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If the fuel/tune combination doesn't induce and knock events and ignition isn't over advanced you aren't likely to have problems, especially if the torque reaction force from the driveline isn't going through the block to a front mount in a drag car.
Yes you are right about what OP said, the plan is to take the flywheel off, drain the engine and just swap out the tension bolts. This will be done one by one acording to mazda pattern. The goal is to raise the lbs the bolts can handle up to 195000 psi as turblown specifications for the specific studs which is much higher than the stock bolts. So i believe this will be very helpfull at high rpm and high egts where the aluminum housings tent to expand more than the irons.
Though i didnt get your point what you mean about Without a tight fit stud you are just getting better clamping?
Here's a crude doodle of the hole fit comparing a tension bolt or a non-machined stud on the left vs a tight toleranced stud on the right. Think of the tension bolts vs the dowels and how tight they are.
One of the major benefits of machining is to take off the rotational load from the 2 stock dowel weakpoints and distribute it through all the machined studs. Which is where people crack and leak oil/pressure out of the irons. Pretty sure mazda may have addressed the castings to help later years, but do you think they fixed it for stock power levels or for 500hp+? Maybe with enough clamp you can stifle this to a degree just off the extra friction alone?
I have never handled the Turblown stud kit, but mass produced irons and aluminum housings likely wont be within a thou on all of those holes diameter or position wise.
Here's a crude doodle of the hole fit comparing a tension bolt or a non-machined stud on the left vs a tight toleranced stud on the right. Think of the tension bolts vs the dowels and how tight they are.
One of the major benefits of machining is to take off the rotational load from the 2 stock dowel weakpoints and distribute it through all the machined studs. Which is where people crack and leak oil/pressure out of the irons. Pretty sure mazda may have addressed the castings to help later years, but do you think they fixed it for stock power levels or for 500hp+? Maybe with enough clamp you can stifle this to a degree just off the extra friction alone?
I have never handled the Turblown stud kit, but mass produced irons and aluminum housings likely wont be within a thou on all of those holes diameter or position wise.
My friend i agree with you 90% of what you said that's the mair reason i open this threat. Because there are a lot of direct replacement studs out there that are not machined and lot of people said there are usefull for high boost applications at high rpm. But no one is mention about how exactly these studs works according to their fitment other than the high psi levels they can handle. I believe the stock stucks might be weakest than those aftermarket studs, but i think they can take away a lot of abuse and forces from the stock dowels because of their machining and the way they fit and hold the whole engine making it one part. Aftermarket studs can handle more psi levels but about the fitment since they are not machined and the gap that remains, this is something no one talks about and this is where i was worried if i will proceed with a replacement as a step further to strengthen my engine and not a step backwards
I checked around some of the old youtube vids I remember people explaining it. Adam with rotary specialties has a vid explaining why he machines and studs.
He seems to call out turblown indirectly. On the other hand Rob Dahm who agreed in many of the same ways across his machining videos also recommended the Turblown stud kit.....so idk
One of the cases Adam brings to attention is if a detonation event happens and the housing essentially gets punched outwards, the only thing to take up the hit is the stock dowel hitting the irons and the friction between the plates from clamp. Will the additional turblown clamp load friction be enough to take the impact and not slam the dowel into the front or rear iron? Maybe it is enough to just lessen the blow and prevent the typical casting damage. I doubt anyone can numerically answer this and it comes down to whatever helps you sleep at night and years of results of all impossibly questionable datapoints.
Another question is how much torque can the factory tension bolts take? Turblown says 77ft-lbs will damage the front iron using their stud kit. They only say to torque to 40ft lbs on their studs. Mazda spec is 30ft lbs, and are 150k psi......... Here is another helpful link where the factory tension bolts were tested and 30ftlbs is correct to avoid potentially yielding at temp. So the turblown would be able to survive and add extra clamp, whether that is worth $600-700 because of the previous points is still up to question. Maybe this price is worth you not wanting to take out the engine though?
Maybe the only reason the dowel casting breaks is due to the stock tension bolts expanding under detonation and then the dowels>irons take most of the force because clamp is lost? Timing wise I'd think most of the forces are distributed between the rotor and the housing, not much of the iron is exposed in the combustion chamber during ignition.
I have to look into any mazda higher hp race engines have info on how studding was done. I am going to assume they machined all of the studs to be slip fit though because the minor cost difference would not be an issue. I doubt we could find the numbers on shank size, thread size, torque, yield, etc.
Last edited by MincVinyl; May 8, 2025 at 08:41 AM.
