317 vs 862
03-23-2014, 12:57 PM
#41
Right on 
I like healthy debate. Ive learned from it and it helps newbies make educated decisions.
lol. you are claiming something based on what head flow tells you it should be. Im telling you that experience(with data) trumps feelings. I HAVE tested 799 vs 862 and when you look at fuel flow data, neither one had an advantage over the other that was about a .4 difference in compression. the 317 will be about a 1.0 difference in compression and I will tell you a stock 862 will outperform a stock 317 hands down. compression wins over flow in these heads.
lets use our cars for comparison since they are both fairly light and fairly similar. btw, I love your car.
yours is 5.3 with a glide, 8.6:1 compression,s475 1.10 t4
mine is 5.7 with a glide, 10.5:1 compression,s475 1.32 t6
your car has run a best 5.703 at 122.72
my--car has run a best 5.995 at 116.92
your car 1.35 60ft launching at 24 psi boost
mine car 1.41 60ft launching at 1 psi boost
your car average psi through the run 23 psi
my car average psi through the run 7.4 psi
you would agree that this kind of makes it clear how big a disadvantage there is by running lower compression. your car has run faster, but it has taken 3x the boost and 24x the launch boost to do it. looking at the info, there is no other explanation I can give for the difference in boost numbers.
what does high boost mean?
1. your turbo is spinning much faster than mine at our boost levels
2 this puts more heat into the system
3. heat reduces density which causes less output per psi as boost increases
4. this heat makes your car more prone to detonate
5. this causes you to reduce timing
6. this causes you to run more boost, which causes you to further reduce timing and before you know it you are running 3x the boost to achieve the same result.
I wont repeat the other problems associated with running high boost since Ive listed them already.
I like these quotes:
"Knowledge is light"
"Give the people light and they will find their way
I like healthy debate. Ive learned from it and it helps newbies make educated decisions.lol. you are claiming something based on what head flow tells you it should be. Im telling you that experience(with data) trumps feelings. I HAVE tested 799 vs 862 and when you look at fuel flow data, neither one had an advantage over the other that was about a .4 difference in compression. the 317 will be about a 1.0 difference in compression and I will tell you a stock 862 will outperform a stock 317 hands down. compression wins over flow in these heads.
lets use our cars for comparison since they are both fairly light and fairly similar. btw, I love your car.
yours is 5.3 with a glide, 8.6:1 compression,s475 1.10 t4
mine is 5.7 with a glide, 10.5:1 compression,s475 1.32 t6
your car has run a best 5.703 at 122.72
my--car has run a best 5.995 at 116.92
your car 1.35 60ft launching at 24 psi boost
mine car 1.41 60ft launching at 1 psi boost
your car average psi through the run 23 psi
my car average psi through the run 7.4 psi
you would agree that this kind of makes it clear how big a disadvantage there is by running lower compression. your car has run faster, but it has taken 3x the boost and 24x the launch boost to do it. looking at the info, there is no other explanation I can give for the difference in boost numbers.
what does high boost mean?
1. your turbo is spinning much faster than mine at our boost levels
2 this puts more heat into the system
3. heat reduces density which causes less output per psi as boost increases
4. this heat makes your car more prone to detonate
5. this causes you to reduce timing
6. this causes you to run more boost, which causes you to further reduce timing and before you know it you are running 3x the boost to achieve the same result.
I wont repeat the other problems associated with running high boost since Ive listed them already.
I like these quotes:
"Knowledge is light"
"Give the people light and they will find their way
“Compression ratio should be set as high as feasible without encountering detonation at the maximum load condition”
To me it seems you are not taking full advantage of your power adder. Why run FI if your not using it to it's full potential?
Your "maximum load condition" is weak sauce compared to what it should be at. Push the turbo to it's limits, then get compression as high as you feasibly can without detonation. To me thats an "efficient" use of the power adder. So for a typical pump gas setup, a 317 head is better suited than a higher compression setup as it will allow you to run the turbo closer to "maximum load" without detonation.
When running 100% meth you can "have your cake and eat it too". High compression and high boost. I'm not suggesting low compression for any 100% meth fueled engine. Though it seems around 9:1 and 40+psi is what the big power SBC alcohol guys are running.
