High RPM?

Seems like a good number of NA builds lean toward boring out and/or stroking for larger displacement (a good way to build torque and hp). But has anyone tried making a high rpm/high compression build? Even at 9000 RPM the piston speed is not even close to what an S2000/s (4605 ft/min vs 4965 ft/min AP1), so I don't see it as stressing the internals too bad. So assuming one were to balance/blueprint the internals, use lighter high comp pistons, stay at 3.0 (to keep moving mass down), and of course all the appropriate head work, one could produce an awesome revving engine. Obviously the challenge would be head flow near the top end but if one could keep even keep 200 ft/lb at 9k that would yield 343hp (and not to mention an awesome noise!). Thoughts on this? Would valve float be an issue? How high of compression could you go on e85 (13.5:1?/14:1?)? Could this be done reliably? Just throwing ideas around

food for thought. sounds interesting. hopefully some more experienced people can chime in im interested to see the results

Here is what one of my friends, who has built some crazy Honda engine combinations, including a de-stroked "K15" (K-series 1.5L engine) that went 246 mph in a CRX at Bonneville had to say:

"I just did a bit of searching to see what the bore-stroke is on an NSX motor (90 x 78), and it'd still be totally reliable at 9,700 RPM. Its no small wonder they last so long, using Honda's redline they never go beyond 4,000 ft/min piston speed. That's just babying that engine."

He then went on to say:

"The 'aftermarket standard' redline for stock bottom end B18C motors is 9,200 with an 87.2 mm stroke (5,262 ft/min), and B16's regularly see 10,000 with a 77.4 mm stroke (5,080 ft/min). The valvetrain in those engines doesn't have any problem with that kind of rpm at all. The F20C at 9,000 rpm with an 84 mm stroke is at 4,960 ft/min and that's the stock Honda redline. The F20C is the only one of them that has forged pistons from the factory, but since the B-series bore is only 81 mm those cast pistons are substantially lighter than the 87 mm pistons in the F20C, hence the loading on the pistons and rods is less as well. At high rpm grams turn into tons! C30 engines have really beefy Titanium rods and forged pistons, so why are they running it at only 4,000 ft/min piston speed? Hell if I know. I limit my endurance engines to 5,400 ft/min but I'm using much stronger rods than Honda does. There are guys drag racing K-series engines that routinely exceed 6,800 ft/min!"

Food for thought...

L_RAO said:

Here is what one of my friends, who has built some crazy Honda engine combinations, including a de-stroked "K15" (K-series 1.5L engine) that went 246 mph in a CRX at Bonneville had to say:

"I just did a bit of searching to see what the bore-stroke is on an NSX motor (90 x 78), and it'd still be totally reliable at 9,700 RPM. Its no small wonder they last so long, using Honda's redline they never go beyond 4,000 ft/min piston speed. That's just babying that engine."

He then went on to say:

"The 'aftermarket standard' redline for stock bottom end B18C motors is 9,200 with an 87.2 mm stroke (5,262 ft/min), and B16's regularly see 10,000 with a 77.4 mm stroke (5,080 ft/min). The valvetrain in those engines doesn't have any problem with that kind of rpm at all. The F20C at 9,000 rpm with an 84 mm stroke is at 4,960 ft/min and that's the stock Honda redline. The F20C is the only one of them that has forged pistons from the factory, but since the B-series bore is only 81 mm those cast pistons are substantially lighter than the 87 mm pistons in the F20C, hence the loading on the pistons and rods is less as well. At high rpm grams turn into tons! C30 engines have really beefy Titanium rods and forged pistons, so why are they running it at only 4,000 ft/min piston speed? Hell if I know. I limit my endurance engines to 5,400 ft/min but I'm using much stronger rods than Honda does. There are guys drag racing K-series engines that routinely exceed 6,800 ft/min!"

Food for thought...

