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The build of the engine...
I'm thinking the following. This is a street car/TSD rally build. Reasonable fuel economy on 91 octane is my goal. 190-200 bhp on a budget. Is it possible?:
-SDS ECU
-7000 rpm limit
-ITBs
-long tube headers
-Wossenor 11.4cr x 100mm pistons. The top would be altered from a 4v to also fit a 2v bringing it down to 10.4 or something?
-Balance Shaft delete to improve oiling. B.S. and P.S. are both deleted to reduce drag.
-Windage tray (wet sump)
-Camshaft (nothing too crazy. Did you have a recommendation?) I was thinking the billet one at 944online or Cat Cams. I am running the late NA cam right now.
-130 lb valve springs
-Cyl head valve job and larger intake valve (you might suggest something else. In a 2.5 n/a is there any reason to up size the exhaust valve)?
-Possibly solid lifters to raise the rpm roof (I don't know if this is a good idea)
-Possibly lightened flywheel.
(Headwork:
Machine & install larger seats
Replace the valve guides
Do a 5 angle valve job).
Noah, I know from all your posts that you like to think outside the box. Good on you. Only as the voice of reason, I might suggest that this will not be a "budget build" by the time you are done, but I guess it is all in the eyes of the beholder. Contact Tom at @T&T Racing and he will give you the exact recipe you need for the best 8V motor. Or do what I did and buy a Cayman.
This guy on eBay sells Wossner 10.6:1 pistons with 100mm bore for the 8v motor. Might be worth a look.
You could also consider just shaving the head to the wear limits like they do for Spec 944 to achieve around 10.5:1 compression ratio.
JRP
Yes, In the past I have had some heads shaved and performed research as to the limits of head shaving. I've come to realize the design would benefit a lot more by shaving the engine deck, similar to using high comp pistons vs shaving head. The benefit of modifying the 16v piston is one could replace the 2v head with an S head or visa-versa. What I don't know is the negative effects of doing this to the combustion chamber. I will post photos of the pistons when they arrive.
Hi Noah,
It is not possible to build a 2.5L, 8V Porsche 944 NA engine to produce 200 hp on pump fuel. The 2478 cc displacement with the standard crankshaft and a Michael Mount prepped cylinder head with oversize intake valves, 1mm larger; competition valve prep; optimized porting does not have sufficient displacement for a fuel/air charge to make 200 hp.
Michael Mount built a Porsche 944 8V engine iron sleeved bored with 101.6 mm (4 in) diameter cylinders, JE 10.8:1 pistons, cylinder head with stock valve size and ported with competition valve preparation, 951 injectors, stock camshaft, stock intake and TB, stock exhaust manifold, modified 951 rods BUT used a 3.0 L crankshaft, race prepped. The 951 rods are modified because with 3.0L crank throw, the standard 951 rod end hits the block. ECU was stock with a tuned chip ( I believe the tuner in MD). The engine made 200 hp at 6000 rpm. There was essentially a flat torque curve from 3600 to 5100 rpm, variation of 12 foot- lbs. He did not post the A/F ratios. I am assuming he removed the stock AFM from the equation
I will post my engine build results as alluded by Harvey later
Last edited by T&T Racing; 08-05-2023 at 06:21 PM.
The build of the engine...
In a 2.5 n/a is there any reason to up size the exhaust valve)?
I'm no expert but, I think it would depend on the cam you choose. According to Larry (inventor of Pipemax) its best to have exhaust valves sized so that the Mach Z-factor is under .7
After that he said the pumping losses will start to overtake the hp gains from scavaging. I could post a pipemax printout for you if you get me the right inputs.
Wow! Some powerful stuff here. Many thanks Harvey, T&T, Spencer & Timbo, JRP944.
Who has used solid lifters? Must be good for 1500 more revs? Where is the best place to perform the conversion, LR? Racer's Edge?
Seems like a pain in the *** to get done. Worth it? I don't know. Likely it is worth in on this n/a. Convince me other wise & I will not do it. Can it be more reliable than hydraulic lifters? I think they should be, no?
V2, I want ITBs because the n/a 8v intake manifold looks boring to me & ITBs are exciting to think about. My faves are the Milledge square body carbon intakes. JRP944's concept look amazing also. I want the "kick" of the ITBs & because they are sexy. I've never driven with them.
Who has used solid lifters? Must be good for 1500 more revs?
I had a conversation with Jon Mitchell of JMG Porsche about this a while back, he said that the stock oil pump and pickup system will cavitate badly around 7500rpm, and if you want to rev any higher he strongly suggests a dry sump system. Obviously we're getting into race car territory at this point.
Hi Noah,
Michael Mount built a Porsche 944 8V engine iron sleeved bored with 101.6 mm (4 in) diameter cylinders, JE 10.8:1 pistons, cylinder head with stock valve size and ported with competition valve preparation, 951 injectors, stock camshaft, stock intake and TB, stock exhaust manifold, modified 951 rods BUT used a 3.0 L crankshaft, race prepped. The 951 rods are modified because with 3.0L crank throw, the standard 951 rod end hits the block. ECU was stock with a tuned chip ( I believe the tuner in MD). The engine made 200 hp at 6000 rpm. There was essentially a flat torque curve from 3600 to 5100 rpm, variation of 12 foot- lbs. He did not post the A/F ratios. I am assuming he removed the stock AFM from the equation
I have no doubt that MM knows exactly what hes doing here, but doesn't it seem like he left significant performance on the table with a stock cam and intake system? Was this build on a specific budget or had a requirement to look stock externally?
Just leaving this here... There is no doubt the 16v is better for track racing but isn't there a sweet simplicity & to the single cam engine? I love this engine. And in the 2.5 size, some say the 16v was a disappointment when the 944 S hit the track.
Oh, does anyone know why JM would pick these square looking throttle bodies over the more common shape? Is it to hide details of the build?
08-04-2023, 11:01 PM
My 200bhp 8v build