03-23-2014, 06:41 PM
#42
i have become of the opinion that the smaller the difference between NA and boost, the better the system is overall.
consider two extreme scenarios. both want make 900hp and run 5.70s , both cars weigh the same and have correctly sized turbos.
scenario 1: 4.8 with stock cam making 300 hp.
it will take approximately 30 psi to make 900 hp.
the converter that will work for 900hp will be very tight at the 300hp level and it will take a long time to get on the converter(ie get to a decent launch rpm and boost). it may even need the help of some nitrous.
being on the converter a long time will put a lot of heat in the trans, reducing its life span
it will also require less timing because of the high boost,making the system even less efficient.
it will also require a pretty nice intercooler, which creates some pressure drop and adds weight, or at least some hefty water injection
scenario 2: 6.0 with correctly sized cam and ported heads, making 600hp
it will take approximately 7.4 psi to make 900hp
it will take much less time to get on the converter, putting less heat in the trans
it may also be easier to race it, not having to employ many strategies to get on the converter, eg bump box
running 8.5 psi may allow it to get by without intercooling
it will also be able to run more timing, creating a more efficient system overall.
will be more streetable than the high boost low na power combo
so, you see,im a believer in making the most power N/A then using the least amount of boost necessary to get to the e.t goal
btw, i notice that your new build is 10:1
consider two extreme scenarios. both want make 900hp and run 5.70s , both cars weigh the same and have correctly sized turbos.
scenario 1: 4.8 with stock cam making 300 hp.
it will take approximately 30 psi to make 900 hp.
the converter that will work for 900hp will be very tight at the 300hp level and it will take a long time to get on the converter(ie get to a decent launch rpm and boost). it may even need the help of some nitrous.
being on the converter a long time will put a lot of heat in the trans, reducing its life span
it will also require less timing because of the high boost,making the system even less efficient.
it will also require a pretty nice intercooler, which creates some pressure drop and adds weight, or at least some hefty water injection
scenario 2: 6.0 with correctly sized cam and ported heads, making 600hp
it will take approximately 7.4 psi to make 900hp
it will take much less time to get on the converter, putting less heat in the trans
it may also be easier to race it, not having to employ many strategies to get on the converter, eg bump box
running 8.5 psi may allow it to get by without intercooling
it will also be able to run more timing, creating a more efficient system overall.
will be more streetable than the high boost low na power combo
so, you see,im a believer in making the most power N/A then using the least amount of boost necessary to get to the e.t goal
btw, i notice that your new build is 10:1
Last edited by 71 chevy; 03-23-2014 at 07:02 PM.
03-24-2014, 07:00 AM
#43
i have become of the opinion that the smaller the difference between NA and boost, the better the system is overall.
consider two extreme scenarios. both want make 900hp and run 5.70s , both cars weigh the same and have correctly sized turbos.
scenario 1: 4.8 with stock cam making 300 hp.
it will take approximately 30 psi to make 900 hp.
the converter that will work for 900hp will be very tight at the 300hp level and it will take a long time to get on the converter(ie get to a decent launch rpm and boost). it may even need the help of some nitrous.
being on the converter a long time will put a lot of heat in the trans, reducing its life span
it will also require less timing because of the high boost,making the system even less efficient.
it will also require a pretty nice intercooler, which creates some pressure drop and adds weight, or at least some hefty water injection
scenario 2: 6.0 with correctly sized cam and ported heads, making 600hp
it will take approximately 7.4 psi to make 900hp
it will take much less time to get on the converter, putting less heat in the trans
it may also be easier to race it, not having to employ many strategies to get on the converter, eg bump box
running 8.5 psi may allow it to get by without intercooling
it will also be able to run more timing, creating a more efficient system overall.
will be more streetable than the high boost low na power combo
so, you see,im a believer in making the most power N/A then using the least amount of boost necessary to get to the e.t goal
btw, i notice that your new build is 10:1
consider two extreme scenarios. both want make 900hp and run 5.70s , both cars weigh the same and have correctly sized turbos.
scenario 1: 4.8 with stock cam making 300 hp.
it will take approximately 30 psi to make 900 hp.
the converter that will work for 900hp will be very tight at the 300hp level and it will take a long time to get on the converter(ie get to a decent launch rpm and boost). it may even need the help of some nitrous.
being on the converter a long time will put a lot of heat in the trans, reducing its life span
it will also require less timing because of the high boost,making the system even less efficient.
