - of interest (in German, but cogent diagrams are also captioned in English)
..since it provides a direct comparison of an M-B inline 3.0 ltr 6 with SOHC hemi-2V & DOHC 'Cosworth-4V' cyl heads..

http://www.pvv.org/~syljua/merc/M104Motor.pdf

[roon]

well if six isnt enough
https://s-media-cache-ak0.pinimg.com/73 ... rcycle.jpg

Test engine? Motorcycle? Photoshop?