3.29s or 3.69s?
12-13-2010, 11:58 PM
#21
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Yeah, that's long before mine... I'll hopefully be ordering my cam soon, after I do my exhaust, though, and kinda just leaving it in the bedroom to look at...
12-14-2010, 12:51 AM
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Contrary to popular belief I do know what I'm talking about. You're just assuming these things. A steeper gear will ALWAYS effect lateral acceleration traction adversely in 2wd vehicles. You're not going to spin a 4x4 under power on a dry road. They suggest the lower gear for offroad and adverse conditions because it allows you to apply the same amount of power at a lower speed so that you can navigate the obstacles more safely. It's not for lateral traction like we're talking about here. There's absolutely no way that going to a GREATER multiplication of torque is going to AID traction.
that all but good luck in your build i cant wait to see it run in person
12-14-2010, 08:32 AM
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Is this car your DD? Do you have DOD? If yes to both of those questions, I would go with the 3.29's because of the gas mileage issue. You might want to look at what application will be better if you are going to spray it. I would imagine a smaller gear ratio would be better with the juice because of the where the gears will move the power band and you could get more out of it. When my tranny craps out on me, I plan on getting a TEP close to MPgeagle's specs. I have already began the saving process and I almost have the funds right now.
12-14-2010, 09:02 AM
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No DoD for a long time now. Gas mileage isn't a concern, I have been a fan of taller gears for bottled cars for a long time because of its effect on the power band. However, when you look at more normal applicatoons, the fdr is in the mind 3.xx:1 range. If traction isn't an issue I don't see where the difference would be.
12-14-2010, 12:28 PM
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Kinda off topic but don't the make a LSD for our cars? And doesn't the comp G come with the 3.29 gearing factory? And with even taller gears wouldn't you be able to adjust the shifts and rpms to match?
12-14-2010, 02:53 PM
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If the 3.69s put you at the top of third going through the traps and drag racing is your main concern, then that's what I would go with. 3.29s are a nice compromise but why compromise?
12-14-2010, 03:02 PM
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I have a friend that had 3.69's in his supercharged Regal (400whp) and he was out of first under normal throttle at about 5 - 7 mph. First gear is a complete waste with the 3.69's. It shifts into second really early. If it was me, I'd stick with 3.29's. You'll still be able to rip 12.(?) second quarter mile times with the 3.29's. With 3.69's your gas milage will be 24% less than it is right now. Good luck with whatever you choose AG.
-Mike
-Mike
12-15-2010, 12:04 PM
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I would recommend the 3.69s for your intended usage. Here are a few reasons why:
1) You should always change gears with a bigger cam, and 3.69s aren't really that steep in the N/A drag world.
2) You probably already have traction issues in 1st. It's better to just get them out of the way early in the pass.
3) Depending on the size of the cam, you might actually need the 3.69s to get the car moving off the line.
4) If you did keep DOD, you would likely get better highway mileage with 3.69s because you could stay in DOD more. They are a better rev match for a 4 cylinder. City mileage is going to go to hell with a big cam no matter what you do.
I disagree... I think that data point doesn't apply here for two big reasons. One, S/C 3800s are torque monsters and eventually run out of steam up top. A cammed V8 has exactly the opposite characteristics. Two, the low speed gear changes are a tuning issue. I'm running (essentially) the stock 1->2 and 2->3 shift mph (ie not scaled for 3.29s) to match powerband of my engine. Also, where did you come up with 24%? Depending on cam size and driving behavior he could easily get worse mileage with 2.93s than with 3.69s. The cam will move the BSFC surface to the right (higher in the RPM range) along with the torque curve.
For my application, I think 3.69s would be a better match to my engine for acceleration. I don't think advancing my cam will change that. 3.29s are still much better than 2.93s, and a good compromise for a daily driver.
1) You should always change gears with a bigger cam, and 3.69s aren't really that steep in the N/A drag world.
2) You probably already have traction issues in 1st. It's better to just get them out of the way early in the pass.
