Desktop Dyno and 951 Head Porting
01-04-2002, 02:13 AM
#1
Desktop Dyno and 951 Head Porting
A friend of mine has an interesting engine simulation program called Desktop Dyno that lets you make modifications to the engine and see what the results are. It had the 944 engine listed and we had to enter the compression ratio and some other info. Since there was no KKK turbo's listed we tried the Schwitzer ones until we found one that gave similar power/torque levels at the right RPM to match a stock 951 S. We used the following info:
Bore: 100 mm
Stroke: 78.9 mm
Compression: 8.0:1
Intake Valve Lift: 0.480
Exhaust Valve Lift: I forget (0.42?)
Does anyone know the stock valve lift and timing?
Since we did not have the size of the valves we used the 180 cfm rating from Lindsey Racings site for the stock head and worked backwards. Anyone have the stock valve sizes on the 951 S?
We also had to guess about the stock intercooler efficiency. We again used info on Lindsey's site and came up with 45%-50% intercooler efficiency. If anyone knows the correct value let me know.
So what did we find out? First we stroked the engine to 2.8 litres and saw only small gains (something like 7 lbs torque and 15 hp) compared to the stock 2.5 engine. The program also has an analyzer that deterimines what displacement would give the best results with the other engine data. It actually chose a 2.8 litre engine as being the best. So I guess I can understand the stroking of these engines if you require the absolute most out of them but I now wonder if it is worth the extra cost.
The most amazing thing was what happened when we got the head to flow more (porting and polishing) Taking it up to 230 cfm we saw some really nice gains - far more than stroking gave us. Very interesting...
We played with different turbo's and it seemed that the stock engine really didn't respond well to larger turbos. It really seemed to prefer small turbos. However, this was using Schwiter info...perhaps KKK turbos are different. Does anyone know where I can find flow rates and compressor maps for KKK Turbos? (26/8 and 27/8 in particular).
Obviously the results are only as good as the data that was put in but I think it can be used as a decent tool when trying to determine what modifications to make.
Bore: 100 mm
Stroke: 78.9 mm
Compression: 8.0:1
Intake Valve Lift: 0.480
Exhaust Valve Lift: I forget (0.42?)
Does anyone know the stock valve lift and timing?
Since we did not have the size of the valves we used the 180 cfm rating from Lindsey Racings site for the stock head and worked backwards. Anyone have the stock valve sizes on the 951 S?
We also had to guess about the stock intercooler efficiency. We again used info on Lindsey's site and came up with 45%-50% intercooler efficiency. If anyone knows the correct value let me know.
So what did we find out? First we stroked the engine to 2.8 litres and saw only small gains (something like 7 lbs torque and 15 hp) compared to the stock 2.5 engine. The program also has an analyzer that deterimines what displacement would give the best results with the other engine data. It actually chose a 2.8 litre engine as being the best. So I guess I can understand the stroking of these engines if you require the absolute most out of them but I now wonder if it is worth the extra cost.
The most amazing thing was what happened when we got the head to flow more (porting and polishing) Taking it up to 230 cfm we saw some really nice gains - far more than stroking gave us. Very interesting...
We played with different turbo's and it seemed that the stock engine really didn't respond well to larger turbos. It really seemed to prefer small turbos. However, this was using Schwiter info...perhaps KKK turbos are different. Does anyone know where I can find flow rates and compressor maps for KKK Turbos? (26/8 and 27/8 in particular).
Obviously the results are only as good as the data that was put in but I think it can be used as a decent tool when trying to determine what modifications to make.
01-04-2002, 09:43 AM
#2
Race Director
I've got cam-timing diagrams for most of the Porsche standard and optional cams on my website at: 951 RacerX website
Here's a compressor map of a K26/6:
Make sure you accurately model the stock cars and get the same power numbers before you start with mods. I've seen a lot of people try to predict top-speeds from HP-ratings when their model doesn't even correctly represent the known stock numbers...
Here's a compressor map of a K26/6:
Make sure you accurately model the stock cars and get the same power numbers before you start with mods. I've seen a lot of people try to predict top-speeds from HP-ratings when their model doesn't even correctly represent the known stock numbers...
01-05-2002, 05:03 PM
#3
Thanks Danno. Anyone know the size of the stock S valves?
On another topic...does anyone know if our exhaust manifold and turbo's are of the divided or undivided kind? I have an RX7 Turbo that is being modified as well and I am using a divided manifold that gives quicker spooling of the turbo. If the manifold on the 944 is undivided I wonder if anyone has considered changing it. Also, I am looking at going with dual 35mm wastegates on the RX7 - they are about the same price as a single 46 mm. I know race teams use this arrangement for better performance. Anyone do anything similar for the 944?
On another topic...does anyone know if our exhaust manifold and turbo's are of the divided or undivided kind? I have an RX7 Turbo that is being modified as well and I am using a divided manifold that gives quicker spooling of the turbo. If the manifold on the 944 is undivided I wonder if anyone has considered changing it. Also, I am looking at going with dual 35mm wastegates on the RX7 - they are about the same price as a single 46 mm. I know race teams use this arrangement for better performance. Anyone do anything similar for the 944?
