:::RHMT::: Real Home Made Turbo
General Category => General Discussion => Topic started by: walter on March 26, 2009, 09:35:58 PM
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today me and friend of mine was discussion about how works a dyno, there is a guy that dynoed his car and guys from shop said him ,they rolled the car in 4th since if they dyno it in 5th will get more power.. i was ..what the f...
friend of mine said me , he was right, since it has to do with gear ratios, they try to find 1:1 gear ratio and then dyno the car for get right numbers..
i alwasy thought that and engine pull same torque/power in every gear..how the hell can make more power in next gear?
i was talking too with a guy that was working on a repair shop when had a dyno too (MAHA Dyno), and said me he play alot with it, and his car alwasy made same power in 3th or 4th gears but with different "loss power" (not sure how you say this thing really ., i transate it literraly)
i know dyno measure torque ,calcula for get power blabalabla.. but what is the deal with gear ratios and this shit? :?:
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Dyno measures torque. You put your car in 1st gear there is a larger gear reduction, hence you put down more torque. Normally you dyno in your 1:1 gear such that the dyno can measure torque and engine RPM to accurately calculate wheel hp.
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it can play with the numbers a little, but HP is Torque x RPM/5252 I think dome dyno's are improperly callibrated. I know for a fact some give up numbers easier than others. When I was building engines for HotToGo up in NY, our dyno would read low compared to others, proven many times, same engine read 10 or so HP more elsewhere. Kinda cool kicking someone's ass and tellling them you have less power.
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Also, if the gear ratio is known, true torque can be figured in any gear, Take the gross torque output and divide by the gear ratio.
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this really doestn reply what i asked :-\
how do you know it's your 1:1 gear? then,that means if you make two pulls in 3th and 4th gears, you will not get the same power since "you are putting down more torque" ?
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Do it in 5th and let us know how it goes :yes:
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weres my vti cluster :P
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the what fuck? I'm thinks me wants also how works a dyno?
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this really doestn reply what i asked :-\
how do you know it's your 1:1 gear? then,that means if you make two pulls in 3th and 4th gears, you will not get the same power since "you are putting down more torque" ?
actually the same HP will be calculated but it will be over a much smaller rpm scale. you might have 1000ft lbs and 140HP in first gear. or 150 ftlbs and 140 HP in 4th gear. think about every time you see the phrase SAE corrected or corrected HP, thats becuase even in 4th gear 1 engine rev is not the same as 1 wheel rev, not 1:1, it could be like 1:1.25, you have to correct by 25%.
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With a turbo engine especially a higher gear can offset the torrque curve a lot by loading the engine more and for a lnoger period of time. The turbo comes into boost at earlier RPM and makes more torque when gear ratios are taken into account. Just like on the street 1st gear might not spool until 5k, but 3rd and 4th may spool at 3k(numbers pulled out of my butt, but you get the idea and most of you have seen it).
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Its mainly HOW the dyno measures. It measures torque, which is how much power you can put into a single 'twist' of the rollers. Some use a stress guage (measures torque via flexing), some use something akin to a generator (eddy current).
The corrections for gear require speed or RPM inputs, otherwise you just get raw data. 1:1 offers the least correction, obviously, and is usually found in 4th gear. However, the final drive still multiplies the torque, you just remove the other gears from the picture.
All that said, you won't see much difference between 3rd and 4th if the dyno is opperating right. Aero's right about boost, depending on the dyno. A no-frills dynojet w/o load cell won't load the engine like a mustang would. If you're tuning, its a good thing to have a loaded dyno.
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I can make a Dynojet/Mustang/Dynapack setups fudge the numbers with ease.
Dynapacks are the easiest. I've seen 15-20 whp gained on a NA motor by changing the slew.
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Inertia dynos (like dynojets) measure HP directly and calculate torque, they do not measure torque. Brake (loading) dynos (like dynapacks) measure torque directly and calculate HP.
What your friend is refering to is a trick many people use on brake style dynos. The slower you sweep them through the RPM range the more power they tend to read. However, I've never heard of doing this by dynoing in a higher gear. It's usually done by adjusting the settings on the dyno.
However, with a turbo car I'd tend to think you would lose power in the higher gear because the engine would be under load for longer and building up more heat.
