Highest-revving SOHC automotive engines?

Our LeMons '86 Civic Si gets shifted at the rev limiter, which is ~7200 RPM. I think that's the same motor mdshaw mentioned, SOHC 1.5 4 banger only we have the US version.

In Reply to Curmudgeon:

Don't think that's the same engine. The JDM D15B was a VTEC engine, and came with the normal SOHC VTEC system in the "EG" chassis, or the really trick 3-stage VTEC system in the later cars.

The JDM D15B is a pretty fun engine. I actually had that swapped into a '94 Integra back in about 2006, sucker pulled something fierce. Stock engine with bolt ons and a 'chipped' ECU that I got when I traded a blown 1.8L LS engine and extra parts for the D15B. I think I was revving it to about 7500-8000. It would doorbang with a friend's B16 powered Del Sol and another friend's 99 Si.

Not sure why you guys are comparing the D series Honda motors, aren't all those 4v/cyl? Isn't the F2T a 2v/cyl? Even if the D is SOHC the flow of those heads should be quite a bit better.

Most of my SOHC experience is with a certain narrow angle six cylinder with a crappy head, so I think it relates decently. 2v/cylinder, 81mm bore, 90.3mm stroke, ohc.

To make power at high revs (with boost) cam choice was is. Running fairly high duration, lift, overlap cams (the same ones we use for big power NA) have worked best. Cam specs: 245°/247°@.050" Lift:.455” Lobe center:112.5° Intake Close:11° BTDC Use:Drag Race*

Combine that with a turbo with a big enough hotside that the turbine inlet to boost pressure ratio is fairly low, this setup can be made to rev, and make power to 8500rpm+.

The rods start coming out of the block due to high rpms though, even with upgraded rod bolts.

I have seen similar things on VW's 8v crossflow 4cylinder engines. It's usually easier to just crank the boost and make a ton of torque than bother revving them out to make the power.

In reply to Paul_VR6:

The F2T is actually a 3valve/cyl engine, with two small intake valves. This was to promote swirl & tumble in the combustion chamber at lower engine speeds, and this is why I brought up the subject earlier.

We're talking about taking an engine that has deep roots in the Mazda R-type four-cylinder diesel of the early 1980's and spinning it like a Honda F20. Only we're using a very pedestrian cylinder head design to get there. I know, porting and cam and big turbo (oh my!) but I wonder if it wouldn't be smarter to focus on the powerband from 3,000 to 6,000 RPM and gear the car appropriately. And I really wonder if the head design on the Mazda F2 is going to make it a big waste of time trying to run the thing that fast.

I do really like this thread; I've got a bunch of seat time in a turbo 626 I used to own, I think there's a lot of cool ideas being tossed around, and I think Swank is crazy enough to really attempt something impressive here.

I brought up D because he mentioned having to screw with the valve cover with high lift cams.

I can focus on the powerband from 3000-6000, or even 3000-7000 on an actual F2, and make power at 7000rpms pretty easily.

But.... more rpms = more "work."

And gearing an F2 appropriately in a Miata with an FD trans means about... a 3.23-ish rear end. If with more revs i can get that rear end up to around a 3.7-3.9 area, it should be quicker under almost all conditions, since the gearing advantage would likely more than outweigh any 1000-3000rpm torque loss of the destroked motor.

The reality of it all is that maybe the head just isn't going to work. If that's the case, i can move to a Kia FE3 head somewhat easily to get the DOHC 16v goodness. This would be an interesting motor because essentially, it'd be an 86/86 motor just like the actual FE3, but with 165.5mm rods instead of 148.8mm rods. Not sure if this would hold any advantage over a "normal" FE3 at this point, as the piston speeds would be the same, but the ratio and therefor, angles would be different. And would this motor be totally gutless?

Obviously, i'm going to just go ahead with a stock F2 at first and see where that gets me and sort the car itself before i try something like this. Luckily, looking at everything, this hybrid bottom end wouldn't cost much at all to throw together.

So it'd effectively be a long-rod FE3? Because that sounds hot. And acceleration of the piston should be a little less aggressive with the longer rods.

I just think you're going to break things trying to get it to 9,000 and have to spend a ton of money & time and such getting an F2T up there.

Wait, are you trying to set a top speed record for an MX-5?

Yeah, it'd pretty much be a long rod FE3.

I'm not sure what i'm trying to do with the car just yet. Standing mile will be something it does, but not necessarily what it's built for. Theoretical gearing will give it a top speed north of 200mph, though. That's going to take a LOT of aero work to be even remotely a sane idea.

It's a no-rules stupid build.

I think I'd be building this in a tin-top FC RX-7 just for the aero, and probably a bit easier to build a better cage in one vs. an MX-5. If you do this right, you could be in for, what, $10k? Think of the magazine articles that you could write about this!

$10k is the halfway-realistic-give-or-take budget to get it up and running in a reasonable fashion initially. I could do it wayyyyy cheaper but it'd be compromised and with my way, i'm looking at probably $3000-$3500 just in a driveline that i can trust to hold the power vs. substantially less than a driveline i can HOPE will hold the power.

Cheaper than the Escort, but certainly not Challenge friendly. You COULD do a Challenge friendly F2T Miata if you got a little creative and were resourceful, but i already have a Challenge car. What i don't have is a project car that doesn't matter in the slightest that's mine and only mine to worry about.

Thanks for the correction on the 3v/cyl, that makes most of the previous conversation make more sense. The few things I read before posting to the thread didn't have it laid out clearly. SOHC vs DOHC makes less of a difference than number and size of valves! Does the F2 have different valve phasing on each valve?

