Highest-revving SOHC automotive engines?

So is....1.72 good? Bad? A number we don't care about?

the answer to your question is 1200 civic...my sp car saw 8300 before valve float-ran it there all the time...add valve springs and a cam and 10000 rpms was easy.i turned 11700 at the 94 chimney rock hillclimb-stock bottom end...these motors were very reliable-if you wont take my word for it call adam malley.

Swank Force One wrote: Does rocker arm ratio play a significant role in any of this? Or is this strictly how cam data may be manipulated due to different rocker ratios? Working with a 1.72 rar.

Only when you start to take advantage of it.

It gives you some real options with cam choice, but the higher lift profiles may start to become a problem at higher RPM's. Higher lift, and higher RPM means higher spring pressures, and more stress on the rockers. Broken rocker arms on OHC applications are not unheard of.

Tell me about your cam choice.

I currently run a Delta 272. I think I can get the full spec sheet. I do know that it's big enough that those who have 88-89s need to swap to a 90-92 valve cover because the rocker arms will hit the baffles.

I'll get the sheet, but I believe numbers are based on a 1.5 ratio in error.

Cams are voodoo magic to me. Delta can and will do a custom grind/weld for me if I can provide numbers.

Note that rocket arm ratio says 1.5. This is incorrect.

Rocker ratios are variable things, especially on an OHC engine where the cam lobe will be wiping on different parts of the follower at various points on the lobe. A ratio number is more or less a guide.

I remember back when I was paying attention to Z-cars, the hot thing was people spacing their cam towers up .100" or so, combined with another change that escapes me at the moment. The end result was an effective change in rocker ratio due to the cam wiping further away from the valve, so more lift from the same camshaft. That's a situation where the cam wipes at the middle of a follower instead of on the opposite end, mind you... I gather that you're playing with a D-series?

(does not apply to the Ford CVH, which has OHV-style lifters and 351C style rockers. It's an OHV engine with no pushrods!)

Nope, mazda f-series.

Awesome street cam. Nearly identical to what I run in my turbo Firefly. It looks like they spec'd you out a cam based on 1.5 rockers, and you've picked up some bonus lift and duration with your 1.7's.

I haven't read the whole thread, but it seems to me that you want to rev this thing high? Ain't gonna happen with that cam.

Delta can and will do a custom grind/weld for me if I can provide numbers.

It doesn't really work that way.

Cams needn't be voodoo. It's what I do, so if you have any questions, please ask.

Oh for sure it won't go that high. I'd have to get a custom welded cam. I'm not sure how far this one will go before it's a restriction.

What sort of profile would you expect to see to make power up to say... 9000? I know it's a bit useless to come up with anything without knowing the motor, but would you expect to see huge lift, huge duration, or both?

Lift and duration are tied together to an extent. The limiting factor is the acceleration rate, so to get a certain amount of lift you will have to have a minimum duration. Thus why OHV guys go ga-ga over rollers or large diameter flat tappets, or increasingly, large diameter rollers.

One thing I believe (I'm not alone in this) is that it's not pointless to lift beyond where the port stops increasing flow. You're only a peak lift for a degree or two, you see, but even if say the port stalls at .450 and you lift to .500, you're going to be at max flow for longer than if you just had a cam that went to .450.

Speaking of stalling... shooting for power is meaningless if you stick with the stock intake manifold. Get that junk off there! It's a huge power limitation on practically every production engine ever, moreso when you start shooting for big RPM. I saw big rotary power gains when I stopped screwing with the stock manifolds and went to something Better. And my 8v VW is definitely going to be breathing through a set of four 48mm blades instead of the stock soda straw intake manifold.

I can't use the stock manifold anyways.... fwd manifolds don't work so well in Miatas.

Sheet metal intake and "bag of snakes" turbo manifold are happening regardless of destroked motor or not.

In reply to Swank Force One:

Lot's of duration. The max lift will be determined by valve/piston clearance, the springs you use, their coil bind height, and the limitations of the valve train. You don't want to have to run so much spring that you're breaking rocker arms. I suspect it won't be a lot higher than what you're already running, but duration will be in the 250 +/- RANGE AT .050".

I realize this is at least in some part driven by a "wouldn't it be cool too ~" mindset, but I believe it's generally easier to build an engine for higher cylinder pressures rather than higher revs.

Just something to think about if the possibility of spending a lot of money on a motor that's going to explode in 300 miles is a problem in your life, which it very well may not be.

You don't drive engines, you drive cars. Getting power through RPM is easier on the drivetrain, easier on the chassis, and easier on the driver.