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Inertia dynos (like dynojets) measure HP directly and calculate torque, they do not measure torque. Brake (loading) dynos (like dynapacks) measure torque directly and calculate HP.
What your friend is refering to is a trick many people use on brake style dynos. The slower you sweep them through the RPM range the more power they tend to read. However, I've never heard of doing this by dynoing in a higher gear. It's usually done by adjusting the settings on the dyno.
However, with a turbo car I'd tend to think you would lose power in the higher gear because the engine would be under load for longer and building up more heat.
ok but then how's possible ppl said on dyno if they pull in 5th gear ill get +10hp or so more.?
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i get 17lbs at 2600 in first, i don't know the meaning of longer gears affecting spool :evil:
I get 10-12psig at as low as 1.5K rpms but that is b/c I use an oversize supercharger. ;D
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i get 17lbs at 2600 in first, i don't know the meaning of longer gears affecting spool :evil:
I get 10-12psig at as low as 1.5K rpms but that is b/c I use an oversize supercharger. ;D
Link?
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Its mainly HOW the dyno measures. It measures torque, which is how much power you can put into a single 'twist' of the rollers. Some use a stress guage (measures torque via flexing), some use something akin to a generator (eddy current).
And inertial units do it be calculating the power required to accelerate a heavy drum.
Some dynos are designed (on the software side) to calculate 1:1 gearing, so if you don't use 4th gear it will vary the power output. Other dynos compare engine speed to the drum speed and correct for 1:1 gearing, so regardless of what gear you are in the power output is the "same."
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i get 17lbs at 2600 in first, i don't know the meaning of longer gears affecting spool :evil:
I get 10-12psig at as low as 1.5K rpms but that is b/c I use an oversize supercharger. ;D
Link?
Here is mine : http://www.realhomemadeturbo.com/forum/index.php?topic=651.0 (http://www.realhomemadeturbo.com/forum/index.php?topic=651.0)
I think I might see more boost all around if I fix all the boost leak issues. ;D
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Inertia dynos (like dynojets) measure HP directly and calculate torque, they do not measure torque. Brake (loading) dynos (like dynapacks) measure torque directly and calculate HP.
What your friend is refering to is a trick many people use on brake style dynos. The slower you sweep them through the RPM range the more power they tend to read. However, I've never heard of doing this by dynoing in a higher gear. It's usually done by adjusting the settings on the dyno.
However, with a turbo car I'd tend to think you would lose power in the higher gear because the engine would be under load for longer and building up more heat.
ok but then how's possible ppl said on dyno if they pull in 5th gear ill get +10hp or so more.?
Because a slower sweep through the RPM's gives a higher power reading on a brake dyno. I think your friend is just an idiot though.
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If we take this chart http://hondaswap.com/reference-materials/honda-transmission-specs-29132/ (http://hondaswap.com/reference-materials/honda-transmission-specs-29132/)
Some transmission are ~1:1 at 4th and some are ~1:1 at 3rd. So we use the 3rd gear in the last case right?
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Arent long 5th gear pulls a no no anyway?
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High speed drive in 5th is not good because the engine is always on load so it creates a lot of heat. That's my conception tho, I'm not 100% sure :P
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Arent long 5th gear pulls a no no anyway?
It was the only way I could get traction to break 800 on the Blueridge car. Apparently they like to pop in 5th in the 700 whp range, we were lucky.
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Why are 5th gear pulls such a bad idea? Wouldn't a long pull on a load dyno be just as bad or even worse because of the lack of enough air through the engine bay?
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I would think that higher gears would have more knock if your tune isn't safe or bad because you're going through the rpm range slower and have more load on the motor.
On the dyno, I don't think it matters if you run boost in 5th gear, or even on the highway as long as you don't prolong it. Thats when the internals really heat up.
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Internals will get hot, meh. If everything's built correctly then you only have to compensate for for how the temperatures hasten the burn.
Talk to some landspeed guys... they spend the last mile or so trying to gain 3-5 mph. They know everything you want to know about some high gear boosting.
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i was thinking then ,dynoinh your car get " real numbers what your engine make".. :-\
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i was thinking then ,dynoinh your car get " real numbers what your engine make".. :-\
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