Just wondering why GM didn't put free floating wrist pins to gain more rpms?
:confused:


[Modified by FatherLarry99Hardtop, 2:26 AM 11/5/2001]

 

Floating pins don't cause additional friction or make any more power. It's mearly a convenience on a race engine that is torn down regularly for inspection, so all you need is a pair of snap ring pliers rather than a press, fixture, and heat. GM Powertrain assumes that you engine will be together for a long time, and it's easier for the plant to do pressed pins in volume.

Duke

 

Actually, you can bring up more rpms with free floating pins. You're right as far as the cost factor. More rpms mean quicker times. The LT1 in 1970 came equipped with the free floating pins, if I remember correctly. By putting them in my e-gaser 327, I gained 1/2 a second. I feel there is definitely an advantage to them. But, I guess for $50,000, you can only get so much. :lol:
Thanks for your response.

 

More rpms will mean more than just free-floating wrist pins. I agree with what you're saying about them. However, the thing already zings to 6600 right? At some point the hyd. roller valvetrain would have to go and in its place solid/mechanical flat tappet or solid roller valvetrain. Too much maintenance on those, of course...at least for a factory warrantied car.

From my understanding even with today's technological advancements with lighter valves, valvesprings, etc., hydraulic roller assemblies are still pretty heavy with regards to their sheer mass...and once you're approaching 7k rpms, you've got to go with something else to maintain efficiency and reliability of the valvetrain.

Hence, "cammer" motors which eliminate some mass in the valvetrain (pushrods, for example).

I'd be curious as to what those MTI guys use for valvetrain components when they're turning these LS1-LS6 motors to 7k.

 

The only recent Chevy engine with floating pins was the sixties vintage L-88 and this was designed as a pure racing engine.

If you gained a half second with your drag racing car, it had nothing to do with floating pins. If you ran dyno tests on two engines, identical other than one with floating and one with pressed pins, you would not detect the difference within the average dyno run error range. As I said before, the fixed/floating pin issue is a matter of convenience, only. There is no difference in internal engine friction, and no difference in power output.

Another issue with floating pins is end play. It must be within a tight tolerance range as either too little of two much can cause the pin to pound out the retainer.

Duke

 

As far as dynoing it, and a change in the chart, when I dynoed my car myself, at Motion Performance, before I took it to the track, there was a nice gain to the chart, which is opposite of your experience. And, if its a matter of "convenience only" then why did they put them in the L88. They also put it in the LT1 1970. Less friction with free floating pins means more rpms and more durability. Naturally, back then, you needed a mechanical cam and solid lifters. As far as high revs, you have a lot of the Euro 4 cylinders that are going to be capable of revving to 12k, hence the argument "is 6k enough". In the future you'll see this small block with 6.6k revs as obsolete. Even cross drillling your crank improves friction and rpms. As far as durability for the free floating pins, when you race an engine, as far as holding up opposed to pressed-in pins, the free floating will outlast them, especially in racing. As far as the Lexus, they're using it on one of their models and those engines go well over 200k miles. Needless to say, there are no crank or cam bearings where it floats between a film of oil. There's a company that produces a lifter and valve spring setup with a special damper allowing you to rev over 7k rpms with a hydraulic lifter. Needless to say, eventually, there will be servos instead of cam shafts, lifters and push rods to do the work. :nono:

 

I'm not debating at all with regards to internals that can be beefed up to support gobs of rpms. Aluminum rods, lightweight/cross-drilled crank, etc...things you mentioned.

Nevertheless, I'm sure its pretty cost-prohibitive at this point with regards to the valvetrain. I guarantee that the Euro motors spinning 12k rpm do not have pushrods but are rather of the DOHC variety. Lighter valvetrain assemblies, less moving parts, etc.

Granted, there's certainly the engineering out there to develop a high rpm pushrod motor, but most of these motors are still solid roller design.--> NASCAR engines are just one example.

 

It's funny that the LS1 and LS6 engines are using technology and performance parts now, that were mods used in the '60's and '70's. For example roller type lifters with cams were after market by some mfg. Off the road heads from GM with a stiffer valve spring with heavy duty damper, and small resistor plugs. It just shows that these parts that were being sold aftermarket contributed to horse power. Especially, the free floating wrist pins concept. Weight was also a factor, but with larger vehicles. With my e-gaser, I took the nose off and put a fiberglass tilted nose in the front with a straight axle, and cut the trunk floors with wheel wells out. I fabricated out of aluminum, all new floors and panels for weight loss. I turned good times with that e-gaser. Low 9's. Had a problem with the clutch being sucked in, after high rpms, just like the Z06's are having today. Went to a heavy duty finger type clutch, instead of the diaphrapm type, with heavier springs, and eliminated the problem. Those diaphrapms could suck wind. Better for cruising around in a street car, less pressure when you depress the clutch, even with the hydraulics. Well, thanks for the reponses.


[Modified by FatherLarry99Hardtop, 2:28 AM 11/5/2001]