Probably worth noting that the vast majority of high load stud and bolt applications are designed for the clamped surfaces to bear the shear force, spreading it across the surfaces (like your wheel hubs, cast alloy and iron aren'tgreat in tension), not bear on the bolts or studs directly one exception to this may be spherical joint mounting bolts but in those applicationsthey are generally oversized, in dual shear and have hardened steel bushings into the parent material. Even with a close fit if the housings are regularly moving enough to significantly radially load dowels you will get fretting of faces and gas bypass. I see numerous large diameter tight fit dowels as a bit of a bandaid for knock or over advance tolerance of drag cars, especially when they are also bearing the entire output torque front the gearbox through to a front cover mounting. An increased clamp and appropriate tune should be adequate for most street and circuit racers who want and setup for long engine life and don't expect any significant plate/housing walk and who constraint torque transmission with gearbox and rear/mid plate mounts and additional oil pan braces.
Maybe the only reason the dowel casting breaks is due to the stock tension bolts expanding under detonation and then the dowels>irons take most of the force because clamp is lost? Timing wise I'd think most of the forces are distributed between the rotor and the housing, not much of the iron is exposed in the combustion chamber during ignition.
detonation is like 10x the force of normal combustion. its going to break things no matter what you do.
detonation is like 10x the force of normal combustion. its going to break things no matter what you do.
True, no dowels or machining will be the saving grace for a bad tune or other issues.
Found another vid from Rob showing the different stud kits he has. Looks like the turblown studs are not close to a tight fit. Brings back to the clamp may help prevent shear movement, but if there is movement or localized distortion they certainly wont limit it in any way.
Guys i am still so confused. To stud or no stud for 600bhp up to 1.6 bar of boost with wmi? So many vids from David, Rob etc but for the stock studs no one mention if they are really worth to upgrade over them with aftermarket studs or not. Yes they might be not as stiff as aftermarket but about fitment no one mention that the stock studs have a screw threat somewhere in the midle and what this threat is used for and why the aftermarket studs that they are just a tight fit but why they dont have this screw threat somewhere in the middle. Other than that nothing. Maybe if there were studs that are stronger + had this screw threat would be a real upgade? What really this threat in the middle is used for?
I'd argue the use of the word strength there is vague and a misnomer. It's almost certainly there to reduce vibration and fatigue cracking from sustained high rpm, high load/vibration operation not change the absolute tensile strength.
Going to higher capacity 10mm studs at a significantly higher load will shift the natural frequency above the factory bolts and reduce displacement/strain from any vibration so probably reduces susceptibility in and of itself, doesn't hurt to apply some form of compound to damp any movement at the mid plate if you are keen.
I'd argue the use of the word strength there is vague and a misnomer. It's almost certainly there to reduce vibration and fatigue cracking from sustained high rpm, high load/vibration operation not change the absolute tensile strength.
agreed, it is a translation from Japanese so its "strength"
Funny story, one of my old bosses used to work for Alfa Romeo, and they would write the parts and service books in Italian. Alfa Romeo USA used to be in New Jersey, and they would send the Italian books to the local college to have them translated.
so there was a group phone call where the dealership managers would be like flip to page 13 and check out that typo!
Had talk the other day about studding vs not, with and without reinforced/billet front bearing.
This isn't my information, just what I was told by someone who has been building and running a rotary race team for over a decade. His father used to race as well, and worked for Mazda building rotaries back in the early days.
The stock stuff allows a little flex, just a tiny bit, but it all flexes together. Shaft, keg, everything has a little room. Once you machine and stud the keg, you take away flexibility from the keg, but the shaft still flexes a bit. This isn't ideal. If you build a really stiff keg, you want a really stiff eccentric shaft and everything else to go with it. He says he uses stock studs in the circuit cars he builds, and all of them make 450-550whp for the series, and the keg is the most reliable part of those cars. I do not know if he uses stock tension, or if there are other mods around the OEM studs to help them last. I've heard of using extra O rings, filling the remaining space with rubber or plastic, lots of tricks out there to help them survive harmonics no ideas which ones actually help.
The other issue with machining for studs, are the inevitable rebuilds. Getting a replacement housing machined to the same tolerance can be time consuming and difficult depending on where you are. The higher you rev, the more likely you will need new housings when the time comes. Hopefully the shop you used still has the same jig and program, hopefully they are still around. This adds cost and complexity on a rebuild that could have been a simple housing swap and seal check, and might cost you a few months of downtime which we all know sucks. Nobody likes waiting on parts.
