this is actually a pretty good thread, generally all parties have contributed info on what will become an increasingly important overall problem w the FD... the drivetrain.

it will be increasingly important in 07 as more FD owners realize that by adding an Auxiliary Injection (my pref methanol) to their cars they can have another 100+ rwhp without racegas.

so instead of tooling around w 400 rwhp you have 500+ anytime you want it.

mix that in w a transmission that won't handle it, a differential that is improperly supported, axles that twist and you have a recipe for a lot of new threads.

as mentioned above there may be a range of options re diff support. most of the players have weighed in on this thread.

we all know there are a number of options depending on what you run and how you use your fd. the LSD also needs to be on the upgrade list as the Torsen isn't up to the task.

back to diff support.

Paul had designed, built and offers a really nice subframe. the PFS should work well by spreading the case load and has been proven to perform in max drag situations. Banzai's adaption of the Dragon brace also looks to have widespread appeal as it is inexpensive, easy to install and reinforces the PPF which is almost up to the job. i recently bought one and will be out and about w it shortly. i am relatively easy on my powertrain as i am a road racer. i had a discussion last night w a board member who is considering casting a new stronger diff case for the fd. he is serious and very capable. then you have the alternate rear ends, Viper, Ford etc.

do not overlook an essential.... the poly diff bushings.

i will be adapting a highly uprated T56 in July and may either adapt the rear of the trans to the PPF or switch out the PPF and do something more like Paul's excellent design.

so there's lots of options and drivetrains will emerge in 07 as an important topic of discussion. lots of ways to skin the cat and probably the only loser is doing nothing.

howard coleman

 

Well put Howard, it will be interesting to see how your T56 works out as its a no brainer they can handle the torque, I take it the thread I started about the T56 added alot of opinions and information on different tranny options. I know Ramy was looking into the supra tranny option as well. I would also be interested to see a stronger casting of the case myself so keep us updated on that. I am sure if any of you wanted more information that ray, ari, dan would def. be more then willing to explain the principles behind the craddle effect.

 

Good correction. The rear pivot points are are actually the bolt holes in the diff bushings.

That's great but it really doesn't matter. The point is that the center (arbitrary approximation) of the diff casing is trying to rise, not the nose as is often described.

 

Not true. If you look closely at how the PPF tends to crack you'd find proof.

The diff case is not rising or falling at either end, it's twisting in reaction to drive torque at the tires. If the axles are turning one way then the reaction is twisting the diff case the opposite way (for every action there is an equal and opposite reaction). That means the nose of the case goes up and the rear goes down in your speak.

Your statement would be correct only when the car was in reverse.

 

That's oversimplification. The casing is an extension of the pinion, not the ring and the climbing force originates where the pinions teeth mesh with the ring teeth. This force acts as a lever accross the pinion shaft and raises the front of the diff until either the PPF, or front mount if used, stops the nose of the diff from raising any further. At this point the pinion is attempting to rise near the front/center of the casing while both the tail and nose of the casing want to remain stationary. There are to rotational arcs at play: 1) the rear casing rotating via rear diff mount and 2) front diff pivoting at the pinion shaft origin, PPF, mount or whatever decides the range of motion for the front most part of the casing. These two arcs are moving in opposite horizontal directions and the end result is cracking and eventual buckling/separation of the diff casing. The brace that Greg is talking about simply reinforces the casing so that it will not buckle/separate under these stresses.

 

If he doesn't do it, I may.

 

Man...you guys need to relax. Sheesh lol. Greg, I think Banzai's getting defensive simply b/c it's a product he sells, which is not necessarily a good idea, but to be expected.

Moreover, I think you make a very good point. While the thread is about wheel hop, I think it would be reckless to recommend to someone a way to avoid wheel hop which may very well result in a more catastrophic failure secondary to eliminating wheel hop. So I think it's good sound advice, esp. given that your point seems to be better supported w/ the experience of many on this forum.

