Building the ultimate LSX...what heads?
08-22-2007, 09:56 AM
#21
Originally Posted by Stang's Bane
Brian, for once I agree with you 
I would contact Tom Nelson or find anything he has on the web about turbo theory, he seems to have a handle on it. I am not saying he is the best, but he does have a pretty good track record
I would contact Tom Nelson or find anything he has on the web about turbo theory, he seems to have a handle on it. I am not saying he is the best, but he does have a pretty good track record
Like I said, a good racer with a proper setup can make big power with a small head, the bigger heads don't pick up a turbo combination like they do N/A, Supercharged or Nitrous due to the bigger heads having big intake valves that promote exhaust gas dilution into the intake port. Most any turbo application has more pressure on the exhaust side than intake side, this is what causes the exhaust gas to go back into the intake port during overlap. Most big heads also have corresponding big exhaust ports, that is not what a good turbo head needs to be. I would have an exhaust port smaller than 100cc, I would think closer to 90cc, and no bigger than a 1.60" exhaust valve, and don't hesitate to go steep seat angles on intake and exhaust, it will help minimize the reversion (dilution)
08-22-2007, 10:30 AM
#22
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I disagree here. The problem with most turbo setups is improperly designed headers and improperly selected turbine wheels and turbine housings along with improperly designed and implement waste gate arrangements . If the turbo kit is designed properly then it should amplify withouth trouble any good NA combo in magnitudes while not killing NA power or changing the shape and look of the curve. If it does rework the kit its screwed up.. Nitrous is a whole different animal however as are blowers.
Originally Posted by Brian Tooley
Turbo combinations tend to suffer from exhaust gas dilution into the intake port. Because of this you either have to run a smaller intake valve, or an intake valve with a steep seat angle, like 55 degrees, to help kill low lift flow (.100"-.200") If a port flows well in the forward direction at low lift it will also flow well in the reverse direction at low lift.
Turbo engines also like smaller exhaust valves and exhaust ports, so don't be tempted to run a nitrous type of exhaust port.
Turbo engines don't tend to need as good of a head to make power as a N/A, blower or nitrous setup. I have seen Ford racers go low 7's with 225cc heads.
Turbo engines also like smaller exhaust valves and exhaust ports, so don't be tempted to run a nitrous type of exhaust port.
Turbo engines don't tend to need as good of a head to make power as a N/A, blower or nitrous setup. I have seen Ford racers go low 7's with 225cc heads.
08-22-2007, 10:55 AM
#23
Originally Posted by LS1curious
I disagree here. The problem with most turbo setups is improperly designed headers and improperly selected turbine wheels and turbine housings along with improperly designed and implement waste gate arrangements . If the turbo kit is designed properly then it should amplify withouth trouble any good NA combo in magnitudes while not killing NA power or changing the shape and look of the curve. If it does rework the kit its screwed up.. Nitrous is a whole different animal however as are blowers.
08-22-2007, 11:25 AM
#24
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Depends on the class rules. I have no problem running 260cc heads on street motors at 346 ci that make killer power. Camshaft camshaft camshaft.
Gas dillution is definately a problem but if its a problem on a FI turbo engine then it should be a problem an NA motor if the exhuast was that wretched.
I refuse to play the velocity game becuase its a wasted argument. you can have small ports with insane local velocitys or you can have large ports with low local velocitys. from what I have seen the port with the best overall average velocitys, and the least amount of low and high velocity zones. That is a port with good average speed throughout with out any higher veolcity or lower velocity zones will always be better then said small or large port.
I would not be lumped into either group saying that a small port will work better then a large port or vise versa. A good exmplae of this is the L92/l76 Gm head. I have seen tremendous power out of these heads and intakes but the trick is in realizing how camshaft specficiations can totally screw this head up.
Thats like how most people ignore the relationship between exhuast efficiency and the effectiveness of overlap. Put to much overlap into a closed muffled exhuast system and watch power drop like a rock.
thats gets back into your arugment on intake port backing up with exhuast.
Same with a turbo application.
Gas dillution is definately a problem but if its a problem on a FI turbo engine then it should be a problem an NA motor if the exhuast was that wretched.
I refuse to play the velocity game becuase its a wasted argument. you can have small ports with insane local velocitys or you can have large ports with low local velocitys. from what I have seen the port with the best overall average velocitys, and the least amount of low and high velocity zones. That is a port with good average speed throughout with out any higher veolcity or lower velocity zones will always be better then said small or large port.