The other issue is hot/cold startups. Mazda literature specifically mentions heat transfer through the studs as a leading cause of cracking irons at the threads in daily driving situations not even race use. Leaving room around the studs stops them from moving heat from the combustion chamber right into the threads, leading to uneven heating and cracking during warmup. If you live in a cold climate, that might be a legitimate concern for you, and it's Mazda's reason for leaving so much room around the studs. Of course having things like a block heater or preheating the oil and or coolant is a legit way to negate this. Not uncommon on work trucks, and then you'll see it in high end motorsports like F1 etc. I can't imagine driving a 600hp fully studded rotary in the snow but mad lads will mad lad.
So really it comes down to personal choice. A fully studded keg with all the supporting mods will hold together at a higher level, but the costs begin to balloon. Maybe just a little tip clearance is all you need. Easier, faster, cheaper rebuilds (which you WILL do at 600+) vs a ton of money going in and then in again.
I'm staying below that threshold. Turblown studs and clearanced rotors for me, they bridge that gap between reasonable cost and full send.
My more reasonable take:
If you're looking at making 600+, get a 3 rotor! You can make 600 all day long on a near stock keg, torque for days, and while it costs a little more up front your rebuilds will be WAY less frequent. And because it's a straight line car at that power level, you should have no worries about a little more weight near the front. But seriously, look at the costs, and ongoing costs, of a 2 rotor at 3x its stock power, or a 3 rotor at 2x its stock power. Resale value of a 3 rotor will also be far beyond that of a highly modified and high strung 2 rotor, if you care about those things.
If you are running a race team you can probably figure out that you just need to purchase one single tapered ream machined to the right diameter and then you simply stack all the plates and run the ream completely through the tension bolt holes.
No issues with old reamed housings mixed with new unreamed housings in the stack either.
If you preserve front plate tension bolt threads instead of through studding you dont stack the front plate when reaming and you may have to re die the stud threads looser and tap the front plate threads looser to get enough slop to get factory tolerances to align to the bores.
Besides filing apex seal grooves, reaming is the simplest maching you get to do on a rotary.
But the other reasons for not running toleranced studs in a circuit race environment are spot on.
I truly think the 600whp+ answer is a 3 rotor. You get back torque, reliability, much longer engine life, and you can go back to pump gas
My friend i agree with you in a lot of what you said but the there are 3 things i like to specify.
1st is that in the country i leave is veey warm climate with 8 months summer and 4 months winter on which there is never negative degrees.
2nd in my country you cant just swap engines and drive legal so 3 rotors and 4 rotors swap ar illegal for fd chassis.
3rd since we dont have the swap legal option we try to find out ways to increase horsepower with the 2 rotor engine with internals etc. But not for crazy horse power level 600whp +, but up to 550-600 whp with wmi to be in the safer side.
So you believe of what i mention above, for warm climate and up to 550-600, no stud needed or it will be safer with studs? Thank you
I make over 900HP with a 2 rotor
OEM through bolts
4 additional mazda dowels
over 50psi of boost(35-45psi of boost over the last 2 years)
Studs are designed to clamp, not to reduce torsional load.
maybe you were just lucky also then?
if i would do anything to the block is to use the hollow dowels from pineapple racing. I wouldnt even do the solid dowels because believe it or not, the hollow dowel is a different material than the solid dowel, (yes i did several metallurgical and hardness tests) and it is much stronger despite being hollow …
And again, the plates and housings aren't separated by a high pressure oil film. Increasing clamp increases interface friction and resistance to block torsion or combustion chamber expansion. I'm not knocking dowels for extreme horsepower applications but you can't ignore basic engineering principles.
Who’s tuning your car? Probably a good conversation to have with your tuner
In the end, it’s up to you if you are the builder. Both work. I’ve heard the argument that studding can help survive a less perfect tune, but that’s just hearsay I haven’t seen evidence of that. If your engine is already together and the clearances are set up for oem or loose fitting studs, probably best to just run it..
Here’s some generalities I’ve noticed…
Puerto Rican dudes seem to prefer adding dowels. Run fast, run rich. This is black magic I’d love to see more. Make do with less kinda thing. Mad drag skills yo!
The Aussies love their studs. And their full billet stuff. Built to shred tires. Aus keeps resetting the 1/4 mile record as well. NZ = OZ here
Japan seems to stay much more OEM. Even a lot of their apex seals are OEM with extra treatments. But you don’t see nearly as many high hp builds, it’s more circuit focused. Tunes also seem to be more on the lean side, but again it’s circuit vs drag.
US has money, likes to buy shiny things. Lots of different shops doing many different things. Studding seems to be getting more popular. Roll racing / highway shinanigans seems to be the use for high power builds. Labor costs a lot, so overbuild it the first time seems to be a thing, sometimes to a detriment.
My final wise words:
The more special stuff you do when building, the more special stuff you’ll have to do during a rebuild.
