Compression Ratio
03-17-2006, 11:55 AM
#41
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Originally Posted by zippy
N/A has alot to do with it. That's a whole different set of number calculation I won't go into, but basicly the engine's actual volumetric efficiency has a big effect on gearing.
If he's running a 265/70/16 tire, he's running too much tire. Keep in mind that propper tire choice isn't what looks good on the truck or what you have around. You can gear according to the tire you're using, but that doesn't make it the correct tire.
If he's running a 265/70/16 tire, he's running too much tire. Keep in mind that propper tire choice isn't what looks good on the truck or what you have around. You can gear according to the tire you're using, but that doesn't make it the correct tire.
Please feel free to go into the calculations, I assure you that you wont lose me.
the engine's VE has ZERO to do with gearing. I dont care if its running 3 power adders or none, vehicle velocity and engine rpm are only related by the gear ratio (and tire).
As far as performance goes, you always run the most amount of gear you can run (assuming he isnt road racing this thing and we'ret talking 1/4 mile)
03-17-2006, 01:46 PM
#42
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The correct tire size isn't relavent to the topic at hand when it comes to street driving. Basicly what he's doing is what most of us do, build the vehicle for track with street abilities. With that being the case his gearing and tire choice are based on what he's going to run at the track with, not what he's going to run on the street. The quickest truck on here runs a 30" tall tire and pulls a 1.3 60' time and runs in the 9's. Why would you be basing gearing on a tire that's 31" tall? If you're chosing a tire based on what you want to run and not what you need to run, then yeah, you need more gear than a 4.10.
The formula reguarding an engines V.E. and it's gearing I have at home and honestly don't care to go into posting it. It is very relavant. I'll go into some minor detail giving numbers just off the top of my head.
XXX cubic inch engine
240hp@5200rpm@80% V.E
300hp@5200rpm@100% V.E.
360hp@5200rpm@120% V.E.
Now this same engine has increased it's power level without adding rpm. when dealing with a naturally asperated only setup you keep the gearing the same and only tire as needed for traction purposes. The reason V.E. has an effect on gearing is that you increase power greatly as the efficiency comes up without raising the shift point/trap rpm. Unless there is something actually wrong with the engine you're going to have the same launch rpm and same shift point. The difference in tire size needed between the three is very minimal since the torque at the launch rpm isn't as great of a difference as the power made after the launch. The 80% V.E. engine in something like say a 4100lb 2wd truck will trap around say 87mph and the same engine at 120% V.E. is going to trap around 102mph. You want any of the 3 engines to cross the traps at roughly the same rpm, now how is the engine's V.E. not affecting what gear you'd run?
The formula reguarding an engines V.E. and it's gearing I have at home and honestly don't care to go into posting it. It is very relavant. I'll go into some minor detail giving numbers just off the top of my head.
XXX cubic inch engine
240hp@5200rpm@80% V.E
300hp@5200rpm@100% V.E.
360hp@5200rpm@120% V.E.
Now this same engine has increased it's power level without adding rpm. when dealing with a naturally asperated only setup you keep the gearing the same and only tire as needed for traction purposes. The reason V.E. has an effect on gearing is that you increase power greatly as the efficiency comes up without raising the shift point/trap rpm. Unless there is something actually wrong with the engine you're going to have the same launch rpm and same shift point. The difference in tire size needed between the three is very minimal since the torque at the launch rpm isn't as great of a difference as the power made after the launch. The 80% V.E. engine in something like say a 4100lb 2wd truck will trap around say 87mph and the same engine at 120% V.E. is going to trap around 102mph. You want any of the 3 engines to cross the traps at roughly the same rpm, now how is the engine's V.E. not affecting what gear you'd run?
03-17-2006, 04:07 PM
#43
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Originally Posted by zippy
The correct tire size isn't relavent to the topic at hand when it comes to street driving. Basicly what he's doing is what most of us do, build the vehicle for track with street abilities. With that being the case his gearing and tire choice are based on what he's going to run at the track with, not what he's going to run on the street. The quickest truck on here runs a 30" tall tire and pulls a 1.3 60' time and runs in the 9's. Why would you be basing gearing on a tire that's 31" tall? If you're chosing a tire based on what you want to run and not what you need to run, then yeah, you need more gear than a 4.10.
The formula reguarding an engines V.E. and it's gearing I have at home and honestly don't care to go into posting it. It is very relavant. I'll go into some minor detail giving numbers just off the top of my head.
