Let's Play - Predict the HP Game!

[jluetjen]

Impressive! Could you do me a favor and just relist the specs as tested?

[TonyG]

Carrera3.5L

You don't win. The deal was, "closest without going over" (see page 1 for the rules)

TonyG

[TonyG]

jluetjen

-'82 34mm port 911SC engine. Stock rebuild with the exceptions listed below.

-Stock pistons, stock heads, new rings, rebuilt cylinder heads, all new valvetrain, all new head studs, all new timing gear... pretty much everything brand new except we didn't split the cases.

-20/21 cams
-SSI headers
-MB911 2in/2out muffler
-40mm PMO carbs
-rebuilt distributor recurved with straight mechanical advance running 32 degrees total advance

Dyno run was with straight 91 octane pump gas.


I think there's another 10-15RWHP with some more ignition timing, and some air/fuel ratio adjustments.

TonyG

PS> Actual HP was over 205RWHP! (without SAE correction factor)

[rdane]

I see the correction factor on the bottom of the sheet but wonder why the numbers are not SAE corrected on the graph? Nice engine either way.

This on a Dynojet 243?

[TonyG]

rdane

The numbers you see on the dynochart including the graph are all SAE corrected.

If you look at the top right, you'll see that the correction factor is SAE.

At the bottom, you can see exactly what SAE equaled at that particular moment in time. In this case the SAE correction factor was .97, meaning that the actual HP was higher.

Thanks for the compliment!

I'm gonna see if I can squeeze another 10+RWHP out of the engine with timing and a/f corrections.


TonyG

[jluetjen]

I'm impressed. That engine is running peak HP intake gas velocities much higher then other engines that I've seen. Most 911 engines develop peak HP no higher then about 100 to 104 meters per second of peak air speed at the tightest point in the intake path. Your engine is pulling about 111 meters per second, behind only Grady's 2.8E at 114 m/s. I suspect that the 20/21 camshaft's small overlap makes it less sensative to intake restrictions compared to camshafts with more overlap. The trade-off is a somewhat peaky powerband with the peak HP engine speed occurring less then 1000 RPM above the peak torque engine speed. Normally in 911's there about 2000 RPM between those two points on the rev range.

A couple of thoughts for the next step: I'm not sure that bigger venturi will help given the 34 mm intake ports. But since the venturi are easy to swap out, it wouldn't hurt to try. Otherwise you may not be able to get many more ponies out of the top end. Given the narrow rev range, a close ratio gear box would also help to keep the engine in it's sweet spot. Alternatively trying to fill out torque curve some as you described with the ignition timing and carb jetting might be productive.

[TonyG]

....:::AND THE WINNER IS..... :::...
(SOMEONE CORRECT ME IF I'M WRONG)

camgrinder @ 196 rwhp

John Dougherty - http://www.drcamshafts.com


Unless someone comes forward to dispute this, I will presume that camgrinder is the winner.

I'll give it until tomorrrow for any disputes to be brought forth.

TonyG

[dd74]

Tony - I'm impressed, too. Great work!

[camgrinder]

Wow wow wow !!

[dd74]

Originally posted by camgrinder
Wow wow wow !!

John - how do you think such a setup as Tony's would react to the larger earlier SC ports?

[KevinS]

Great stuff. Glad I lost (190) and the horse power was higher. I get 193.8157 with the correction factor, that'd make 193 the winner????

[TonyG]

My factory Porsche owners manual indicates that the factory power is 172Hp (crank) for the 1982 USA model 911SC.

This means that the 40mm PMO's, 20/21 cams, SSI, recurved distributor, and 2in/2out muffler are worth a combined total of about 70 crank HP!

205 Actual Wheel HP (SAE is used for comparision purposes)
------------------------
.85

=> 241 crank hp

=> 241 crank hp - 172 crank hp (stock)

=> 69 crank hp (and possibly more) increase over stock


Looks like Bruce Anderson is incorrect in his calculations with respect to the added HP for each modification (which people have quoted).

Thoughts? Corrections?

TonyG

[TonyG]

KevinS

The correction factor is already factored in.

Without the correction factor of .97, the actual wheel hp is 205RWHP.

TonyG

[KevinS]

Even better.....................

[rdane]

Thoughts? A few...

3.0 liter, 9.8:1 pistons, 964 or 20/21 cams with SSIs and 2/2 mufflers typically get 190/195hp at the wheels. Getting 5 to 10HP over that from the addition of carbs is impressive.

As John noted very good gains but I am really surprised at the torgue curve compared to every other 20/21 cam I have seen.
A lot peaker than expected and drops off sooner as well.

Good data points and a great engine Tony. Well done! Looks like everyone is surprised but Camgrinder

[Carrera3.5L]

Originally posted by TonyG
Carrera3.5L

You don't win. The deal was, "closest without going over" (see page 1 for the rules)

TonyG

Damn you and the fine print! And here I was thinking I was going to get a free tank of piss poor 91 octane.

Good job anyway!

Ralph

EDIT: If you tell people the motor makes 199 rwhp, then John wins. If you round up (and I know you will) and tell your friends your motor makes 200 rwhp, then I should win, right?

[sushinav]

Boys,
I think we all won today. Tony this was a hella fun thread.

Please tell me, a Cali newbie, how the heck you gonna smog that thing? I need the secrets so I can toss my cat and muff!

[camgrinder]

With early 3.0 sc heads I would expect another 10 hp at the peak, which wold be closer to 6500. I think the dip in the torque curve can be tuned out and another 5 to 8 ft lbs picked up.
Of course the engine needs a different cam

Is that $60 bounty in cash or check ?

[dd74]

Originally posted by camgrinder
With early 3.0 sc heads I would expect another 10 hp at the peak, which wold be closer to 6500. I think the dip in the torque curve can be tuned out and another 5 to 8 ft lbs picked up.
Of course the engine needs a different cam

Is that $60 bounty in cash or check ?

Tuned out with venturis, right? Or by timing?

Different camshafts? What do you recommend?

[camgrinder]

With pmo carbs I like closer lobe centers. like 108 degrees. this along with some more duration will pick the engine up in the 4500 to 6500 range. Im a little surprised Tony's engine fell off after 6000.
How is the distributor advance curve set? If the advance comes in too fast it can hurt torque.
When I see a dip in the torque curve like this, it usually means an exhaust system or intake system length. In a back up pull the dip might not show, meaning the engine just skipped a beat on this pull.