I am looking at swapping out my OEM crank pulley for the ATI unit or the RFY unit. I know that the ATI is a good unit but I can not find any information on the RFY one. Is it safe to run on the car? Looking for advice on which direction to go. Thanks.
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Crank pulley questions
- Thread starter Rope
- Start date
Thanks, I am all for increasing engine response and freeing up HP. Based on DAL's notes on the NSX he is under the belief that do to the engine's internal balancing being as good as it is as well as the driveline attached to the rear of the crank that a traditional balancer is not needed. He ran with a custom built pulley for similar to the RFY unit which is why I would like to learn more about it.
DAL's notes are great to read but over time, some of the suggestions have turned out to be incorrect (the EGR valve and VVIS come to mind). Regarding the crank pulley, DAL writes "I think this balancer feature is there as insurance in case time or unknowns change the tolerance of the internal balance [of the engine]."
Since DAL wrote that, one of the engineers on the NSX's original design team became active on the NSX Club of Britain's website. He has posted about the crank pulley so we no longer have to hypothesize regarding its purpose. Kaz wrote:
"While for most of the production cars, the pulley counter weight is acting mainly for the damping purpose to cope with the sudden reverse torque/changes in the load by the aux units such as A/C compressor, etc, it is different for our NSX.
While it still acts as the damper, the main purpose of the pulley weight is to shift the resonance frequency out of the usable rpm range to protect the TB itself.
I heard from my friend that during the development stage at the engine dyno, the engineers found that at a certain rpm, there was a resonance frequency that could significantly shorten the life span of TB."
So the balancer is not there for the reason DAL hypothesized. The OEM pulley should be replaced regularly (for example at every timing belt change) because it falls apart over time. However, if you replace it with an aftermarket pulley, just be aware that it may not address the resonance of the timing belt. A solid aluminum pulley will not address the resonance of the crankshaft, either, which is what ATI targets according to their literature in order to increase horsepower.
Since DAL wrote that, one of the engineers on the NSX's original design team became active on the NSX Club of Britain's website. He has posted about the crank pulley so we no longer have to hypothesize regarding its purpose. Kaz wrote:
"While for most of the production cars, the pulley counter weight is acting mainly for the damping purpose to cope with the sudden reverse torque/changes in the load by the aux units such as A/C compressor, etc, it is different for our NSX.
While it still acts as the damper, the main purpose of the pulley weight is to shift the resonance frequency out of the usable rpm range to protect the TB itself.
I heard from my friend that during the development stage at the engine dyno, the engineers found that at a certain rpm, there was a resonance frequency that could significantly shorten the life span of TB."
So the balancer is not there for the reason DAL hypothesized. The OEM pulley should be replaced regularly (for example at every timing belt change) because it falls apart over time. However, if you replace it with an aftermarket pulley, just be aware that it may not address the resonance of the timing belt. A solid aluminum pulley will not address the resonance of the crankshaft, either, which is what ATI targets according to their literature in order to increase horsepower.
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Sooooo ATI good and RFY bad? I was wondering the same thing since I am up in the air on which one to get.
Correct. When Kaz speaks you should listen. Alum pulley only good for race cars where engine rebuilt every season.
Yep, got with ATI
Running ATI myself, feels smooth and it's good insurance knowing my OEM one can't fail on me when it's not installed 
this condition is highly possible and can only/most likely be detected when using an engine dyno like mother Honda but much less noticeable when using a chassis dyno but that does not mean its not there. since we dont' know what specific rpm the natural frequency occurs, its difficult to tell and using ATI or RFY kits is a shot in the dark. Usually if you know the rpm range, you can stay away from it but that is a band-aide solution. But, if its way up there and you don't hit it often, you just might get away with it. Thus, IMO the oem pulley is the safest to use cuz the NSX engine is quite expensive to replace.
There was a thread awhile back where Billy "broke" his crank under normal driving condition. I don't claim I know the reason but a prolong natural freq. over time that is not damped, could put unnecessary stress on parts and break them. OTOH, a different intake system, SC, turbo..etc. could shift the freq. range along with other things.
IIRC, only Comptech used engine dyno to test their engines for Real Time so they will know the danger zone. I don't think ATI was avail to them but I could be wrong.
You can change the resonance of the TB too just by adjusting it's tension - a tight TB will have a higher resonance frequency between a given pulley distance, while a loose TB will have a lower resonance frequency between a given pulley distance.
A tight TB places additional stress on the belt and crankshaft, cams, pulleys, etc and wastes power. A loose TB runs the risk of skipping cam or crank pulley teeth. It took me a long time to go through Kaz's EXTREMELY helpful videos and adjust my TB tension (out of the car too) to where he recommended it. Without the correct test equipment, who knows the effect the tension adjustment has, and also the effect of the heavy OEM pulley.
