I'm looking for 944 N/A power upgrades
04-24-2004, 12:30 AM
#46
When I rebuilt my engine, I used .040 over pistons. Is it likely that I really have a measurable increase with these over standard bore diameter with all else stock? (never dyno'd to find out).
04-24-2004, 12:42 AM
#47
Race Director
Originally posted by Mike C.
When I rebuilt my engine, I used .040 over pistons. Is it likely that I really have a measurable increase with these over standard bore diameter with all else stock? (never dyno'd to find out).
When I rebuilt my engine, I used .040 over pistons. Is it likely that I really have a measurable increase with these over standard bore diameter with all else stock? (never dyno'd to find out).
How long ago did you source these 40 over pistons and where? I need a set (that I hopefully won't have to mortgage the farm for).
04-24-2004, 01:05 AM
#48
Race Car
Originally posted by URIN 2ND
The higher numbers were based on Anderson's work and conversations I've had with Milledge.
The higher numbers were based on Anderson's work and conversations I've had with Milledge.
If you like Anderson's work, I can give you a smokin' deal on an AMW shortblock (it has only ~3 minutes of run time)!
04-24-2004, 03:37 AM
#49
TRB0 GUY
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WOW.... I can cut the tension in here with a knife. Let's all be nice, guys.. no need to catfight. I'm just kidding, don't flame me for that, it was a joke
"and if you got a racing cam with that much compression would the valves get knocked up?
knocked up...heh"
The impression I got from Ashton's statement was that it was in referece to a previously posted statement on putting new cams in ALONG WITH upping the compression. In other words, he's asking "wouldn't the valves get bent with higher compression an a long-duration cam?"
Camp... is that what you were saying??
"and if you got a racing cam with that much compression would the valves get knocked up?
knocked up...heh"
The impression I got from Ashton's statement was that it was in referece to a previously posted statement on putting new cams in ALONG WITH upping the compression. In other words, he's asking "wouldn't the valves get bent with higher compression an a long-duration cam?"
Camp... is that what you were saying??
04-24-2004, 05:11 AM
#51
Race Director
" The impression I got from Ashton's statement was that it was in referece to a previously posted statement on putting new cams in ALONG WITH upping the compression. In other words, he's asking "wouldn't the valves get bent with higher compression an a long-duration cam?"
Ok, most of the bases have been covered by others and Geo (he knows what he's talking about), so I'll just touch on the compression and cam interactions. If you're gonna be building a racecar, then just about all the mods that's been dicussed on getting more power from a 944NA goes out the window. What we want in a racecar is RPM! The higher-the RPM and the higher the power-peak, the lower the gear we can use and take advantage of the torque-multiplication through the gear box. So plan on a powerband in the 5000-7000rpm range. A 6-speed gearbox would allow you to keep the revs working in this short span.
The high revs also allows you to take advantage of ported & poslished. Well it requires it. You want to install slightly larger, flatter and lighter valves. Modern materials allow you to shrink the valve-stem from 9mm to 7mm for minimal port obstruction. Then D-port the head to the maximum size for best flow (extend porting into the intake-manifold).
Assuming that high-octane race-gas will be used, you can take advantage of the gasoline by increasing your compression to maximum. Somewhere around 13:1 should do. Then to really make the most of your compression and head work, you'll need a cam ground specifically for this application. You'll need a cam with more overlap AND a later intake-closing (like 20-degrees later). Something like with 270-degrees duration and lobe-centers of 110-115 degress for later intake closing.. Valve-lift doesn't make as much of a difference, so you want to keep max-lift close to stock. The general rule is no more than 25% of the valve-diameter is the maximum life you'd want to use.
Ok, most of the bases have been covered by others and Geo (he knows what he's talking about), so I'll just touch on the compression and cam interactions. If you're gonna be building a racecar, then just about all the mods that's been dicussed on getting more power from a 944NA goes out the window. What we want in a racecar is RPM! The higher-the RPM and the higher the power-peak, the lower the gear we can use and take advantage of the torque-multiplication through the gear box. So plan on a powerband in the 5000-7000rpm range. A 6-speed gearbox would allow you to keep the revs working in this short span.
