High horsepower on the OEM stock tension bolts
 

This is something many of us want to know if OEM stock tension bolts are good up to 500+whp on the REW. At this point many of you may know already and have experience on what’s the highest wheel horsepower that the OEM stock tension bolts can hold without being in the dangerous side.

I've heard of 1200+.

Hell I have heard of 700+whp on an unopened MANA keg. Big turbo an Q16.

The tension bolts are not a problem and never were a problem in a turbo application. (N/A applications, yes, harmonics at high RPM can break them) Studs are the new method of pinning/doweling engines, which has its own flaws but is fine for 8 second bursts.

stock bolts are actually better. up to maybe 700hp. the JDM tuners start to use the bigger 20B tension bolts at that level.

This is why I made this thread because some have said that going over 500whp with the OEM tension bolts gets dangerous. Have you experience this or know of someone that have achieved this power level with the OEM tension bolts?

Makes sense for turbo and NA application. I want to achieve 500-550 whp on my FD with a 66mm on 93 pump and water meth.

The main reason for studs is that they dowel the rotor housings in place. Doweling is mostly a crutch for detonation, which can happen to even the best of us.

I'm a little out of the loop but your power goals seem... ambitious. The turbo sounds pretty small even with a piston engine, and rotaries need more turbo for the same power level. And on pump... well I suppose it could be done if you want to prove a point, but you're holding onto a grenade with the pin pulled and slippery fingers.

If you were talking a larger, more efficient at high flows/boost turbo, and E85 or a proper race fuel so that you don't risk the slightest hiccup in your water injection system resulting in a catastrophic oops...

to double the stock HP there are a bunch of things you need to do, but the tension bolts are not really on the list..

https://www.rx7club.com/time-slips-d...-rwhp-1000747/

Peejay, you may already know that turbo lingo goes by compressor inducer (small end) rather than exducer/major diameter (overall diameter) since the inducer sets the foverall fow and the exducer sets the pressure ratios available.

66mm inducer is T04Z or EFR 9180 size which is kind of a sweet spot for the rotary. Spools well enough to do low boost and ~400rwp on the street, low boost high flow on big overlap circuit cars ~500rwhp or high boost for drag cars for 600+rwhp.

Dont get me wrong, it can be laggy as hell with the wrong set-up- but done well its like magic.

OP
Studs are a pretty recent way of doweling the block (popularity rising in last decade). Look at engines done before that- they still made power.
Weakest link against detonation is stock 2mm apex seals (can do stock 3mm to be kind to housings or aftermarket seals and tear up housings), 9.0 comp rotors are weak and dent too (sub in older heavier 8.5 or 9.4 cr rotors/counterweights) then you get to side housings breaking once you strengthen those. Dowelling or studding is done to keep side housings from cracking at the upper dowel at the front and rear housings under detonation.

Once you fix all those the sheer heat of detonation will still warp seals and sack out the seal springs as well as break any cornerseal you can get- so its best we try to avoid detonation.

The only reason why I tend to go for studs is that most engines I've played with seem to have been built by the hulk with no torque wrench, this is from reputable builders as well.

Edit: Oh yeah, or as has been mentioned vibraty sustained 9000 rpm + race engines - no turbo, no power.

I thought the 9180 was MUCH larger than 66mm inducer. Color me educated. OTOH the EFR is also newer tech. When I think 66mm, I think of the Precisions that I used to put on Buicks that would do mid-500s rwhp at 20psi-ish.

Now I want to know what an EFR would do for a Buick.

Not that great since the gn heads just dont flow, same issue as pre ls small blocks. Doesnt matter that the turbo can flow 94lbs/hr if the heads cant.

But put a 9180 on a honda or 2j and you can get 1,000hp.

