hacker-pschorr

Twin Turbo Todd:

https://rennlist.com/forums/928-foru...ar-wheels.html

He made some interesting observations while installing the stock Gates timing belt on his new motor (5 liters, different pistons, different rods, nikasil block, worked over heads, stock valves, stock crank, stiffer valve springs).

Todd spent a considerable amount of time studying lifters and valve springs, bench testing about a dozen different valve springs to find the exact setup he wanted for this engine.
He ended up using is a non-Porsche spring that is about double the spring pressure of a stock 928.

While manually rotating the engine with a stock Gates timing belt, he noticed a considerable amount of stretch before the camshafts started to turn, "rubber band" came to mind.
Thankfully he already had a Gates Racing Belt from Roger @ 928's R Us to test.
The racing belt had zero stretch.

Since the racing belt new for Todd, he asked me to take some comparison photos as a reference to look back on as he puts miles on the new belt.

I figured these should be shared with the 928 collective group.

http://www.erik27.com/cars/928beltcomparison/


Please note - this post is not saying the stock Gates belt is not adequate for a stock 928.


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The Fixer

Thanks for posting this.
Matt

ROG100

Thanks for sharing - we have sold over 150 Gates Racing belts and I am sure a large percentage of them are already on cars.

Apart from being stronger the goal was to make them last a lot longer than the stock belt. Gates engineering made the following statements ---

LIFE DIFFERENTIAL (OEM = 1)

Tooth Shear Life = 2 times
Tooth sheer is important with high rpm, high performance engine due to the constant fluctuation in acceleration and deceleration where tooth stability is critical.

Heat Resistance Life =3 times
Heat is a major factor in timing belt degradation and high performing engines run much hotter. Heat resistance is essential for long belt life.

Tensile Strength Life = 2 times
Conditions such as heat and contamination damage the longitudinal cords used in a timing belt. But the real devastator to the cord is the continual bending and straightening of the belt. Tensile strength is extremely important in keeping the belt from breaking during the billions or rotations it must endure

Contamination Life (oil & coolant) = 2 times
Coolant is another element that can cause damage if not addressed. Contamination resistance is also very important in a timing belt. One of the most detrimental elements to rubber is petroleum products such as oil.

Key material enhancements are ----
Cord - T196R High heat & water resistance high strength glass cord.
Rubber - T196R Formulated for higher temperatures and higher tooth loads.
Jacket - High load & wear resistant nylon jacket

NickT

Great set of pictures, so from a visual point of view they are very very similar.

I wonder if there is a way to capture in an image the stretch that was noticed. Kinda tough I would think..

danglerb

I still have my original question about a stronger belt, what is going to break instead of the belt when something in the system locks up?

SeanR

I've not mentioned it yet but this thread is about as good as any.

Last year, just before supercharging, I put on a new Gates Racing belt on my car. No big deal right? Wrong, I left the old gears on, and those where at the point that I would replace them on a customers car. I also added the Porken Tensioner at the same time and wanted to run an experiment as to what this combo did to gear wear.

I took some measurements with a nice little mm flat edge and measured the wear on a few spots on the gears. Took notes and just before Spring Fling this year (almost a year later) I pulled it all apart to check it out. I have over 8000 miles on this set up, with the Super Charger on it. There was ZERO additional wear on my cam gears. These gears had the coating just scrubbed off to the point where it starts to wear the gears. Not only that, my cam timing via the PK 32Vr thingy, the timing was EXACTLY where I set it the year before.

Granted, this is not a scientific test, do not try it at home etc.

PorKen

I am running a test on my '88 as well. 1-4 has a used gear, 5-8 has a new 01 gear (old style).


I have noted also that the Racing belt shows little to no stretch.

With the Racing belt, you can check with the 32V'r at #1 or #6, T|0 or 4|5 with the same result.

With a regular belt, only T|0 #1 shows the true reading, the others are about 2° off because of differing valve spring tension.

No stretch should mean more accurate cam timing at high rpm.



Because it does not stretch, I would not recommend using a stock tensioner with the Racing belt.

The stock tensioning system needs some belt pre-stretch to work 'properly'.

hacker-pschorr

Todd is using the stock tensioner.
He's comfortable manually setting tension. I don't think he uses any tensioning tool.
He did design the tensioner on the Murf928 Supercharger system and a couple other supercharger applications.

ptuomov

Tell us more about this new motor.

hacker-pschorr

That's a different thread, be patient.
Todd has a lot of ideas he's playing with. We don't have the bandwidth to explain them all

ROG100

Up until now I have never recommend a racing belt for a stock car - two simple reasons ---
1) Price $34 v $167
2) I cannot say that the RTB will last X times longer than the stock to justify the price difference - maybe in 15 years I will know different.

polecat702

My personal opinion is just that, my opinion. I think the real difference is Ken's tensioner, not the difference in belt construction.

When I did the TB/WP job on my 89 every thing was new, I bought all my seals, tensioner, 32Vr timing tool, every thing for the job from Roger, except the radiator, Ed's water pump, and new Porsche timing gears. My car is bone stock. We'll see how every thing handles the 120 plus summer heat in Vegas.

928 at last

Hacker, What's a timimg belt ????

And that's with spellcheck.....

Mongo

Considering that most of us do not race our cars, I think we should be okay with the regular Gates belt. They are afterall better than a Conti in terms of stretching.

hacker-pschorr

IMO the belts almost never fail.... on their own, unless they are really old or the car is used in some very extreme conditions.
Tensioners fail, water pumps lock up, gears get old and eat into belts etc......

The racing belt should last longer under this abuse and hopefully give the owner time to fix the situation before the belt breaks.

Take a locked up water pump. Usually they lock up and even before you notice the temp rising, the belt snaps from rubbing on the stationary pulley. Maybe the racing belt will last a bit longer buying you some time to shut down the engine.
No one really knows, just a theory bouncing around my head.

Todd is also running without belt covers, if something does get up into the belt the racing unit should be more durable.

+1
I don't think the standard Gates belt stretches at all in the scenario like this with stock internals.

Todd was in a hurry to install the engine so I didn't get a chance to film the belt stretching on the bench. The next motor he puts together with similar specifications we plan to take a short video of it. Might not be easy to see but we will try non the less.