2.5 Engine Build sheet

[Ben M]

Anyone have the build sheet/specifications on the 2.5 liter engine built to run in IMSA GTU years ago?

THANKS!

[Ben M]

How about recommendations on building a 2.5?

[Henry Schmidt]

Most of the teams racing GTU back in the 2.5 IMSA days were privateers so the engine builds were as diverse as the field.
I had the chance to participate in a few builds of these type and I'll give you what I remember.
Short stroke 2.5 296 horse power
66 mm crank, some with 906 titanium rods.
89mm Mahle pistons (10.4+:1 compression ratio), extremely thin light weight wrist pins and cylinders flow relieved
7R mag case:
.....Shuffle pins
.....Boat tail (although later dyno testing showed no benefit from this mod)
.....Case savers
.....Enlarged piston squirters
..... Oil By pass mod
..... Welded main webs in bell housing area
908 oil pump
Lightened intermediate shaft and gears
Solid tensioners
Shrick cams (272/260 @ .050" with .520"/.500" lift on a 98 lobe center)
Aasco valve springs
Titanium retainers
906 solid rockers
Twin plug 906 distributor
910 slide valve with a modified 2.0 S Bosch MFI pump or 46 mm Webers
Highly modified production heads. Hugh ports (40-42mm) Ty valves for sprint races.
Light weight flywheel
I even saw one attempt at roller rockers.

[Ben M]

Pretty dam good memory Henry. THANK YOU!

PS: Were these durable engines?

[Henry Schmidt]

Durable? really?
If you believe 30 hours between rebuild is durable.
These little gems were twisted pretty hard and when you wind any engine up to it's max, durability is a relative concept.

[neilca]

I would say that is durable enough for a 24 hr race.