ViribusUnits

Why is the 928 engien so darn big?

The engine is simply huge. I know part of the issue is caused by the engine being "upgradeable" to 6.5l. But why is it so wide?

All the domestive V8s are 90 degree motors, with similer stroke lengths. Are the conning rods on the 928 just hat much longer, or is it partly because the heads are sloped in the other diriction?

Or just a bunch of little things that add up?

Thanks.

V-Fib

To make a better ANCHOR!
Sorry VU, good question though.



Anthony Tate
79/928 Silver Metallic

GlenL

Overhead cams?

Also, the water jacket looks kind of wide.

Gregg K

Ninety degrees! And OHC.

Jim @ EuroWerks

Aluminum was cheap!

Giovanni

to prove: size matters :-)

Normy

Porsche designed the 928 exterior around a wooden trophy given to a junior member of the staff at a banquet in 1972- it is said that Ferry Porsche saw the wooden "Porsche" on top of the trophy and handed it to Tony Lapine, with the instructions "Lets do something like this for our 911 replacement".

The trophy had a long, flat "shark" nose. This striking detail demanded a low engine. Our engines are 24 inches tall, yet 31 inches long and wide. This is about the same, though flatter, as a typical big-block American engine.

-So much for the small block comparisons!

Overhead cam engines are always large. The engineers at gm like to say they stay with the antiquated pushrod valve trains just for this reason. Funny thing- if you look under all but the corvette's hood, you'll see that there is plenty of room for cams in the cylinder heads-

Viribus, a better question might be WHY this engine typically weighs 565 pounds. All aluminum V8 of 4.5- 5.4 liters? Hello? Must have been heavily overbuilt....

N!

atb

It's in the hemi-heads, and the OHC's don't help either.

Ever look at a a 426 Hemi or a Boss 429? Mmmm....big.

-Adam

Gregg K

The first time I saw a Jaguar V12 engine in the junkyard, I thought it looked the size of a coffee table.

ViribusUnits

Cool, so it's bascily a large number of things that add up.

Normy, I used to have a thing aginst push rod engines.

Then I realized, they may not rev as high, and such can never can make as much hp/l, but they typicaly are lighter for a given displacement.

Something just occured to me as to why a 928 engine weighs so much. You have 4 times the number of camshafts, the associated camshaft drive, on realy a 6.0l block/head. (the 968 block is as I understand it, has nearly the same external dimitions as the 928 block, just some redesigned internals and 3 liters so the 928 engine is comprably good for 6.0l) You have 4 times the number of various odds and ends for the cams, as it's "extra" metal on top of the head, instead of makeing the block and crank case houseing do double duty.

So, I guess a heavily build 366 cin hemi 32v dohc engine should weight alought more than a 16v traditional push rod wedge shaped combustion chamber 350.

A stroked 104mm 928 engine is as we all know 6.5l, or a mear 396 cin, thats begining to verge on big blocks. Not quite there, but getting darn close. IIRC, that more than your typical 350 stroker at 383 cin...

Anyways, I got to thinking, a 350 may not make that many hp/l, but I'll bet it does just as good as the Hondas in the hp/lb catagory. And in truth, we both know thats what really matters for proformance driveing. If you can get more displacement for the same weight. Hum... Where can I look up the weight of a Honda VTEC engine...

Intersting...

User 4221

Rumor has it..... I think from Eifert's trip to Euro 928 last year with a discussion with Tony Lapine....... That the 928 was originally supposed to be about 6 inches wider than it stands today. However, when the prototype was delivered, they could hardly fit it on the roads in Europe and was narrowed for production.

It they had stayed with the original width, changing the clutch master would be a snap!

Tony

Ill vouch for the weight of the heads! dang! Surprised me when i pulled them off!

...oh, and another thing.
When you have your pulled engine in the stand and have the oil pan off, DONT be in a hurry to roll the engine over to have a nice look. You will get to about, MMmmm, 20 degrees and then the motor rolls over by itself.
quite quickly and forcefully i might add!
IT is very top heavy in the stand, for those pulling a motor.

GoRideSno

Viribus,
I think I have figured out your method of spelling. It seems that you spell phonetically from a southern accent. Long ago when I first read one of your posts I thought you were from the UK.
You should try living in LA w/ a southern accent like me.

The heayds are reayl heavy. I bet the crank is reayl heavy too.


Andy K

drnick

it is, easily apparent to ourselves here in the uk, where the majority of posts originate from!

Doug Hillary

Hi,
Gregg - yes they are real factors - a 90deg V & DOHC.

With a 90deg design V8 the free forces/moments of the first and second
order and the ignition intervals tend to make the engine easier to balance
But the "footprint" is rather large with DOHC

Ford Germany made 60 deg V6 engines in the 1960s ( common today ) and whilst primitive OHVs they were extremely smooth at mid to high revs. They also made a 60deg V4 ( used by SAAB too ) that sounded good but but was "rough". It fitted into the SAAB's "engine room" in place of a three cylinder two cycle engine and were quite durable

Our engines are a product of the CAD of the time ( minimal ) but it amazes me to hear of their durability if well maintained - a great design

Personally, I think the older USA made OHV V8s were a truely great example to the world of a mass produced quality but simple product of outstanding durability. Testament to a great era in the US auto Industry

GM got it wrong recently though with their all alloy V8 so even the greatest design resources available don't always get it right at the manufacturing stage either

Regards