I would not be lumped into either group saying that a small port will work better then a large port or vise versa. A good exmplae of this is the L92/l76 Gm head. I have seen tremendous power out of these heads and intakes but the trick is in realizing how camshaft specficiations can totally screw this head up.
Thats like how most people ignore the relationship between exhuast efficiency and the effectiveness of overlap. Put to much overlap into a closed muffled exhuast system and watch power drop like a rock.
thats gets back into your arugment on intake port backing up with exhuast.
Same with a turbo application.
Originally Posted by Brian Tooley
I will have to agree with you on many points you have made. However, how many small heads have you seen on turbo engines that made big power and shouldn't have, and how many big heads have you seen that should have made killer power that didn't really do that great? Do you disagree that exhaust gas dilution into the intake port is a problem, and that the problem can be aggravated with bigger intake valves? How many turbo combinations have you prepared heads for? Thanks.
08-22-2007, 02:59 PM
#25
Originally Posted by LS1curious
Gas dillution is definately a problem but if its a problem on a FI turbo engine then it should be a problem an NA motor if the exhuast was that wretched.
Originally Posted by LS1curious
A good exmplae of this is the L92/l76 Gm head. I have seen tremendous power out of these heads and intakes but the trick is in realizing how camshaft specficiations can totally screw this head up.
08-22-2007, 03:08 PM
#26
Originally Posted by Brian Tooley
Most any turbo application has more pressure on the exhaust side than intake side, this is what causes the exhaust gas to go back into the intake port during overlap.
Still boggles my mind, that a motor could run effectively at all, with higher exhaust pressure than intake pressure. Just doesnt make sense in my little pea brain.
I understand the theory, and why, just am kinda
Sorry for the hijack. Just wanted to comment on that remark.
08-22-2007, 03:54 PM
#27
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The 60 psi your commenting on would be the problem I am reffering to. A properly designed and engineered turbo system can actually run the other way. 30 intake 15 exhuast. It takes an absolute ton of work and alot of tunning work to make it spool but when it does it makes great power. You should look into old indy FI setups. They had pressure I/E ratios that were insane.
Most of the turbo kits out there today flat out suck.
Most of the turbo kits out there today flat out suck.
Originally Posted by Brian Tooley
A N/A engine has roughly 14 PSI of intake pressure and the same 14 PSI of exhaust pressure. A turbo engine with 30 lbs of boost now has 44 PSI on the intake side but may see close to 60 PSI on the exhaust side. This is what makes a turbo engine so much more prone to the exhaust gas dilution, it always has more pressure on the exhaust side than intake side. I think I now know the answer to one of my questions I asked you above...
I'm probably the first guy on this site who let everyone know how important cam timing events are on a L92 head and got bashed, it is so sensitive to cam timing events due to the oversize intake valve.
I'm probably the first guy on this site who let everyone know how important cam timing events are on a L92 head and got bashed, it is so sensitive to cam timing events due to the oversize intake valve.
08-22-2007, 04:33 PM
#28
Originally Posted by edcmat-l1
Thats the info I got from two of the big name turbo companies, while trying to hunt down info on why a certain turbo car we had wouldnt put up the numbers.
Still boggles my mind, that a motor could run effectively at all, with higher exhaust pressure than intake pressure. Just doesnt make sense in my little pea brain.
I understand the theory, and why, just am kinda
Sorry for the hijack. Just wanted to comment on that remark.
Still boggles my mind, that a motor could run effectively at all, with higher exhaust pressure than intake pressure. Just doesnt make sense in my little pea brain.
I understand the theory, and why, just am kinda
Sorry for the hijack. Just wanted to comment on that remark.
Once you understand the pressures in the ports and how they interact with each other during overlap you can better understand what makes certain combinations work better than others. Which also means you can probably understand why I say a big intake valve on a turbo application can be a problem, and also why reducing the low lift flow (.100"-.200") actually helps the thing make more power. You can classify smaller intake valves or steeper seat angles as "intake anti reversion tactics"
I posted it before and I will post it again. I had a C6 Corvette customer with an APS TT kit with a stock LS2 short block and heads. He removed the stock 243 castings and installed L92 heads and intake and lost 40 HP.
What was the combination that you spoke of? What were the heads?
