ITT: Your ideas for increasing torque output
12-26-2011, 09:39 AM
#61
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Falcon, unfortunately you have a recipe for dog, whether you knew that was on the menu or not.
You have a small displacement engine. You have low compression pistons. You have large cams. You have a centrifugal blower. Any of these will yield somewhat lower torque numbers in the lower RPMs. All of these together will make it a real schnauzer down low. It's what you picked and you can moderate things a bit but it will be what it will be. But is should run like hell up high (300whp is strong for a 1.6!).
There are many valid points that others have voiced above and a few that may not help. Your cams and your Rotrex are designed to make power in a higher RPM range so you should keep your engine there. The tighter spacing of the gear changes on the 6 speed as Savington pointed out would certainly help you to keep your peaky engine in it's optimal operational range. Your lower compression pistons will let you use more boost and make more peak power without detonation, which is good, but they are another reason you need to keep the engine in its peak range.
As Miata2fast and Nitrodann have said, a larger exhaust may yield more high RPM power and be optimal for the range where your other components make peak power. As they pointed out, a larger header primary diameter and collector/exhaust diameter will negatively effect low and mid range torque due to poor primary velocity and scavenging. This is a very widely known and accepted fact with fifty plus years of testing to support it. Turbocharged vehicles are the only exception. With the change to a 6 speed helping your "being out of peak RPM range" issue, you may find that you will make more useful power up in the 5-8000 RPM operating range with the 3 inch exhaust. Experimentation will bear this out.
One of the classic mistakes in hot rodding was to pick components that did not work in the same RPM range with each other. Another classic mistake was to pick components that did not work in the range that the car would be operated in. Lots of muscle cars with ridiculous tunnel ram intakes sticking out of the hood have been beaten by far less flashy cars with better matched components. And likewise huge lumpy cams were often employed without enough compression, headwork, or bottom end strength to allow the cams to ever spin up into their effective peak range.
The point is that your car has several major features that are optimized for 5-8000 RPM so everything should be targeted to optimize power in that range if you want to make the most of what you have. Or you could tone it down and make less power by reverting to stock cams and increasing the ease of driveability (which is going backwards) and have a significantly slower car on the track.
Now, along with the 6speed you can make some more supporting mods to go faster and use the RPM range where you do make the powah. You have dialed in the cams on the dyno and that is good.
1. 3 inch exhaust, try it and see if it makes more power in the high RPMs. Your car will always be a low-RPM dog so go for it on top end.
2. Have you optimized your intake manifold with shorter, larger diameter runners yet? The factory runners are optimized for something like 3-4500k RPM.
3. How about a lighter flywheel with that 6 speed? It would likely help with snappier shifts and blips. This might be more important if you are shifting more often with an extra gear.
4. An extra pound or two of boost if your engine can take it. More power is more power. It should help a little bit everywhere.
5. Meth was suggested above but you have to beware of relying on it. An additional point of failure on a racecar is not usually advisable. Using it for cushion only can't hurt.
6. Reduce weight. A peaky engine with little low end torque is never a good match for a heavy car. Drag racers will run really low (high numerically) gears if they are stuck in this situation just to try to overcome the disadvantage. It takes torque to effectively move weight and you don't have much of it so you have to trim weight down if you are serious. Rotating mass and unsprung weight are of the first importance, then sprung weight. When you have very low torque it makes a much bigger difference. You will also have the benefit of being able to brake and corner better with less weight. It helps everywhere.
My advice is to make it better and try to keep it in the RPM range where it is already good and not to try to make it into something it isn't designed to be.
You have a small displacement engine. You have low compression pistons. You have large cams. You have a centrifugal blower. Any of these will yield somewhat lower torque numbers in the lower RPMs. All of these together will make it a real schnauzer down low. It's what you picked and you can moderate things a bit but it will be what it will be. But is should run like hell up high (300whp is strong for a 1.6!).
There are many valid points that others have voiced above and a few that may not help. Your cams and your Rotrex are designed to make power in a higher RPM range so you should keep your engine there. The tighter spacing of the gear changes on the 6 speed as Savington pointed out would certainly help you to keep your peaky engine in it's optimal operational range. Your lower compression pistons will let you use more boost and make more peak power without detonation, which is good, but they are another reason you need to keep the engine in its peak range.
