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vegasviper
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You would think with bigger CI we can boost moore?
ViperGTS
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why?
With the volume of air needed to fill 488 Cu In instead of...what? 116 Cu in the effeciency of the blower is going to need to be very good.
Less effeciency means more heat, more heat is a big problem. Aftercoolers either air to air or air to water reduce boost.
I had to overspin my S-trim just to make 9# of boost on my old 383 small block chevy. Going back to a 350 boost jumped 2# with the same pulley ratio. It probably would have pushed 50# on a Honda....it the starter would turn it over
Carl
Less effeciency means more heat, more heat is a big problem. Aftercoolers either air to air or air to water reduce boost.
I had to overspin my S-trim just to make 9# of boost on my old 383 small block chevy. Going back to a 350 boost jumped 2# with the same pulley ratio. It probably would have pushed 50# on a Honda....it the starter would turn it over
Carl
Gerald
Enthusiast
Do you realize how much air is need to make 10# of boost on a 488 c.u. motor vs a 1.3 litre?
Torquemonster
Enthusiast
A *** engine that comes boosted from the factory is typically over-engineered for boost and will tolerate more than 1 bar boost (14.7lb) for a while if tuned right. Not many will like 19lb boost on a stock engine for very long without some significant upgrades however - the Ricer workshops are full of blow ups from clowns that wind the wick up too far.
The *** engine also runs 4 valves per cylinder and double overhead cams - two known efficiency mods where the 4V heads in particular are far less prone to detonation than a typical OHV 2V head.
Having said that - a Viper engine could EASILY be built to take 19 - 22lb boost on pump gas - most easily with twin turbochargers as in the upper boost levels they are head and shoulders ahead of a blower and give far less problems. But where the hell would you drive it?
A properly built twin turbo at that boost range would top 1500hp That might sound impressive - until you tried to use it.
There is a reason Vipers stick between 5 and 12lb boost typically - from 700rwhp on up - things get tricky, and from 900rwhp on up you'll face a near death experience everytime you floor that sucker on a public road either because you can't get traction or because you are going so fast in the upper gears in order to use all that power - anything that goes wrong is likely to be permanent.
I'll consider building my Viper engine adjustable to 1.5 bar on top of atmospheric (22lb) - but you can rest assured I'd never use that level of boost on the street - ever!
There are cars (not Vipers) running 2000hp+ on the street - but they do not see full throttle ever except at the track, and they are useless for anything but a bit of posing and part throttle demos. They run 1000lb valve springs to keep those valves from bouncing and that kind of pressure doesn't like an hour in LA traffic - know what I mean?
The *** engine also runs 4 valves per cylinder and double overhead cams - two known efficiency mods where the 4V heads in particular are far less prone to detonation than a typical OHV 2V head.
Having said that - a Viper engine could EASILY be built to take 19 - 22lb boost on pump gas - most easily with twin turbochargers as in the upper boost levels they are head and shoulders ahead of a blower and give far less problems. But where the hell would you drive it?
A properly built twin turbo at that boost range would top 1500hp
That might sound impressive - until you tried to use it.There is a reason Vipers stick between 5 and 12lb boost typically - from 700rwhp on up - things get tricky, and from 900rwhp on up you'll face a near death experience everytime you floor that sucker on a public road either because you can't get traction or because you are going so fast in the upper gears in order to use all that power - anything that goes wrong is likely to be permanent.
I'll consider building my Viper engine adjustable to 1.5 bar on top of atmospheric (22lb) - but you can rest assured I'd never use that level of boost on the street - ever!
There are cars (not Vipers) running 2000hp+ on the street - but they do not see full throttle ever except at the track, and they are useless for anything but a bit of posing and part throttle demos. They run 1000lb valve springs to keep those valves from bouncing and that kind of pressure doesn't like an hour in LA traffic - know what I mean?
treynor
Enthusiast
I'd jump in here, but Torquemonster beat me to it. Suffice to say you certainly CAN run a lot of boost in a properly-built Viper engine, but you can NOT use the power which results except on the dragstrip, and even then only with a reworked driveline.
The highest boost I ever saw on my DLM RT was 30 PSI... because that was where the gauge maxed out
The highest boost I ever saw on my DLM RT was 30 PSI... because that was where the gauge maxed out
Russ M
Enthusiast
The only reason why a Viper motor cant run very high boost is because of the head bold layout. There is a fairly large gap on the bottom of the cylinder head which is missing a bolt to keep the gasket from popping.
