Heads for 2.8l Race Engines?

[zuffenhausen]

Hopefully some of you GT-4 racers will see this thread and reveal some of your engine innards...

I have a 2.7 that I will soon be rebuilding as a 2808cc race engine under PCA GT-4 class rules and I'm wondering what heads are best to use. I imagine a set of RSR 2.8 heads would be ideal, but the chances of finding those are slim and the chances of paying for them slimmer. The 2.7 heads are in serviceable condition, but the valve and port sizes are a far cry from those of the RSR. It is worthwhile to have them ported and larger valves installed, or is there another type of head that would be readily available and/or work better?

BTW, the specs on the RSR 2.8 heads are 49mm (I) / 41.5mm (E) valves and 43mm (I&E) ports.

Thanks!
-zuff

[Early_S_Man]

Well, SC heads would seem like a good starting point, though some extra, non-traditional machining and TIG-welding work would be required ... besides the usual dual-plug machine work!

1. Mill head stud clearance inwards 3 mm and enlarge pockets and spot-face seating area for barrel nuts.

2. Build-up head spigot area for 92 mm barrels OD, and remachine ...

3. Bore and tap for MFI injectors.

4. Intake porting required will actually be slightly more than with 2.2/2.4/2.7 MFI 'S' heads out near manifold mating surface, but less inwards near the valve, since SC heads have a much larger port that flares out at about 1.75" into the head ...

3.0 SC 49 mm intake valve:

Manifold face -- 1.349" x 1.324" ... 34.26 mm x 33.63 mm
0.5" in -- 1.359" x 1.383" ... 34.52 mm x 35.13 mm
1.0" in -- 1.398" x 1.421" ... 35.51 mm x 36.03 mm
1.5" in -- 1.405" x 1.467" ... 35.69 mm x 37.26 mm
2.0" in -- 1.731" x 1.763" ... 43.97 mm x 44.78 mm

... vs 'S' MFI head with 46 mm intake valve:

Manifold face: 36 mm
1/2 inch in: 37 mm
1 inch in: 38 mm
1 1/2 inch in : 39 mm
2 inches in: 40 mm

[82SC]

answer to your prayers

FACTORY 2.8RSR ENGINE etc.etc.... FOR SALE

[dtw]

Warren-

If this much creative machine work is required, what makes the 3.0 heads a more attractive starting point than the 2.7 heads? The thermal reactor ports?

Zuff-

Have you decided what form of induction you will be using on this engine? Engine management?

[Early_S_Man]

Dave,

I think the SC head volume, larger valves, and the port pocket already enlarged to go with the larger valves are the deciding factors. Others may have different views.

Bear in mind that the 2.8 RSR head was larger in volume ... just like the SC heads, and was used with racing pistons that had crowns sized to that specific head volume ... and that 2.8 pistons used with 2.7 heads give a much higher compression ratio than the nominal figure the factory engineers designed it for!

[Wayne 962]

I've got a set of factory twin-plug heads from the 933 motor (Turbo airplane engine). Exhaust port 39.6mm, intake 41.2mm, 49mm intake valve, 41.2mm exhaust valve.

Probably going to auction them on eBay soon...

-Wayne

[dtw]

Raid the Aase yard, Wayne?

[zuffenhausen]

Dave:

I'll probably be starting with a set of Webers /PMOs and maybe move to Motec (or similar) later.

Warren:

Thanks for the info regarding using the SC heads. That may be the way to go. It figures that I happen to have a set in my garage, but they're the smaller port version from an '80.

Also, I am aware of the CR problem caused by using the 2.8 P/Cs with the 2.7 heads, but that was primarily a problem for street applications. The resulting 11.75:1 is reasonable for a racing engine. Additionally, I'll be using JE pistons so achieving a proper CR shouldn't be a problem so long as I know the combustion chamber volume.

-zuff

[Roland Kunz]

Hello

2,8 RSR heads are rare becourse they had been very thin and tended to crack or to drop the valve seat.

Most use modified 3,0 heads.

Grüsse

[zuffenhausen]

(bump)

Just one quiet bump to see if there are any other options before I go buy a set of SC heads that will need $1K in machine work.

-zuff

[Mr Beau]

Can someone confirm the RSR head volumes, and that of the 2.7L heads? I'd like to do some compression ratio calculations...

Thanks.

[Mr Beau]

...or how about the dome size of the Mahle 92mm RSR pistons?

[Tim Walsh]

I belive that the head volume sizes, port sizes, and valve sizes are all in BA's book including a comparison of the 2.7 heads vs. the 2.8 heads.

[Mr Beau]

Unfortunately mine is packed up right now and not accessible. Anyone have the info handy?

Much appreciated.