928 GTS Cam upgrade
04-25-2011, 03:54 PM
#61
Nordschleife Master
MK,
Please do some research on LSA (lobe separation angle), and the effects that it has.
For your benifit, here is some information.
So now then, reading those two pieces of information you can see that a wider LSA gives slightly less torque, but shifts the peak torque curve further up the RPM curve. It also give a wider power band, better idle etc.
With a narrower LSA, you will have slightly higher peak torque, but it will be at a lower RPM. Due to a narrower LSA creating more overlap. If you have a good flowing exhaust with proper scavenging it means that you get almost a precharged vacuum in the cylinders leading to a greater peak HP.
So lets review, wider LSA torque higher in the curve, wider power band, but less peak power due to less scavenging. Narrower LSA more torque but at a lower RPM, narrower power band but a higher peak HP number.
For race cars, they run a narrow LSA for peak power used in a specific RPM band. For a street car, you run a wider LSA (LS7 is 120LSA), for a wider and smoother power band with better idle and drivability.
Please do some research on LSA (lobe separation angle), and the effects that it has.
For your benifit, here is some information.
EFFECTS OF CHANGING LOBE SEPERATION ANGLE (LSA)
Tighten (smaller LSA number).........Widen (larger LSA number)
Moves Torque to Lower RPM............Raise Torque to Higher RPM
Increases Maximum Torque .............Reduces Maximum Torque
Narrow Power band.........................Broadens Power Band
Builds Higher Cylinder Pressure.........Reduce Maximum Cylinder Pressure
Increase Chance of Engine Knock......Decrease Chance of Engine Knock
Increase Cranking Compression........Decrease Cranking Compression
Increase Effective Compression.........Decrease Effective Compression
Idle Vacuum is Reduced....................Idle Vacuum is Increased
Idle Quality Suffers...........................Idle Quality Improves
Open Valve-Overlap Increases...........Open Valve-Overlap Decreases
Closed Valve-Overlap Increases.........Closed Valve-Overlap Decreases
Natural EGR Effect Increases..............Natural EGR Effect is Reduced
Decreases Piston-to-Valve Clearance..Increases Piston-to-Valve Clearance
Tighten (smaller LSA number).........Widen (larger LSA number)
Moves Torque to Lower RPM............Raise Torque to Higher RPM
Increases Maximum Torque .............Reduces Maximum Torque
Narrow Power band.........................Broadens Power Band
Builds Higher Cylinder Pressure.........Reduce Maximum Cylinder Pressure
Increase Chance of Engine Knock......Decrease Chance of Engine Knock
Increase Cranking Compression........Decrease Cranking Compression
Increase Effective Compression.........Decrease Effective Compression
Idle Vacuum is Reduced....................Idle Vacuum is Increased
Idle Quality Suffers...........................Idle Quality Improves
Open Valve-Overlap Increases...........Open Valve-Overlap Decreases
Closed Valve-Overlap Increases.........Closed Valve-Overlap Decreases
Natural EGR Effect Increases..............Natural EGR Effect is Reduced
Decreases Piston-to-Valve Clearance..Increases Piston-to-Valve Clearance
Overlap what does it do?
At high engine speeds, overlap allows the rush of exhaust gasses out the exhaust valve to help pull the fresh air/fuel mixture into the cylinder through the intake valve. Increased engine speed enhances the effect. Increasing overlap increases top-end power and reduces low-speed power and idle quality.
At high engine speeds, overlap allows the rush of exhaust gasses out the exhaust valve to help pull the fresh air/fuel mixture into the cylinder through the intake valve. Increased engine speed enhances the effect. Increasing overlap increases top-end power and reduces low-speed power and idle quality.
With a narrower LSA, you will have slightly higher peak torque, but it will be at a lower RPM. Due to a narrower LSA creating more overlap. If you have a good flowing exhaust with proper scavenging it means that you get almost a precharged vacuum in the cylinders leading to a greater peak HP.
So lets review, wider LSA torque higher in the curve, wider power band, but less peak power due to less scavenging. Narrower LSA more torque but at a lower RPM, narrower power band but a higher peak HP number.
