bad_monkey

The way I see it, we can make HP on the NA engines in all the standard ways (everyone has their list!) - the problem is that we're starting from a more advanced point than with most engines of the time. Except for perhaps an E30 M3. - apparently in full race trim, some of those 2.5L inline 4's were making up to 340hp.

The question then becomes - what can we change easily?

CR is among many appealing options in this regard - but to me the real glue that will bring any modifications together is the ECU. I'm holding out a lot of hope that the Microsquirt ECU will give us a cheap option in this department. Apparently it is working, but requires mods to the circuit board to get the trigger wheel working.

An idea I had was to try running a variable intake tract - basically you could build a "trombone" intake tract controlled by servo that would tune the intake resonance to the RPM. Someone please tell me I'm crazy

Apparently the stock cam could do with more overlap to aid exhaust scavenging - but I'm really not as qualified as any of you guys to make that observation. Has anyone looked at the improved cams that Milledge sells?

67King

Compression ratio has nothing to do with mechanical efficiency. It affects thermal efficiency. As I said, you need to understand the two if you are going to go talking about making the kind of power from this engine you are talking about. You can't just throw cams and fart cans at it to get that result. THere have been some words and assumptions regarding compression ratio that are HORRIBLY wrong. Linear benefit? Anyone claiming that should be asking questions, not making statements. Nothing wrong with asking questions, I've got two engineering degrees from a top tier engineering school, and I asked a whole boatload of questions when I started working on engines in my career.

At peak volumetric efficiency (114%), the last engine I worked on had an IMEP of 238 PSI. The FMEP was only 32 PSI. That is 87% mechanically efficient, and a resultant BMEP of 206 PSI. At peak power, where VE was 98%, the IMEP was 205 PSI, the FMEP was 43 PSI, giving a mechanical efficiency of 79%, and a BMEP of 161 PSI. At 0 RPM, and engine is 100% mechanically efficient.

V2Rocket

993s had this called varioRam

mechanically moving tubes that based on rpm would engage the intake port or pull away, to either have a long runner for torque or short runner for top end

V2Rocket

i wonder how much bigger you could go with the 2.5 16v head in terms of valve area, i think that engine would be the better candidate to start on to try to break 200HP NA (considering its at 190 as-is and has the highest rev limit of all 944s). it also already has knock protection.

bigger ports/valve area + little higher revving and a chip and you might make it

67King

Valves are the same size as the S2, which is already well over 200. Valve size determines horsepower capability - displacement is more about torque than power. Throw in the slightly longer duration cams of the S2 and a header, and you are probably there with an S engine. The best thing to do would be to fab an intake with shorter runners. I'd think the slightly larger (39mm, rather than 37mm) valves from a 968 would be overkill, but you could get even more power out if you needed to.

Running some quick numbers, the 16V engine should be capable of 6,000 RPM stock. That boxes pretty well with the factory rating. A 12mm lift cam would get you to about 7200 RPM for peak power (assuming your losses aren't too great from the intake tuning). That'll easily get you over 200 horsepower (I assume that everyone here knows that horsepower = 5252*RPM/torque). If you really want to go nuts, and put in 39mm valves as well, you can rev to a screaming 7600 RPM. This is using Taylor's Z-factor (aka Mach index) approximation, for those who know what I'm talking about.

Another HUGE advantage the 16V head gives is spark plug location. It will drastically improve your thermal efficiency. I'm not sure what the stock CR's are, but generally speaking, the central plug will allow you to get 0.7-1.0 points more compression out of the engine, which further helps thermal efficiency.

V2Rocket

16v engine stock redlines at 6800 so with some solid lifters and uprated springs you should be over 7000 safely.

consideration should be paid to the intake design of the S; it was a compromise between peak HP and driveable torque (to keep the S as a sensible daily car while still making it very fast). in the search for a dedicated high-hp car some driveability could be sacrificed which is where the large plenum/short runner design comes into play (or ITBs).

someone with an S should throw in an S2 cam set and see if they best 200. although i find it interesting you bring this up since many S2 guys throw in two "S" exhaust cams for performance. this needs to be clarified.