it will also require a pretty nice intercooler, which creates some pressure drop and adds weight, or at least some hefty water injection
scenario 2: 6.0 with correctly sized cam and ported heads, making 600hp
it will take approximately 7.4 psi to make 900hp
it will take much less time to get on the converter, putting less heat in the trans
it may also be easier to race it, not having to employ many strategies to get on the converter, eg bump box
running 8.5 psi may allow it to get by without intercooling
it will also be able to run more timing, creating a more efficient system overall.
will be more streetable than the high boost low na power combo
so, you see,im a believer in making the most power N/A then using the least amount of boost necessary to get to the e.t goal
btw, i notice that your new build is 10:1
I think a 600hp NA 6.0 would cost 3-4 times (maybe more!) than a 4.8 would. Making the cost of a $950 converter a mute point. My trans temps taken at the pan never went over 220*. Thats launching at twice the boost most do. I saw less than 6% slippage up top and boost built fast enough I could still cut a great light. (not that I often did)
I build my setups based on HP per $ invested. Don’t have a lot to invest in this hobby so I try to make the most out of what I can afford. I went with a 10:1 motor this time because it was an alum gen4 motor for $500 that already had the better flowing 243 head on it. I also run an alcohol based fuel so I should be able to get away with it. Honestly if my 317 heads weren't damaged I would have sold the 243's to recoup most of the motor cost and ran the 317's. I also believe lower compression gives you more of a "cushion" when tuning.
Last edited by Forcefed86; 03-24-2014 at 02:01 PM.
04-25-2015, 04:18 PM
#44
Staging Lane
Join Date: Jan 2008
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good info here! I have a friend doing a stock bore/stroke 5.3 with forged rods and pistons and arp 2000 bolts. He found a cheap set of 862 heads that have a little "pocket porting" He's going to try to run a 91mm turbo with a .96 t6 exhaust. Needs to get the correct cam. With a turbo 400 transmission and a 3:50 rear gear. What kinda power should it make on C16?
04-27-2015, 11:02 AM
#47
Back form the dead!
The DCR is what determines actual cylinder pressure and is radically affected by the cam timing. If you shorten the IVC point, less SCR is required to build the same DCR. With the correct cam an 317 head can have the same DCR as 862 head. The shorter the duration, the earlier the motor will peak power/RPM wise. OEM parts (intakes, valve-train, heads, etc...) peak at a relatively early RPM anyway. So a high SCR is not always needed to make power efficiently. Many times a lower SCR and smaller cam will give you more average power across a stock engines RPM range. This is what wins races, not peak dyno numbers.
It's all a "give and take" relationship. You can't throw a big cam in a low RPM/SCR engine and expect great performance. Many times this is the case when you hear someone talking about a "doggy" low compression engine.
A 317 head flows more air, period. Power lost by the drop in SCR is easily made up with additional boost. If response is a major concern, upping the DCR with the cam is the way to go with "JY" builds. No reason to run smaller head IMO.
The DCR is what determines actual cylinder pressure and is radically affected by the cam timing. If you shorten the IVC point, less SCR is required to build the same DCR. With the correct cam an 317 head can have the same DCR as 862 head. The shorter the duration, the earlier the motor will peak power/RPM wise. OEM parts (intakes, valve-train, heads, etc...) peak at a relatively early RPM anyway. So a high SCR is not always needed to make power efficiently. Many times a lower SCR and smaller cam will give you more average power across a stock engines RPM range. This is what wins races, not peak dyno numbers.
It's all a "give and take" relationship. You can't throw a big cam in a low RPM/SCR engine and expect great performance. Many times this is the case when you hear someone talking about a "doggy" low compression engine.
A 317 head flows more air, period. Power lost by the drop in SCR is easily made up with additional boost. If response is a major concern, upping the DCR with the cam is the way to go with "JY" builds. No reason to run smaller head IMO.
Last edited by Forcefed86; 04-27-2015 at 11:32 AM.
04-28-2015, 01:36 PM
#48
Staging Lane
Join Date: Jan 2008
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good info here! I have a friend doing a stock bore/stroke 5.3 with forged rods and pistons and arp 2000 bolts. He found a cheap set of 862 heads that have a little "pocket porting" He's going to try to run a 91mm turbo with a .96 t6 exhaust. Needs to get the correct cam. With a turbo 400 transmission and a 3:50 rear gear. What kinda power should it make on C16?