For race cars, they run a narrow LSA for peak power used in a specific RPM band. For a street car, you run a wider LSA (LS7 is 120LSA), for a wider and smoother power band with better idle and drivability.
04-25-2011, 04:01 PM
#62
Inventor
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My '85 5-speed consistently makes 298-305 rwhp and tq (sae) on a Dynojet 248x (so it must be right 
).
Stock airbox/paper filter, 32V cat downpipes converted to Y-pipe, stock '84 16V single rear exhaust w/modded rear muffler. No airpump/engine fan, stock cam timing.
).Stock airbox/paper filter, 32V cat downpipes converted to Y-pipe, stock '84 16V single rear exhaust w/modded rear muffler. No airpump/engine fan, stock cam timing.
04-25-2011, 04:04 PM
#63
Nordschleife Master
My '85 5-speed consistently makes 298-305 rwhp and tq (sae) on a Dynojet 248x (so it must be right ).
Stock airbox/paper filter, 32V cat downpipes converted to Y-pipe, stock 16V single rear exhaust w/modded rear muffler. No airpump, stock cam timing.
).Stock airbox/paper filter, 32V cat downpipes converted to Y-pipe, stock 16V single rear exhaust w/modded rear muffler. No airpump, stock cam timing.
04-25-2011, 04:18 PM
#64
Rennlist
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I wanted high rpm torque. I hated the way stock S4 and GT torque curves fall off the table after 4000 rpm. If you look at the torque curve on my engine, Jim & Bill made my wishes come true. 
I also specifically chose to base the cams on S3 cores in order to have a wide LSA and late intake valve closing.
Anyway that's all old news. Screamer Motor v2.0 has been built & installed (thank you Jim & Bill AGAIN) and it incorporates all the old stuff plus:
All of this needs to be re-tuned. It'll take some time before we'll have any results as Jim has a bunch of fun projects in his hobby queue and I'm suffering under a ridiculous workload (I'm writing this from the office at 10pm on a Sunday).
Keep the debate & info flowing. I find these threads a whole lot more interesting than the "look at this POS 928 on ebay" or "will these 11x19 ET63 wheels fit on the front of my 928" threads.
I also specifically chose to base the cams on S3 cores in order to have a wide LSA and late intake valve closing. Anyway that's all old news. Screamer Motor v2.0 has been built & installed (thank you Jim & Bill AGAIN) and it incorporates all the old stuff plus:
- Morton Engineering Stage 2.5 intake manifold porting
- 928 R US intake manifold spacer
- Morton Engineering Stage 3 valve seat modification
- Porsche 968 intake valves (39 mm)
- Kao Racing Stage 2.5 cylinder head porting
All of this needs to be re-tuned. It'll take some time before we'll have any results as Jim has a bunch of fun projects in his hobby queue and I'm suffering under a ridiculous workload (I'm writing this from the office at 10pm on a Sunday).
Keep the debate & info flowing. I find these threads a whole lot more interesting than the "look at this POS 928 on ebay" or "will these 11x19 ET63 wheels fit on the front of my 928" threads.
Interesting side note, here....the best flow that I've seen from heads with 968 valve seats (other than ones worked up on flow bench) was taken on a "raw" casting that had just had the seats installed and were not touched, other than that. Ridge under the seat and all!
Pretty amazing stuff, engines are.
Keep us informed.
__________________
greg brown
714 879 9072
GregBBRD@aol.com
Semi-retired, as of Feb 1, 2023.
The days of free technical advice are over.
Free consultations will no longer be available.
Will still be in the shop, isolated and exclusively working on project cars, developmental work and products, engines and transmissions.
Have fun with your 928's people!
greg brown
714 879 9072
GregBBRD@aol.com
Semi-retired, as of Feb 1, 2023.
The days of free technical advice are over.
Free consultations will no longer be available.
Will still be in the shop, isolated and exclusively working on project cars, developmental work and products, engines and transmissions.
Have fun with your 928's people!
