S4 intake manifold facts and ideas
10-05-2015, 09:22 AM
#241
Nordschleife Master
Thread Starter
Calvin Elston said it well. I'll paraphrase. There's a tradeoff between pulse tuning and pumping losses. Strong pulses mean high pumping losses. But if you are not going to use pulse tuning because your cams have no overlap, you might as well make the pumping losses as small as possible with big pipes. I think this explains everything.
Now that Hans is CNCing flanges and everything, maybe the next step is for him to CNC a flange with a tongue that inserts into the intake port bottom and reduces the cross-section.
Or alternatively, can we get that S3 engine that has those GB headers to play with? That combo is not as grotesquely oversized either ont he intake or the exhaust side as most other late-model 928s. I say we put in real overlap cams to that thing and see what it can do with the S3 intake manifold and headers.
Now that Hans is CNCing flanges and everything, maybe the next step is for him to CNC a flange with a tongue that inserts into the intake port bottom and reduces the cross-section.
Or alternatively, can we get that S3 engine that has those GB headers to play with? That combo is not as grotesquely oversized either ont he intake or the exhaust side as most other late-model 928s. I say we put in real overlap cams to that thing and see what it can do with the S3 intake manifold and headers.
Are the 928 32V intake ports too large? The answer is yes and no. For an all stock engine running small cams with hardly no overlap it works good. If we like to build a high performance 5 liter NA engine the intake ports are too large unless you want to build a very high revving engine which I have not seen yet. The port CSA at the flange (injector cutout not included) is 1700 mm2 or 2.635 sqin. 40mm intake valves (3mm oversize) will match the port size. Porting shall be concentrated to the divided ports and the valve seat area including optimizing of the valve head shape. Everything optimized for maximum power output (cams, porting, ITBs headers etc), we will end up with an engine having max power at about 9000 to 9500 rpm which is extremely high up. If we put the same stuff onto a 7 liter stroker we will end up with an engine having much more torque (probably about 40% more) at lower rpm and peak power will be at about 7000 rpm, a much more driveable engine.
The 9000 rpm engine is not unrealistic at all. A couple of years ago I built a V2 Moto Guzzi road racing engine for a customer. The stroke 78mm is same as for the 928 engine. The bore 95mm is same as for the 4,5 liter 2V engine. The Moto Guzzi is a 2-valve pushrod engine with limitation of how much valve lift can be used. The valves are 50/40mm, lift 11mm, carburetors 41,5mm, stepped headers 1.75" to 1.875" to 2.0". The engine did put out 100 hp at the wheel at 8500 rpm, red line at 9250 rpm, max torque at 6500 rpm. According to the owner the engine is pulling good from 3000 rpm.
The picture is showing an intake port having unchanged CSA at the flange but ported for 39mm valves (398 CFM @ 14mm). I did not bother polish the port which was made for flow testing only. Polish is a lot of additional work and it does not bring anything in respect of flow but looks nicer.
Åke
The 9000 rpm engine is not unrealistic at all. A couple of years ago I built a V2 Moto Guzzi road racing engine for a customer. The stroke 78mm is same as for the 928 engine. The bore 95mm is same as for the 4,5 liter 2V engine. The Moto Guzzi is a 2-valve pushrod engine with limitation of how much valve lift can be used. The valves are 50/40mm, lift 11mm, carburetors 41,5mm, stepped headers 1.75" to 1.875" to 2.0". The engine did put out 100 hp at the wheel at 8500 rpm, red line at 9250 rpm, max torque at 6500 rpm. According to the owner the engine is pulling good from 3000 rpm.
The picture is showing an intake port having unchanged CSA at the flange but ported for 39mm valves (398 CFM @ 14mm). I did not bother polish the port which was made for flow testing only. Polish is a lot of additional work and it does not bring anything in respect of flow but looks nicer.
Åke
