2.7 Build - DC40/Mod-S or DC/GE60 cam on stock valve springs?
 

Hi all,

I've just spent the past couple of days combing through and searching for cam recommendations. Lots of info but couldn't find experiences with the same specific set up as I'm looking at.

Background - i'm in the process of having my 74 2.7 ROW motor rebuilt. This motor had relatively few kms on it and is the small port cooking model. I'm having the bottom end shored up (case savers, line bore, shuffle pinned) and will be installing ARP bolts and supertec head studs with new bearing all round. I'm also fitting a 996 turbo oil pump with the shorty 930 connecting shaft to ensure good oiling.

I'm rebuilding this as a relatively hot motor - this isn't a daily driver, just a weekend play toy and occasional track tool. I'm looking for something revvy and peppy on the street, but not undriveable. I do like revvy things though, and have streeted and tracked 2-stroke motorcycles in the past which was always fun :)

The parameters for the rest of the engine rebuild - 9.5 or 10.5 JE 90mm pistons, opening up the ports to 36/35mm I/E, 40mm IDTP webbers and new but standard valve springs and standard valves. Given the bottom end work i'm looking forward to an increased rev ceiling (7-7300rpm) but working within the confines of the standard valves and rods. I'll be running this exclusively on 98 RON fuel, and am considering dual plugging.

So my actual question (at last) is on cam selection. I was originally looking at running an early S cam, but am now vacillating between the DC40/Mod-S profile and the DC/GE60. From what I understand, keeping the rev ceiling up around 7-7300 on the stock valve springs & retainers was largely achieved by the factory by running relatively sedate ramps on the cams.

Given the GE60 has quite a bit more lift than the S or even the DC40/Mod-S cams, I'm looking for feedback from anyone with experience running the GE60 on the stock 2.7 valves, springs and retainers, and whether this offers any real advantage over the S/Mod-S profile while keeping the rev ceiling to around 7300 rpm and 36/35mm ports. I like the idea of a bit more top end but concerned it won't eventuate without going to larger ports and a higher rev ceiling that the stock springs wouldn't accommodate, particularly with the more aggressive ramp of the GE60.

Sorry for yet another camshaft thread...I have been diligently searching!

Cheers,
Neil.

Eibach makes a "high lift" spring that should work with 60s for a reasonable price.
I've had good luck with them.

It can be done, though probably isn't ideal. I have 60+ hrs on a track engine running an Elgin 310-296 cam (I believe it's a little hotter than the DC60) using early S springs, revving to 7500. I shimmed up my springs as high as possible without reaching coil bind, and they seem to be OK. I haven't missed a shift fortunately ... I am not sure how well this top end would take an overrev.

There are more options these days for springs, and Eibach springs sound like a good choice and are pretty reasonably priced as mentioned.

Thanks guys. I'd like to stick with the stock springs I think, at least for the time being, as our exchange rate isn't real flash at the moment (should have bought a couple of years ago :) ) and the cost of shipping bumps up the cost of the eibach springs. Which I guess puts me on the fence a bit (just for a change!).

If you don't mind me asking, what sort of port sizes were you running on your track motor? What's the seat of the pants power spread feel like to 7500rpm?

I'm running 40 mm intake port size and 38 mm exhaust. The car takes off like a scalded cat starting at 5500 RPM. I limited revs to 7500 to keep things reasonable but its probably really an 8000 RPM motor. It would probably not make a very nice street motor, but I'm pretty sure the specs for the 310-296 cam are hotter than the DC60. Elgin's web site should have the specs if you want to compare to your cam profile, but I seem to recall that my cam is similar to Dougherty's DC80.

Scott