Opinion on Engine Buildup - Short Stroke 2.5L

[andrew15]

Ok - I've got most of the components together for my short stroke 2.5L build up (actually a bit bigger displacement) and came into a bit of extra $$, so it may take place sooner than I thought. I'd really like any helpful tips, opinions or suggestions on the components to use. So far I have:

7R Case (To have case mods done)
66mm Counter Weighted Crank
92mm RSR Pistons / Cylinders (Cylinders to be replated by EBS)
Early S Cams
Cylinder Heads with 38mm ports
RS Distributor
40mm Webers

I guess some questions I have are:
- Can I use a stock oil pump from a 2.7l engine? Would a 964 pump be better?
- Are 38mm Intake and Exhaust ports to big for mostly street use?
- What head studs to use? Steel, Dilivar, ARP/Raceware?

Thanks,
Andrew M

[jluetjen]

My $0.02...

The 38 mm intake ports should be OK, but I doubt that you'll see much of an difference over the normal S's 36 mm's. The 36 mm ports might be marginally better for street use while the 38 mm intake ports might also work fine with a bigger cam. But at 38 mms, your intake gas speeds (81 meters/second at peak HP, 67 m/s at peak torque) will be slower then most of the E's (87-100 m/s at peak HP), but faster the most of the S's (73-83 m/s for the S's and 92m/s for the RS).

As far as your exhausts are concerned, I wouldn't open them up bigger then 36 mm's since you really want to keep the exhaust velocity up. Just my thoughts after keeping track of all of the different configurations.

As far as the oil pump is concerned, as near as I can tell, new is better. But for street use, it may not really make a big difference since you are not being agressive with rev's or scavenging. It might be a better use of your money to just get a bigger tank with baffles in it as CStreit did.

You haven't mentioned your carb chokes, but I would guesstimate that you're going to want to use about 34 mm venturis. The 32's should work but may choke off the upper rev range a bit. But that may be an OK compromise for street use. 36's will be too big for anything but full race use.

There are a lot of others who know more about head studs then I do. But I believe that it has a lot to do with the type of cylinder that your using. If the cylinders are Iron (T) or Byrol (early E and S), then steel is best. If the cylinders are the later aluminum pieces, then Dilivar or one of the new pieces are best. To be honest I haven't paid as much attention since I'll be running Iron cylinders in my current engine project.

[jgparker]

My 2 cents. Sounds like a really great engine combination...

The stock 2.7 oil pump is adequate but do the bypass mod.
38mm ports is overkill for a street engine.
Use 993 steel studs (Cheap and never break).
If you are worried about consistant torque at temp, use only brand-new 993 dilivar studs.
My 36mm venturies are great for streat use, but my engine is a little bigger than yours.

Good luck and keep us posted,

JP

[andrew15]

Thanks for the thoughts so far - Personally, I would like a smaller port (36mm), but the heads had the porting done when I got them. If it is overkill, and would reduce intake speeds too much, I may have to get a different set of heads worked over.

Regards,
Andrew M

[Steve@Rennsport]

Andrew:


Given the cams you will use and your displacement (2.6 litres), I would get another set of heads and do the 35mm intake/35mm exhaust setup.

I would also ditch the 2.7 oil pump. Use either a Carrera pump or 3.6 pump. Personally, we use either GT-3RS or Turbo ones as these mag-cased engines tend to lose oil pressure when hot and these larger pressure/scavenge oil pumps help the engine run cooler from better scavenging and provide much better hot oil pressure.

As long as your 7R has case-savers, you'll do very well with steel head studs.

[Wayne 962]

Originally posted by Steve@Rennsport
Use either a Carrera pump or 3.6 pump.

Steve, the Carrera pump has the same pumping specs as the late 2.7 pump. What would be the advantage, in your opinion, of using the Carrera pump over the four-line magnesium 2.7 pump?

-Wayne

[Steve@Rennsport]

Hi Wayne:

Carrera/SC pumps do much better than the 2.7 pumps as they do not expand as much when hot. We've used both in race and street cars and hot oil pressure is improved.

3.6 pumps are an economical solution as you know, but the GT-3 or Turbo ones are well worth the money, IMHO for any engine that will see 7000 RPM or above.

[pjv911]

Did this engine ever materialize ? I would be interested in your rsr pistons (want spares) if your not going foward with this engine .

Kurt Williams

[andrew15]

Hi Kurt - I do still have the RSR pistons, but I'm planning on using them to do the rebuild this summer. This fall I took delivery of a 1970E w/ a 2.2 S engine. It's a blast to drive, but it needs badly so that is the new winter project.

Regards,
Andrew M