SlakkerRacingDev

We had a chance to do some back to back testing of 91 vs 101 octane on our latest 4.1L capacity conversion for this 997.1S engine that ate a valve before failing. We did not change the tune between the two runs and allowed the ECU to adapt instead.




Keep an eye on our dyno headers on this video…

https://youtube.com/shorts/Cwp4SBaHSIs?feature=shared

Ob917

interesting, keep these findings coming please. Cant wait till you start really getting into the 9a1 stuff.

steveP911

Wow. 406 hp at the crank. Could you explain the 82 mm plenum and TB-101? I thought the TB would be 82 mm. Not sure which plenum that is. Also, any reason you chose 91 octane versus the normal "high-test" 93?

Thanks for sharing all of this!

SlakkerRacingDev

This is the same ebay "plenmum" and 82mm GT3 throttle body combo that has consistently been performing well in our tests. Stock plenum and TB topped out at 395hp on this build.


91 is the standard premium pump gas at most places around here. Even the station that sells the 101 race gas at the pump, only sells 91 for their premium.

steveP911

I wanted to see how much Slakker had improved engine performance versus the stock engine, so I put these two graphs side by side. First is from the 997.1 owner's manual (with power and torque peaks in SAE format). I tried to stretch the Slakker graph to match the y-axes so the comparison is more visually obvious. It's not perfect but I think it demonstrates a few things, all of which Brandon is of course free to correct as needed. Sorry, Brandon, I couldn't help myself. This is roughly where my motor is currently headed so it's hard not to get excited.

What I find most striking is the new torque curve. Bumpy but fairly "flat", not dipping below the stock engine's peak torque value. Looking at 3500 rpm, which is a typical level I might find myself in when I don't want to downshift through tight/slow turns on a track, a stock engine only offers about 260 ft-lbs in that range but the Slakker motor is in the low 300's. A 15+% improvement in torque. At even lower rpm's (which I would not lug the engine at), the Slakker motor is still >300 ft-lb. Pretty amazing.

Thanks Brandon. I hope I didn't go overboard or err.

sburke91

It would be very interesting to see data logs (especially timing and knock sensing) from the vehicle during these two dyno runs. Octane isn't 'magic horsepower' -- higher octane just prevents knock (or to be more correct, prevents early ignition), allowing more timing advance. The fact that these runs were done with no change in tune indicates that the ECU is sensing knock (or sensing it earlier) on the 91 octane run and pulling timing out earlier--logs would show this as part of each run.

Is the tune stock or a custom tune for the 4.1?

spessx

I know different dynos arent really comparable but thats a lot of extra torque in lower rpm ranges. Just guesstimating but maybe a 50ft lb difference at 2k rpm. Driveability and ability to ham it up on backroads is probably much improved.

I’d also like to know if this is the factory ECU tune or a special tune for the 4.1.

Oh, and Brandon - thank you for sharing. Always great to see your posts here and on the FB groups.

C2-996

@SlakkerRacingDev very cool to see your progress! Question, will you guys be offering a service for head work and porting work on the intake side (something similar to what Hoffman does)
I noticed your website mentions some head re-working but didn’t know if a further performance porting option would be available as well. From what others on the form have discussed, some of the port work does show some differences across the curve when increasing the displacement on these motors.
Definitely liking your 4.1 liter option and will be heavily considering it in my future for my 997

SlakkerRacingDev

You nailed it. Our “dyno tune” has the MAF and injectors rescaled for the displacement upgrade, optimized variocam and varioram, runs a little richer through the requested lambda table, and uses a “stock ignition timing”.

The Bosch ME7.8 ECU has an optimum ignition timing table and 4 maps it switches between in trying to achieve it. It also has number of factors, including knock threshold, that are used to retard the timing on the fly. So not near as simple as typical 2D ignition mapping table in a standalone ECU. We were seeing ECU retardation on the pulls and the higher octane reduced but didn’t eliminate them, which tells me knock is a factor but not the only factor. Our combustion analysis logger showed knock to be within typical oem thresholds of 1 bar of intensity per 1000 rpm.

