2.5L options
 

(repost from tech forum, meant to post here)

Hey guys,

Was talking with someone the other day about Porsche race engines for vintage cars and we got on the topic of the 2.5L engine. I know there were a number of different options for this engine but I couldn't remember what all the different combos were out there.

Can anyone give me the "typical" 2.5L's?

THere are two types of 2.5L motors. The first is an overbore of a 2.0 or 2.2. This uses 90mm bore x 66mm crank. These have excellent rod/crank ratios and can easily be used at high rpm with the right oil mods.

The second is an overbore of a 2.4L. This uses 86.5(?)mm bore x 70.4mm crank. These are not as common as the Short stroke version.

The short stroke 2.5 is a great combo since it's so easy to make. Start with a 2.7 7R case motor and then swap out the crank and rods from a 66mm motor. Add P+C of your choice! Voila!

89 x 66 is another possible combo.

THanks guys. What are the relative specs on these engines? ('Reasonably' acheivable HP/Tq)

Maybe 250 hp? A factory 89 x 66 race engine with 10.3:1 was 275@8000 rpm (courtesy of bruce's wonderful handbook).

It is pretty much top end specific. A nice port job to around 38mm w/ MFI or EFI and GE60 (I prefer DC62) cams should easily be good for 100HP/L at 7800 RPM.

I went this route with a 2.3L and should have impressions in early Spring.

2.5
 

We have built some full house long stroke engines for HSR and have made over 300 @ the FW, range is 5500 - 8000 RPM, short stroke about the same numbers but HSR has mandated an RPM rule and passes out MSD chips to 8200.

Mike Bruns JBRacing.com

Here is the Dyno for my 2.5L short stroke at the rear wheels. GE80 cams, Stock 2.7 valves, opened up ports, CW crank, 2.2L rods, true 10.5:1- Almost 100 hours now and coming out for a refresh- 2.5L #2 is ready to take its spot :)
http://forums.pelicanparts.com/uploa...1229054339.jpg

I Also have a few questions. I have a 72T euro motor that I would like to build a 2.5 with. Can I just bore my iron cylinders? Is there any pistons that will work with the iron T cylinders? I think there iron anyway....

Thanks

The T iron cylinders can be bored out, but reliably, really no more than to 85mm. Plus, if you do end up making the horsepower that is expected, the T cylinders don't have the needed cooling capacity.

255 crank HP - nice!

I'm guessing one would need MFI, carbs or EFI to make a 2,5SS perform?

I was thinking of making my 175hp 2,7 into a SS, but I'd rather not part with the CIS.

A nice street 2.5 can be had by using the Mahle high compression 90 mm 2.7 RS kit (if it is still available) with a 66 mm crank. Nominally 10.4:1 compression with a 70.4 mm crank, this kit makes 2518 cc and around 9.5:1 CR with the 66 mm crank.