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This is Mike Lindsey's Info on the Cylinder Heads (2.5 & 2.7) & the Exhaust bore sizes.....
Which may explain why with my smaller 2.5 valved head on the 3.0 Block and the small 1.88" ID Exhaust bore that I've created is a very efficient and torquey motor.....
I think your combination of head and cylinder bore is better than what Porsche did with the 2.7L head. If you study the numbers on the 88US car and the 89 2.7L, the 2.7 only touts 4 more HP and no additional torque. Either the 2.7L is way under rated, or the combination doesn't really work. How can you go from a 100mm bore to 104mm, raise the compression and not gain any torque? Something is wrong there...
My port guy is not a fan of the 2.7L head, he doesn't like the big bowl at the base of the valve. The port velocity numbers aren't that good either considering the size of the valve. The 2.5L head can easily be made to out perform the 2.7L head, in both flow and port velocity. I think that is where you are finding a lot of that torque, especially down low in the RPM's. Now I do think the 2.7L head does have a fit, that is on a 3.0L turbo motor that can fill that big bowl and overcome poor velocity characteristic's.
Exhaust Gases
The whole velocity thing changes as the air cools down. The molecules in the hot exhaust are moving very fast and can travel through smaller diameter pipes at high speeds.
When they begin to cool and slow down is where the larger diameter pipes become necessary
I'm on the same train of thought - I have a small section of exhaust 2" OD (probably same ID as yours) and my car makes more torque than a regular NA with the same peak HP, stock-for-stock.
I'm on the same train of thought - I have a small section of exhaust 2" OD (probably same ID as yours) and my car makes more torque than a regular NA with the same peak HP, stock-for-stock.
Ok,
After the 2 into 1 Downpipe mines 1.8" ID all the way to the end, and just (1) oval straight through
Wool packed aluminium core perforated tube rear silencer box...
This is my 78 "Gramps" with nothing but a driver's seat (gutted interior & no a/c). But all steel & glass with the 2.0 engine, so I'd believe 1010 kg for the 2.7 924S.
Thanks, it's been one hell of a challenge and the longer the project went on, the more I took my time....
Many times it did seem even to my high standards to be a little pointless and over the top.........but,
The way it drives is, as you can imagine with so many NEW parts just amazing for a (30 yr old car next year), not to mention agile, quick, great on fuel ! and a machine which not only stops, handles and leaves many modern cars for Dust! but is not gaining in respect,,
The design is now 40 years old and I believe it's starting to be seen as more like a classic than it has for a few decades...
The "Poor's man Porsche" Tag and engine in the wrong place doubters will always be about! but I've had many high Performance Sports cars pull in behind me to take a closer look.....instead of blasting past and laughing.....
This is my 78 "Gramps" with nothing but a driver's seat (gutted interior & no a/c). But all steel & glass with the 2.0 engine, so I'd believe 1010 kg for the 2.7 924S.
Hi,
Have You changed weight of crankshaft, connecting rod or piston? I assume weight of balance shafts is related to those listed items - please correct me if wrong.
Have You noted some vibration due to modification?
Hi,
Have You changed weight of crankshaft, connecting rod or piston? I assume weight of balance shafts is related to those listed items - please correct me if wrong.
Have You noted some vibration due to modification?
The crank is 6.6lbs lighter than stock (Knife edged by Lindsey Racing)
The Rods are Forged 968
The Pistons forged Wossner
The crank / Flywheel was balanced
As were the rods & pistons......
The Engine is very smooth, no vibrations on NEw Porsche liquid filled Engine mounts..
The standard 924 is a very nimble car and it's turning radius is INCREDIBLE. The skinny tires on factory 6" wheels are very easy to break the rear loose, which is fun. This car is a blast in mud and gravel... and tarmac
I don't like the big steering wheel though. The steering is too slow a ratio, and plus the difference in the braking make the transition from the late 944 to the 924 kind of tough. The 944 is more confidence building while the 924 is sure to be an adventure.
The standard 924 is a very nimble car and it's turning radius is INCREDIBLE. The skinny tires on factory 6" wheels are very easy to break the rear loose, which is fun. This car is a blast in mud and gravel... and tarmac
I don't like the big steering wheel though. The steering is too slow a ratio, and plus the difference in the braking make the transition from the late 944 to the 924 kind of tough. The 944 is more confidence building while the 924 is sure to be an adventure.
I've never driven the 1st incarnation the 2.0 N/A 924, but can only imagine it must be similar to what my 92S 2.5 was without the better brakes and engine...
My original steering wheel was 365mm, but I've gone bigger to 380mm the rack is a quicker ratio the same as the 924 Turbo...The extra diameter helps hussle in and out of tight bends with better leverage as it's a NON Power system....
My car also has a relatively skinny set of wheels & tyres (All 4 are 7x16 and 205/55/16) and it doesn't wheelspin easily with 200+ bhp...It does have a Wavetrac LSD and a good right foot though!
I should rename it 924S2 really ! I'd say the 20 piston braking system, not to mention the performance is far superior to any of the production models inc the last model (968 CS)........
Attached the Actual Final & Best run Power & Torque Graph,
(For those that I've seen posting on other forums their Sceptical thoughts that it's from another engine etc....think what you want !....But it's the figures of the very lump that's under my bonnet and there's no disputing on the road it produces the goods)
My GOAL has been acheived which was to have a HIGHER BHP power to weight ratio than every Production Transaxle apart from the rare 968 Turbo S
BHP Per Metric 1000kg - ton
924 2.0 108
944 2.5 130
924S 2.5 133
944 2.7 135
944 2.5S 145
924 Turbo 147
944 3.0 S2 156
968 / CS 173
924 Carrera GT 175
944 2.5 Turbo S 183
924S RR27L 203
All These figures are based on the Manufacturers Power figures which are in most cases not correct!
In reality they are much less, also the Curb weights Porsche quote are more in reality...
My RR figures and the 4 Racing corner weight scales pad figures are recent and far more accurate.
08-12-2016, 06:00 AM