XXX cubic inch engine
240hp@5200rpm@80% V.E
300hp@5200rpm@100% V.E.
360hp@5200rpm@120% V.E.
Now this same engine has increased it's power level without adding rpm. when dealing with a naturally asperated only setup you keep the gearing the same and only tire as needed for traction purposes. The reason V.E. has an effect on gearing is that you increase power greatly as the efficiency comes up without raising the shift point/trap rpm. Unless there is something actually wrong with the engine you're going to have the same launch rpm and same shift point. The difference in tire size needed between the three is very minimal since the torque at the launch rpm isn't as great of a difference as the power made after the launch. The 80% V.E. engine in something like say a 4100lb 2wd truck will trap around say 87mph and the same engine at 120% V.E. is going to trap around 102mph. You want any of the 3 engines to cross the traps at roughly the same rpm, now how is the engine's V.E. not affecting what gear you'd run?
The formula reguarding an engines V.E. and it's gearing I have at home and honestly don't care to go into posting it. It is very relavant. I'll go into some minor detail giving numbers just off the top of my head.
XXX cubic inch engine
240hp@5200rpm@80% V.E
300hp@5200rpm@100% V.E.
360hp@5200rpm@120% V.E.
Now this same engine has increased it's power level without adding rpm. when dealing with a naturally asperated only setup you keep the gearing the same and only tire as needed for traction purposes. The reason V.E. has an effect on gearing is that you increase power greatly as the efficiency comes up without raising the shift point/trap rpm. Unless there is something actually wrong with the engine you're going to have the same launch rpm and same shift point. The difference in tire size needed between the three is very minimal since the torque at the launch rpm isn't as great of a difference as the power made after the launch. The 80% V.E. engine in something like say a 4100lb 2wd truck will trap around say 87mph and the same engine at 120% V.E. is going to trap around 102mph. You want any of the 3 engines to cross the traps at roughly the same rpm, now how is the engine's V.E. not affecting what gear you'd run?
Estimate your trap speed, find your redline, pick the correct gear. VE is torque.
Regardless, your whole assumption is wrong.
If ANYTHING, NA will have the LEAST amount of variation in VE between engines. Power NA is going to come from Revs, given a displacement. VE varriance is going to be HUGE in boosted engines.
Unless you're a damn good engine builder (read: professional. Get paid tons of money to pick a cam), you aren't going to top 105ish VE NA. And the higher your VE, the sharper the torqueband will be (more peak, less flat). In order to get near and over 100VE, you have to do a LOT of things correct and time the harmonics/pulses of the engine. Your intake lengths will generally only be "right" for a small range.
I'm willing to bet there aren't many NA engines on this forum topping 105VE. I honestly doubt there are any. If I had to guess, 95% of them fall between 80ish (stock) and 95VE. 120 VE numbers are insane. 120 VE is sheetmetal intakes, custom tuned headers etc.
Boosted engines can range from 100 to well over 200VE.
03-17-2006, 04:59 PM
#44
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Over 100% V.E. is from boost or nitrous. I'm not assuming anyone on here is going to have 100% V.E. on a naturally asperated engine. An engine's V.E. is essentially calculated by how much air it can get into each cylinder per intake stroke. The more air you get in there, the more power it will make. You also say V.E. is torque and that trap speed is measured by power, not torque. This may seem odd, but torque at a peticular rpm is calculated into HP. That's kinda how it works. 
Now let me understand your way of thinking on picking your gear. You pick whatever tire looks good on the truck and from there you pick the gear?
I say you pick the tire that it's going to take to launch at the power level you're going to be launching at, then pick your gear to match your estimated trap speed with the rpm you want to cross at.
Now let me understand your way of thinking on picking your gear. You pick whatever tire looks good on the truck and from there you pick the gear?
I say you pick the tire that it's going to take to launch at the power level you're going to be launching at, then pick your gear to match your estimated trap speed with the rpm you want to cross at.
03-17-2006, 06:42 PM
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Originally Posted by zippy
Over 100% V.E. is from boost or nitrous. I'm not assuming anyone on here is going to have 100% V.E. on a naturally asperated engine. An engine's V.E. is essentially calculated by how much air it can get into each cylinder per intake stroke. The more air you get in there, the more power it will make. You also say V.E. is torque and that trap speed is measured by power, not torque. This may seem odd, but torque at a peticular rpm is calculated into HP. That's kinda how it works.
Now let me understand your way of thinking on picking your gear. You pick whatever tire looks good on the truck and from there you pick the gear?