Sure am. Only thing I'm waiting on is Carlos to get better so he can move forward with making a few copies of his kit. Which reminds me...I gotta call him and see how he's doing. Hopefully he's doing much better now.

Hmm...I'd like to know if Ray would sell one of those cradles?

I also want to get your opinions on the JUN Auto Subframe, and if it would help at all...https://www.rx7club.com/3rd-generation-specific-1993-2002-16/few-little-known-but-great-jdm-parts-642390/

~Ramy

 

Hey Ramy,
I,m fairly certain that the Jun subframe will not address the diff issues because The diff is karate chopping itself from the inside out while the rear mount and PPF or front mount act as the supporting hands (think about a person holding each end of a board that is to be karate chopped), stiffening the rear mount flanges won't change that, plus they are already in a nice elevated position to begin with. I will try to write out a detailed explanation of exactly what I think is going on with the diff when I get back to the UK, I think it has been incorrectly explained for years (myself included).

The jun S-frame may be a nice suspension upgrade however :o)....

 

Hey Ramy,

Thanks for the support, actually I will hit you up later and tell you what the opinions of the other real experience drag racers/shops think about Banzai's brace, but I wont do it here as it will just cause more drama, but you are totally right, its just a product he is sells and is taking defense to criticism.

Ray Will sell you a craddle, but its just been sooo busy at the shop, no time has been available to make them. FYI, Ernie has the craddle on his car now and hasnt broken a rear case and is putting 700+whp down. Maybe we should try the "other guys" brace and see how well it holds up, hehe. But seriously, I am getting one made for me, as I will be extracting more then what I just made very soon...

 

I actually agree with you Greg, I just think it's being explained wrong. People describe the force acting on the diff casing as if the PPF was trying to raise the nose of the diff when in fact the front/middle of the diff is trying to rise where the pinion acts as a lever against its bearing. There are two arcs at play and the banz brace probably does increase the efficiency with which high HP engines stress the casing as you politely pointed out; however, I think we should keep our minds open to the fact that for moderate HP apps, diff failure usually occurrs as a result of wheel hop. So while the casing's rang of motion has been reduced, placing it in a more vulnerable position as you described, the absense of wheel hop and reduced roll torsion may supercede this issue up to a reasonable RWHP before the sheer torque produced by the engine is enough to snap the casing in the absense of wheel hop. It's certainly not a black and white issue. For high HP apps it may be a very bad idea to use a Banz brace, however it is uncertain whether most applications fit into this category.

The PFS brace just keeps the casing from separating/buckling. It's the equivalent of bolting an extra board on the surface of another thinner board that is being karate chopped. The PPF and diff mount are the hands holding the board (casing) and the pinion is the striking hand. While the diff appears to only be rotating around the diff mounts, if you videotaped a casing failure I am certain that you would be able to see the front 1/3rdish of the diff traveling with an opposing arc that causes buckling/separation at the diff casing's weakest point. Using the same metaphor -> Installing a banzai brace is like resting the front edge of the karate board against a ledge (banz mount), having your buddy hold the other end up with his hands (diff mount) then karate chopping the board down the center (pinion)-> certainly it is easier to break the board when it's motion is constrained by the ledge (banz mount); however you must also account for the changes in karate chopping techinque (reduced wheel hop).

Lame metaphor I know

 

Thanks Rob, you're right, and actually, the craddle is a two peice design, there is a bottom half and a upper half, so the complete craddle encases the whole entire diff, but Ray and Ernie only used the bottom half. So if one were to use the complete design upper and lower, all the stress would be taken by the craddle.
And what you mentioned is what was explained to me about mounting the bracing point at the nose like banzai, the T-brace, it seems as if it makes it more prone to split when under extreme drag conditions because again, the load isnt being spread across the length of the diff.