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Great info! So 9k is just scratching the surface, now it would be a matter of getting enough flow to not choke out at that RPM. What are the downfalls (if any) with high compression (on e85)? It should increase the responsiveness as well as power right? And I cant imagine it would stress the internals more than a sc/turbo setup. I hear people saying things like, "A high power NA engine will have just as crappy drive-ability as a high power FI engine" but I don't see why, unless you are running super aggressive cams. And are high lift cams at 9000rpm going to increase the chance of valve float significantly? Maybe the regrinded/mild cams WOULDN'T be such a bad idea for a build like this... Feel free to correct me if I'm wrong, I'm still learning the in's and out's of motor work.

USAFguy22 said:

Great info! So 9k is just scratching the surface, now it would be a matter of getting enough flow to not choke out at that RPM. What are the downfalls (if any) with high compression (on e85)? It should increase the responsiveness as well as power right? And I cant imagine it would stress the internals more than a sc/turbo setup. I hear people saying things like, "A high power NA engine will have just as crappy drive-ability as a high power FI engine" but I don't see why, unless you are running super aggressive cams. And are high lift cams at 9000rpm going to increase the chance of valve float significantly? Maybe the regrinded/mild cams WOULDN'T be such a bad idea for a build like this... Feel free to correct me if I'm wrong, I'm still learning the in's and out's of motor work.

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Piston speeds are one of many variables. With upgraded cams and a higher rev limit springs and retainers would always be advised. With the proper parts valve floating shouldn't be an issue.

High horsepower FI vs High HP N/A would be very relative high HP FI would be 2-3x more power than N/A in my book, 2 Completely different animals. Lets just compare 400whp N/A vs 400whp Turbo. The turbocharged one can be done on a stock motor with pump gas. Meanwhile the N/A motor most likely needs to be a stroked, high compression motor with ITB's, likely running on E85. ITB kits cost almost as much as a supercharger kit these days. The biggest advantage the turbocharged engine has is its ability to combat heat. The turbocharged engine compresses air in 2 stages with cooling in between. First the turbo compresses the air, and then the intercooler cools off the pressurized air, and then again the motor compresses the air further with fuel keeping the air cool long enough for ignition. If the setup fails to combat heat from the turbocharger problems could ensue.

At 400whp it may be possible to have fairly drivable N/A setup. I would say beyond 400whp that it would be impractical for almost any N/A setup, while FI setups with built motors could drive like a stock NSX at 700+whp, even capable of better than stock gas mileage. Reliable....another topic for another day lol.

The biggest reason people aren't running 9000+rpm? The engine doesn't flow enough air at that RPM. Now people like to think of the NSX's C30 as a high revving engine, but in reality it loses torque beyond 7000rpm. I'm not sure what the biggest restriction may be though, I'm not an N/A guru my any means.

The biggest issue holding back an NA NSX is going to be the cams; per my engine guy the older rubbing block VTEC valvetrains are fine to 9500 RPM. It's really the cam profile that limits the power band. That's not to say they valvetrains can't be improved upon - the K-series have roller tip rockers for reduced friction, weigh less, and have larger ratios (1.75 vs. 1.55 for the B/C series).

As to a cam design, you have to think of it on a single cylinder basis; the C30 has 500 cc per cylinder. That is relatively large considering the B16A is 400 cc per cylinder and the B18C is 450 cc per cylinder.

So that means the C30 is going to want lots of lift. My engine guy says that 12.0 mm should be the starting point, assuming that piston-to-valve clearance is there.

I'm going to contact some of the domestic cam manufacturers who have made B-series cams; in order to save a lot of time and money on R&D, I'm going to start with some of their B-series grind profiles they already have; that way they just have to make blanks that are properly sized to fit in the C-engines.

L_RAO said:

The biggest issue holding back an NA NSX is going to be the cams; per my engine guy the older rubbing block VTEC valvetrains are fine to 9500 RPM. It's really the cam profile that limits the power band. That's not to say they valvetrains can't be improved upon - the K-series have roller tip rockers for reduced friction, weigh less, and have larger ratios (1.75 vs. 1.55 for the B/C series).

As to a cam design, you have to think of it on a single cylinder basis; the C30 has 500 cc per cylinder. That is relatively large considering the B16A is 400 cc per cylinder and the B18C is 450 cc per cylinder.