04-25-2011, 04:30 PM
#65
Rennlist Member
Colin, can you miss more information and data if you tried???
so, lets start with this........ HE HAS AN 85!! its a 5 liter, yes, but it has a different intake, much smaller valves and lower compression. so, bolt on the bigger valve S4 heads, put on some racing headers and open the exhaust up and yes, i dont think any normal person would doubt a 15 to 20hp gain over his dyno run values. (by the way, it puts him at exacty what Ron and I made as far as HP. 320rwhp to (335rwhp at the holbert cars best)
by the way, you must have missed the point that my car has been on dynos all over nor cal, making the same power everywhere. 320-325ish after a few seasons of racing, and near 320 after 8 full racing seasons. keep in mind, all on dynojet 248e, and a couple of runs on the brake dyhno (mustang) where we got near 318rwhp).
I think the only thing he will see is the effects of the larger intake valves from a 968. like you said, that might be negated with port work, if that isnt done absolutely perfecty. these heads are not like BMW heads where you get some pretty large gains by hogging them out and do all the polishign work.
It will be interesting to see what he comes out with HP wise.
Well, lets see. is there any way shape or form where you couldnt have made 305rwhp, if that was the actual number? If so, i would sure like to hear how?
you either spun up the drums at a rate worthy of that value or you didnt.
did someone change the weight of the drums? did someone change the RPM sensor for detecting speed?
By the way, have you tried to dyno the KN, but also making sure the air box was sealed . (key point due to my findings during WOT with all filters on stock air box) . not many people have. Ill bring a paper filter to my next dyno run for giggles and do the test again. I seemed to remember a 5hp loss for the paper, but that was sealed. remember, not sealed and the air can just bypass the filter at the edges, and negates the test validity.
so you are still fairy restrictive with the exhuast. you also have a stock filter, which is restrictive. (presssure drop), and what are the elgin cams again? are they same as dennis? or are they just 85s modified for S4, gts?
so, lets start with this........ HE HAS AN 85!! its a 5 liter, yes, but it has a different intake, much smaller valves and lower compression. so, bolt on the bigger valve S4 heads, put on some racing headers and open the exhaust up and yes, i dont think any normal person would doubt a 15 to 20hp gain over his dyno run values. (by the way, it puts him at exacty what Ron and I made as far as HP. 320rwhp to (335rwhp at the holbert cars best)
by the way, you must have missed the point that my car has been on dynos all over nor cal, making the same power everywhere. 320-325ish after a few seasons of racing, and near 320 after 8 full racing seasons. keep in mind, all on dynojet 248e, and a couple of runs on the brake dyhno (mustang) where we got near 318rwhp).
It will be interesting to see what he comes out with HP wise.
What a great "back to back" experiment this is! I can hardly wait to see the dyno results. Every single (without exception) set of heads with 968 intake valves (that I've flowed) that were not worked up on a flow bench (seats with blended intake ports) has lost air flow over the stock heads. I had a set from Utah that lost over 15% flow!
Interesting side note, here....the best flow that I've seen from heads with 968 valve seats (other than ones worked up on flow bench) was taken on a "raw" casting that had just had the seats installed and were not touched, other than that. Ridge under the seat and all!
Pretty amazing stuff, engines are.
Keep us informed.
Interesting side note, here....the best flow that I've seen from heads with 968 valve seats (other than ones worked up on flow bench) was taken on a "raw" casting that had just had the seats installed and were not touched, other than that. Ridge under the seat and all!
Pretty amazing stuff, engines are.
Keep us informed.
you either spun up the drums at a rate worthy of that value or you didnt.
did someone change the weight of the drums? did someone change the RPM sensor for detecting speed?
By the way, have you tried to dyno the KN, but also making sure the air box was sealed . (key point due to my findings during WOT with all filters on stock air box) . not many people have. Ill bring a paper filter to my next dyno run for giggles and do the test again. I seemed to remember a 5hp loss for the paper, but that was sealed. remember, not sealed and the air can just bypass the filter at the edges, and negates the test validity.
My '85 5-speed consistently makes 298-305 rwhp and tq (sae) on a Dynojet 248x (so it must be right ).
Stock airbox/paper filter, 32V cat downpipes converted to Y-pipe, stock '84 16V single rear exhaust w/modded rear muffler. No airpump/engine fan, stock cam timing.