If DLM is making 30psi of boost there must be significant amount of modification made to the motor to make it hold.
Your typical *** motor say a supra 2jz, can withstand 45psi stock, yes you read that correct stock.
But then again there is no reason to make that kind of boost on a properly setup Viper engine. With 488ci on tap a properly set up turbo system can make way more power than the Viper block will hold at 15-20 psi of boost.
If DLM is making 30psi of boost there must be significant amount of modification made to the motor to make it hold.
Your typical *** motor say a supra 2jz, can withstand 45psi stock, yes you read that correct stock.
But then again there is no reason to make that kind of boost on a properly setup Viper engine. With 488ci on tap a properly set up turbo system can make way more power than the Viper block will hold at 15-20 psi of boost.
Physics is the answer. There are many factors that impact the maximum safe boost level. Some that come to mind are the distance the flame travels, which is effectively a time dimension, as flame speeds vary within a relatively small band. The longer the flame travel distance (or time) the greater the potential for detonation or preignition (that is the intake charge furthest from the ignition point is getting pressurized and heated prior to the flame reaching it. At some point it self ignites, in a much more instantaneous event. That event is called detonation, which will damage the engine over time. Detonation also increases the localized temperatures and pressures which can lead to preignition. That is when you hole a piston or otherwise destroy the engine and get a tow home. Other factors such as surface to volume ratio enter into the equation as well as the greater the ratio the more heat transfer can occur. The heat transfer increases the charge temperature, thus reducing the available time for the flame to travel before detonation. Then there is charge motion, which impacts the flame velocity, and a host of other variables.
All things held equal but in different proportions a smaller displacement cylinder will be able to withstand a higher effective compression ratio (or cylinder charge) and lower octane fuel than the larger displacement cylinder.
One way to avoid this paradox is to add cylinders. More complex but a higher specific power potential. Can anyone say V16? Ah, but then friction becomes a larger variable. You just cannot win when competing against physics. In reality you choose the optimal compromise for the intended use. With 525 lb-ft I think the Viper is doing a good job of that.
All things held equal but in different proportions a smaller displacement cylinder will be able to withstand a higher effective compression ratio (or cylinder charge) and lower octane fuel than the larger displacement cylinder.
One way to avoid this paradox is to add cylinders. More complex but a higher specific power potential. Can anyone say V16? Ah, but then friction becomes a larger variable. You just cannot win when competing against physics. In reality you choose the optimal compromise for the intended use. With 525 lb-ft I think the Viper is doing a good job of that.
Torquemonster
Enthusiast
The first upgrade for any big engine that will see higher cylinder pressures is to instill top quality head gaskets with a decent gasket o-ring, the next is to replace head bolts with head studs. That combo will be good for mild boost beyond what a stock gasket and head bolt is good for under sustained wide open throttle.
Beyond that - the fix is to o-ring the block and sometimes even the head, then install copper gaskets that bite into the o-rings upon clamping with the head studs. That setup seals all serious race engines including a Top Fuel engine.
Beyond that - the fix is to o-ring the block and sometimes even the head, then install copper gaskets that bite into the o-rings upon clamping with the head studs. That setup seals all serious race engines including a Top Fuel engine.
You guys are forgetting some of the main reasons.
One main reason that the import engines can run such high boost levels is that they are low compression engines. For example the Mitsu engine comes in 7.8:1 , 8.5:1 and 8.8:1 compression stock. I ran 18psi on pump gas on my mitsu engine for 158,000 miles (10years) and ran 20psi with race gas many times since the car roadraces, autoxs, drag races as well as takes me to work every day. So the engine is very reliable at high boost for a very long time because it's low compression.
Another main reason is that boost is just a measure of the restriction in your intake. With a 2.0l or 3.0l engine you can fill the cylinders really fast and get to the part where there is a restriction. With a 8l V10 you have a lot of cylinder to fill and a huge intake volume to fill.
Another reason is the Octane level. Most domestics are made to run on low Octane just in case the owner decides to use low Octane. That's why chips do much more for domestics than import cars. The import cars are designed to use more risky maps and then add sensors to protect the engine from the owner with the cheap gas. The domestics are more likey to use the maps to protect the engine and then add only a few sensors. With the new Gov regulations coming around 2006 we'll see more and more domestics being able to run high boost.
