full groove main/roadrace

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bentvalves
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full groove main/roadrace

Post by bentvalves »

assembling a turbocharged road race 1800cc Mazda engine to be used strictly in time-attack. Car will be on track for roughly 30 mins at a time.

MAHLE is showing an optional full groove main bearing for this engine. Is this something I should be looking in to?

edit: engine came in with 2 spun rod bearings and a few bent rods.
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Re: full groove main/roadrace

Post by Walter R. Malik »

bentvalves wrote: Fri Jun 18, 2021 5:47 pm assembling a turbocharged road race 1800cc Mazda engine to be used strictly in time-attack. Car will be on track for roughly 30 mins at a time.

MAHLE is showing an optional full groove main bearing for this engine. Is this something I should be looking in to?

edit: engine came in with 2 spun rod bearings and a few bent rods.
Full groove main bearings help the oil flow to the rod bearings at the expense of load carrying capability of the mains.
That is your decision to make.
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Re: full groove main/roadrace

Post by rustbucket79 »

No bearing technology can make up for an uncovered oil pump pickup or aerated oil. Has this been addressed?
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Re: full groove main/roadrace

Post by mag2555 »

Unless those 2 failed rods hit the heads you need to look else where for why the rods bent because it was not lack of oil!
I would prefer to first cross drill the crank if it’s not already to feed more oil to the rods then run fully grooved bearings in terms of a motor running boost!

I might consider half groove bearing though!
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Re: full groove main/roadrace

Post by BILL-C »

Installing a turbo on a road race Miata? Rough times ahead. The oil control gets real bad as soon as you start to go fast with those cars. They burn up bearings like it's their job when the chassis and driver are good.And that's without a turbo.
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Re: full groove main/roadrace

Post by dannobee »

Carrillos and an Accusump. Mazda's bend (stock) rods when boosted.

As Walter said, fully grooved mains are a tradeoff; yes, the rods will get oil 100% of the time, but the main bearings won't carry the same load.
When rods are weak, the sides pull in at high engine speed and pinch the crank, causing the bearings to touch the crank, then spin. Better rods and bolts will likely fix your "bearing" problems. And won't bend when boosted.
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Re: full groove main/roadrace

Post by jed »

I have built 100+ of the 1600/1800 aspirated/turbo and supercharged Miata engines. Never had a bearing failure. I always
Used the acular aluminum standard bearings no full grove. I was not to picky about clearances .0018/.003. Always used stock pan, windage tray and pump.
Most everything I did was short block and cylinder heads. The customer did their own assembly.
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Re: full groove main/roadrace

Post by PackardV8 »

dannobee wrote: Sat Jun 19, 2021 9:25 am Carrillos and an Accusump. Mazda's bend (stock) rods when boosted.
No Mazda experience here, but is it boost pressure which bends the rods or detonation? If it's boost, how much to bend the rods?
dannobee wrote: Sat Jun 19, 2021 9:25 amWhen rods are weak, the sides pull in at high engine speed and pinch the crank, causing the bearings to touch the crank, then spin. Better rods and bolts will likely fix your "bearing" problems. And won't bend when boosted.
Agree as to high engine speeds. The good news is turbocharged engines don't have to turn the very high RPM which increases the inertial loading to the point it stretches the big end out of round.
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Re: full groove main/roadrace

Post by dannobee »

Miata rods aren't very strong from the factory. Seems like 250hp is about the safe limit before she goes boom. Racing seems worse. I have experience with the autocrossers and that seems to be the consensus. Boost-wise, that puts it at roughly 15psi on these cars.

If it's one of the other Mazda's and not a Miata, all bets are off. Don't know those too well.

With respect to turbos, they make a lot more torque, and torque is what seems to bend the rods, even in the higher end turbo cars like the Porsche's. And don't get me started on Subaru's.
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Re: full groove main/roadrace

Post by jed »

I should have mentioned that all my boosted engines were with H beam rods. Stock rods and boost don’t mix. your asking for spun bearings and bent rods.
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Re: full groove main/roadrace

Post by bentvalves »

thanks fellows.

you all touched based on some very important things to keep in mind.
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Re: full groove main/roadrace

Post by BILL-C »

jed wrote: Sat Jun 19, 2021 10:33 am I have built 100+ of the 1600/1800 aspirated/turbo and supercharged Miata engines. Never had a bearing failure. I always
Used the acular aluminum standard bearings no full grove. I was not to picky about clearances .0018/.003. Always used stock pan, windage tray and pump.
Most everything I did was short block and cylinder heads. The customer did their own assembly.
Any of these engines serious road race?
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Re: full groove main/roadrace

Post by jed »

Short answer yes. However I have to clarify there were no turbo Miata sanctioned road race classes when I was building them. Most were daily drivers and week end racers.Hobby road racers. I built a lot of SCCA spec Miata’s. Those things would run 10/15 races a year and last 3/5 years before being freshened up. I was building 1800 turbo Miata’s with forged pistons and H beam rods before the after market offered them. I was using B18 Honda forged pistons and B16 H beam rods.
There is no magic in building import engines that last. I was building stock car and sprint car engines in the 70s/80s/90s with very
little bearing problems. So when I started building imports in the late 90s I used the same procedures used in building sprint car
engines and guess what those procedures worked no bearing problems.
I hope this answers your question
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Re: full groove main/roadrace

Post by BILL-C »

My shop builds 120 -150 performance engines a year with 50+ of them road race. Additionally we do machine work for many road race prep shops that like to do their own assembly work. A trend that we see is the faster cars in the class are the first ones to see the oil pressure gauges wave in the corners and and have the bearing issues. The maniacs burn their stuff up too quick and the slow guys go forever.
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Re: full groove main/roadrace

Post by jed »

Bill I have no business telling a veteran engine builder like your self how to build engines. Looking at your web sight and pictures of cars you build engines for your shop and clientele far exceeds any shop I ever had. I am sure you are aware and use accusump, dry sump oil systems and any parts and means available to keep oil at the oil pump pick up. But there are always maniacs who will defy the odds and tear stuff up.
Keep up the good work and keep looking for solutions.
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