Motorsport Aurora Engine Handbook...

[OldsMike]

As a purveyor of all things Oldsmobile, I picked up the subject book online and it came to the house today.

I've already thumbed through it and it's basically a step by step buildup of the 4.0 IMSA WSC and the 4.5 GTS-1 engines. Some pretty cool pics, I know that I'm going to need to pickup a junkyard 4.0 sometime and do some experimenting with some of this newfound information.

I haven't found any Dyno results which is a disappointment and the pictures only come in B&W.

I found interesting that the 4.0 has a bore of 3.75" and a stroke of 2.75". The 4.5 has the same bore, of course, and a stroke of 3.10". Increasing the stroke to 3.75" would yield gobs more torque without any appreciable impact on horsepower. don't know if the geometry would allow a 1 to 1 ratio bore vs stroke (or higher) but I did notice that Scat makes the crank and Carillo, the rods. Both would make whatever you wanted to obtain in terms of stroke.

A good enhancement to your Aurora or Oldsmobile literature collection. My copy cost $16.00.

[SupaStealth]

now with that increase in stroke, are they still able to use the same block and oil pan? or did they just basically change the crankshaft and rods.

[OldsMike]

SupaStealth said:

now with that increase in stroke, are they still able to use the same block and oil pan? or did they just basically change the crankshaft and rods.

There is a separate block. No details to the differences between stock and hi-perf version. If I assume that the geometry is the same (that's probably a safe assumption), then the hi-perf block block has increased web thickness and all the standard hot rod updates for ultra high horsepower. Those IRL engines had high horsepower but I'm not so sure what the torque was. The race cars the Aurora engine went into were very light. Producing high torque in a stock block to push a 4000 lb car around is a completely different situation. Would be fun to get the race heads, cams, the HD bottom girdle with the stock block to see what kind of torque to HP could be made. A early 70's A body or a mid 80's G body would be a cool transplant with a hot rodded 4.0 Aurora powerplant. For that matter, a heavily hot rodded 4.0 in a Aurora would be fun too! ;D

[Aurora40]

Just as an FYI, the IRL Aurora V8 and the IMSA Aurora V8 were very different from each other. The IMSA block was probably closer to the production motor, and was not as high-tech. The IRL V8 made almost 700hp from 3.5L, the 4.5L IMSA motor didn't make that much.

However, both motors were dominating, and both were pretty awesome.

[nthums1]

Wow, almost shocking geometry. Just from the bore and stroke, I would have guessed ford. GM generally were under-square. (small bore, long stroke). One exception that comes to mind, but not sure if it became under square with the mod, was 69? Camaro RS. May have been in some Yenko's as well. It had a 302, which was really a 327 down stroked. Mostly a shorter crank. It could develop a lot of RPM qquickly.

[oldsauroraman1]

GM - The Mark of Excellence.

[Marc]

The Motorsport Aurora Engine Handbook is still available.
Go to the site noted below & scroll down to its listing.


www.gmgoodwrench.com/perfpartsjsp/partlist.jsp?cat=9279§ion=pp

[oldsauroraman1]

Great link Marc. Also, wouldn't the valving need to be changed to do this?

[Marc]

The valves would need mods to be able to breathe adequately at 10,000+ RPMs.

[Aurora40]

nthums1 said:

Wow, almost shocking geometry. Just from the bore and stroke, I would have guessed ford. GM generally were under-square. (small bore, long stroke). One exception that comes to mind, but not sure if it became under square with the mod, was 69? Camaro RS. May have been in some Yenko's as well. It had a 302, which was really a 327 down stroked. Mostly a shorter crank. It could develop a lot of RPM qquickly.

You are thinking of the Camaro Z28. It was for Trans-Am racing, and came out in 1967. The shorter stroke was for elevated rpm operation, I believe it could run to roughly 7,000 rpm.

It's interesting you think GM motors are generally undersquare, as the 350 smallblock, probably the most ubiquitous motor ever (though the Buick V6 might be close) is oversquare, with a 4.00 bore and 3.48 stroke. The Chevy big-block and Buick V6 are also oversquare. The LT5 and LSx motors are also oversquare, though less so than the GenI/II 350's.

[adam]

The chevy 302 was actually a 327 small journal block with a dz code 283 steel crank. It was in the camaro's and two other cars for less than 3 years.