High-revving 3.0 16v

[WP0ZZZ]

I'm thinking about a crazy (and expensive) project at the moment. What's the top rpm range people is achieving for track S2/968 engines? Is it better to keep the balancing shafts?

I would like to keep the stock block, the Elmer engine block does not count ;-)
https://elmerracing.com/raceshop/race-engines/thor-billet-engine-detail

[Dimi 944]

I know of engines that made 8500-9000rpm

Dimi P
Flying Horse Motorsport LLC
flyinghorsemotorsport@gmail.com

[JackMan]

I used to race in GTS2 in NASA with a 1989 944S2 that was highly prepped with many lightweight or lightend reciprocating parts in the drive train and engine. I kept my max RPM at 6,800 and ran for six years on the same engine. Just after every wreck I had (2) we swapped the lower bearings in the engine. I also changed oil after every race/DE weekend and did an oil analysis. I tensioned the cams frequently and was fastidious about keeping the engine in tune. I got 209 rwhp out of the car and total dry weight was about 2,800 lbs. I could have made her lighter but all that would do is kick me into GTS3 where I wouldn't . be competitive.

In my opinion you can't push these valve trains much higher that 6,800 or you are going to be blowing up some engines. The limitation on these engines is the valve train. OH, and if you toss the balancing shafts you engine will eventually go KABLOOYYYYY

Dimi makes a good point. You can rev these engines to 10k rpm if you want. The real question is how often do you want to rebuild your engine?

Now, if you want to buy that Thor engine for a 944/968... why don't you just slip in an LS3? Much cheaper and less maintenance. If you are going to race the LS3 you'll need a dry sump to keep from starving the engine for oil in high g load corners. But it's your money, do what you want and let us know how it works out for you. Cars are just rolling experiments.

[v2rocket_aka944]

dry sump, solid lifters + cam and springs to match, short runner intake (stock S/S2 is tuned for around 4000rpm torque peak), lightly touch up the port walls (clean up casting lines, but don't enlarge anything)...much lighter+stronger Rods and lighter pistons will help a lot.

I ran a built-to-the hilt 3.0 968 motor for several track seasons. Shared the car with my daughter, plus was an instructor, so the car got driven a lot. The redline was at 7700, but I seldom ran it above about 7K, since mostly what it made above that was noise. I was meticulous about oil changes.

The motor lasted for a good long while without a rebuild, but I waited just a bit too long. When the engine went, it went big. Broke the number 4 JE piston at the wrist pin boss. When the Carrillo rod got loose it literally sawed the block in half. My daughter was at the wheel, on track, when it blew up. It was memorable for her.

[v2rocket_aka944]

[WP0ZZZ]

Very interesting replies. Thanks.

Originally Posted by Dimi 944

I know of engines that made 8500-9000rpm

Do you know the rough spec of those engines and how often did they need a rebuild?

Originally Posted by JackMan

In my opinion you can't push these valve trains much higher that 6,800 or you are going to be blowing up some engines. The limitation on these engines is the valve train.

Would race springs somewhat mitigate the problem?

Originally Posted by v2rocket_aka944

dry sump, solid lifters + cam and springs to match, short runner intake (stock S/S2 is tuned for around 4000rpm torque peak), lightly touch up the port walls (clean up casting lines, but don't enlarge anything)...much lighter+stronger Rods and lighter pistons will help a lot.

What sort of max rpm would you expect from those mods?

Originally Posted by madcorgi

I ran a built-to-the hilt 3.0 968 motor for several track seasons. Shared the car with my daughter, plus was an instructor, so the car got driven a lot. The redline was at 7700, but I seldom ran it above about 7K, since mostly what it made above that was noise.

Do you have dyno plots from the engine running up to 7700?

[v2rocket_aka944]

depends on the cam mostly but 8000 is a pretty good limit IMO.
997/991 GT3 cars don't do much more than that, and remember there is so much cubic capacity in a 944S2 engine that you just don't need revs as much.

8000 rpm in a 3.0 S2 engine is ~ the same amount of CFM as a 2.0 Honda at 12,000...

[WP0ZZZ]

Originally Posted by v2rocket_aka944

depends on the cam mostly but 8000 is a pretty good limit IMO.
997/991 GT3 cars don't do much more than that

8000 rpm would be pretty good!

991.1 GT3 redline is at 9000 rpm.

Originally Posted by v2rocket_aka944

remember there is so much cubic capacity in a 944S2 engine that you just don't need revs as much.

I would be looking for 300+ hp without forced induction so even if it's a 3.0 it will need to rev fast. I know that getting to that power with a turbo would be muuuch cheaper but that's not what I'm looking for.

[9FF]

Originally Posted by WP0ZZZ

8000 ...I would be looking for 300+ hp without forced induction so even if it's a 3.0 it will need to rev fast. I know that getting to that power with a turbo would be muuuch cheaper but that's not what I'm looking for.