).Stock airbox/paper filter, 32V cat downpipes converted to Y-pipe, stock '84 16V single rear exhaust w/modded rear muffler. No airpump/engine fan, stock cam timing.
04-25-2011, 05:36 PM
#66
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Lots of air flow modeling and flow bench work has played its part in the port work / re-valve installs I do / supervise. By no means is the work is not done "in the dark" or results "faked" (as suggested).
I have access to a great valve job guy and with this, I have been able to do some cool "tricks" to the 968 intake valve install, port choke size / shape. If you or your head guy (or gal) is creative, you can simplify the install and make better flow than if you use the std. 968 valve seat. A good, rigid and accurate valve guide / seat machine is a must.
I have access to a great valve job guy and with this, I have been able to do some cool "tricks" to the 968 intake valve install, port choke size / shape. If you or your head guy (or gal) is creative, you can simplify the install and make better flow than if you use the std. 968 valve seat. A good, rigid and accurate valve guide / seat machine is a must.
04-25-2011, 06:32 PM
#67
Rennlist Member
I kinda figured as much!
what are you expecting on the next dyno run? 400rwhp? that would be amazing out of a 5 liter 928 engine.
all this work, and Im amazed we havent yet seen, after 8 years of knowing about it, a CF intake on a stock 5 liter >(or ITBs for that matter)!
Mk
what are you expecting on the next dyno run? 400rwhp? that would be amazing out of a 5 liter 928 engine.
all this work, and Im amazed we havent yet seen, after 8 years of knowing about it, a CF intake on a stock 5 liter >(or ITBs for that matter)!
Mk
Lots of air flow modeling and flow bench work has played its part in the port work / re-valve installs I do / supervise. By no means is the work is not done "in the dark" or results "faked" (as suggested).
I have access to a great valve job guy and with this, I have been able to do some cool "tricks" to the 968 intake valve install, port choke size / shape. If you or your head guy (or gal) is creative, you can simplify the install and make better flow than if you use the std. 968 valve seat. A good, rigid and accurate valve guide / seat machine is a must.
I have access to a great valve job guy and with this, I have been able to do some cool "tricks" to the 968 intake valve install, port choke size / shape. If you or your head guy (or gal) is creative, you can simplify the install and make better flow than if you use the std. 968 valve seat. A good, rigid and accurate valve guide / seat machine is a must.
04-25-2011, 06:36 PM
#68
Nordschleife Master
Colin, can you miss more information and data if you tried???
so, lets start with this........ HE HAS AN 85!! its a 5 liter, yes, but it has a different intake, much smaller valves and lower compression. so, bolt on the bigger valve S4 heads, put on some racing headers and open the exhaust up and yes, i dont think any normal person would doubt a 15 to 20hp gain over his dyno run values. (by the way, it puts him at exacty what Ron and I made as far as HP. 320rwhp to (335rwhp at the holbert cars best)
by the way, you must have missed the point that my car has been on dynos all over nor cal, making the same power everywhere. 320-325ish after a few seasons of racing, and near 320 after 8 full racing seasons. keep in mind, all on dynojet 248e, and a couple of runs on the brake dyhno (mustang) where we got near 318rwhp).
so, lets start with this........ HE HAS AN 85!! its a 5 liter, yes, but it has a different intake, much smaller valves and lower compression. so, bolt on the bigger valve S4 heads, put on some racing headers and open the exhaust up and yes, i dont think any normal person would doubt a 15 to 20hp gain over his dyno run values. (by the way, it puts him at exacty what Ron and I made as far as HP. 320rwhp to (335rwhp at the holbert cars best)
by the way, you must have missed the point that my car has been on dynos all over nor cal, making the same power everywhere. 320-325ish after a few seasons of racing, and near 320 after 8 full racing seasons. keep in mind, all on dynojet 248e, and a couple of runs on the brake dyhno (mustang) where we got near 318rwhp).
tongue in cheek with that comment, in other words it was rhetorical.
However your comment there is wrong. From all the research I can find a good portion of the 928S4 motors actually CC out to be closer to the 9.3:1 range. Where the 85/86 motors CC out to be true 10:1 range.