3) Depending on the size of the cam, you might actually need the 3.69s to get the car moving off the line.
4) If you did keep DOD, you would likely get better highway mileage with 3.69s because you could stay in DOD more. They are a better rev match for a 4 cylinder. City mileage is going to go to hell with a big cam no matter what you do.
I have a friend that had 3.69's in his supercharged Regal (400whp) and he was out of first under normal throttle at about 5 - 7 mph. First gear is a complete waste with the 3.69's. It shifts into second really early. If it was me, I'd stick with 3.29's. You'll still be able to rip 12.(?) second quarter mile times with the 3.29's. With 3.69's your gas milage will be 24% less than it is right now. Good luck with whatever you choose AG.
-Mike
-Mike
I disagree... I think that data point doesn't apply here for two big reasons. One, S/C 3800s are torque monsters and eventually run out of steam up top. A cammed V8 has exactly the opposite characteristics. Two, the low speed gear changes are a tuning issue. I'm running (essentially) the stock 1->2 and 2->3 shift mph (ie not scaled for 3.29s) to match powerband of my engine. Also, where did you come up with 24%? Depending on cam size and driving behavior he could easily get worse mileage with 2.93s than with 3.69s. The cam will move the BSFC surface to the right (higher in the RPM range) along with the torque curve.
For my application, I think 3.69s would be a better match to my engine for acceleration. I don't think advancing my cam will change that. 3.29s are still much better than 2.93s, and a good compromise for a daily driver.
12-15-2010, 12:57 PM
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I think it depends on what was done to the S/C 3800 which decides if it runs out of steam up top or not. After he put the 3.69's in and had it for a while he was kicking himself by not going with the 3.29's. By deleteing DOD there is a 12% drop in gas milage right there. And with the steeper gearing it will easily drop off another 10%. Intense and ZZP even tell you your gas milage will drop by going from 2.93's to either 3.29's or 3.69's. If it will be just a 1/4 mile car then by all means go with the 3.69's. If it was me I'd rather have good driveability and decent gas milage. With the 3.29's I think you get both of best worlds. Of course this is just my opinion. Whatever AG chooses I am sure he'll be happy with.
-Mike
-Mike
12-15-2010, 01:29 PM
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I think it depends on what was done to the S/C 3800 which decides if it runs out of steam up top or not. After he put the 3.69's in and had it for a while he was kicking himself by not going with the 3.29's. By deleteing DOD there is a 12% drop in gas milage right there. And with the steeper gearing it will easily drop off another 10%. Intense and ZZP even tell you your gas milage will drop by going from 2.93's to either 3.29's or 3.69's. If it will be just a 1/4 mile car then by all means go with the 3.69's. If it was me I'd rather have good driveability and decent gas milage. With the 3.29's I think you get both of best worlds. Of course this is just my opinion. Whatever AG chooses I am sure he'll be happy with.
-Mike
-Mike
Back on topic, if you are going with a large cam you are gonna want 3.69's. you already said mileage and traction aren't going to be a problem....Please let me know if you need me to go into more detail.
12-15-2010, 03:29 PM
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Don't worry I won't comment about this again. I know, I am a dumb ****....(sarcasm...)
His car would beat the **** out of all our cars on here (besides turbo.) Honestly, I don't care what people do anymore....! Good luck with whatever... This isn't directed towards you AG.
-Mikw
His car would beat the **** out of all our cars on here (besides turbo.) Honestly, I don't care what people do anymore....! Good luck with whatever... This isn't directed towards you AG.
-Mikw
12-15-2010, 04:51 PM
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Mike, there is no reason to get angry because someone disagrees with you. It's a forum, and no one said anything about you personally. I make no apologies for disagreeing, or for stating a few points to back up why I disagree.
Forget V6 vs. V8, etc. The comparison is supercharged engine vs. big cam engine, and they are very different. A positive displacement supercharger builds nearly instant pressure at low RPMs, but as RPMs climb the heat made begins to offset the gains. These engines have their minimum BSFC (Brake Specific Fuel Consumption) at lower RPMs than comparable N/A engines. By comparable, I mean a larger displacement engine with a "mild" camshaft. Think supercharged small block vs. mild cam N/A big block... similar mileage, torque curves, and gearing needs.