As Miata2fast and Nitrodann have said, a larger exhaust may yield more high RPM power and be optimal for the range where your other components make peak power. As they pointed out, a larger header primary diameter and collector/exhaust diameter will negatively effect low and mid range torque due to poor primary velocity and scavenging. This is a very widely known and accepted fact with fifty plus years of testing to support it. Turbocharged vehicles are the only exception. With the change to a 6 speed helping your "being out of peak RPM range" issue, you may find that you will make more useful power up in the 5-8000 RPM operating range with the 3 inch exhaust. Experimentation will bear this out.
One of the classic mistakes in hot rodding was to pick components that did not work in the same RPM range with each other. Another classic mistake was to pick components that did not work in the range that the car would be operated in. Lots of muscle cars with ridiculous tunnel ram intakes sticking out of the hood have been beaten by far less flashy cars with better matched components. And likewise huge lumpy cams were often employed without enough compression, headwork, or bottom end strength to allow the cams to ever spin up into their effective peak range.
The point is that your car has several major features that are optimized for 5-8000 RPM so everything should be targeted to optimize power in that range if you want to make the most of what you have. Or you could tone it down and make less power by reverting to stock cams and increasing the ease of driveability (which is going backwards) and have a significantly slower car on the track.
Now, along with the 6speed you can make some more supporting mods to go faster and use the RPM range where you do make the powah. You have dialed in the cams on the dyno and that is good.
1. 3 inch exhaust, try it and see if it makes more power in the high RPMs. Your car will always be a low-RPM dog so go for it on top end.
2. Have you optimized your intake manifold with shorter, larger diameter runners yet? The factory runners are optimized for something like 3-4500k RPM.
3. How about a lighter flywheel with that 6 speed? It would likely help with snappier shifts and blips. This might be more important if you are shifting more often with an extra gear.
4. An extra pound or two of boost if your engine can take it. More power is more power. It should help a little bit everywhere.
5. Meth was suggested above but you have to beware of relying on it. An additional point of failure on a racecar is not usually advisable. Using it for cushion only can't hurt.
6. Reduce weight. A peaky engine with little low end torque is never a good match for a heavy car. Drag racers will run really low (high numerically) gears if they are stuck in this situation just to try to overcome the disadvantage. It takes torque to effectively move weight and you don't have much of it so you have to trim weight down if you are serious. Rotating mass and unsprung weight are of the first importance, then sprung weight. When you have very low torque it makes a much bigger difference. You will also have the benefit of being able to brake and corner better with less weight. It helps everywhere.
My advice is to make it better and try to keep it in the RPM range where it is already good and not to try to make it into something it isn't designed to be.
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12-26-2011, 10:45 AM
#62
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what rpms do you spin it to?
8k?
Whats stopping you from spinning to 9k? rotrex, valvetrain?
Doesn't look like your power or tq is dropping off at 8k yet so I would suggest you keep reving out unless something is in teh way of doing that.
8k?
Whats stopping you from spinning to 9k? rotrex, valvetrain?
Doesn't look like your power or tq is dropping off at 8k yet so I would suggest you keep reving out unless something is in teh way of doing that.
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12-26-2011, 11:16 AM
#63
I agree with the crowd: you built this engine to be this way, and just about every component is optimized for a torqueless/peaky curve. Don't try to make it something its not. You'll end up losing what you currently have, and I HIGHLY doubt you'll make any torque in the process. So FAIL and FAIL.
The trans idea, to me, sounds like a fantastic one. You built the motor to spin to 8k, so gear the driveline to use more of that band.
GEARING is a TORQUE MULTIPLIER. Think about that
Keep the engine at its boiling point with highest fd rp you can find, a 6sp, and smallest diameter wheels you can get away with
OR
Just sell this setup to someone that actually wants this kinda power curve and start over with a 1.8+turbo like you should have from the start
The trans idea, to me, sounds like a fantastic one. You built the motor to spin to 8k, so gear the driveline to use more of that band.
