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Yes, the stroke is shorter. GTS stroke. 5873cc. Less stroke, more revs. I don't recall Mike's pistons, can't find any pics anywhere, at least not the undersides. I did find a reference to them being J&Es, which are what I have in the GTS's stroker. The new Zombie motor pistons are CPs.
Simard's 7 liter ITB motor and Andy G's 6.5 ITB stroker both make more hp than the Zombie motor, N/A, for whatever trivia points that's worth.
Mark, what cams are you running over your stroker block? Anderson's got two sets of race cams that might give you more AUC than what you're using now, depending on what you're using now.
Think this is the kind of pistons Tuomo is talking about. The advantages are lower weight and improved support of the wrist pin. The pin bosses are sitting closer to the con rod small end compared to what usually can be found on american made full skirt pistons. The last picture is from Mike Simard´s engine where the small gaps between con rod and pistons can be viewed. The short wrist pin contributes to lower weight.
Åke
Last edited by Strosek Ultra; 10-09-2015 at 04:44 AM.
Ah yes, that type- Anderson has a used F1 piston as a paperweight, similar design. Very cool. Any idea what that style costs? The CPs going in this motor are roughly $2K, with rings. A relative bargain compared to the current prices for 968 pistons....
If it's a custom piston anyway, the style is less important for pricing than the series. When the x-forging or box-in-box pistons first came out, they were a little bit more expensive for early adopters...
It's a complex question what style is most reliable for each engine. Turbo pistons tend to be made for low rpms, require long compression height (crown thickness and ring land width) and thus short rod, have high thrust face loadings, etc. Those often have a full skirt. The normally aspirated pistons nowadays have the ring close to the top, short compression height, long rod, need to be very light, etc. those often seem to be the style that Ake posted.
Both styles will probably work very well in a 928 as the engine won't ever be revved to the moon.
Originally Posted by Rob Edwards
Ah yes, that type- Anderson has a used F1 piston as a paperweight, similar design. Very cool. Any idea what that style costs? The CPs going in this motor are roughly $2K, with rings. A relative bargain compared to the current prices for 968 pistons....
If it's a custom piston anyway, the style is less important for pricing than the series. When the x-forging or box-in-box pistons first came out, they were a little bit more expensive for early adopters...
It's a complex question what style is most reliable for each engine. Turbo pistons tend to be made for low rpms, require long compression height (crown thickness and ring land width) and thus short rod, have high thrust face loadings, etc. Those often have a full skirt. The normally aspirated pistons nowadays have the ring close to the top, short compression height, long rod, need to be very light, etc. those often seem to be the style that Ake posted.
Both styles will probably work very well in a 928 as the engine won't ever be revved to the moon.
good points.. the 928 engines we are building and using will never really have to see more than 7000rpm so the pistons dont have to be like those bmw and porsche motor build that twist the motor up to 9000rpm.
we are 7000rpm and less actually, based on the HP curve of the zombie motor, anything in the 6800 to 7000rpm was optimal, even though he could go a little higher.
Yes, the stroke is shorter. GTS stroke. 5873cc. Less stroke, more revs. I don't recall Mike's pistons, can't find any pics anywhere, at least not the undersides. I did find a reference to them being J&Es, which are what I have in the GTS's stroker. The new Zombie motor pistons are CPs.
Simard's 7 liter ITB motor and Andy G's 6.5 ITB stroker both make more hp than the Zombie motor, N/A, for whatever trivia points that's worth.
Mark, what cams are you running over your stroker block? Anderson's got two sets of race cams that might give you more AUC than what you're using now, depending on what you're using now.
yep, thats why it looked like the pin position was going for shorter stroke especiallly with the longer rod.
im running 85 86 cams on my engine now. basically GT cams. nothing special.. i think 1mm lift less than the zombie original cams.. why are you not using them? differences? what do the cams you are going to use look like as far as goal of performance? what are the ones you saw at Marks that might work?
thanks!!!!!
This motor's kind of all about what one needs to do (on the intake side, mostly, but to some extent fuel control) to keep making hp up to 7K. Cams are slightly more aggressve than the Zombie cams, and feeding only 5.8L. Looking forward to spinning this engine on Roger's dyno
EDIT- Can't use the Zombie cams, as they broke a few teeth off each intake cam sprockets in the last blowup. Webcam says they can be welded, but I've got a good alternative set with better specs, and intact teeth.
This motor's kind of all about what one needs to do (on the intake side, mostly, but to some extent fuel control) to keep making hp up to 7K. Cams are slightly more aggressve than the Zombie cams, and feeding only 5.8L. Looking forward to spinning this engine on Roger's dyno
EDIT- Can't use the Zombie cams, as they broke a few teeth off each intake cam sprockets in the last blowup. Webcam says they can be welded, but I've got a good alternative set with better specs, and intact teeth.
