3.0ltr sc engine to 74 3.0rs spec -questions

[advtracing]

Hi Guys , i have purchased a damaged (burnout) 79 targa of which i am using the big port 3.0 euro engine and rebuilding it to 74rs spec on webers for my r-gruppe car.
now from the details i have via the performance books everything looks the same between the two except the pistons /compression and the cams ?
i can't find a cam comparison , so can anyone advise what cams are 74rs spec ? and how they differ to the euro sc cams , plus can the sc cams be ground to rs spec?

anything else i'm missing ?

[Bill Verburg]

Originally Posted by advtracing

Hi Guys , i have purchased a damaged (burnout) 79 targa of which i am using the big port 3.0 euro engine and rebuilding it to 74rs spec on webers for my r-gruppe car.
now from the details i have via the performance books everything looks the same between the two except the pistons /compression and the cams ?
i can't find a cam comparison , so can anyone advise what cams are 74rs spec ? and how they differ to the euro sc cams , plus can the sc cams be ground to rs spec?

anything else i'm missing ?

The bottom end is also different, the '74 RS 3.0 would have used the same 2.7 crank as the other mg case 2.7s, the later SC3.0 use the somewhat more robust 930 crankshaft though for increased revs stronger rods, Pauter, Carillo, or SC/RS would be good choices

The SC heads/valves are essentially the same as those used on the '74RS 3.0 so you are good to go there

the cam used on the '74 3.0RS was the same S cam as used on the '73 2.7RS, no surprise as it also use the same MFI w/ updated space cam,

the p/c is going to be the issue, you need pistons w/ deep valve pockets for use w/ the S cams, 95mm version of these were available at one time, don't know how available they are now

You could also use the 98mm versions for 3.2L displacement
the 98mm p/c set w/ deep valve pockets for use on an SC bottom end is
930.103.984.98
these are 98mm bore 85.6mm cyl height, and use 22x58mm wrist pins, cr 9.8

there was also a 3.3 high compression version
930.103.962.10
100mm, 85.6mm cyl height, 22x61mm wrist pin, 9.8cr, these are just a larger alternative to the first set.

If you want to stay at 3.0 liters then the SC/RS p/c set
930.103.937.00
10.3cr

[Phares]

Sub'd

[advtracing]

wow , everything in one hit great .
so we need to find the deep pocket pistons (either option), try to keep around the 9.8.1 compression ( as 10.3:1 would be a bit more than i want as i am building a 2.5st engine for a ST i don't need 2 hairy cars)

rods etc... easy upgrade , so cams- S cam made for MFI how is that going to run with webers ? or we need a cam with a grind to match the S performance that works with webers

[advtracing]

Originally Posted by Bill Verburg

the p/c is going to be the issue, you need pistons w/ deep valve pockets for use w/ the S cams, 95mm version of these were available at one time, don't know how available they are now

maybe this is the ticket

[Eagledriver]

Those won't work with "S" cams. Those are CIS pistons. You probably would need to go with JE pistons to get compatible pistons.

"S" cams work fine with Weber carbs, but there are bette choices. GE 40 is similar to "S" cams but with better lower end torque. GE series cams need racing valve springs.

-Andy

[KTL]

Yeah I bet the factory 95mm pistons are going to be a tough find. You might find you're better off with the 98's like Bill said. Pelican doesn't show the Mahle Motorsports in their catalog, aside from the Yellowbird pistons, but they could likely get others for you. Guys like EBS, Steve Weiner or Henry at Supertec could be a good resource for the specific pistons you want. For instance EBS has a suitable 98mm set for carbs/MFI

Porsche - Mahle Motorsport Piston & Cylinder Sets

[lindy 911]

If your cylinders are in decent shape, JEs are a great choice. You could use the money saved on twin plugging the heads and a 12 wire distributor and build something worthwhile. 10.5:1 is a big difference than 9.5:1 staying at 3.0 l. Personally, 95mm jugs, 10.5 JE pistons, twin plug '79 SC heads, GE 60 cams, 46 Webers and headers and you done. 275 FW hp without trying real hard (6800 rpm).

Exceptionally street-able engine.