Forged Rods - Suggestions?
 

Had a "small" engine issue....

I beleive I have read a few years ago here, chinese is "okay".

So just checking what the "forums" current consensus and advice on rods might be. Iif it was just the rods, we would spend the money on Manly...but we also need a crank and possibly a block and all the machining/balancing etc that goes with it, so budget and saving a few hundred here or there is an issue (as usual).

Full race engine. Rev limit 7500 - 8000 depending on torque curve. Borg Warner turbo running max of 22 psi around 350 whp.


Landed in NZ.
Manly - Supermiata approx $790.00
Eagle $650.00
Maxpeedingrods $450.00

appreciate any advice for or against whats listed or anything else to consider?

K1 - I bought these after reading that they were lighter than many of the Chinese branded rods - engine builder didn't need to do much work to balance them so was happy with them too.

FWIW - I've had Eagle rods in my NB1 for about 10 years now. They've survived two rebuilds and I'm not (that) gentle on my engine. I don't do WTW racing, but regularly do HPDE's.

Just a data point.

My maxpeedingrods are doing just fine, at 300hp.
I do street, autox and track days, I dont abuse my engine 7k redline and I usually shift around 6-6.5k rpm

I'm running secondhand Brian Crower rods, for another data point. Over 300 whp doing HPDE but shifting at 7100.

The Manley rods are listed for $359 on SPM's page. Is the cost to import that high? They all start out in China except for the Carrilo. On your budget I would go for The K1's or Manely. Next would be Eagle. Before you spend money on balancing make sure your know why and what your trying to accomplish. On an inline 4 the crank is balanced to zero and the indvidual components are balance to each other. The aftermarket pitsons and rods are very well balnanced. The factory specs for the crank that I have seen are good.

gonna guess NZD which is at 0.63 USD - the rods alone would be 570 NZD

What was the small issue that took out the entire short block?
All of the rods you mentioned should work (after proper inspection).
I have found Chinese products with a brand association are higher quality than the no-name.
I would lean to Manly then Eagle and pass on Max-speeding.

However, your car is top of class and used in competition.
You are about as hard core as they come. It's not a street car occasionally used for track days.
You have a race car that is occasionally used for street duty.
Carrillo A-beams is what I'd want for your application. Super light and made in USA.
I'd also want suggestions from Supermiata.
I'd give more weight to their suggestions over everyone else...

What rods were you using and how did they die?
I'm always looking for the root problem; so often this is overlooked and the new fancy parts end up trashed in the same manner.

Carrillo A beams best suite to high RPM N/A builds. We run the much beefier Carrillo H for F/I builds. On a budget, the Manley's will tolerate either 500hp or 8000rpm, but not both.

Thanks for the advice everyone. Will ponder what to buy/spend.


At this point we believe the root cause was a miscalculation/mistake on our behalf when installing the K-Miata ZF Gearbox kit.

The clutch master that was supplied in the kit wouldn't fit in the left hand drive vehicle.So we looked up the size of the original BMW Master for the vehicle the ZF comes with (E36 etc) and replaced with a shorter unit that did fit.

Turns out that we should have specifically replicated the size of the supplied unit (it turns out it was different) rather than the original BMW one as we believe in hindsite that we ended up with enough clutch preload to completely ruin the thrust washers on the crank but had zero clutch slip.

There were indications of things not being right but the ZF is a sealed, internal slave setup so you cant check that freeplay (that we are aware of yet, wil be looking further in to that) and with zero clutch slip we never really thought it was possible...but it turns out it is :)

Amazing it lasted so long, about 18 months and 5-6 race meetings, various drives around town. We thought the ZF gearbox was quite noisey and I had ordered a spare, and the idle was sort of vibey in the car which we never really figured out. The nosie turns out to be a thrust Bearing always on and my guess is the vibes were the crank with zero end float. though this might still be my imagination.

Ruined crank in thrust washer area (one half was gone, the other almost gone), possbily block for same reason and the number 4 rod big end is out of round due to the bearing failing in that end of the motor (A good, loud knock was the final death call).

Engine rebuild and then back to figuring out why we have massive overboost issues with the Bog Warner EFR 6758.

Would the Carillo A beams work for a lower boost 10-12psi and 250whp with a 7k redline application?

I have Carillo A beams in my motor, running 18-20 psi and 350-ish rwhp. 7500 RPM redline. That's about the advertised limit for them.

--Ian

More than enough. They're far stronger than OEM. The concern is the 5/16" WMC bolts that those heavy pistons are tugging on. We have never seen one fail though. High comp N/A pistons are even heavier than shorter turbo pistons which is why we don't use A's for N/A builds that will spend a lot of time above 8000. The H's use 5/16" CARR bolts. Manleys and most other China rods use 3/8" ARP 2000 bolts. A trick set of high rpm rods would be A's with the 5/16" CARR bolts. That is something I'd be comfortable spinning to 9k.

We have run Manleys in motors that saw 8500 rpm. No failures but more rapid bearing wear even running thick ol, oil cooler and lots of pressure. I think that's the result of that heavy N/A piston, heavy rods and lots of revs.

Thank you for the info.

I run Crower A beams in my N/A engine to 9k constantly. That is with high compression Wiseco pistons. Several events back I hit an overrev to 10,800 and the engine stayed together which tells me the rods and bolts aren't at their limit at 9k. They only run 3/8" ARP 2000 bolts though.

Weight?

I'm not sure actually. I'm pulling the engine this week so I'll weigh one and see. They do have a larger looking beam than the Carillos so I'm guessing they are a bit heavier.

My Brian Crower rods look beefy too. They definitely have some heft compared to stock ones that came out.

As per Crowers webpage. B93791-4 MAZDA MIATA 529gr

Close to OEM then. Not light, same as weight as Manley.