I say you pick the tire that it's going to take to launch at the power level you're going to be launching at, then pick your gear to match your estimated trap speed with the rpm you want to cross at.
Now let me understand your way of thinking on picking your gear. You pick whatever tire looks good on the truck and from there you pick the gear?
I say you pick the tire that it's going to take to launch at the power level you're going to be launching at, then pick your gear to match your estimated trap speed with the rpm you want to cross at.
It has been made exceptionally clear to me that you are repeating what someone else told you, with no actual understanding of how this whole thing words. Your close, but still far.
You dont pick gears based off VE. Really, all you need is a remotely close guesstimate of trap speeds and the redline (point where engine torque*next gear ratio = engine torque* current gear ratio; or where you will accelerate faster in the next gear assuming we aren't worried about things breaking). There would be a bit more to it if you had your choice of any gear ratio, but since we are forced to choose from a relatively limited number of ratios (3.73s, 3.90, 4.10), its not that hard to pick the "right" one.
This should also compliment your stall speed. Higher revvers need more stall and more gear. Higher stall needs more more gear to get off the line. big stalls and tall gears are a mess, sometimes litterally. Anyway, gearing it up is THE WHOLE POINT of revving higher.
Making 400ft lbs at 5000rpm instead of 2500rpm will get you a ton more power. If you use the same gear ratios, all those revs are essentially pointless. The idea behind making your force at a higher velocity is that you can send it through a transformer (gears) and "exchange" the velocity for force.
Look up what a transformer does. Force * velocity in = Force * velocity out, assuming its an ideal transformer. Force = mass times acceleration.
NA, Boosted, VE, mother maiden name, and lunar position aren't needed to pick a gear.
PS: Force * velocity = power. Suprised? Dyno a car in each gear. Tell me which gear makes the most power.
Then lie to the computer about your gear ratio. run again. Tell me what happens.
03-17-2006, 10:48 PM
#46
Easy...
Trey you're understanding of VE seems a bit off to me, but you don't seem all that receptive to actual conversation as an exchange of information.
Sounds to me like you're advocating picking the tallest gear you can (i.e. one size fits all) regardless of NA, FI, cam, heads, etc. I certainly wouldn't pick gears like that and expect to win (let alone have a drivable DD). Just my $.02
Trey you're understanding of VE seems a bit off to me, but you don't seem all that receptive to actual conversation as an exchange of information.
Sounds to me like you're advocating picking the tallest gear you can (i.e. one size fits all) regardless of NA, FI, cam, heads, etc. I certainly wouldn't pick gears like that and expect to win (let alone have a drivable DD). Just my $.02
03-18-2006, 12:24 AM
#47
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The comment about go with the biggest gear you can couldn't be more wrong.
Let's lay some ground rules here. I *will* be running 31" tires on the street, I'm not changing them. Period, end of story. At the track, I currently have some 27" slick. They will be that way for a while.
THe truck isn't being made for the track, but be drivable, it's being made as a fast daily drivable, functional TRUCK that just happens to be fast. In other words, it must be reliable and functional as a truck to get me and my **** in the bed or attatched to the hitch before it's a race truck.
Trey, like Erik said .. you seem to not be at all receptive to other points of view. Power level has EVERYTHING to do with gear selection. If you have no idea of what kind of power you're looking out, where are you pulling this magic trap speed number from?
Further more ... this is WAY off topic, all this has nothing to do with compression and how much is safe on pump gas running a big *** cam.
Let's lay some ground rules here. I *will* be running 31" tires on the street, I'm not changing them. Period, end of story. At the track, I currently have some 27" slick. They will be that way for a while.
THe truck isn't being made for the track, but be drivable, it's being made as a fast daily drivable, functional TRUCK that just happens to be fast. In other words, it must be reliable and functional as a truck to get me and my **** in the bed or attatched to the hitch before it's a race truck.
Trey, like Erik said .. you seem to not be at all receptive to other points of view. Power level has EVERYTHING to do with gear selection. If you have no idea of what kind of power you're looking out, where are you pulling this magic trap speed number from?
Further more ... this is WAY off topic, all this has nothing to do with compression and how much is safe on pump gas running a big *** cam.
03-18-2006, 02:31 AM
#48
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I'm not repeating what someone told me, I've taken the time to learn all of this and more many years ago. I can't believe you'd think that a high revving engine is going to need more gear. A 4.8L for example that makes 400hp and revs to 7k has no reason to need more gear than say a 408 that makes 400hp and only turns 5500. The 408 needs more tire due to the extra torque. The shorter tire is where the extra rpm is going to come from.