Though you still havent addressed the cam information that I posted disproving you.
All in good fun bud, I know no one could possibly know more than you when it comes to all this stuff.
04-25-2011, 07:41 PM
#69
Rennlist Member
I am sure there will be a 5 litre ITB engine running before the end of this year...
04-25-2011, 07:46 PM
#70
Three Wheelin'
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I hate to guess dyno numbers, but I'd like to see 5 or so percent over the past "best" runs.
As a fun fact, I purchased the dyno used for Dennis' tests as besides Dennis' efforts, I have other works in progress that I did not want to lose the baseline dyno numbers. To afford the dyno, I have partners who will co-own and operate it with me. Right now, we are completing the in ground facility work and hope to test the dyno against baselines since its move within a few weeks.
Once baseline has been re-established, I plan to improve some of the data acquisition to add more information directly onto the torque/hp curves. Within this effort is a basic upgrade to the PC and operating system, also with the intent of improving the testing service. I would like to have video with time sync to the dyno pulls. $$$ and available time will likely throttle what we get done.
As a fun fact, I purchased the dyno used for Dennis' tests as besides Dennis' efforts, I have other works in progress that I did not want to lose the baseline dyno numbers. To afford the dyno, I have partners who will co-own and operate it with me. Right now, we are completing the in ground facility work and hope to test the dyno against baselines since its move within a few weeks.
Once baseline has been re-established, I plan to improve some of the data acquisition to add more information directly onto the torque/hp curves. Within this effort is a basic upgrade to the PC and operating system, also with the intent of improving the testing service. I would like to have video with time sync to the dyno pulls. $$$ and available time will likely throttle what we get done.
04-25-2011, 09:11 PM
#71
Addict
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But we'll have to see. One never knows with these things.
04-25-2011, 11:18 PM
#72
Rennlist
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The whole horsepower thing is such a crock of crap...it really doesn't matter, as long as you are the one in the front.
Rob Rossitto's stroker made 330RWHP. or something close to that. He sucked the doorknobs off a 525rwhp supercharged 928 GTS at the drags....time after time.
He had fun. The guy with the supercharger...not so much.
Good luck with the new engine. Let us know what you come up with, when you guys have time to finish it up.
04-26-2011, 01:13 AM
#74
Drifting
04-26-2011, 03:35 AM
#75
Rennlist Member
I know. all in fun
seriously, what are you talking about.
s4 motors have bigger valves. 85s have smaller valves
S4 motors have higher compression. Ive cced them and posted results here.
S4 motors have a better intake for power, but that is debatable.
so, what cam information are you refering too? your mods to the cam to make more power up top vs more peak torque. you must not read what I write
The original point was more torque at higher RPM and that is more peak hp and its more peak HP at a higher rpm.
maybe ask the question to me in another way. or show me how more torque at higher rpm is not more hp.
seriously, what are you talking about.
s4 motors have bigger valves. 85s have smaller valves
S4 motors have higher compression. Ive cced them and posted results here.
S4 motors have a better intake for power, but that is debatable.
so, what cam information are you refering too? your mods to the cam to make more power up top vs more peak torque. you must not read what I write
The original point was more torque at higher RPM and that is more peak hp and its more peak HP at a higher rpm.
maybe ask the question to me in another way. or show me how more torque at higher rpm is not more hp.
MK,
tongue in cheek with that comment, in other words it was rhetorical.
However your comment there is wrong. From all the research I can find a good portion of the 928S4 motors actually CC out to be closer to the 9.3:1 range. Where the 85/86 motors CC out to be true 10:1 range.
Though you still havent addressed the cam information that I posted disproving you.
All in good fun bud, I know no one could possibly know more than you when it comes to all this stuff.
tongue in cheek with that comment, in other words it was rhetorical.
However your comment there is wrong. From all the research I can find a good portion of the 928S4 motors actually CC out to be closer to the 9.3:1 range. Where the 85/86 motors CC out to be true 10:1 range.
Though you still havent addressed the cam information that I posted disproving you.
All in good fun bud, I know no one could possibly know more than you when it comes to all this stuff.