Lorax

Ok what I meant to say is that it does affect overall energy efficiency. since we are talking about a motor here changing only the CR ratio the difference between thermal efficiency and overall energy efficiency (Useful work performed per BTU, right?) doesn't matter because friction is a constant between the two and we can just take it out of the equation.

I never claimed linear benefit - I just took the measurable benefit that we know is correct (the 8hp for a .5 increase) and tried to guess an average that would take into account the diminishing returns (The 5hp number) just for the sake of discussion if you see what I'm saying. Even a scale with a diminishing return is going to have an average, I just guessed an average for the sake of this discussion. Do you think it was a bad guess?

67King

The numbers I was using were in reference to peak power, not redline. When I checked on the advertised peak power, it listed 6,000 RPM. If you are trying to hit a specific number, redline is irrelevant (assuming it is after the target, of course). What happens is that when your intake air velocity over the intake stroke hits a value of about 0.6*the speed of sound, your VE falls off of a cliff. In well tuned cars, this happens at peak horsepower. In more mundane cars, the cam selection and intake design may cause the tuning to be such that you don't hit 0.6 at peak power, if ever.

Depends how you define "performance," I suppose. And of course, I may be mistaken in thinking the S2 cams were longer - after all, "performance" to a lot of people means more top end horsepower. Anyway, shorter cams may give the engine more midrange torque, which may be more useful overall. Everything is a tradeoff. Actually, that's perfectly analogous to the intake design you were talking about. Longer runners make it more drivable, but shorter runners give higher RPM tuning. What was the goal of the S2 guys who did this?

If you make a 200 horse 8V engine as we're talking about, you probably won't want to drive it on the street. It'll be a dog in the low and midrange RPM's. It would almost certainly need bigger valves, FWIW.

Lorax

I wanted to build a turbo 2.5l 16v engine with a 9.5:1 CR and run the same boost as I do on my 8v 2.5l and people said I was an idiot.

Lorax

I remember reading about the record holding norwood ultra short stroke 1.6l (?) mr2 top speed car... it was setup in such a way that it had a massive torque hole about halfway through the rev range before it could start making power... the most difficult part was getting the car over that torque hole, after that the car made gobs of power.

MAGK944

For the 8v na here are the Broadfoot Racing 200hp+ options:

Engine option IV

200 HP 2.8 liter N/A engine with Darton steel sleeves, JE Racing forged pistons with 12.5:1 compression (100 octane race fuel only), knife-edged and cross-drilled, and stoked to 88mm crank, Carrillo race rods, race cam, race springs, O-ringed head, major port work to head, larger intake valves, 3.0 bar fuel reg., and completely built, with new seals, gaskets, rings, rollers, adjusters, belts, water pump, etc. Price: $9,600 Parts and labor.

Engine option V

220 HP 3.0 liter N/A engine with Darton steel sleeves, JE Racing forged pistons with 12.5:1 compression (100 octane race fuel only), knife-edged and cross-drilled, and stoked to 88mm crank, Carrillo race rods, race cam, race springs, O-ringed head, major port work to head, larger intake valves and seats installed, 3.0 bar fuel reg., 951 fuel injectors, laptop controllable piggy-back fuel controller, and completely built, with new seals, gaskets, rings, rollers, adjusters, belts, water pump, etc. Price: $10,200 Parts and labor.

He builds some very nice engines:

Lorax

Why only 100 octane fuel? It seems like they would be able to bump compression up even higher if they built it for better fuel.

And why does that engine have a turbo motor mount?

Calmchaos

How much does a good LS engine cost? In comparison to those 10K broadfoot built engines.

MAGK944

That picture is just an example of what he builds - very pourdy! He does all p-car engines and is well known in these parts (FL) for his builds. Website is a pain to navigate but worth searching through (no affiliation).

krystar

just gas up with E85 in that engine, i'll run beautifully