Flyer, going with a 4.10 gear and using the cam that you were looking into with your tire size it would put you able to be crossing the traps at 6500@127 if you had the converter locked. With the power level of a 408 built to the spec's you were looking into I'd guess you'll be crossing at around 122-125 which would put you around 6500 crossing the traps with the converter unlocked. I'd say that would be a great combo in your truck.
On to your compression issue, this reminds me of a Nova that was in Hot Rod Magazine a few years ago. He was running a 406 with 14.5:1 compression on pump gas. He even drove it on the power tour that way. It had no problems running mid to high 10's on the pump gas and low 10's with race fuel added and the timing moved accordingly. His trick to running that high of compression was to keep the engine under as little load as possible and as cool a possible. He was running something like a 5.13 gear with a 5500 stall and some outstanding radiator with Evans cooling system coolant to keep the temp at a consistant 160. This was all done without a pcm, all old school stuff. I'd say 12.5:1 could even be ran with todays technology. You could do alot of dyno tuning to get the dragstrip tune where you wanted it, but you'll be spending most of your time on the street tuning using the ECT and IAT spark adding and subtracting tables. Those tables alone allow for considerable control of your timing based on heat which is where most KR* is created from. You can also add more fuel in the PE table based on ECT and IAT to help richen it up when the engine is getting hotter or the underhood temps are getting hot to assist in cooling it down. Both of these area's are things in the tune that can increase your success in running as much timing as possible all the time without worrying about KR* because of it being hot out or the engine being under alot of load causing high underhood temperatures.
Another area where you can help yourself out with running high compression on pump gas is in the trans tables. The TCC table will allow you to run the converter unlocked at low speeds to keep low rpm heavy loads which are the main cause for KR*. The TCC table will also allow you to unlock the converter as soon as the engine begins to load itself heavily, again a main cause for KR*. You can also spend alot of time in the part throttle shift points to keep the engine from being in too high of a gear causing low rpm heavy loads. Over the time that I've spent tuning, I've gotten to see about every aftermarket mail order tuning and these area's are almost always left stock. (the tcc table, part throttle shift table, ect timing and pe table, and iat spark timing and pe). If i recall you're doing all of your own tuning so that isn't going to be a problem, but I'd just highly recomend that you get familier with those tables if you aren't already. Those with the right tuning can get you excellent results running pump gas on higher octane.
Stay away from dome pistons for sure as they are good for causing KR*. Run a small chamber head and a flat top piston to get your desired compression ratio. That will also be a big help in your goal. Run the coolest thermostat you can find and if at all possible put a cowl induction hood on the truck. You'll be amazed at the difference in underhood heat. In testing i've found one customers truck to drop underhoood temperatures almost 40 degrees by installing a cowl induction hood with no underhood liner. They release the heat very well.
I certainly like your idea for the 408. I'm hoping to get an 03'-05' truck next year to do the same. I'd like a black regular cab 2wd with around 12.7:1 compression and a 408. I figure that built right it could go a low 11 rather easily and with a 100 shot mid 10's would be attainable. I've driven a couple of naturally asperated 408 trucks and man I tell you, the torque is awsome. It is available at just about any rpm.
Just a few thoughts i figured I'd post concerning the topic at hand. I'm open for discussion on them.
Flyer, going with a 4.10 gear and using the cam that you were looking into with your tire size it would put you able to be crossing the traps at 6500@127 if you had the converter locked. With the power level of a 408 built to the spec's you were looking into I'd guess you'll be crossing at around 122-125 which would put you around 6500 crossing the traps with the converter unlocked. I'd say that would be a great combo in your truck.
On to your compression issue, this reminds me of a Nova that was in Hot Rod Magazine a few years ago. He was running a 406 with 14.5:1 compression on pump gas. He even drove it on the power tour that way. It had no problems running mid to high 10's on the pump gas and low 10's with race fuel added and the timing moved accordingly. His trick to running that high of compression was to keep the engine under as little load as possible and as cool a possible. He was running something like a 5.13 gear with a 5500 stall and some outstanding radiator with Evans cooling system coolant to keep the temp at a consistant 160. This was all done without a pcm, all old school stuff. I'd say 12.5:1 could even be ran with todays technology. You could do alot of dyno tuning to get the dragstrip tune where you wanted it, but you'll be spending most of your time on the street tuning using the ECT and IAT spark adding and subtracting tables. Those tables alone allow for considerable control of your timing based on heat which is where most KR* is created from. You can also add more fuel in the PE table based on ECT and IAT to help richen it up when the engine is getting hotter or the underhood temps are getting hot to assist in cooling it down. Both of these area's are things in the tune that can increase your success in running as much timing as possible all the time without worrying about KR* because of it being hot out or the engine being under alot of load causing high underhood temperatures.