STOCK GN heads don't flow. There's a racing class where they have to be "stock appearing" - stock head and block castings, stock appearing turbo, etc. They are still limited to about 1000hp by the block strength, but they need about 30-35psi boost to get up there. This needs about 100psi exhaust manifold pressure to do, too. (They are in the 8s with a 3800lb minimum weight)

There are plenty of aftermarket solutions for head flow for the GNs. It helps that Buick raced these engines with turbos at Indy, and they also raced them in the Busch Grand National series (where the car got its name), so there is plenty of practical knowledge and parts to find or duplicate in the aftermarket. It's easy to bolt on heads with better geometry and intake manifolds that flow worth a damn (the real problem) and gain a whole lot of flow. It is very easy to make enough power to start to have problems with lifting the heads or splitting the block, both of which can be fixed with an Indy style block with the two extra rows of head bolts... which coincidentally most aftermarket heads are built to be able to use.

Yup, thats what I meant. You have to work hard to get a stock gn much over 500rwhp.

Its pretty awesome the knowledge and skill is out there to elevate the performance of our old engines.

It is also pretty awesome you can go to the junkyard and grab a stock engine that Yamaha (1jz, 2jz), Honda or Chevy has alrwady done the engineering on and built from the factory to perform at the same level or higher. Makes for a lot less time and $ when you need to replace parts.

I asked my engine builder about studding/doweling my rew for high hp and he said it wasn’t necessary, when i quizzed him he said on the street with street tyres there would be “give” in the driveline from the tyres meaning less stress on the engine, and since he knew i was looking at going efr turbo, with a much wider power band than a larger more laggy/torque turbo he said it wouldn’t be needed!!

He said if i were racing the engine on the strip with heaps of grip, the stress would go back down the driveline to the engine and put a lot of stress on it, now thats not word for word and i am a bit dyslexic and have most likely not understood/explained it how it was meant to be, but as he was explaining it, it did make sense (hmmm, for me anyways!!)

krem

Tension bolts are another of an unending list of decisions we face especially when going single turbo. Given the motor is going to be making a multiple (stock rwhp is 217) of stock power all items deserve a look.

Certainly head bolts on moderate to highly modified piston engines receive the red carpet treatment and with good reason. While not exactly similar, our motors generate very high internal forces/ combustion chamber pressure/ yet are five plates bolted together. i do see evidence (galled rotor housing flanges) of interplate movement. not life threatening generally but.

there are two issues:

A: whether the factory tension bolts are up to the (bigger) job...

it may just be that some of the many coolant loss issues could be sidestepped with 30 to 45% more clamp. the factory says to discard any rotor housing that is out of parallel by .0024! out of parallel causes coolant communication with the combustion chamber pressure. just the slightest non proforma stretch in the tension bolt and it is rebuild time.

it may also be that the cracked front irons/ due to detonation causing the rotor housing to move radially/ moving the dowel pin outward and cracking the front iron might also be helped with a bit more support.

B: whether YOUR tension bolts have been compromised by being overtorqued by a prior builder. please see the link for a proper explanation on this. i consider this factor very important. you are rolling the dice by reusing tension bolts in a motor that has been previously rebuilt by someone other than Mazda.

should you decide to go with with aftermarket stud kits if you pick the wrong vendor you might be losing almost half the clamp of the OE option. They look alike but don't test alike..

i tested them with surprising results.

for a more complete treatment please see:

TENSION BOLT TECH

makes sense Howard, now you should go the next step and dyno an engine with the stock bolts and then swap to studs. its a lot of work, but i heard about a test like this being done, and engine looses power if you clamp it too tightly, it wants to float

The engine does stretch above the 550rwhp levels, been measured with a strain gauge on an engine dyno. OEM studs block moves.

Its not like it instantly grenades itself, so thats why its not clear cut to everyone.

Sounds like the main webs deflecting side to side .003" on certain four cylinder engines. Makes you wonder what the point is of making everything perfect, since iron is flexible by an astounding degree.

"iron is flexible by an astounding degree."

i have added significant new content to the Tension Bolt Tech Section of my site including a picture of a couple of irons that apparently exceeded the "flexible to an astounding degree" and why that might tie in to making a decision on how you are going to join the five plates that make up our motors. too long to post here.

http://www.colemanprecisionrotaries....bolt-tech.html

So is it safe to say that 550 whp and below is on the safe zone for stock bolts?