GEARING is a TORQUE MULTIPLIER. Think about that
Keep the engine at its boiling point with highest fd rp you can find, a 6sp, and smallest diameter wheels you can get away with
OR
Just sell this setup to someone that actually wants this kinda power curve and start over with a 1.8+turbo like you should have from the start
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12-26-2011, 03:09 PM
#64
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I think his 4.10 gear with a 6 speed will keep him pretty busy rowing gears and keeping it on boil up to, what, 140mph or so? I'm too lazy to chase the FM calculator down to see what 8k with a 4.10 yields.
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12-26-2011, 09:24 PM
#69
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Yeah, especially if he's only on tracks that he can only run 140 and below. But with a 3000+ RPM powerband I think he will be just fine with the 4.10s. First gear will be quicker than a hiccup as is, but he should find better useful overlap in 3,4,5 than he was used to.
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12-27-2011, 09:05 AM
#70
Thanks for that long post sixshooter it kind of opened my eyes a bit with the way you explained it. You're right my motor has everything (except perhaps the exhaust) that tailors to the high RPM. I have a lot of what you listed already, a GotPSI IM, light FW/clutch (maybe I'll go with the 949 in the near future) and it's making just shy of 17PSI at 8kRPM. I could gear the blower a bit higher as it's still under the limit by 100RPM or so. IIRC you can overspin them %5 with a good oil cooler and not really worry about them grenading.
A 6sp is on the list now. Although it's going to be hard to find one here in BC. May have to ship or scavenge the parts yards.
And techsalvager, the bottom end would not likely last at 9kRPM. The head should be OK (although the springs may be on the edge) but the bottom end is only statically balanced and the flywheel was not balanced with the assy. 8k is enough anyways
.
A 6sp is on the list now. Although it's going to be hard to find one here in BC. May have to ship or scavenge the parts yards.
And techsalvager, the bottom end would not likely last at 9kRPM. The head should be OK (although the springs may be on the edge) but the bottom end is only statically balanced and the flywheel was not balanced with the assy. 8k is enough anyways
.
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12-27-2011, 09:09 AM
#72
Oh, and my local track I top out at 185kph. So I think a 140/150MPH limit is not the end of the world. I doubt I would be hitting much higher at Seattle but Portland and the new Ridge Motorsports Park are quite high speed. But 150mph high speed? Not sure... I think I will leave the 4.1 for now if I feel I want a higher final drive I can swap it out.
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12-27-2011, 11:17 AM
#73
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Its to bad, looks like your losing out on power up on top due the camshafts, tq hasn't even fallen off yet. Personally I wouldn't think of going with that cam if you aren't gonna spin it out. No idea how much R&D it took for those cams but I'd look into a cam that would bring the power band back eariler into the rpm range.
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12-27-2011, 12:41 PM
#75
Lol, I just logged in to come mention that...
Cams have nothing to do with the torque not falling off. IIRC TrackDayHookey's car runs stock cams and his car is a beast and the power just keep climing.
Anyways....
6Sp
15's
3'' exhaust
add lightness
That's what I'm doing and leaving the rest of the car as is. I'm kinda getting tired of spending money....
Cams have nothing to do with the torque not falling off. IIRC TrackDayHookey's car runs stock cams and his car is a beast and the power just keep climing.
Anyways....
6Sp
15's
3'' exhaust
add lightness
That's what I'm doing and leaving the rest of the car as is. I'm kinda getting tired of spending money....
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12-27-2011, 01:01 PM
#78
If you are not willing to spin the motor high enough to fully utilize the camshaft you are running, you have a serious combination problem. You need to either pull the motor and fix the bottom so it is capable of spinning to the rpm of the cylinder head/cam combo, or install a camshaft that will peak out in the rpm you are willing to run.
You need to dyno the car at a higher rpm to see when the motor runs out of steam. I would at least run it to 8500. If you have a good balancer and flywheel, you should be ok with a few dyno pulls.
Then determine what final drive gear ratio by doing the calculations.
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12-27-2011, 01:03 PM
#79
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dude. because of the way the boost is built, there will unlikely ever be a drop in torque. Look at the above TURBO setup on stock 1.6L cams. We all know those cams drop torque at 5K.
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