The bigger the cam, the farther to the right the power band moves, and minimum BSFC moves with it. This also means that torque production at low RPMs drops off, etc. All of this points to needing a higher gear ratio to keep up your torque at the wheels. People always debate torque vs. horsepower, but the simple answer is answer is torque at the wheels is king. You can make that torque outright with displacement or supercharging or you can make that torque at the wheels by moving engine torque up in the RPM band with a cam, making more power, and combine that with a steeper gear ratio to get more torque at the wheels.
For any given engine, transmission, tire size and driving style there is an optimum gear ratio. 4 bangers usually come with cams that are relatively bigger than V8s to up their power, and are run with steeper gears for both acceleration and fuel economy. Running shorter gears can hurt fuel economy depending on the engine's characteristics. AB has already deleted DOD, so that's out (GM cites 6-8% gain from DOD, too). The ~7% fuel economy loss you see quoted on those sites is refering to the observed results from a supercharged V6 and may or may not apply to any given situation. I think claiming a 24% loss is excessive, especially because my average fuel economy increased a bit when I went from 2.93s to 3.29s. I'm not claiming that will be the case for everyone, but it was for me. Now the cam cost me a couple MPGs, but a lot of that is because of how much BSFC increased at lower RPMs. I haven't looked hard, but once I'm above about 2000 RPM my mileage is the same or slightly better than stock.
As to your point that your buddies S/C 3800 car is faster, that may be. I have consistently said that if you want to drag race a W-Body, start with the N/A 3800 to keep you initial cost down and go turbo or do a top swap. I've also never heard of a S/C 3800 that was still pulling hard at 7000 RPM for a lot of reasons (not the least of which is the oiling system which carries over from the small block Buick V8 design the engine is based on), and it doesn't need to because you can make good power under 6000 RPM with forced induction.
Forget V6 vs. V8, etc. The comparison is supercharged engine vs. big cam engine, and they are very different. A positive displacement supercharger builds nearly instant pressure at low RPMs, but as RPMs climb the heat made begins to offset the gains. These engines have their minimum BSFC (Brake Specific Fuel Consumption) at lower RPMs than comparable N/A engines. By comparable, I mean a larger displacement engine with a "mild" camshaft. Think supercharged small block vs. mild cam N/A big block... similar mileage, torque curves, and gearing needs.
The bigger the cam, the farther to the right the power band moves, and minimum BSFC moves with it. This also means that torque production at low RPMs drops off, etc. All of this points to needing a higher gear ratio to keep up your torque at the wheels. People always debate torque vs. horsepower, but the simple answer is answer is torque at the wheels is king. You can make that torque outright with displacement or supercharging or you can make that torque at the wheels by moving engine torque up in the RPM band with a cam, making more power, and combine that with a steeper gear ratio to get more torque at the wheels.
For any given engine, transmission, tire size and driving style there is an optimum gear ratio. 4 bangers usually come with cams that are relatively bigger than V8s to up their power, and are run with steeper gears for both acceleration and fuel economy. Running shorter gears can hurt fuel economy depending on the engine's characteristics. AB has already deleted DOD, so that's out (GM cites 6-8% gain from DOD, too). The ~7% fuel economy loss you see quoted on those sites is refering to the observed results from a supercharged V6 and may or may not apply to any given situation. I think claiming a 24% loss is excessive, especially because my average fuel economy increased a bit when I went from 2.93s to 3.29s. I'm not claiming that will be the case for everyone, but it was for me. Now the cam cost me a couple MPGs, but a lot of that is because of how much BSFC increased at lower RPMs. I haven't looked hard, but once I'm above about 2000 RPM my mileage is the same or slightly better than stock.