Another reason is that import engines are inline engines. They aren't V engines and thus can take more stress due to the better bearing design in an inline engine and the fact that the engine isn't trying to pull itself apart.
When you start with those things stock and then spend a little for o-ringing, head gaskets, and forged components which are better than the stock forged components you can run a lot of boost with some high octane gas.
One main reason that the import engines can run such high boost levels is that they are low compression engines. For example the Mitsu engine comes in 7.8:1 , 8.5:1 and 8.8:1 compression stock. I ran 18psi on pump gas on my mitsu engine for 158,000 miles (10years) and ran 20psi with race gas many times since the car roadraces, autoxs, drag races as well as takes me to work every day. So the engine is very reliable at high boost for a very long time because it's low compression.
Another main reason is that boost is just a measure of the restriction in your intake. With a 2.0l or 3.0l engine you can fill the cylinders really fast and get to the part where there is a restriction. With a 8l V10 you have a lot of cylinder to fill and a huge intake volume to fill.
Another reason is the Octane level. Most domestics are made to run on low Octane just in case the owner decides to use low Octane. That's why chips do much more for domestics than import cars. The import cars are designed to use more risky maps and then add sensors to protect the engine from the owner with the cheap gas. The domestics are more likey to use the maps to protect the engine and then add only a few sensors. With the new Gov regulations coming around 2006 we'll see more and more domestics being able to run high boost.
Another reason is that import engines are inline engines. They aren't V engines and thus can take more stress due to the better bearing design in an inline engine and the fact that the engine isn't trying to pull itself apart.
When you start with those things stock and then spend a little for o-ringing, head gaskets, and forged components which are better than the stock forged components you can run a lot of boost with some high octane gas.
poweradded
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i ran 20 psi on the stock blower on my 03 cobra, people are running 30+ psi and a shot of nitrous, in fact one ran 9.49 just the other day...still a pos mustang though
Russ M
Enthusiast
BXRSUPRA,
Well there are not many Japanese motors built like the 2jz with more than 4 cylinders. But there are a few 6 cylinder motors out there that will accomplish the job. The short list;RB26/7mgte granted neither of these is up to the 2jz strength but both are close.
Besides the argument is about holding boost not what a 2jz is capable of.
Well there are not many Japanese motors built like the 2jz with more than 4 cylinders. But there are a few 6 cylinder motors out there that will accomplish the job. The short list;RB26/7mgte granted neither of these is up to the 2jz strength but both are close.
Besides the argument is about holding boost not what a 2jz is capable of.
RussM, you don't have to look far the Buick GN & TTYPE 3.8 turbo motor could run 30 plus lbs of boost. The problem is detonation most people run C16 to C20 racing fuel when wicking it like that. Also remember the motor will not live long with that kind of boost levels. Problem with 10 cylinders would be crank, rods, and head gasket blowing out because that boost level would lift the head etc. In this case smaller V8's like the Ford 302 or 351 or Chevy 350 is a better choice for running big boost.
The only GN motors I have seen running that much boost with a large turbo that could support high HP (800+ HP) have had built motors. There's a big difference between running 30 PSI with a turbo capable of making lots of HP and a small turbo PEAKING at 30 PSI in the lower RPM's but making "only" ~550 or 600 HP.
Supra you are correct but we were talking about boost levels not horespower levels. There is girdle's for the 3.8 and built motors are running in the 9's with the stock block. Most turbo guys are not running no stock turbos, most in the TSM class run T70 turbos.
I hear you on the boost issue. I believe Russ M. is speaking of large turbos when he's talking of stock 2JZ's running 45 PSI. The big difference of course being that it is far more stressfull on an engine to run 30 PSI producing 1000 HP than it is to run 30 PSI producing 600 HP.
9's on a stock block is very impressive. I'm assuming that's what you meant with this line? "There is girdle's for the 3.8 and built motors are running in the 9's with the stock block." If so I was not aware they were running 9's on stock short blocks.
9's on a stock block is very impressive. I'm assuming that's what you meant with this line? "There is girdle's for the 3.8 and built motors are running in the 9's with the stock block." If so I was not aware they were running 9's on stock short blocks.
viper newbie
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O.K. just to straighten out the boost issues for you.