So that means the C30 is going to want lots of lift. My engine guy says that 12.0 mm should be the starting point, assuming that piston-to-valve clearance is there.

I'm going to contact some of the domestic cam manufacturers who have made B-series cams; in order to save a lot of time and money on R&D, I'm going to start with some of their B-series grind profiles they already have; that way they just have to make blanks that are properly sized to fit in the C-engines.

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That would be outstanding!

Back in 1994, Danny said he was at 9000 RPMs. He then went on to FI, and IIRC, has the record for most powerful NSX (~1000HP):
http://nsxprime.com/forum/showthread.php?t=81540


I'd worry about the oil pump above 8k RPM too. OEM gear disintegration, and potentially cavitation if tracking:
http://www.nsxprime.com/forum/showthread.php?p=1545108

Also, since the race Toda engines running at 9k RPMs used their own custom forged cranks, I'd be worried about our OEM forged splayed crank exhibiting some weird harmonics and failing at those higher RPMs. This 90degree V6 just has a lot if inherent drawbacks for no apparent benefits IMO.

BTW - Before my engine rebuild, I did a lot of detailed researching and estimating on a custom K-series swap. I probably should have gone that route :frown:

My $0.02.

Dave

L_RAO said:

I'm going to contact some of the domestic cam manufacturers...

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It’s great to see the work you’re doing!

Make sure the cam manufacturers take valve to valve clearance into account as well as valve to piston clearance. NSXs have a very wide angle between the intake and exhaust valves (62° according to Mac Attack’s measurement). Click on this picture for a good view:


Because there’s such a large angle between the intake and exhaust valves, there’s a limit to how much overlap your cams can run before you start getting valve to valve contact.

Also interesting in that picture is the mating surface between the intake manifold and the cylinder heads. Since the mating surface is not at a right angle to the airflow, a 1” spacer would create two sharp edges the air would have to flow around. There is probably one thickness for the intake manifold/cylinder head gasket which creates the least amount of turbulence.

Mac Attack said:

I'd worry about the oil pump above 8k RPM too.

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I agree. I have heard from an informed source that the internal oil pump parts have a resonance vibration point just over 8,000 rpm. If you over-rev the engine, the oil pump could crack immediately or at a later date because of the over-rev. So if you want to rev beyond 8,000, get stonger (perhaps billet) oil pump gears.

My engine builder was the first to play around with the S2000 oil pump into the K-series modification.

I'm sure when we get in there, if there's anything that needs to be done, he'll be able to do it.

The one thing he wants to do immediately is plumb an external oil line to the cylinder heads/valvetrain. In non-VTEC he measured the valvetrain sof both the B- and K-series as getting about 10% of the oil they do while under VTEC. His plumbing job reduces wear and keeps the entire valvetrain cool (and happy).

Maybe Honda designed it this way for a reason? When in VTEC they need the oil to lubricate the valvetrain obviously but also pressurize the VTEC engagement system. I the valvetrain needs a massive amount of oil especially at low rpms with stock valvetrain at least. The only wear I've seen on hondas were the rocker arms from heavy valve spring weights.

With the lift and duration I'm trying to get out of the camshafts (I'm trying to get made), a valvespring upgrade will most likely be necessary.

Maybe Honda designed it this way for a reason? When in VTEC they need the oil to lubricate the valvetrain obviously but also pressurize the VTEC engagement system. I don't think the valvetrain needs a massive amount of oil especially at low rpms with stock valvetrain at least. The only wear I've seen on hondas were the rocker arms from heavy valve spring weights.

greenberet said:

It’s great to see the work you’re doing!

Make sure the cam manufacturers take valve to valve clearance into account as well as valve to piston clearance. NSXs have a very wide angle between the intake and exhaust valves (62° according to Mac Attack’s measurement). Click on this picture for a good view:


Because there’s such a large angle between the intake and exhaust valves, there’s a limit to how much overlap your cams can run before you start getting valve to valve contact.

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Here is his response:

Sounds like Endyn... Is this coming from Larry?

