Are forged rods/cranks needed for durability/reliability?

[mangusta1969]

Are forged crankshafts and rods really a necessity for good reliability and durability on a TT car?

Unless I am misreading their recent posts, both 90Callaway and 91Callaway have performed complete engine rebuilds due to broken non-forged rods, even with pretty low miles on their 90 and 91 TT cars.

What is the forum consensus and history on this? My understanding is that Callaway only used Carillo forged rods and Callies (?) forged cranks on the very last of the production run. If this is true, does anyone know the serial number cutover for the stronger forged items?

thanks,

Steve

 

[RalleyRed]

I think you'll find that any motor considered HiPo will last much longer with forged materials.

A twin turbo is definately High performance!!!


Rick

 

[90Callaway]

Yes, a forged bottom end is an absolute requirement

However, you may have somewhat misread the recent posts. The "stock" TT comes with a forged, nitrited, cross drilled, balanced and polished crank. It has never been noted as a weak spot. I am not aware of the brand.

They also take the original two bolt main Corvette block and have it machined for splayed four bolt mains, align bored, decked and pressure checked.

The rods are also replaced with GM "pink" rods. They are the forged rods that were originally offered starting in the LT1 350 used in early '70s Corvettes and Camaros. They are quite a bit stronger than stock but not strong enough to survive with 12lbs of boost and detonation. There aren't too many parts out there that are.

My belief is that if you have a TT and it's running correctly and it's properly maintained you will probably never break it. Unfortunately, most people don't understand the workings of the car and they often do not run correctly. If you run it hard under these conditions it will break as most any engine with a power adder such as turbo(s), supercharger or nitrous would.

If you do get one of these cars you should put your money into making sure it is running 100% and not trying to re-engineer the motor.

 

[mangusta1969]

Re-engineering or Being Careful?

90Callaway,

Thanks for the reply and info. My questions on the crank and rods both really arise from your previous post:

"Some of the very late '91 TTs and the cars that were fitted with the "100+" package got better internal parts and 8.5:1 compression. The 100+ package gave about 100hp more than stock. I think they all got stronger Carrillo
forged rods. I'm not sure if they all got the better Callies forged crank or not. I got both when mine was rebuilt and I think 91Callaway did as well."

Obviously there have been both metallurgical and machining advances in the 10-15 year period since these cars were engineered and assembled. My question was whether it made sense to apply some of these advances to to head off or reduce the costs and pain of known problem areas. I guess you could call this re-engineering with current technology. I think this is what Callaway themselves are doing by using stouter parts when they rebuild motors.

Can I expect 100K miles out of a stock 90 or 91 TT that is not abused? Was your car low on oil or over-revved when it broke a rod? I am just trying to see what the common failure modes are (if any) and whether there are some sensible pre-emptive actions possible. I have four English cars and two Italian cars so I am unfortunately pretty familiar with failure modes.

thanks,

Steve

 

[90Callaway]

I understand where you're coming from Steve. I do believe that Callaway learned some things between '87 and '91 after building close to 500 of the TT cars and adapted the design points to fix potential weaknesses. If it wasn't "broken" they would not have fixed it right? Keep in mind that one thing they found was that people abused the cars and didn't know a damn thing about them. That's what breaks parts. Most if not all of the TTs that threw rods were probably overboosted, running lean due to microfueler issues and/or detonating. The original design wasn't really flawed in my opinion. But certainly there were stronger parts available. In working with a manufacturer like GM they usually mandate the specs and price points. Callaway built a system around the requirements handed down by GM.

I think I did attempt to answer your question. I personally don't believe it makes sense to completely tear down a perfectly good motor to replace the rods. Like I said, you'd be better served to make sure the car has been well cared for, it is running 100% and is properly maintained going forward. I think you'd see many many years of trouble free service by doing this. If money is no object and you feel better about having stronger bottom end compenents that's up to you. Piece of mind is hard to put a price on.

As far as my car I really have no idea what the circumstances were when it blew up. I wasn't there. I do know that the original owner was not a car guy. He just put gas in it and then ran it hard.

 

[mangusta1969]

Turbos require extra care and feeding

90Callaway,

I hope you are right about abusive use accounting for most or many of the rod and turbo problems. You are exactly right, an uninformed or careless owner can pretty easily hurt a high power turbo car. Reading a number of UltraSlows posts on another forum about his long term/safe racing uses of his bulletproof TT makes me a lot happier.

Even though my turbo BMW has been 100% reliable and fault free for 120K+ miles, I could go out tonight and probably blow it up by staying constantly on high boost while going up a hill or by putting less than good gas in it. The constant boost would overtemp the valves and the turbo; the bad gas and staying on it would cause broken pistons and rods due to detonation.

Turbo cars just have to be monitored a lot more closely. If something is not working correctly (fuel enrichment too lean under boost, for example), then you have to detect and fix this minor problem before it becomes a big problem for your motor.

What types of experiences have other owners had or been told about?

thanks,

Steve

 

[SCVette]

Steve,
I recently replaced the injectors with new ones. The '90 started running like $&!^ after warming up. I did not suspect that 4 of the injectors would go out in 25k miles, so I spent several month throwing parts at it like new MSD ignition, egr, fuel pressure regulator, etc. I guess the higher than stock temps under-hood might have been the cause. She runs even better than before.
Taylor

 

[91callaway]

i was on a highway entrance ramp. i was accelerating in 4th gear.(moderate at best) as soon as i got into traffic i heard a dull thud and lost all power. i looked in the rear view mirror and saw the trail of bue white smoke. i almost lost control because of oil spray on rear tires. i pulled over and oil and coolant was pouring out underneath. i knew. i never abused mine. my big thrill was going above 100 mph often but always in 6th gear. i do think the old rods are THE weak link. now i have stronger rods. callaway told me name but forgot. mike zoner probley knows. e-mail him at callaway.

ps a white bmw that was behind me stopped and screamed at me. his car had a oil and coolant coating. thats all i needed.

 

[mangusta1969]

BMW Rustproofing Job

91Callaway,


Damn, you should have charged the BMW guy for a body and chassis rustproofing job. I can't believe the guy yelled at you after you lunched your motor. Talk about kicking a guy while he is down...

Well, I am a bit concerned about your experience. That certainly does not qualify as abusive behavior in my book and is just about exactly how I would expect to drive. With the sparse instrumentation on the TTs, you MAY have had a lean condition going, though. That's why I think both Exhaust Gas Temp and an Air/Fuel gauges are essential to monitor things closely. Even with these, you need to learn to observe what is normal and what is not in terms of sound and "feel" of a boosted car.

Did you hear any signs of detonation in the days or minutes before you broke the rod? Did you just break one rod? Did the shop tell you if there was any evidence of detonation on the tops of the pistons when they rebuild the motor? Sorry to be so curious, but these are pretty big money events to try and avoid.

thanks,

Steve

 

[90Callaway]

Keep in mind that the initial damage may have already been done to 91 Callaway's motor by the previous owner. Metal fatigue sometimes takes a while to reach the point of catastrophic failure. It could have been a ticking time bomb waiting to let go. It sounds like he is a pretty conservative driver.