In a traction limited situation I'll take 300hp @ 9000 over 300hp @ 5000 anyday. And if traction isn't limited, then there's just not enough power

"The max lift will be determined by valve/piston clearance..."

P to v clearance has virtually nothing to do with peak lift. When the valves are open at peak the piston is way down the cylinder. It's during overlap when the piston coming over TDC is chasing the exhaust valve closed and the intake valve opening is chasing the piston back down the bore that valves get close to the piston. Increasing duration is primarily what closes exhaust valves later and opens intake valves sooner causing tighter and tighter p to v clearance. Exhaust side more critical than intake because the piston is coming up to meet it AND float hangs the valve out there longer once the spring fails to control.

DaewooofDeath and Knurled, I think the truth is somewhere between those two statements. If you are making full boost and the engine's 'natural' (na/pre-boost) ve peak at too low of an rpm, it becomes hard to make high peak power without blowing the engine up at low rpm. So that's 'too low rpm/too high cylinder pressures' and you should move the powerband up. On the other hand, usually at or before 9000 rpm is where it starts to make more sense to build out in displacement than up in rpm(to shift the powerband down). If you CAN keep making so much power that you're still limited by rpm at 8500-9000+, you build a bigger motor to keep the rpms low so that you don't have to have a completely custom valvetrain and a trans that won't shift anyway and belt-driven stuff that either explodes or doesn't work at idle because it's so underdriven. Etc.

Vigo wrote: DaewooofDeath and Knurled, I think the truth is somewhere between those two statements.

Indeed. As a rule of thumb though, high torque engines break drivetrains and low torque yet high RPM engines are easier to "pedal". But it's EASY to make a high torque engine, just throw turbo at it. But what you save in engine expense you spend in drivetrain.

My personal happy zone is about 180ft-lb, and whatever RPM the engine won't explode at...

In reply to MichaelYount:

Read the whole thing.

I'm still thinking about the combination of the factory 6500 RPM redline, the high-swirl & tumble aspects of the cylinder head, and trying to make solid power all the way to 9,000 RPM. The problem I have is a lack of knowledge of how this "should" work out, and I think the Alfa Driver is probably going to be a useful source of info.

I know good port work and good flow can help but I still wonder about swirl/tumble and taking that sort of head out to 9k. At what point does the inherent flow characteristics of this head become a limiting factor? Can you have a lot of swirl and still make good power up there?

Well... in strictly non-scientific terms, current motor is already rocking to 6500rpms+ with no signs of running out of breath or getting choked. (Factory limit is 6200 I think) I've seen 7000 on mazda's super accurate tach. This is a damaged stock 212k mile original bottom end.

Really... we're "just" talking about ~2000rpms more with the addition of an inherently more rev-able bottom end with slightly less displacement, a better ported head, bigger cam, and some custom manifolds. And a bigger turbo.

It's never going to be an f20c, but there's a lot, and I mean a LOT of improvement to be made over what I've got now, let alone stock.

You made 500 plus lb/ft, right? If you can achieve that at 6000 rpm you've got, really more power than you could ever use in an FWD, right?

DaewooOfDeath wrote: You made 500 plus lb/ft, right? If you can achieve that at 6000 rpm you've got, really more power than you could ever use in an FWD, right?

I haven't strapped my car to the dyno, but someone recently did make 547ftlbs to the wheels, yes.

But i think that was at around 4000-4500rpms.

If that number can be achieved at 6000rpms, we're talking major power. At 9000rpms, ridiculous power.

But i'm not planning on doing this in a FWD car. My FWD motor will remain as it is right now, probably "settle" for 400whp/450wtq-ish area, only revving to 7000rpm max.

Swank Force One wrote: Really... we're "just" talking about ~2000rpms more

RPM's expense is a logarthymic scale. 7000rpm on most imports isn't terribly hard to get, but every step above that gets more and more expensive.

Also see prior discussion about duty cycles.

Knurled wrote:

Swank Force One wrote: Really... we're "just" talking about ~2000rpms more

RPM's expense is a logarthymic scale. 7000rpm on most imports isn't terribly hard to get, but every step above that gets more and more expensive. Also see prior discussion about duty cycles.

Well... i'm more worried about head/valvetrain at that point than i am bottom end.

I'm not about to attempt to do 9000rpms "well" on a normal F2 bottom. Sounds silly.

Honda D15B - JDM version - Supertech springs, ARP rod bolts, micro polished & balanced crank - 9500rpm.