1. boost is not ******* rods and cranks(to an extent)
2.Big motors can run big boost( I have a big block chevy 496 cu.in. with a T-100 that regularly sees 25 psi, with stock rods and crank, good pistons)
3.The valve design only helps efficiency not the ability to make more or less boost.
4.A stock shortblock GN 3.8 can stay together with 30+ psi (been there done that with a T-70) for 40,000 miles
5.2JZ's are incredibly strong. Currently have a 94 twin turbo that is run on a daily basis with 22 psi.
6.You don't have to have O-rings to run that much boost (they are kind of a fail safe) 45+ requires O-rings
7. The two main things to remember about making a turbo motor live on High boost are very simple to understand.
I. STAY AWAY FROM DETONATION. N/A CARS CAN ACCOMMODATE DETONATION. FORCED INDUCTION MAKES IT VERY RISKY.
This is the main reason for blown head gaskets in a turbo application. Thus the reason you run stock or a fel-pro stock replacement gasket. It is much more forgiving to blow a head gasket than break pistons and throw rods.
II.Never even get close to stoichiometric for an N/A car. As this is very lean on a forced induction car. Good air/fuel ratios for most forced induction cars is in the 11.0-11.5:1 area. 12.0 will tend to make the most power but you loose the margin of safety.
Note: lean conditions are the number one cause of detonation in a forced induction car.
I could go on and on, but this post would be 50 pages. I have turboed just about everything that wasn't turboed and have had one of just about everything that was. Please understand that I do not mean to step on anyones feat here, I am simply telling you the very basics of turbo motors and how to make them live. The only other reccomendations I could give you is this for a viper.
1. dome combustion chamber to lower compression
2. run thickest head gasket available to lower compression.
3. run a good timing retard system i.e. MSD 6BTM
4. run overkill on fuel system i.e. if you want 800 hp. use fuel system components for 1000hp (these are crank ratings)
5. tune carefully and slowly (stay very rich and take lots of timing until you reach your desired boost level. Slowly lean out until you reach 11.0-11.5 A/f ratio with out Knock. Then slowly reduce timing retard until you see the slightest bit of knock and go back till you have no knock.
Conclusion of how to Boost 101. Drew
1. boost is not ******* rods and cranks(to an extent)
2.Big motors can run big boost( I have a big block chevy 496 cu.in. with a T-100 that regularly sees 25 psi, with stock rods and crank, good pistons)
3.The valve design only helps efficiency not the ability to make more or less boost.
4.A stock shortblock GN 3.8 can stay together with 30+ psi (been there done that with a T-70) for 40,000 miles
5.2JZ's are incredibly strong. Currently have a 94 twin turbo that is run on a daily basis with 22 psi.
6.You don't have to have O-rings to run that much boost (they are kind of a fail safe) 45+ requires O-rings
7. The two main things to remember about making a turbo motor live on High boost are very simple to understand.
I. STAY AWAY FROM DETONATION. N/A CARS CAN ACCOMMODATE DETONATION. FORCED INDUCTION MAKES IT VERY RISKY.
This is the main reason for blown head gaskets in a turbo application. Thus the reason you run stock or a fel-pro stock replacement gasket. It is much more forgiving to blow a head gasket than break pistons and throw rods.
II.Never even get close to stoichiometric for an N/A car. As this is very lean on a forced induction car. Good air/fuel ratios for most forced induction cars is in the 11.0-11.5:1 area. 12.0 will tend to make the most power but you loose the margin of safety.
Note: lean conditions are the number one cause of detonation in a forced induction car.
I could go on and on, but this post would be 50 pages. I have turboed just about everything that wasn't turboed and have had one of just about everything that was. Please understand that I do not mean to step on anyones feat here, I am simply telling you the very basics of turbo motors and how to make them live. The only other reccomendations I could give you is this for a viper.
1. dome combustion chamber to lower compression
2. run thickest head gasket available to lower compression.
3. run a good timing retard system i.e. MSD 6BTM
4. run overkill on fuel system i.e. if you want 800 hp. use fuel system components for 1000hp (these are crank ratings)
5. tune carefully and slowly (stay very rich and take lots of timing until you reach your desired boost level. Slowly lean out until you reach 11.0-11.5 A/f ratio with out Knock. Then slowly reduce timing retard until you see the slightest bit of knock and go back till you have no knock.
Conclusion of how to Boost 101. Drew
