RS 2.7

as you guys may know, i am trying to sell my 944 so i can buy a miata and turn it into an autocrossing beast.

well, as i was reading about the miata i found out that the only problem with not changing your timing belt is that it will leave you stranded when it breaks since it is a non-interference design.

is it common to have a design that will bend valves when the t-belt breaks or is it more common to have a non-interference design?

how does the non-interference design work? and if it is easy to do this, why didnt porsche do this for the 924/944/928/968 series?

*Michael.*

You will not be disappointed with a Miata. I own a '90 model. I have only run it on an Auto-X track once and it was great. I haven't done anything to it yet as far as suspension goes but I do have some KYB AGX's sitting in my garage. I am not sure which springs I am going to go with quite yet. If you go with bigger sway bars buy the Sway bar reinforcement kit that <a href="http://www.racingbeat.com" target="_blank">Racing Beat</a> sells. If you buy a new set of wheels I would go with some Rota wheels. They aren't very expensive and they are super light. If you have any Miata questions just email me. This is the second one I have owned mike@sembach.af.mil

If you haven't already found it, take a look at <a href="http://www.miata.net" target="_blank">www.miata.net</a>

83 TX 944

A miata, find another board please.

RS 2.7

thanks for the info michael adkins-

yes i have already checked out miata.net and its very helpful. one of the first mods i will do is the racing beat suspension package b/c they said they had a car equipped w/ it that set the slalom record and achieved 1.2 g's on the skidpad. very impressive

SoCal Driver

Miata's. Interesting. When they were first being marketed I was listening to a radio add, yes driving in my 944, about how the exhaust was designed to sound like an expensive sports car.

No kidding! I laughed about that for weeks!

I have nothing for or against Miatas.

As to why the interferance. Has to do with flame path. The way the combustion takes place in the cylinders. Wish it didn't. I've always wanted to see how much material would be needed to be removed from the pistons to clear the valves.

944Fest (aka Dan P)

No expert here, but the items that help an engine breathe, as in, lift of the valves (how far they open) and duration are two variables, and maybe piston head surface shape. Porsche designed all of these to produce maximum power in our engines. If they designed a piston with cut outs for valves, and barely opened the valves to keep them out of the travel of pistons with "bad timing", then you would have a non-interference engine. But then you would also have a wheezing dog.
They do things for a reason, and it may seem stupid when your timing belt breaks, but on the victory podium it seems like a great idea.

just my .02

<img src="graemlins/beerchug.gif" border="0" alt="[cheers]" />

Steve Lavigne

[quote]Originally posted by Dan P:
<strong>But then you would also have a wheezing dog.</strong><hr></blockquote>

Case in point, first generation MR2. It had a 1.6 liter 16 valve twin cam engine with a non interference design that made a wheezing ~106 hp. Most of the head modifications popular for this engine required it to become an interference design. This same basic engine in a much higher state of tune with an interference head makes 260 peak hp with the same displacement and no forced induction.

Danno

Since no one mentioned it, the ridge around the valve cut-outs in the pistons can get very hot in a non-interference design. That's because there's less metal around it than other areas of the piston top. So this hot crescent-shaped ridge can be a source of detonation. You won't be able to run as high of a compression-ratio as an interference design, thus not make as much power.

Brian McCoy

So the interferance part is a good idea... why not add a LITTLE mor weight and give the whole system a hivo chain, or gears? My motorcycle has gear-driven cams and was #1 for a few seasons - and this is on a motorcycle where weight is much more important.

I wouldn't think it would be that big of a deal to further bullet-proof a higly capable engine.

RS 2.7

wow...very interesting responses. thanks for your input guys, it is definitely cool thinking about this sort of thing

sweanders

I wnet to the track and drove with the local Miata Club, got a ride in a pretty modded car. Rollcage, slicks and all..

It was pretty impressive but not even close to stock.

So I took a drive in a new six speed Miata at the dealership and was not one bit impressed... It just felt all wrong somehow.

It was nice to drive the 944 again after that..

Tabor

[quote]Originally posted by Brian McCoy:
<strong>So the interferance part is a good idea... why not add a LITTLE mor weight and give the whole system a hivo chain, or gears?</strong><hr></blockquote>

Because timing belts are a lot quieter. Also, most cars can go 60-80,000 miles before a scheduled timing belt change. Porsche did not anticipate the expansion problems that our cars have.

PS- Hondas are interference design, and everybody loves their "reliability". Also, the 924 is non-interference.

*Michael.*

[quote]Originally posted by Tabor Kelly:
<strong>
Porsche did not anticipate the expansion problems that our cars have.
</strong><hr></blockquote>


Do the cars have the problems or is it that people don't keep up with maintenance...

[quote]Originally posted by SoCal Driver:
<strong>the exhaust was designed to sound like an expensive sports car.

No kidding! I laughed about that for weeks!

</strong><hr></blockquote>

So it isn't good that Mazda tried to make their exhaust sound good? If I put a nicer sounding exhaust on my 944 would you laugh at me for weeks?

Brian McCoy

[quote]Originally posted by Michael Adkins:
<strong>So it isn't good that Mazda tried to make their exhaust sound good? If I put a nicer sounding exhaust on my 944 would you laugh at me for weeks?</strong><hr></blockquote>

Reread that.. it's designed to SOUND like... not perform like.

It's a 'turbo sound simulator' device, only it simulates the sound of a performance exhaust (as opposed to putting a good exhaust on there in the first place).

*Michael.*

[quote]Originally posted by Brian McCoy:
<strong>

It's a 'turbo sound simulator' device</strong><hr></blockquote>

Huh?? Turbo Sound Simulator? Could you tell me a little more about this device? Where in the exhaust is it located?