Why not bore and stroke a 3.0L, you should be good for an extra 300-400cc with wet sleeves and an offset grind. Together with some other minor enhancements and a good standalone I’m guessing you won’t be far off your 300hp. Plus the engine will be 100x more reliable than one revving at 8k rpm to achieve the same aim.

[Jfrahm]

I think you could buy a used R8 for what it'd cost to get this thing breathing and not blowing up at 8K RPM.

[v2rocket_aka944]

upping the displacement will only help because it reduces the RPM requirement.

really basic rule of thumb math but 300 hp from a 3.0L with fixed cam timing and fixed intake geometry will take 8500-9000 rpm assuming you tune the intake/exhaust to work at those RPM ranges and can squeeze say 105% VE up there.

but a 3.3L could do it at 7500...


and that 4.0L THOR engine will do it at stock redline

or take a look at this link, and call MM...
https://rennlist.com/forums/924-931-944-951-968-forum/601298-330hp-na-street-engine.html

[WP0ZZZ]

Originally Posted by 9FF

Why not bore and stroke a 3.0L, you should be good for an extra 300-400cc with wet sleeves and an offset grind.

Originally Posted by v2rocket_aka944

upping the displacement will only help because it reduces the RPM requirement.

Increasing the displacement is certainly an option. There's a balance between increasing stroke/diameter and increasing the redline though...

Originally Posted by v2rocket_aka944

or take a look at this link, and call MM...
https://rennlist.com/forums/924-931-944-951-968-forum/601298-330hp-na-street-engine.html

Very relevant and interesting. Thanks!

Power curve looks really strong with more than 300 hp from 6000 rpm up to 7500 rpm. A related thread that I also found interesting:

https://rennlist.com/forums/924-931-944-951-968-forum/628347-how-to-get-more-power-out-of-na-looking-for-400hp.html

Originally Posted by Jfrahm

I think you could buy a used R8 for what it'd cost to get this thing breathing and not blowing up at 8K RPM.

Call me stupid but I would rather drive a well sorted, light and powerful NA 944 than an R8. Unless you are talking about an LMP R8, of course...

[v2rocket_aka944]

Originally Posted by WP0ZZZ

Increasing the displacement is certainly an option. There's a balance between increasing stroke/diameter and increasing the redline though...

not really with a 944. not enough stroke to worry about piston speed.

max offset ground stroke on a 944 is 94mm or so. stock 3.0 is 88

a rev happy Honda K24 is 99...and a 7000rpm LS7 is 101.6.

[flash968]

i regularly spun my 968 engine to 7400, but i did a LOT of work to get there.

as stated, the valve train will not let you go there. the valves float just above 6300. you will need stiffer springs to deal with that.

the DMF will also be a problem, as it does not adjust well to changes in velocity at that rpm, causing clutch failures.

the factory rods are not built for those rpms. i had to go with carillo.

balancing and blueprinting are a must. vibrations are a real issue at higher rpms. you will need to go to great lengths to ensure that everything is matched.

the head will require some work too, in order to flow evenly at those rpms.

all in all, you'll have to spend about $15k to get there.

[951and944S]

The oil system is definitely the limiting factor.
You can get creative with original wet sump factory system by lessening the strain, deleting balance shafts, orifice limiting main thrust bearing, custom wider pump gears or additional tooth count, etc.

Factory 944S valve train/springs are good to 7500 and given that the S2 3.0 uses the same dimension valves as the 2.5S, there should be no problem there. The larger 968 intakes weigh more and might take extra precaution but the exhausts valves are the same size throughout the 16v line. Titanium valves or at least hollow stem stainless alone will increase valve train integrity by 500 rpms.

Building a 7500 rpm 2.5 16v right now using 4.11 ring and pinion.

7500 definitely doable, but 9000...?
No way without dry sump and a ton of money.

T

[9FF]

Originally Posted by flash968

...you'll have to spend about $15k to get there.

Really? That is very cheap, I’d expect to pay an builder upwards of $25k for what the op is after.

[951and944S]

Originally Posted by 9FF

Really? That is very cheap, I’d expect to pay an builder upwards of $25k for what the op is after.

If you sub the whole thing out, supply a core engine and collect a complete engine, that's probably realistic.

T

[flash968]

please note that i said $15k for an engine that would rev 7400. i did not quote a price estimate for an engine that would rev 9k. i can't imagine one doing that for very long, regardless of what was spent. it would certainly involve a different crank, a dry sump, and a very stiff girdle.

[951and944S]

Originally Posted by flash968

please note that i said $15k for an engine that would rev 7400. i did not quote a price estimate for an engine that would rev 9k. i can't imagine one doing that for very long, regardless of what was spent. it would certainly involve a different crank, a dry sump, and a very stiff girdle.

Yep, with very low hour service interval too.

Not a one time investment but a constant ongoing thing.

T