[grantsfo]

Don't the 986 engines have intermediate shaft failure issues?

M96 motor in the Boxster has a variety of failure modes. Intermediate shafts fail on a number of motors, earlier 2.5 liter motors in 97 to 99 had some casting issues. My 99 had a cylinder sleeve slip and it caused all sorts of havic, broken rod bolt, piston tore everything up, block was a total loss. Some motors have D chunk issues where poor casting allows cylinder to crack in shape of a D. Rumors of oil starvation issues. Newer motors have addressed some of these problems.

To the other question above the M96 due to thin cylider walls and high compression doesnt lend itself to forced induction too well.

I bought a cheap used Boxster motor to stuff in the car while I look at a long term conversion. I'm thinking an Audi V8 is way to go. I think the Audi V8 and Porsche V8 are basically the same motor but there arent many people I know of doing Porsche V8 conversions. Mostly Audi V8's.

I think biggest question with Boxster tranny is related to starter motor and whether its in the right place. I havent seen enough pictures of the tranny or motor to know. I was hoping to find if anyone has tried bolting the Audi V8 to a Porsche Boxster tranny of any kind.

My original Boxster motor carnage pictured below

 

[grantsfo]

Did they fix these problems by the time the 2002 model rolled around?

No there are failures with those motors too. Just not as often. There is a great aftermarket developing but its expensive. Resleeved blocks, new IMS bearings that are made to last, etc.

One company is coming along with ways to address issues. My motor even made their hall of fame!

http://www.flat6innovations.com/engine- ... llustrated

 

[grantsfo]

Ah the M96 sounds like a disaster of an engine, we don't see a whole lot of those sort of failures on the Audi side of things.

I'm not so sure the Porsche V8 and the Audi V8 are of common origin. While I have not studied the Porsche V8 engines closely I remember something about the early 928 engines being of some relation in bore/stroke possibly valvetrain design to the 944 2.5L I4. If that were true the Porsche V8 is not like the Audi V8, the bore spacings are probably different and as such they are not the same engine. The picture I just dug up of the Cayenne's turbo V8 shows a front mount chain drive... the 079 Audi V8 is chain drive but the chain drive is rear mounted. Audi also used roller rockers on a lot of the V8 engines and in some engines 5v/cyl design heads. Porsche looks to be using lifters in the Cayenne... again signs of different engineering.

The Audi V8 engines can withstand turbocharging, that much has been demonstrated on this forum. Marc Swanson is bonkers for boost and he has been tinkering with the V8 engines, I think he managed over 350awhp from a 3.6L V8... plenty of power for a Boxster.

If you don't have room for the V8 you may be able to fit the V6 or more specifically I'd consider maybe assembling a hybrid. The 2.8 and 2.7T are both 078 engines and you can supercharge the 2.8, and folks use the 2.8 heads on the 2.7T... so maybe if you don't have space for the turbochargers of a 2.7T an Eaton blower mounted in the valley of a hybrid V6 with upped boost pressures (limited by intake air temps and fuel type, E85 might work well here) could yield a potent engine in a smaller package than the V8.

I think Boxster has plenty of room for a compact V8 like the Audi motor. I like the 2.7 T as well - have seen it used with Porsche 914's. V8 just has more appeal to me.

When I say Porsche V8 I mean current version in Cayenne. Porsche guys say its very close to Audi, but I think Audi has more aftermarket support.

I just would like to find somone who has actually tried to hook up a Boxster tranny to the Audi motor for a mid engine car to hear what parts are needed. That will save me some time and $$$$.

 

[grantsfo]

It can't be that close to an Audi engine, as the current bore spacing of even the 4.2L won't allow for much more displacement than that. The whole reason why we have the 4.2L is because Audi changed the bore spacing from the standard 88mm to 90-something. I believe all Audi V8's (3.7, 4.0TD, 4.2TD, 4.2FSI/tt, etc) since the ABH use the larger bore spacing and similar block size, which as I said, doesn't allow for much more displacement. If Audi hasn't gone larger than 4.2L in a V8 since 1991/1992 there is a reason. The V10 had a little room left despite the 88mm bore spacing, which meant it could go from 5.0L (two banks of 2480cc) to 5.2L (two banks of 2583cc IIRC).

Goog point but exteriors, intakes, etc appear to look very similar. So I suspect that based on smaller bores the Audi motor is a little smaller than the Porsche which would be better. Does somone have all the exterior dimensions of the 4.2 liter Audi V8? Is there a cutaway view of this motor somwhere?

 

[grantsfo]

Your talking ALOT of body work as the V8 engine is quite a bit taller than the engine in the boxster. You'd loose quite a bit of trunk space, and there would possibly be some intrusion into the passenger compartment.

The Boxster uses a 5 speed very closely related to the 012. The Boxster S 6 speed is of the 0A2 variety.

Boxster motor has big tall intake and a bunch of systems on top of the motor. Audi V8 intake nestles down in between heads. I dont think it would be too tall, but with measurements I will start to learn what will need to be done. There is already a big hole over the top of the stock engine compartment with a removable cover. Tis is located under the convertible top. Firewall also already has a cut out as well with a plate that bolts over the area. I dont have a convertible top anymore. Car has a hard top. So if it was just a matter of making square just a little bigger I dont know if that would be too much sheetmetal work. I dont think its much longer lenght wise. Trunk is way in back of car over the tranny so dont think I'd lose any trunk space.

Porsche 914 guys shove Chevy V8's in their little mid engine cars all the time with no or very little sheetmetal mods.

Somone is doing a SBC conversion on a Boxster now. I will be getting lots of info from that build.

Here's a picture of my current car. You can see hole on top and plate in front.

 

[grantsfo]

Interesting... I've never seen that view of a Boxster.

This is even better shot

 

[grantsfo]

I'm gathering information for somone who will likely do one first. I will learn from mistakes and build mine after this.

I still havent found anyone who has hooked up an Audi V8 to a Boxster 5 speed. I'm getting the demensions of the engine bay soon to determine how much cutting if any will be required.

 

[grantsfo]

Brad is making lots of progress with an LS1! Given that you can pickup Boxsters with blown motors for under $4K it seems to me V8 conversions are way to go!

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