As to your point that your buddies S/C 3800 car is faster, that may be. I have consistently said that if you want to drag race a W-Body, start with the N/A 3800 to keep you initial cost down and go turbo or do a top swap. I've also never heard of a S/C 3800 that was still pulling hard at 7000 RPM for a lot of reasons (not the least of which is the oiling system which carries over from the small block Buick V8 design the engine is based on), and it doesn't need to because you can make good power under 6000 RPM with forced induction.
12-16-2010, 06:18 AM
#35
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It just makes me wonder if anyone on here has driven or ridden in a "fwd" with 3.69's? Well, from personal experience those "sites" are correct. Before my mods (stock) I got 20.2 miles per gallon, after all the mods I now have a whopping 13.2 mpg. Seems like a mpg loss to me but again I am no scientist...
I actually discussed this situation with the guy who owns the Regal and he told me if he put's 3.69's in his car you can forget 1st gear and the torque steer is awful. It is way worse than a car with 2.93's or 3.29's. I was just talking from "personal experience" because I have ridden in both cars. Oh, and you do not know what is done to his (s/c v-6) car to make assumptions. Just because it's a different engine doesn't mean it can't behave in a similar manner. Like I said people can do whatever they want as I don't really care. I was just trying to help out a friend.
-Mike
I actually discussed this situation with the guy who owns the Regal and he told me if he put's 3.69's in his car you can forget 1st gear and the torque steer is awful. It is way worse than a car with 2.93's or 3.29's. I was just talking from "personal experience" because I have ridden in both cars. Oh, and you do not know what is done to his (s/c v-6) car to make assumptions. Just because it's a different engine doesn't mean it can't behave in a similar manner. Like I said people can do whatever they want as I don't really care. I was just trying to help out a friend.
-Mike
12-16-2010, 02:24 PM
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Mike, I don't agree with your numbers or assumptions, and all I have done is state that and post some data to back it up my points. For someone who is taking a lot of offense to a percieved slight in a post with a counterpoint, you are certainly comfortable implying a lot about me.
Here is my mileage break down (Highways are 70mph in MI, most major roads are 45mph in SE MI):
Stock: 19.5 - 20.5 (19.8 Typically)
3.29s Only: 19.4 (One week only, and I was horsing it)
3.29s and LS6 Intake: 21 - 22.5
3.29s, LS6 Intake, 224/232 Cam, Headers, etc (DOD Off, DCFCO Off): 12 - 13
3.29s, LS6 Intake, 224/232 Cam, Headers, etc (DOD On, DCFCO Off): 16.5 - 19
3.29s, LS6 Intake, 224/232 Cam, Headers, etc (DOD On, DCFCO On): 18 - 19.5
13.2 mpg sucks for the power/acceleration mods in your sig (FWI, Rockers, Headers, !Cat, 3.29s), so I would look extremely hard at your tune. Also, that 160* thermostat could be causing some serious issues. I won't even look at logged data with a coolant temp below 190* and intake valve temp below 320* because the fuel doesn't properly atomize when it hits the intake valve. The closed loop switching voltage is still rich at 160* (600mV instead of 475mV), and there is a minimum temperature for TCC lock-up that you are probably not hitting until you've driven for longer that you would have to when stock.
Shifting Strategy:
1st Gear and Final Drive for Comparable Cars (with lower horsepower and torque, but see my next point):
3.06 x 2.93 = 8.97 (Stock LS4)
3.06 x 3.29 = 10.07 (3.29s)
3.06 x 3.69 = 11.29* (3.69s)
4.48 x 2.77 = 12.41 (Stock V6 Malibu)
3.58 x 3.84 = 13.75 (Stock Cobalt SS, Manual, no torque multiplication, I know...)
RWD Cars that don't have torque steer, but do have similar shift points:
4.06 x 3.27 = 13.15 (Stock 2010 Camaro SS, bigger wheels, but this is direction that things are going!)