 

Sounds pretty nice Greg, thanks for sharing. Looks like I will have to pick one of these bad-boys up from Ray when I finally decide to seek a lil FI action ;o)

My last incohesive rant....

Well the stock diff casing does have a brace of sorts built in, that is, the cast splint that runs almost the entire length of the bottom casing, not that it does much....

To me, the PFS brace is really just a means of reinforcement that doesn't change the dynamics of the way pinion distributes it's leverage on the casing from the inside out. The added beef afforded by the PFS brace helps keep the front and rear of the casing angularly aligned by simply not allowing the casing to buckle. I really don't think it's doing anything other than resisting the casing's temptation to buckle, but that's great because that's all it needs to do.

I think the reduced slop/ range of motion at the front of the diff/PPF and the tighter front arc radius are the main points of interest with the banzai/brace. The pinion's pivot point becomes semi-ridgidly positioned at the banzai brace instead of being distributed across the flexible PPF and as a result changes the way that the pinion interacts with the ring gear.

Keeping that in mind, these features that may make it a safe wheel hop reducer for 400ish and below RWHP cars (arbitrary guess) may also make it a recipe for disaster for a 500+ RWHP launch as pressure points become more focused.

A little of topic but.... It took me a while to understand the PPF setup to appreciate how it works. I've dogged Mazda for using the PPF on the RX-7 in the past, but now I better understand why they did it - granted it has shortcomings, namely its excessive vertical movement. If you think about the way that it bolts to the diff you will eventually understand the role that the PPF plays in keeping the front/middle of the diff from trying to climb up and away from the rest of the casing in an arc that is moving horizontally opposite of the diff mount pivot arc. (to help clarify this in your mind, visualize the arcs of winshield wiper blades both traveling veritically but in opposite horizontal arcs); I know, a drawing would be worth 1000 words here but unfortunately I don't have time at the moment to draw this out.

The fact that the Banzai brace limits the range of motion of the PPF (reducing the risk of snapping PPF mounting fingers as well) is good for reducing wheel hop and getting power to the ground, but it's also tough on the diff casing as stated before. The PFS is great for addressing casing failures, but I don't see how it could do anything for wheel hop or nose slop. To be honest I think a combination of the PFS casing reinforcement brace and the Banzai PPF Brace may be a good combo in the fight to bring smooth, affordable and reliable traction to the FD. The way I see it, they are two different products doing two completely different things; one should not be considered a replacement for the other. As long as we all realize that there is no wonder cure to solve all of these problems there will be nothing left to debate but prices

have a good one,
Rob

 

Now PLEASE. I dont give a f*ck about launching loads so with this in mind IF I have 850bhp (whatever you calc this to be in rwhp) Will the diff casing break in ingear rolling on from second gear onwards??? saying using ANY bracing methods that reduces wheel hop (which is the banzai after reading all this **** fighting going on)

i dont drag launching and i do not care about that effect of instant inertia loading with near zero shaft speeds.

please give me a direct answer to my question thankyou.

i am interested in reducing wheel hop ONLY has anyone ever broken a diff casing while doing a full throttle run in 3rd or 4th gear???? or is all of this crap simply focused around drag launches with near zero ground speed.

 

No, not to my knowledge.

Dynamic (vehicle in motion) drivetrain stress is always significantly lower than static (standing start) drivetrain stress, unless you're doing clutch drops/kicks where you're purposely jolting the drivetrain at lower vehicle speeds to break the tires loose. Drivetrain stress also decreases in higher gears as axle torque (gearing multiplication) decreases.

Basically, yes.

Wheel hop is caused by excessive unsprung weight, insufficient shock damping, or (more commonly) by poor torsional axle control. Stiffen the suspension bushings and differential mount bushings (if applicable) and you'll go a long way towards eliminating wheel hop.

 

Blitzed33- Can you please post a picture of this cradle you/Ernie are running?

I want to see it.

or email me a pic if it is too big for here: gnx7@hotmail.com