No. He is local to me, and is not a big fan of Larry's business practices - though he says that Larry is a more than competent engine builder.

i hit past 9k by accident yesterday?! I'm going to have a talk with my engine tuner to turn on my rev limiter. scared the bejesus outta me when i went WOT and some slippery unforeseen asphalt and WHOa!

no engine issues. probably helps that my engine was blue printed, balanced, and used lighter pistons and valves

BATMANs said:

i hit past 9k by accident yesterday?! I'm going to have a talk with my engine tuner to turn on my rev limiter. scared the bejesus outta me when i went WOT and some slippery unforeseen asphalt and WHOa!

no engine issues. probably helps that my engine was blue printed, balanced, and used lighter pistons and valves

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as long as your oil pump gears are ok........maybe do an oil analysis at your next change.

exactly my intention.....

Is it a built motor batman? Even stock I wouldn't worry too much. Definitely double check the tune to make sure the rev limit is appropriate for you build though.

I recall there being high revving builds in Japan years back last time i read/heard about those would be '06 I guess.
Anyway it should be doable just take a look at a SuperGT NSX, those are stock block based engines.

Will take some R&D, (condensed)
First of all mapping the edge of what's possible in the current envelope, certainly in terms of valve angels/overlap.
Then runner flow if you'd map all that out with hard that you could calculate where your custom cam should be at.
Then the issue of increasing valve spring strength (on C32/C35A Legend's small block chevy springs are used)

L_RAO

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Can't wait I'd be really interested!

L_RAO said:

Here is what one of my friends, who has built some crazy Honda engine combinations, including a de-stroked "K15" (K-series 1.5L engine) that went 246 mph in a CRX at Bonneville had to say:

"I just did a bit of searching to see what the bore-stroke is on an NSX motor (90 x 78), and it'd still be totally reliable at 9,700 RPM. Its no small wonder they last so long, using Honda's redline they never go beyond 4,000 ft/min piston speed. That's just babying that engine."

He then went on to say:

"The 'aftermarket standard' redline for stock bottom end B18C motors is 9,200 with an 87.2 mm stroke (5,262 ft/min), and B16's regularly see 10,000 with a 77.4 mm stroke (5,080 ft/min). The valvetrain in those engines doesn't have any problem with that kind of rpm at all. The F20C at 9,000 rpm with an 84 mm stroke is at 4,960 ft/min and that's the stock Honda redline. The F20C is the only one of them that has forged pistons from the factory, but since the B-series bore is only 81 mm those cast pistons are substantially lighter than the 87 mm pistons in the F20C, hence the loading on the pistons and rods is less as well. At high rpm grams turn into tons! C30 engines have really beefy Titanium rods and forged pistons, so why are they running it at only 4,000 ft/min piston speed? Hell if I know. I limit my endurance engines to 5,400 ft/min but I'm using much stronger rods than Honda does. There are guys drag racing K-series engines that routinely exceed 6,800 ft/min!"

Food for thought...

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What do you suppose he could do with the 1.3L in my Civic hybrid:tongue:

hybrdthry911 said:

Is it a built motor batman? Even stock I wouldn't worry too much. Definitely double check the tune to make sure the rev limit is appropriate for you build though.

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http://www.nsxprime.com/forum/showthread.php?t=154927&page=4

Floyd said:

What do you suppose he could do with the 1.3L in my Civic hybrid:tongue:

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With $$$ anything is possible. :biggrin:

I actually have a Civic Hybrid as well...that thing is terribly underpowered. I'm looking to put together a cheap/small turbo kit.

BATMANs said:

i hit past 9k by accident yesterday?!

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Are you still using the stock powdered metal oil pump gears? If so, consider what Kaz posted on the NSXCB's website:

“Please make sure to replace the Oil pump if you have ever over-revved the engine in the past.
In Japan, I saw at least three NSX engine failures due to the cracked oil pump.
Just over 8,000rpm, there is a resonance vibration point on the internal oil pump parts.
The crack could happen immediately at the time of over-rev or sometimes, at later date.”​

If you don’t know Kaz or why you should listen to him, see this thread: http://www.nsxprime.com/forum/showthread.php?t=166791