SlakkerRacingDev

It is tough to compare dyno numbers between dyno. A lot of dyno graphs that we see are done on inertia dynos where they are calculating the torque based on how quickly a heavy roller is being accelerated. We are using a water brake dyno which is essentially hooking the engine to a water pump that Pumps water through a valve. The smaller the valve opening, the more load that is put on the engine to force water through it. The actual torque of the engine is then measured with a load cell that has been calibrated. So the high initial torque value is because the dyno is holding the engine at 2000 rpm’s, with a wide open throttle, until we hit the go button, and then it allows the engine to accelerate at 400 rpm’s per second until 7000 RPM, measuring the actual torque the entire time.

The measurements are then “corrected” based on temperature, humidity, and barometric pressure, among other things, which we have a probe that constantly monitors and updates . There are 2 prevalent corrections methodologies, SAE and STP (also called STD). Some will claim SAE is more accurate, but there is no basis for this. STP is used by NASCAR and many others. We use STP because these are our “marketing numbers”, and STP will typically show 4% higher than SAE. So we assume our engines on a chassis dyno will show 9% less and we subtract another 4% if it’s an SAE corrected chassis pull.

In addition automakers have to publish “net” SAE horsepower instead of gross (measured) thanks to a California law passed in the early 70’s. That’s why their numbers are always lower than expected.

So all of that to say the only way to get a true comparative, is to do before and after dyno pulls on your engine. Which is currently the plan as I’m just as curious as you are. What I’m estimating we will see is a 7% increase from the capacity upgrade, 2% from the fresh rings and valve job, and 2% from the plenum/TB upgrade.

spessx

Thanks for the response.

I’m curious - are there any benefits to staying at the stock displacement when we have you do our rebuilds? For instance, better driveability on an oem ecu tune or better engine longevity/reliability, gas mileage (sorry for asking), ability to pass emissions inspections?

SlakkerRacingDev

The short answer is yes.

We had a customer send us a set of M96.01 heads that were stage 1 ported by one of the prominent head specialists for use on their build. Based on reputation, we were excited to get them in and start analyzing and measuring them so that we could then hopefully see how well the flow numbers transferred to the dyno. But we didn’t end up using them. The springs were new however the cryo treatment dropped their dampening force to about half of what a new set of OEM springs measures. And the flowbench numbers were slightly better at high lift but worse at lower lifts than pur customer’s original heads we refreshed.




We have a set of 987.1/997.1 heads (cayman S and 997 3.6L use the same part # head, cam, and intake manifold) at another porting specialist that is well known on RL and are looking forward to getting those back to test for a build along with a custom set of cams. But based on the X51 tests, I’m not sure they will make a difference.

The 997 X51 heads flowed about 3% better than 997.1S heads and I was fairly certain I was seeing the difference on the dyno numbers. Right up until this engine produced nearly the same power when using the same intake/plenum/tb combo.

So essentially, the current stock head/cam combo seem well suited to meet the current “supply” requirements of the 4.1L engine based on a target power band of 3500-7000. But we will continue testing to see if this holds true.

Where I do believe porting will come into play, is when we do a higher rev build and move the power band up higher as well. But there is a lot of work to do for this project (stability testing valve train components, dual resonance flap plenum and custom gearing to name a few) and we will have moved the porting work internally by then.

SlakkerRacingDev

The displacement upgrades are awesome. Unless it is a PCA spec race cars where it isn’t an option, there is no downside. Increased power throughout the entire rev range, better fuel economy by allowing the use of higher gears without bogging down, easy for an ECU that already covers 2.7L-3.8L to be adapted to, reliable enough to win the British endurance championships last year, and increased resale value.

C2-996

Looking forward to hearing more updates of your builds as you progress, please share at your convenience!

Had a question regarding plenum options

You guys had very healthy gains with the 82mm eBay/Spyder plenum and 82mm throttle body, combined with the 3.8 intake- quite nice under the curve (on your intake testing thread)

Have you guys attempted bolting on an 82mm IPD competition plenum? Wonder if you would see if any further airflow benefits making use of the Y cast distribution vs the traditional T shape distribution?

zbomb

I find it very interesting that even with the high octane the ECU is pulling timing. It would seem kind of amazing to me the engine at the type of normal octane limited compression ratios and cylinder pressures I would assume this engine is running is actually getting into any knock activity worthy of timing degradation unless the timing upper target is something bordering on unreasonable. I guess I need to do some research on combustion analyzers to conceptualize the 1 Bar/1K RPM you reference.

I wonder if the knock sensing strategy is an area worth seeking improvement.