2.92 x 4.11 = 12.00 (Built F-Body with 4.11s and 4L60, Included because shift points are almost the same as a 4T65)
The * indicates the combo I have not personally driven. The Malibu does not shift at 5-7 mph, and Cobalt doesn't need to be shifted either. If I kept looking I could find plenty more cars, especially now that 6 speeds are becoming more common. Again, I would look hard at any tune that shifts at 5-7 mph. As for forgetting first gear, well, that's drag racing. AB wasn't asking about parking lot manners.
Torque steer:
It's a bitch.
If your buddies' S/C V6 W-Body doesn't make big torque at 2000 RPM and pull hard to 6000 RPM, I'll conceed that your buddy has a unique combo that is outside of my experience. If the torque curve of his S/C V6 looks anything like mine, which builds from 3200 RPM to 5800 RPM and doesn't fall off hard until well past 7000 RPM, I'll eat a healthy serving of crow.
I firmly believe that for the combo AB has described, 3.69s will give the lowest ET. I agree that 3.29s would be better for highway mileage, but he said he doesn't care about that and 3.69s will not be 24% worse than 3.29s.
Here is my mileage break down (Highways are 70mph in MI, most major roads are 45mph in SE MI):
Stock: 19.5 - 20.5 (19.8 Typically)
3.29s Only: 19.4 (One week only, and I was horsing it)
3.29s and LS6 Intake: 21 - 22.5
3.29s, LS6 Intake, 224/232 Cam, Headers, etc (DOD Off, DCFCO Off): 12 - 13
3.29s, LS6 Intake, 224/232 Cam, Headers, etc (DOD On, DCFCO Off): 16.5 - 19
3.29s, LS6 Intake, 224/232 Cam, Headers, etc (DOD On, DCFCO On): 18 - 19.5
13.2 mpg sucks for the power/acceleration mods in your sig (FWI, Rockers, Headers, !Cat, 3.29s), so I would look extremely hard at your tune. Also, that 160* thermostat could be causing some serious issues. I won't even look at logged data with a coolant temp below 190* and intake valve temp below 320* because the fuel doesn't properly atomize when it hits the intake valve. The closed loop switching voltage is still rich at 160* (600mV instead of 475mV), and there is a minimum temperature for TCC lock-up that you are probably not hitting until you've driven for longer that you would have to when stock.
Shifting Strategy:
1st Gear and Final Drive for Comparable Cars (with lower horsepower and torque, but see my next point):
3.06 x 2.93 = 8.97 (Stock LS4)
3.06 x 3.29 = 10.07 (3.29s)
3.06 x 3.69 = 11.29* (3.69s)
4.48 x 2.77 = 12.41 (Stock V6 Malibu)
3.58 x 3.84 = 13.75 (Stock Cobalt SS, Manual, no torque multiplication, I know...)
RWD Cars that don't have torque steer, but do have similar shift points:
4.06 x 3.27 = 13.15 (Stock 2010 Camaro SS, bigger wheels, but this is direction that things are going!)
2.92 x 4.11 = 12.00 (Built F-Body with 4.11s and 4L60, Included because shift points are almost the same as a 4T65)
The * indicates the combo I have not personally driven. The Malibu does not shift at 5-7 mph, and Cobalt doesn't need to be shifted either. If I kept looking I could find plenty more cars, especially now that 6 speeds are becoming more common. Again, I would look hard at any tune that shifts at 5-7 mph. As for forgetting first gear, well, that's drag racing. AB wasn't asking about parking lot manners.
Torque steer:
It's a bitch.
If your buddies' S/C V6 W-Body doesn't make big torque at 2000 RPM and pull hard to 6000 RPM, I'll conceed that your buddy has a unique combo that is outside of my experience. If the torque curve of his S/C V6 looks anything like mine, which builds from 3200 RPM to 5800 RPM and doesn't fall off hard until well past 7000 RPM, I'll eat a healthy serving of crow.
I firmly believe that for the combo AB has described, 3.69s will give the lowest ET. I agree that 3.29s would be better for highway mileage, but he said he doesn't care about that and 3.69s will not be 24% worse than 3.29s.