You shouldn't have to change the stroke to get it to rev like that as long as you can get the top flowing right. Cam and turbine selection are key, as I stated earlier. I don't think rod length makes as huge a difference here. I haven't seen big differences in similar motors built with a 144m rod and a 159mm rod, with an appropriate change in deck. I think it helps with wear more than anything when combined with even longer than stock strokes.

Paul_VR6 wrote: Thanks for the correction on the 3v/cyl, that makes most of the previous conversation make more sense. The few things I read before posting to the thread didn't have it laid out clearly. SOHC vs DOHC makes less of a difference than number and size of valves! Does the F2 have different valve phasing on each valve? You shouldn't have to change the stroke to get it to rev like that as long as you can get the top flowing right. Cam and turbine selection are key, as I stated earlier. I don't think rod length makes as huge a difference here. I haven't seen big differences in similar motors built with a 144m rod and a 159mm rod, with an appropriate change in deck. I think it helps with wear more than anything when combined with even longer than stock strokes.

Well... the rod length thing is getting confusing now, i think.

There's been a few motors mentioned.

Stock F2:
86mm bore
94mm stroke
158mm rod

F2 "destroked long rod"
86mm bore
86mm stroke
165.5mm rod
No changes to deck height

FE3:
86mm bore
86mm stroke
148.8mm rod
DOHC 16v

F2 "destroked long rod" w/ FE3 head:
86mm bore
86mm stroke
165.5mm rod
No changes to deck height (uses F2 block)

I don't believe the valve phasing is different for each valve. Intake valves open at same time.

I can get valve sizes here in a minute, as well as a picture of the combustion areas on the head. It's not pretty.

< talking out of my ass >

The 12v head may work OK at high RPMs given the reduced displacement and high R/S ratio. (Talking about the "destroked long rod" version.)

The cylinders should be able to fill more efficiently, not just because there is less volume to fill, but because the pistons are not traveling so far down into the bore. The intake charge doesn't have as far to travel.

And while the pistons' "lazy," less abrupt changes in direction, due to the high R/S ratio, aren't desirable from a cylinder-filling standpoint, maybe that will be compensated for by the 3V head's more "constricted" flow and resulting higher intake charge velocity.

< / talking out of my ass >

Intake valve diameter: 32.5mm
Exhaust valve diameter: 34mm

Here's some pictures of the head.

Is the intake/exhaust cam duration and lift typically the same? With those valve sizes and the difference in area, cam selection and design is going to be key. Unlike other engines, this one might actually be limited by that exhaust valve size and the port.

I'm not sure if i have data anywhere on the stock cam, but the spec sheet of the Delta 272 i posted is fairly "normal" when it comes to aftermarket cams as far as i know. I believe it's also one of the more "aggressive" cams available for these things.

Stock cam has really low lift, really low duration, and NO overlap at all.

There is a source for a 1mm larger exhaust valve, think it's from a 300zx or something, but i don't see that doing a ton to help things.

Ok, I just went and checked that cam chart. The cam specs look like they're made as a sport cam for a 4v head with "normal" valve size differential. I am sure someone with more cam knowledge can chime in, but I would think that something much more aggressive on the exhaust lobe would go a long way with little downside.

What's also funny about this is that Mazda used the same cam in both the 12 valve NA motors as they did with the turbo flavor of the same. I think this is part of why they can last so long if treated well; they have gentle torque curves and are pretty low-power for what they could be.

pres589 wrote: What's also funny about this is that Mazda used the same cam in both the 12 valve NA motors as they did with the turbo flavor of the same. I think this is part of why they can last so long if treated well; they have gentle torque curves and are pretty low-power for what they could be.

True, what he said.

The only differences between the motors are the pistons and the turbo motors have sodium-filled valves.

Most appliance manufacturers do that. The turbo motor should have more cam, but almost never does.

FWIW, I recall those 3V motors not behaving much differently than the 2V ones they replaced. You'd think, with all that intake valve area that you'd have to be really careful with inlet timing, but apparently that's not the case. Treat it like you would a 2V.

Having dynoed aftermarket "turbo" cams that have less duration and/or overlap than other sport cams and make a ton less power, I will agree that even the non OEMs get it wrong a lot.

ZW shooting you a PM on an unrelated topic, pls reply if you can. Thanks.

Funny you should say that. A guy on the truck forum I'm on is turboing his Colorado, and asked something about the stock cams. Of course, I made a recommendation, and immediately got shot down because everybody knows the stock cams are best for turbo.

I blame Corky Bell.

Zomby Woof wrote: Most appliance manufacturers do that. The turbo motor should have more cam, but almost never does. FWIW, I recall those 3V motors not behaving much differently than the 2V ones they replaced. You'd think, with all that intake valve area that you'd have to be really careful with inlet timing, but apparently that's not the case. Treat it like you would a 2V.

Soo.... lots of exhaust work on the cam?

Is it even worth pursuing putting 1mm bigger valves with the appropriate work to do so correctly with such a huge disparity?

Zomby Woof wrote: Funny you should say that. A guy on the truck forum I'm on is turboing his Colorado, and asked something about the stock cams. Of course, I made a recommendation, and immediately got shot down because everybody knows the stock cams are best for turbo. I blame Corky Bell.

LOL, i had good ol' Corky in my head as soon as the first "stock cams" was seen in your post.

I would sure like to see someone have a set of pistons made for these motors which gave a "combustion chamber floor" that actually matched up with and made the best of the 3-valve head. That would mean two pairs of mirrored pistons...So if these were made, you might have to buy two sets (four "lefts" and four "rights"), mix them together, and have two engine's worth.