And again, the plates and housings aren't separated by a high pressure oil film. Increasing clamp increases interface friction and resistance to block torsion or combustion chamber expansion. I'm not knocking dowels for extreme horsepower applications but you can't ignore basic engineering principles.
They do, but only marginally. Machined studs make a much larger impact. Dowels make the most difference especially near the combustion face because that’s the main point of pressure and deformation
Methanol 13B turbo - factory Mazda cast FD irons, 60+psi boost, factory Mazda thru bolts, 4 extra dowels on the combustion side. 6.63 on the 1/4 mile, 3/4 chassis FD. Unsure of power level in the end but must be north of 1300hp. Has had a couple of dented rotors over the years but no cracked irons.
I've seen a couple of engines at the track and on the internet missing the spark plug side of the front or center iron - all running 1/2" studs in every hole. I've also seen plenty of 1/2" studded irons from 500-800hp engines with cracks between every stud hole. It seems Mazda knew what they we're doing with the factory thru bolts. Extra doweling for the win.
I checked around some of the old youtube vids I remember people explaining it. Adam with rotary specialties has a vid explaining why he machines and studs. Link He seems to call out turblown indirectly. On the other hand Rob Dahm who agreed in many of the same ways across his machining videos also recommended the Turblown stud kit.....so idk Link
One of the cases Adam brings to attention is if a detonation event happens and the housing essentially gets punched outwards, the only thing to take up the hit is the stock dowel hitting the irons and the friction between the plates from clamp. Will the additional turblown clamp load friction be enough to take the impact and not slam the dowel into the front or rear iron? Maybe it is enough to just lessen the blow and prevent the typical casting damage. I doubt anyone can numerically answer this and it comes down to whatever helps you sleep at night and years of results of all impossibly questionable datapoints.
Adam sells machining services like extra dowels because it makes him money, anything else out of his mouth is bloviating.
Originally Posted by rx72c
I make over 900HP with a 2 rotor
OEM through bolts
4 additional mazda dowels
over 50psi of boost(35-45psi of boost over the last 2 years)
Studs are designed to clamp, not to reduce torsional load.
What is the reason for the additional dowels? Not trying to be a pain, just genuinely curious what failures you see that are helped with additional dowels. About the worst I've seen is slight bending of the dowels making disassembly difficult, but that's about it. I live in low power pissboy 450-550whp road course land though.
Adam sells machining services like extra dowels because it makes him money, anything else out of his mouth is bloviating.
What is the reason for the additional dowels? Not trying to be a pain, just genuinely curious what failures you see that are helped with additional dowels. About the worst I've seen is slight bending of the dowels making disassembly difficult, but that's about it. I live in low power pissboy 450-550whp road course land though.
I *think* the added dowels, especially around the combustion side is to make sure nothing moves(torsion).
Sheesh, a lot of varying opinions on the larger stud/dowels. lol.
I am about to embark on a 600+hp 2 rotor build. I intend to have Howard Coleman build my motor, with Adams larger dowel/studs for all holes. I am looking to do this for the same reason Rob pointed out, torsion of the motor and not necessarily clamping force. I would assume in higher HP applications any torsion of the motor, even with a balanced E shaft/rotors, would potentially place additional stress on the corner seals/apex seals if the motor is twisting at all?
I guess for me, adding the larger stud/bolt to all holes is is like the overkill version of adding the stock Mazda dowels, but tighter tolerance. I am going for 600-650rwp on a street driven car, so I hope to have good longevity but I guess we will see!
US has money, likes to buy shiny things. Lots of different shops doing many different things. Studding seems to be getting more popular. Roll racing / highway shinanigans seems to be the use for high power builds. Labor costs a lot, so overbuild it the first time seems to be a thing, sometimes to a detriment.
My final wise words:
The more special stuff you do when building, the more special stuff you’ll have to do during a rebuild.
For me, I am trying to overbuild for my HP goals. I had a 500rwp FD years ago and broke transmission and rear end. Since I am shooting for up to 650rwp, for highway fun, I am trying to just spend the money now instead of breaking thing every month.
I'll start by saying I haven't read the whole thread but I offer a little advise.
Turblown's studs are good, use them at Turblown's recommended torque. This won't offer the same as full length dowels or additional overzised "pins" dowels or studs but will definetely add clamping strength to the engine assembly.
Use a SPRUNG Clutch, Exedy Twin Cerametallic or ACT Twin Organic.
Add a Tilton Clutch flow valve, this together with the sprung clutch will reduce drivetrain shock and extend the life of your trans/diff.
Mind your tires, if you use very sticky ones Third gear or the diff can get chewed up even with smooth torque application just if the torque is too high and there's no slip.