The high revs also allows you to take advantage of ported & poslished. Well it requires it. You want to install slightly larger, flatter and lighter valves. Modern materials allow you to shrink the valve-stem from 9mm to 7mm for minimal port obstruction. Then D-port the head to the maximum size for best flow (extend porting into the intake-manifold).
Assuming that high-octane race-gas will be used, you can take advantage of the gasoline by increasing your compression to maximum. Somewhere around 13:1 should do. Then to really make the most of your compression and head work, you'll need a cam ground specifically for this application. You'll need a cam with more overlap AND a later intake-closing (like 20-degrees later). Something like with 270-degrees duration and lobe-centers of 110-115 degress for later intake closing.. Valve-lift doesn't make as much of a difference, so you want to keep max-lift close to stock. The general rule is no more than 25% of the valve-diameter is the maximum life you'd want to use.
04-24-2004, 11:17 AM
#52
Actually Matt, you're incorrect here. The factory used to produce 0.5mm and 1.0mm overbore pistons. That translates to 0.020" and 0.040" overbore. A 0.010" overbore would be virtually nothing.
George - that was kind of my point :>) What I was getting at, however poorly I did it, was that .010 is not much of an overbore if any and IF you were going to do it you would want to either use a Porsche stock piston, of which there is more than one tolerance group, as you know OR you would want to go full monty, sleeve the block and use JE pistons (or whoever your favorite is).
For the money, I dont think either is worthwhile. The reason is that the 3.0L will accomplish everything that a person generally wants, is pretty easy to come by and is going to cost less in the end (factoring in selling a good 2.5). It is also, relatively speaking, plug and play and plenty of others have done it already.
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George - that was kind of my point :>) What I was getting at, however poorly I did it, was that .010 is not much of an overbore if any and IF you were going to do it you would want to either use a Porsche stock piston, of which there is more than one tolerance group, as you know OR you would want to go full monty, sleeve the block and use JE pistons (or whoever your favorite is).
For the money, I dont think either is worthwhile. The reason is that the 3.0L will accomplish everything that a person generally wants, is pretty easy to come by and is going to cost less in the end (factoring in selling a good 2.5). It is also, relatively speaking, plug and play and plenty of others have done it already.
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04-24-2004, 11:26 AM
#53
Race Director
Originally posted by Matt H
George - that was kind of my point :>) What I was getting at, however poorly I did it, was that .010 is not much of an overbore if any and IF you were going to do it you would want to either use a Porsche stock piston, of which there is more than one tolerance group, as you know OR you would want to go full monty, sleeve the block and use JE pistons (or whoever your favorite is).
George - that was kind of my point :>) What I was getting at, however poorly I did it, was that .010 is not much of an overbore if any and IF you were going to do it you would want to either use a Porsche stock piston, of which there is more than one tolerance group, as you know OR you would want to go full monty, sleeve the block and use JE pistons (or whoever your favorite is).
I grok fullness.
Originally posted by Matt H
For the money, I dont think either is worthwhile. The reason is that the 3.0L will accomplish everything that a person generally wants, is pretty easy to come by and is going to cost less in the end (factoring in selling a good 2.5). It is also, relatively speaking, plug and play and plenty of others have done it already.
For the money, I dont think either is worthwhile. The reason is that the 3.0L will accomplish everything that a person generally wants, is pretty easy to come by and is going to cost less in the end (factoring in selling a good 2.5). It is also, relatively speaking, plug and play and plenty of others have done it already.
04-24-2004, 07:48 PM
#54
Campeck Rulez
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yes.
This is what I meant.
With the higher compression pistons, lets say 13:1 and with a racing cam with the valves staying open longer then wouldnt it be possible that the piston touch the ehaust valve on the exhaust stroke? or hit the intake valve at the top of the intake stroke?
This is what I meant.
With the higher compression pistons, lets say 13:1 and with a racing cam with the valves staying open longer then wouldnt it be possible that the piston touch the ehaust valve on the exhaust stroke? or hit the intake valve at the top of the intake stroke?