08-22-2007, 04:37 PM
#29
Originally Posted by LS1curious
The 60 psi your commenting on would be the problem I am reffering to. A properly designed and engineered turbo system can actually run the other way. 30 intake 15 exhuast. It takes an absolute ton of work and alot of tunning work to make it spool but when it does it makes great power. You should look into old indy FI setups. They had pressure I/E ratios that were insane.
Most of the turbo kits out there today flat out suck.
Most of the turbo kits out there today flat out suck.
Last edited by Brian Tooley Racing; 08-22-2007 at 06:00 PM.
08-22-2007, 04:55 PM
#30
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Check out old indy stuff from back in the day. All the info is there.
Originally Posted by Brian Tooley
I don't know of anyone that knows anything about turbo kits that will tell you there will be less exhaust pressure than intake pressure.
Most kits run 1.5:1 ratio of exhaust pressure to intake pressure, it is when the ratio gets to 2:1 that you have REAL problems.
Most kits run 1.5:1 ratio of exhaust pressure to intake pressure, it is when the ratio gets to 2:1 that you have REAL problems.
08-22-2007, 07:49 PM
#31
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i personaly reckon on this topic-as what i can see money is not the problem-from where i come from i have seen people match parts to late and get them wrong-
i reckon the list should start with the turbo's-like choose the turbo u want for their rating-then move to the ehaust manifold set-up then to the heads to suit turbo+pipes+then valvetrain gear+then to intake set-up to injectors-then short block-
i have seen others go out and buy big stuff only to cry when they don't get what they want-
i reckon its down to matching things to things for the application-
i think we have all seen hi-tech combos and basic combo's-the basic one 80% of the time runs problem free and makes more hp-torq-
this combo needs good planing from the get go-
2000hp would be insane-thats for sure
lets see some pics and progress when the time comes-
i reckon the list should start with the turbo's-like choose the turbo u want for their rating-then move to the ehaust manifold set-up then to the heads to suit turbo+pipes+then valvetrain gear+then to intake set-up to injectors-then short block-
i have seen others go out and buy big stuff only to cry when they don't get what they want-
i reckon its down to matching things to things for the application-
i think we have all seen hi-tech combos and basic combo's-the basic one 80% of the time runs problem free and makes more hp-torq-
this combo needs good planing from the get go-
2000hp would be insane-thats for sure
lets see some pics and progress when the time comes-
08-22-2007, 07:50 PM
#32
Originally Posted by Brian Tooley
Exactly, the theory is, "take the power curve of a N/A engine and with turbo(s) it will raise the whole curve" When in reality there is far more going on.
Once you understand the pressures in the ports and how they interact with each other during overlap you can better understand what makes certain combinations work better than others. Which also means you can probably understand why I say a big intake valve on a turbo application can be a problem, and also why reducing the low lift flow (.100"-.200") actually helps the thing make more power. You can classify smaller intake valves or steeper seat angles as "intake anti reversion tactics"
I posted it before and I will post it again. I had a C6 Corvette customer with an APS TT kit with a stock LS2 short block and heads. He removed the stock 243 castings and installed L92 heads and intake and lost 40 HP.
What was the combination that you spoke of? What were the heads?
Once you understand the pressures in the ports and how they interact with each other during overlap you can better understand what makes certain combinations work better than others. Which also means you can probably understand why I say a big intake valve on a turbo application can be a problem, and also why reducing the low lift flow (.100"-.200") actually helps the thing make more power. You can classify smaller intake valves or steeper seat angles as "intake anti reversion tactics"
I posted it before and I will post it again. I had a C6 Corvette customer with an APS TT kit with a stock LS2 short block and heads. He removed the stock 243 castings and installed L92 heads and intake and lost 40 HP.
What was the combination that you spoke of? What were the heads?
Long story short, spent some time on the phone with Gale Banks and some others, only to find out it was normal.
And yeah, I can understand the "check valve" theory, how it works, and how you can manipulate both the intake and exhaust valves and seats to keep down the reversion.
08-23-2007, 09:03 AM
#33
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You must remeber there are 2 types of turbine drive setups.
Pressue and Pulse.
A constant pressure drive system runs at high back pressure out of nessecity. A Wave Pulse system runs at the minimum pressure possiable.
A constant pressure system mashes all of the exhuast pulses together into one constant stream of back pressure. This is the bulk of turbo charging system out there even with good headers and merge collectors.
