N421LV

I'm sure this has been discussed before, but I often get asked this question by non-Porsche types (vette owners, in particular ) when they learn about the admittedly short replacement interval of our timing belts. So...all you engine design experts out there....any ideas as to why Porsche went with a timing belt instead of a timing chain on the 928 & 944? What are the tradeoffs?

Nicole

It was done to keep the engine length shorter.

From what I understand, if they would have driven water pump, oil pump, and the cam gears with separate chains, that would have taken more space length wise.

Also see "Project 928", page 31.

EspritS4s

I don't have Project 928 handy, but I don't understand this assertion. Why couldn't the timing sensitive portions (cams) have been chain driven with the remaining accessories belt driven? Aside from noise, what are the other downsides to a chain?

hacker-pschorr

Let's do a 180 - why use chains? I have a Mercedes Engine with bent valves wth a cam chain.

RyanPerrella

ferrari dosent use chains

there is nothing wrong with a belt. They need to be serviced. Big deal, pay attention to them and your fine. The belt is well made and very strong.

hacker-pschorr

Ask your Corvette buddies why it took Chevy 50 years to win LeMans.

CaseyH

Let's not forget to focus on the question at hand. He asked what the advantages to a belt are over a chain. He didn't say there was anything wrong with it.

hacker-pschorr

We covered that - noise and it would have made the engine bigger.

CaseyH

You beat me to the punch. I missed Nicole's post the first time. I was a little late on deleting my pointless post.

hacker-pschorr

When you have 12,000 pointless posts you can start to feel dorky

tomcat

Didn't someone say, before my time, that the engine expands - 1/2" specifically from cam cover to cam cover. Therefore a chain couldn't be used. I don't think I would want to stretch my belt 1/2" either. Sounds like BS to me, but what do I know.

Bill51sdr

Corvettes break timing chains/gears too. A guy in my SCCA region had a C5 Z06 that did just that. The engine was toast.

danglerb

There is no point in picking apart what Porsche chose to do 24 years ago, we LIKE the end result, and most of it there is no practical way to change. I don't know how you can look at the front of the 928 motor and not scratch your head a bit and wonder what Porsche was thinking.

***************** pointless post padding below.

Lets see, warranty is 5 yrs and 50,000 miles, TB needs to be replaced 6 years or 60,000 miles, DAMN that is fine German engineering.

I forget how long did it take Ford to not just win at lemans but to totally dominate it, 3 years something like that?

Chevy engine has some water pump issue (how odd eh?) that people modify to go to a double timing chain thats more reliable. Racing breaks parts or you aren't having fun.

Wade T

Timing chain = more rotating mass - hurts performance

Belts are superior. But after working on Toyotas many years for I can honestly the 928 TB design is far more complex than need be.

danglerb

Modular is what I think of with the 928 motor, Porsche made "local" changes and left the rest of the motor alone as much as they possibly could. The 16v -> 32v its kind of like they just "added" another of the same cam setup.