924Board.org

[ericgb35]

what modifications have to be made to fit a 944s 16v head on a 924s if it can be done?

[gohim]

I don't think it would be practical. From what I remember from looking at this. The 944S engine block is a different casting with lumps cst on the block that are drilled and tapped in placed that do not exist on a 944 NA block.

Besides, to make the additional hp that the 924S engine does not, there are more changes than just the cylinder head. The pistons are a full point higher compression, and the ignition electronics are different with the 944S engine getting a knock sensor that the 924S engine did not get.

If you want 16V hp, then you need to buy a complete 16V engine with electronics. You should also get the reinforced transmission (with revised gear ratios) that the 16V engined cars got.

[Raceboy]

IMO 16V head with lower compression pistons are perfect combination for turbocharging.
_________________
'83 924 2.6 16v Turbo, 470hp
'67 911 2.4S hotrod
'90 944 S2 Cabriolet
'78 924 Carrera GT replica
'84 928 S, sold
'91 944 S2, sold
'82 924S/931 "Gulf", sold
'84 924, turbocharged, sold.
http://www.facebook.com/vemsporsche

[ESC944]

Well any head that is capable of breathing better is by far for any kind of boosting, super or turbo -charging, you get more air in and out and you will see more power.

Provided you can supply more fuel and tune accordingly. Of course a DOHC adds more complexity to your timing setup.

Personally I like 12v and sohc 16v designs. But then... the 924S and 944/968 engines don't have that kind of setup.

They do have the 16v and 16v variocam.

[special-tool]

Some of you guys are a little confused on these heads...

The 16 valve "S" head bolts directly onto ANY 2.5 block - turbo, NA and S.
You will need to change pistons.

My car is making almost 600 crank HP with a modified 8 valve head. These heads are better for torque, and since they are all low-rev engines, this is where you want to be.
I have 2 16 valve S heads on my bench, they will be sitting there for a while.

Also - the early Porsche 16 valve needs a custom made girdle for higher revs and boost pressures combined. The lifter bores are too short. Experience talking, not bullshit.
_________________
951 566/485 HP/TQ at the wheels - pump gas
924S GTR conversion project
Honda 250R- PWK 35mm flat slide, 205 static, Boyesen, Wiseco, DG front/back, Uni, 14/42,

[gohim]

Yes, the head bolt holes are the same regardless of which 944 based engine is being assembled.

But there are some differences in the holes that are drilled and tapped for brackets, and accessories. For instance, the early 944 blocks do not have the cast lump on the engine block that the later engined have drilled and tapped to mount the auto belt tensioner. So if you were moving from a later block to an earlier block, you would lose the auto belt tensioner because there is no place to drill and tap on the block to mount the auto belt tensioner.

In other cases, the lumps exist on the block, but they may not be drilled or tapped. In those cases, you could probably drill and tap to add the missing component if you wanted.

[special-tool]

Yes- noone knows the dfference between old NA block and new better than I.
I was talking about head mounting.
ANY 2.5 head will bolt directly onto ANY 2.5 block, and it will use any standard gasket.

Also - the auto -tensoner dfference does not make one bit of dfference to bolting a 16 valve head onto a mech. tensioner head - won't even slow you down 15 seconds - bolts straight on, stick the belts on and tension it - done.

The 924S DME can easily be used to run an engine wth a 16 valve head wth a chip change only - available from Vitesse racing. I have all contact info for anyone interested.

A major reason for this swap is that the 16 valve head has only recently become legal in SCCA ITS class. This will be an engine configuration much more competitive against the BMW's and Mazdas.
_________________
951 566/485 HP/TQ at the wheels - pump gas
924S GTR conversion project
Honda 250R- PWK 35mm flat slide, 205 static, Boyesen, Wiseco, DG front/back, Uni, 14/42,

[CBass]

So what is the effective change in compression from going to an 8v head to a 16v? Are the original 8v pistons compatible at all, or is there too large a compression difference, or interference with the valves?

Also, I assume the 3.0 liter blocks are a different casting? 104mm seems to be a larger bore than simple overboring would allow for.
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'81 931 in various states of assembly

[special-tool]

You need to use 16 valve pistons. The combustion chamber is completely different.

The 2.7 liter 8 valve, or the 3 liter 16 valve heads will bolt onto the 3 liter block. The 2.5 heads will not bolt onto the 3 liter heads.
_________________
951 566/485 HP/TQ at the wheels - pump gas
924S GTR conversion project
Honda 250R- PWK 35mm flat slide, 205 static, Boyesen, Wiseco, DG front/back, Uni, 14/42,