A wave or pulse charging system works alot differently. A wave system basically works like a good NA header. IT uses each individual pulse to drive the turbine one pulse at a time. This requires a very large turbine area or a very well laid out waste gate setup.
Banks has been at turbocharging for a long time but if you ask him about the differences between constant pressure and Pulse driving he has loads of info.
Pulse systems typicall run at half the intake pressure if they are working well. There is some good info on the ecotech drag car engine development and how they achivied the pressure cross over.
Pressue and Pulse.
A constant pressure drive system runs at high back pressure out of nessecity. A Wave Pulse system runs at the minimum pressure possiable.
A constant pressure system mashes all of the exhuast pulses together into one constant stream of back pressure. This is the bulk of turbo charging system out there even with good headers and merge collectors.
A wave or pulse charging system works alot differently. A wave system basically works like a good NA header. IT uses each individual pulse to drive the turbine one pulse at a time. This requires a very large turbine area or a very well laid out waste gate setup.
Banks has been at turbocharging for a long time but if you ask him about the differences between constant pressure and Pulse driving he has loads of info.
Pulse systems typicall run at half the intake pressure if they are working well. There is some good info on the ecotech drag car engine development and how they achivied the pressure cross over.
Originally Posted by edcmat-l1
The combo was just a stock LS1 with a STS. During the diagnostic process to figure out why it was such a terd, I did a backpressure test. BAD IDEA!! I got so wrapped up in why it had more BP than boost, I got tunnel vision.
Long story short, spent some time on the phone with Gale Banks and some others, only to find out it was normal.
And yeah, I can understand the "check valve" theory, how it works, and how you can manipulate both the intake and exhaust valves and seats to keep down the reversion.
Long story short, spent some time on the phone with Gale Banks and some others, only to find out it was normal.
And yeah, I can understand the "check valve" theory, how it works, and how you can manipulate both the intake and exhaust valves and seats to keep down the reversion.
08-23-2007, 09:29 AM
#34
this sounds overly simplistic, but you only have limited choices of six bolt heads.
they all flow great, and its a turbo motor.
to be honest, it really doesnt matter. pick one of the six bolt heads with a nice thick deck, pray it stays on, and if it doesnt make enough power... shove more air in there until it does.
they all flow great, and its a turbo motor.
to be honest, it really doesnt matter. pick one of the six bolt heads with a nice thick deck, pray it stays on, and if it doesnt make enough power... shove more air in there until it does.
08-23-2007, 10:01 AM
#35
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Originally Posted by MrDude_1
this sounds overly simplistic, but you only have limited choices of six bolt heads.
they all flow great, and its a turbo motor.
to be honest, it really doesnt matter. pick one of the six bolt heads with a nice thick deck, pray it stays on, and if it doesnt make enough power... shove more air in there until it does.
they all flow great, and its a turbo motor.
to be honest, it really doesnt matter. pick one of the six bolt heads with a nice thick deck, pray it stays on, and if it doesnt make enough power... shove more air in there until it does.
LOL, I like the way you think, but gambling with this kind of price tag is a little stupid. I'd rather do the research and come up with the best theoretical combination, that way if it doesn't make the power I can't say I didn't do my best...
If it was a street car with a T-76 single... you bet I'd just throw it together and turn up the boost!
08-23-2007, 10:11 AM
#36
Originally Posted by Dubnali
LOL, I like the way you think, but gambling with this kind of price tag is a little stupid. I'd rather do the research and come up with the best theoretical combination, that way if it doesn't make the power I can't say I didn't do my best...
If it was a street car with a T-76 single... you bet I'd just throw it together and turn up the boost!
If it was a street car with a T-76 single... you bet I'd just throw it together and turn up the boost!
thing is, its not really a gamble.
you only have a choice of a great head, a great head and a great head.... no one makes a crappy 6bolt head. lol.
your only other options would be:
how do i want to port/modify these castings
or
a totally custom head (like the canted valve ETP)... and thats most likely out just due to price...
if it was me, i would go with the stock castings.. and worse case, if you dont like it, pop off the heads and have them ported... its not like you wont be popping the heads on and off occasionally anyway, its a race motor.
i donno, i suppose im on a "just do it" attitude kick.. i know exactly where you're coming from.. thats a lot of cash to just make a casual decision... but of your choices, i really dont think the head will end up being the deciding factor for this motor. you cant buy a crappy flowing 6bolt head.