When you say more aggressive, what do you mean? Do you mean longer duration, higher peak acceleration, higher velocity (i.e., riding closer to the lifter edge)? I'd be curious about the specs of those cams that you're planning to use for the 5.8L/7k rpm engine. If you post them here, you'll get some opinions to filter! ;-)
Also, how do you compute the area under the curve? I think that you should probably give about zero weight to the segment of the area under the curve above the peak piston velocity, additional lift above what it is at that point probably won't do anything for you. Also, some would argue that the are under the curve right at the opening and closing points is actually counterproductive. I'm not so sure about that, and regardless there probably are some ways to kill the low lift flow with a valve job...
Area under lift curveA popular method for measuring the quality of a cam profile is the area under the lift curve. I have frequently heard the statement, "All that matters is the area under the lift curve." This simply is not true. The graph at the right shows a lift curve, with three different areas indicated. The area indicated by A is the heart of the lift event and the area here is very important, therefore it should be counted as 100%.
First, note that the graph give net cam lift. This removes the effects of valve lash.
Suppose this cam is used with a rocker ratio, so the net valve lift wll be greater than 0.450. As the valve is first opened, the flow increases rapidly, but as the valve opening become large, say 0.300 to 0.400, the flow begins to diminish. Usually, you will get very little additional flow by increasing the valve lift above 0.500. For this reason, the area indicated by B should not count as much as that in area A. We might give area B a weight of only 50%. It is not detrimental, but it does not improve the profile to the same extent as the area at lower lifts.
The Cam Performance page discusses the importance of a quick opening and closing cam. A slow opening and closing cam, i.e. one with a large area C, will be a poor performer. It will have poor idle quality and poor off idle performance. For this reason, the area C should count against the quality of the profile, i.e. it should have a negative weighting.
In summary, area under the lift curve is not the best way to measure the quality of a cam profile. It should be used with caution. It would be better to use a weighting factor for the various portions of the curve, i.e. a weight of 1 for area A, a weight less than 1 for area B and a large negative weight for area C.
Another .1 mm of lift, and a couple more degrees of duration- I will graph the profile of the Zombie cam lobe vs. the Zombie 2.0 cams so I can understand where the differences are in terms of AUC. Overall the AUC difference is only about 2% (though I don't know where) but it's feeding 10% less displacement and the piston speeds will be 10% less. The calculation is provided (in mm^2) by the lift/duration report function in Cam Analyzer.
It'll take me some time to graph these things- I measured every 2 degrees of cam rotation so it takes some manual interpolation in Excel to convert everything to crank degrees. The basic version of Cam Analyzer won't let you overlay multiple lobe profiles for comparison. And for some annoying reason Excel limits you to 255 rows of data when graphing, so I had to upgrade my license of Sigmaplot to the tune of $600. These hobbies are getting expensive....
For whatever it's worth, I agree that AUC isn't necessarily a valuable metric- GTS cams have an AUCs of 339 and 291 mm2, vs. 310 and 273 for S4 cams. That's an 8% increase, but no one's lining up to put GTS cams in their S4...
I need to measure my spare S3 cams, for comparative S&Gs. Hopefully will make it to the garage tonight but I need to re-assemble the GTS for SF15.
Another .1 mm of lift, and a couple more degrees of duration- I will graph the profile of the Zombie cam lobe vs. the Zombie 2.0 cams so I can understand where the differences are in terms of AUC. Overall the AUC difference is only about 2% (though I don't know where) but it's feeding 10% less displacement and the piston speeds will be 10% less. The calculation is provided (in mm^2) by the lift/duration report function in Cam Analyzer.
It'll take me some time to graph these things- I measured every 2 degrees of cam rotation so it takes some manual interpolation in Excel to convert everything to crank degrees. The basic version of Cam Analyzer won't let you overlay multiple lobe profiles for comparison. And for some annoying reason Excel limits you to 255 rows of data when graphing, so I had to upgrade my license of Sigmaplot to the tune of $600. These hobbies are getting expensive....
Originally Posted by Rob Edwards
For whatever it's worth, I agree that AUC isn't necessarily a valuable metric- GTS cams have an AUCs of 339 and 291 mm2, vs. 310 and 273 for S4 cams. That's an 8% increase, but no one's lining up to put GTS cams in their S4...
I need to measure my spare S3 cams, for comparative S&Gs. Hopefully will make it to the garage tonight but I need to re-assemble the GTS for SF15.
The AUC may not be the ideal measure, but it's better than what most people talk about!
I think .xls is the way to go. I don't think that my MS Excel has a 255 row limit for graphing?
In my opinion, it's the CFM @ 28" per lift and lift per crankshaft degree that together give the most relevant curve, CFM @ 28" per crankshaft degree. That curve should match the piston flow demand between EVC and maximum piston speed point.
Before EVC, the engine lives off the pipe. After the maximum piston speed point, it surfs the wave. But there's that 9-5 civilian working stiff period there in the middle where the piston just draws in air...
This is a definition of "aggressive cam". Very aggressive cam profiles are only suited for drag racing. Good for the performance but hard on the valve train and the high lift velocity may require oversize lifters or the lobe will ride on the edge of the lifter. I would never use very aggressive cam profiles for a hot street or road racing engine. http://www.tildentechnologies.com/Ca...Aggresive.html
Åke
10-08-2015, 08:42 PM