Another area where you can help yourself out with running high compression on pump gas is in the trans tables. The TCC table will allow you to run the converter unlocked at low speeds to keep low rpm heavy loads which are the main cause for KR*. The TCC table will also allow you to unlock the converter as soon as the engine begins to load itself heavily, again a main cause for KR*. You can also spend alot of time in the part throttle shift points to keep the engine from being in too high of a gear causing low rpm heavy loads. Over the time that I've spent tuning, I've gotten to see about every aftermarket mail order tuning and these area's are almost always left stock. (the tcc table, part throttle shift table, ect timing and pe table, and iat spark timing and pe). If i recall you're doing all of your own tuning so that isn't going to be a problem, but I'd just highly recomend that you get familier with those tables if you aren't already. Those with the right tuning can get you excellent results running pump gas on higher octane.
Stay away from dome pistons for sure as they are good for causing KR*. Run a small chamber head and a flat top piston to get your desired compression ratio. That will also be a big help in your goal. Run the coolest thermostat you can find and if at all possible put a cowl induction hood on the truck. You'll be amazed at the difference in underhood heat. In testing i've found one customers truck to drop underhoood temperatures almost 40 degrees by installing a cowl induction hood with no underhood liner. They release the heat very well.
I certainly like your idea for the 408. I'm hoping to get an 03'-05' truck next year to do the same. I'd like a black regular cab 2wd with around 12.7:1 compression and a 408. I figure that built right it could go a low 11 rather easily and with a 100 shot mid 10's would be attainable. I've driven a couple of naturally asperated 408 trucks and man I tell you, the torque is awsome. It is available at just about any rpm.
Just a few thoughts i figured I'd post concerning the topic at hand. I'm open for discussion on them.
03-18-2006, 05:13 AM
#49
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Originally Posted by zippy
On to your compression issue, this reminds me of a Nova that was in Hot Rod Magazine a few years ago. He was running a 406 with 14.5:1 compression on pump gas. He even drove it on the power tour that way. It had no problems running mid to high 10's on the pump gas and low 10's with race fuel added and the timing moved accordingly. His trick to running that high of compression was to keep the engine under as little load as possible and as cool a possible. He was running something like a 5.13 gear with a 5500 stall and some outstanding radiator with Evans cooling system coolant to keep the temp at a consistant 160. This was all done without a pcm, all old school stuff. I'd say 12.5:1 could even be ran with todays technology. You could do alot of dyno tuning to get the dragstrip tune where you wanted it, but you'll be spending most of your time on the street tuning using the ECT and IAT spark adding and subtracting tables. Those tables alone allow for considerable control of your timing based on heat which is where most KR* is created from. You can also add more fuel in the PE table based on ECT and IAT to help richen it up when the engine is getting hotter or the underhood temps are getting hot to assist in cooling it down. Both of these area's are things in the tune that can increase your success in running as much timing as possible all the time without worrying about KR* because of it being hot out or the engine being under alot of load causing high underhood temperatures.
I know of very respectible engine builders that will still tell you today that you can't run more than 9:1 on 93 on an DD. They are old guys that are still stuck on the combustion chambers that looked like a square block with and arch on one end and .070" quench area. Man times have changed.
03-18-2006, 09:28 AM
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Originally Posted by TurboBerserker
Easy...
Trey you're understanding of VE seems a bit off to me, but you don't seem all that receptive to actual conversation as an exchange of information.
Sounds to me like you're advocating picking the tallest gear you can (i.e. one size fits all) regardless of NA, FI, cam, heads, etc. I certainly wouldn't pick gears like that and expect to win (let alone have a drivable DD). Just my $.02
Trey you're understanding of VE seems a bit off to me, but you don't seem all that receptive to actual conversation as an exchange of information.
Sounds to me like you're advocating picking the tallest gear you can (i.e. one size fits all) regardless of NA, FI, cam, heads, etc. I certainly wouldn't pick gears like that and expect to win (let alone have a drivable DD). Just my $.02
How much gear you are willing to put up with is totally different than what will make you run the fastest. Its pretty simple, more gear = more torque = more accelertion. just dont run out of revs by the end of the track!