Cracked plate. Now options for block. Stud or Big bolts
 

This has probable been answered before but here goes. (Trying to figure out sell or rebuild first) Motor cracked a rear plate. new motor 1200km.

1988 S4 block stock. BNR turbo etc. Cracked rear plate on a pull on they hwy at 16-17psi. (Not sure why boost went that high or what is wrong. No datalog. I was not there during the tuning. Found spark plug wire sitting on one of the signal wires to the trailing coil, fuel issue?)

So I could buy big bore S5 plates but they are hard to find.
Could also go these two options? Expensive though...

13B Engine Stud Kit - Turblown Engineering
Goopy Performance Engine Bolts

Turblown options is nice because no need to machine the housings but not sure it does the same thing for strenghting the block. As it is I will be buying the big bore plates (Reinforced dowel) as this should help. I do have two or three S4 plates as spares too. Limited budget so don't even want to spend anything any more. Could have bought a porsche GT4 for what I have in this lol. I just got this to pass emission (Cat converter insert was $1000 easy!!)

Car will be used mainly for street and a few track days. Not sure why I would even need any of these because I ran my old setup on a TO4B stock block ported motor, stock seals for years and years and that motor was fine. Even saw a few 20++ pulls, Two tuners, two ems's, track days etc etc.

What do you all think? Stock S4 plates and try again or spend more money on some options of strenghting the block.

You could just buy an S5 TII rear iron with the larger dowel pin landing.

I just ran into the same problem. I cracked the front and rear iron from when I lost vacuum reference to the FPR and detonated. I ended up finding a late FD-style S5 reinforced rear iron. From the look of my failed irons, the cracks were no were the gusset is on the the normal reinforced S5. My point, you can still find the late irons, but they're rare. BUT you can buy a NEW S4 or S5 rear iron from Mazdatrix and it comes with the FD style dowel. Last I checked they were ~$400 for an S4 and ~$450 for S5. There is very little difference between the two. Since you need a new rear iron anyways, that would be cheaper than a used S5 iron and a stud kit.

We just bought a new S5 for a customer that had an earlier S5 and cracked it doing a 9K launch at 24 psi


https://cimg7.ibsrv.net/gimg/www.rx7...c25d274d10.jpg

looking for these. Thanks for the reponse.

Just an FYI if you are cracking plates you have a major issue. No mods can 100 percent prevent them from breaking. I have seen engines with 12.7mm stud kits split irons in half.

Could be, and the fun begins trying to find the fault. I suspect we may have harmed the block even before it went out for tuning when I installed the IGN coils. It would not run on sequential setup.. I never heard a car backfire that bad when the tuner rev'd the car up. I was expecting engine chunks out the exhaust. Funny thing the car ran fine with stock coils. Once switched to sequential not so. I notice the tuner set the map with the triggers reversed in the adaptronic to get the car to idle and run right. Slick catch on his part. It is quite possible the wires in the patch harness are reversed. This was not apparent running stock but once in sequential it was noticed. Either way issue needs to be found and I will have to pin out the harness, make sure the sequential coil harness is far away from the signal wire, and run new wires to the fuel pump. Or just pray that I found out what the cause was. Been rotary for over 2 decades so maybe its time to move on anyhow. But its like a bad habit:)

Cracking plates is from detonation. Period. Trust me I should know lol...

First, you should always be there when your car is being tuned. Second, back firing has nothing to do with cracking irons. Back fire is normal when your mixture is nice & rich in the tune. It's possible your tuner has the timing too aggressive and may need to tweek that. My advice is, get in contact with a really good (rotary)tuner and either request remote tuning or fly him there.

I was told there was no detonation and that the fuel ratio's were fine. I don't think anyone is around when this tuner tunes really. He does both street and dyno. The outcome would probable be the same if I was there I would think.

Ya ErnieT I remember you breaking a few motors:)

Been calling everyone I know for these big casting plates. Hard to find parts. I though of not doing anything as the car should be fine at 15psi without any of these mods. Or at least I thought so.

Pulled my motor out last night and checked me water injection kit settings. So I found my AEM water controller settings at 5psi start, 15psi full on AEMS biggest water nozzle that comes with the kit. I'm beginning to think with the rich A/F and alot of water at 17psi on the hwy at 120km that I could possible have had a misfire or hydraulic lock?

Depending on the Severity of the crack, Goopy Performance may be able to help repair it.

pictures? i've heard its near impossible to hydro lock a rotary.
wheres your log of the event?

Pictures of the crack or internal? I'm just trying to figure out what happened to my engine. You don't think spraying 1000cc a minute at 15psi on 5th gear 120km whatever rpm that is, is not too much water?
I posted some pictures on the canadain forum my 10thae face lift thread. I'm on my cell phone right now and its a chore just to post anything.

any new rear plate from mazda should be the revised design.

I cracked my rear plate and ordered a new one from mazdaspeed and it was the big casting S5.

If it's just a crack you can grind it, push the metal into the crack with a pin punch and fill it with devcon or jb weld to keep the oil from seeping out. Fix the detonation problem and it will be ok!

Don't even bother buying a s5 plate I broke 2 in a month a/f were right but that power Fc in a fc chassis wiring for coils just didn't work right . I wasn't fully tuned but still even on low boost I cracked one . pin it that's what all the drag racers do . I was gonna do the stud myself but the pinning is better worth the money . I got a adapotronic PNP unit gonna add another fuel pump got a jocobs ignition box to . Going for 480+ whp on pump gas

Ive ran a power fc on a fc for years with the modded trailing coil. Sounds like a tuning issue to me.

Well I gave up on it . tried everything .

Also cracked a plate in S5 with AP eng PFC while running the engine in. learned the hard way that sotck FC fuel pump wiring is a bad idea.

Fixed the wiring and used another stock small dowel land S5 housing. then then WG bushing on the Stage 4 BNR seized and he cracked the tip of a stock mazda 2 piece seal. swapped the old tech BNR for a gt35r kit I bought here on the forum and went for single piece NRS 2mm. car never ran so well. running 1.1 bar with stock top mount and RR pre comp WI. pulls really strong and doesnt even show the slightest sign of detonation even with 95 oct. now owner is running same tune on 98 for extra safety. estimate around 400 at the crank seat of the pants dyno. spin 255 wide tyres in second gear when interocoler is cold.

I think if you crack a plate either being small or big dowel pin boss you should look where it comes from. just blaming the small dowel land housing is a weak excuse unless running 3x or more boost. I heard from Carlos from CLR that a good way to prevent cracking the housing would be to just cut the ribs in the rotor houing around the dowel. I have not tried it myself but thinking about it is not a bad idea. the inner evelope of the housing is very flexible and in case of severe detonation it could absorb the energy that would otherwise crack the plate. nonetheless the best way would always be to make sure the a/f mixture and timing is safe and enough safety margin exist for transient events.