The harmonic dampener also plays an important role in protecting your oil pump gear. Small crank end resonance oscillations can result in over-stressing the gear. Again, I don't know what that resonance is - I trust ATI for my engine.
It's interesting that when doing the resonance calculations, it's always assumed that the other end of the crank is basically "fixed." This is because it contains the much heavier clutch assembly (relative to the harmonic dampener). When you drastically change the clutch/flywheel weight, you are potentially shifting the crankshaft resonance frequency and amplitude out of the range that mother Honda designed the OEM harmonic dampener for....
I looked at Billy's case when rebuilding my engine... IIRC it was a used crank from Japan. There are too many variables based on past usage that I couldn't pin the failure on one thing. Therefore, I stuck with a relatively heavy clutch (RPS carbon that was balanced together with my crank), went with an ATI dampener, and I also hand-radiused every sharp edge on the crankshaft before cleaning/polishing/balancing. Those edges are extremely sharp and are significant stress-risers. I guess you could do some surface stress-relief if you wanted to with local peening, but I thought that was way overkill.
I'm disappointed with the 90-degree V6. I understand why Honda did this (for their future V8), but it resulted in a weak crankshaft with 30-degree crank pin shifts in order to quell vibration. I don't have the money for a nice billet crank, so I tried to take care of what I had. I'm sure I am pushing it's limits.
Bottom line is it's hard to go wrong with a new OEM dampener, or an ATI. I would not use a solid pulley.
Dave
A tight TB places additional stress on the belt and crankshaft, cams, pulleys, etc and wastes power. A loose TB runs the risk of skipping cam or crank pulley teeth. It took me a long time to go through Kaz's EXTREMELY helpful videos and adjust my TB tension (out of the car too) to where he recommended it. Without the correct test equipment, who knows the effect the tension adjustment has, and also the effect of the heavy OEM pulley.
The harmonic dampener also plays an important role in protecting your oil pump gear. Small crank end resonance oscillations can result in over-stressing the gear. Again, I don't know what that resonance is - I trust ATI for my engine.
It's interesting that when doing the resonance calculations, it's always assumed that the other end of the crank is basically "fixed." This is because it contains the much heavier clutch assembly (relative to the harmonic dampener). When you drastically change the clutch/flywheel weight, you are potentially shifting the crankshaft resonance frequency and amplitude out of the range that mother Honda designed the OEM harmonic dampener for....
I looked at Billy's case when rebuilding my engine... IIRC it was a used crank from Japan. There are too many variables based on past usage that I couldn't pin the failure on one thing. Therefore, I stuck with a relatively heavy clutch (RPS carbon that was balanced together with my crank), went with an ATI dampener, and I also hand-radiused every sharp edge on the crankshaft before cleaning/polishing/balancing. Those edges are extremely sharp and are significant stress-risers. I guess you could do some surface stress-relief if you wanted to with local peening, but I thought that was way overkill.
I'm disappointed with the 90-degree V6. I understand why Honda did this (for their future V8), but it resulted in a weak crankshaft with 30-degree crank pin shifts in order to quell vibration. I don't have the money for a nice billet crank, so I tried to take care of what I had. I'm sure I am pushing it's limits.
Bottom line is it's hard to go wrong with a new OEM dampener, or an ATI. I would not use a solid pulley.
Dave
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I remember when it was the flavor of the month to swap to billet (non dampened) pulleys on 20v 4age and the b16c b18b engines. Similarly the engines mentioned are factory 'balanced' just like the c30 and c32 and the same arguments applied. After a few months of anecdotal evidence and quite a few blown motors the carnage suggested that non dampened pullys caused some of the motors to fail on track.
Im with Mac on this one. OEM (replaced every 50k) or ATI are KNOWN to work. For me at least its not worth the chance when weighing gains vs. risk. especially if you haven't addressed other reciprocal components that will net the same, and better, gains elsewhere that are much safer to do. Do a dry sump and lose that whole oil gear assembly all together, talk about reciprocal weight savings..
Im with Mac on this one. OEM (replaced every 50k) or ATI are KNOWN to work. For me at least its not worth the chance when weighing gains vs. risk. especially if you haven't addressed other reciprocal components that will net the same, and better, gains elsewhere that are much safer to do. Do a dry sump and lose that whole oil gear assembly all together, talk about reciprocal weight savings..
Nope. The ATI pulley needs to be overhauled about as often as the OEM pulley needs to be replaced. In both cases because the rubber hardens over time and the harmonic balancer then no longer does its job. The cost of overhauling the ATI pulley is about the same as replacing the OEM pulley.
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This is good info, thanks for sharing.
I installed the ATI damper on my car, with the thought of less rotating mass quicker response. I was very disappointed when I put the old and new on the scale and they were basically identical. The main physical difference is ATI is friction fit and OEM is not, which makes for a slightly more complicated timing belt replacement. If I had to do it again I would just replace with OEM.
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