BP/BPT/BPD Underdriver Pulleys

[project.r.racing]

Hiya everybody,

After working on my BP, BPT and BPD engines for the last 2 weeks. There is something I noticed between the pulleys on the engines. The 94-98 NA and BPD engines have underdrive pulleys fitted. Oh I never knew this.

Anyways, this means nothing to BA or GTR owners but if you know a GTX or BG then there this is a cheap and easy way for some extra power to be had by going down to your local wrecker and buying these pulleys and fitting them to your BG or GTX.

Hope this helps a few peoples out.

Ryan

[Dutchy]

Nice observation.

Ive got a few questions tho...
is it just the crank pulley/boss that is smaller? And how much smaller in comparison?
Is the fitment still the same? (just the single woodruff key on the crank)
and do they still have the v grove for the altenator/waterpump belt and the 4 rib grove for the other side?

If all this is ok this could well be a good little mod.

Jeremy

[Ian]

What sort of gain would you be looking at?

[BigMal]

Aren't the pulleys a combined pulley/harmonic balancer.
So an underdrive pulley thats good for hi revs by not overdriving the alternator
etc and you want to achieve that by adding a pulley/balancer from another
engine thats not balanced to your engine ??
I will keep it in mind for future rebuild thou. Thanks.

[project.r.racing]

Originally Posted by deejayryry

and i wouldn't worry about using different pulleys cos the balancer should all be the same, don't quote me on that though, someone with more technical knowledge like cosmo would know more than me about it.

look i did say something like that due to my uncertainy of the mechnical knowledge i am unsure of it's application onto different motors. i am not a mechanic but a mechanic has told me that they are fine to swap over. but that was only his word. if i knew for certain then i would have said so, and not given myself a window of uncertainy in my posts.

thanks for your warnness and friendly words towards me, i'll remember that for future reference. sorry that i am not a turbo king like you. but i'll be using the underdrive pulley as my engine already comes with the desired one required. cheers.

ryan

[BigMal]

Originally Posted by deejayryry

and i wouldn't worry about using different pulleys cos the balancer should all be the same, don't quote me on that though,

If you refer to b2-6 of the GTR suplement which shows a picture of the GTR pulley you will see its a combined pulley/balancer. When you balance a motor the usual place to do your fine adjustments is in the harmonic balancer as flywheels often get replaced and cranks can get real tricky to fix if you overdrill them with using mallory metal so the easiest item to work on for fine balancing is the harmonic balancer. So where as its great you mentioned the pulleys are underdrive on the GTR and N/A it would have been better if you left out the "I wouldn't worry but I have no idea what I am talking about" quote as randomly adding pulleys balanced to different motors with an intention of running high revs to make use of the underdrive is an accident waiting to happen. Each to their own but do a search on underdrive pulley failure and read the responses about failures due to inbalance even to so called internally balanced engines such as most 4cylinders.

[project.r.racing]

uh i have checked again the they are the same, BP 97 motor and BP GTR motor. only the pulley section that runs the air-con and power steering look to be smaller.

bigmal: - can i ask why a balancer for a 97 BP would not work on a 92 BP engine please? or a BP GTX motor? especially since the bottom end is completely the same in all of the BP engines. i'm not asking to be a smart arse. i'm asking cos i wanna learn.

ryan

[Cosmo Dude]

If you are going to remove the balancer/pulley then please invest in some threadlock for the woodruff key. If it has any movement then it will move around and start to chew the front of the crank, that is bad news and really expensive.
It took almost 20 years on the 929 but it did happen.

[BigMal]

What I am saying is mass produced components are not perfectly balanced and the easiest place to make adjustments is to remove weight from the pulley instead of the crank. The pulley itself will happily swap against any other 27mm nosed bp crank but will the motor remain balanced. I accept that moden engines are a world away from old externally balanced chev engines, you may well get away with it but then again if you read some of the posts about the failures in the search I suggested you would see a lot dont. I did mention in my first post that I liked the idea and would keep it for a future rebuild where I can have it all balanced together rods, crank and underdrive pulley. I dont have any issues with you personally but I do attack any remarks where there is a "Use this without any worries" without the benefit of absolute fact. The only absolute I will say is I am not a self proclaimed Turbo Guru I know far less than some of the other members here but I do spread any info I learn especially if it is adding caution to a "No worries" string. One thing in my own defense of why I sometimes get narky is the pm's I answer of the "I read on the forum I can run 26psi on a na engine with stock internals" type dribble (not real example) where someone on the forums has made a "You should be ok" post without any further info or backup. You know the newbies take a lot of what is posted by older reps and I include you as an older rep as gospel and wouldn't ask a mechanic. I think "you should be ok" should not be used by anybody if they dont know 100% its ok & not just because they dont know why it wont work.

If you took personal offense I do apologise. I am blunt but only usually cruel to Exodus cause he deserves it. Nah only kidding there to.. maybe

[project.r.racing]

All good Mal,

After putting the TX3 (BPD) up on the hoist and my car also (BP) and going out the back to look at the BPT sitting there. The pulleys are not as different 1st thought. They are only slightly different/smaller in diameter and probably wouldn't be worth swapping. But as long as they have the same woodruff key then it wouldn't be a problem swapping it over, (fact and mechanic friend can back it up.)

They are different because the BG + GTX pulleys have a flat belt and pulleys. Where the BA + GTR have a V-ribbed belts and pulleys, which gives less slippage under load and high revs, eg: - tight cornering out at 5,500 rpm giving better steering as belt isn't slipping while doing this.

Ryan