6 replies to this topic

[Pauljb]

Hi peeps. Silly question time again...
I've got a 998 engine sat in my garage that needs overhauling. Im thinking of converting it to a 1098 as I've heard they are a better engine for road use and im certain the only differes between the 2 are the crank and pistons. Would a 998 head go back on or would I need a 1098 head? (the head needs replacing anyway, but I want to make sure I get the right one).
Thanks in advance guys.
Paul B

[timmy850]

The 1098 head is the 12G202, which has slightly larger inlet valves than the standard 998 type ones. They also have a larger combustion chamber to suit the larger stroke. The 1098 head would be a better starting point if you had both, however a 998 head could be worked on to get similar performance. 

 

You will also need a different or tuned distributor as the ignition advance curve won't be right. I'd also make sure the crank is crack tested and pretty close to stock bearing sizes before buying.

[Spider]

A 998 head will work, but a 1098 head would be way better, the casting no. is a 12G202. They did use the same casting on the 997 Cooper, but they had ever so slightly bigger Inlet Valves, almost academically so.

 

Also, if building it as a standard 1098 engine top to bottom, them all the tuning details are in the workshop manual, from the carb needle to the distributor curve.

[Cooperman]

Just make sure that you do the comp ratio measurements and machine accordingly.
Personally I think the 998 is a much better engine overall as it has a shorter stroke and revs better than a 1098.

[Pauljb]

Ok thanks guys. I need to strip the engine anyway for a reborn so if I was to do it I'd go all out on it and upgrade everything. Just wouldn't want to ruin it all by putting on all smaller sized head.
Cheers for the advice though guys!

[Agus1601]

Hi! I used a 1098 12g202 on my 998 and my performance figures with an aldon yellow distributor were excelent. Much better than the original 998 and it gets more flow through the engine. An awesome head for me and my next engine will have it

[Turbo Phil]

Although the porting is better and the 202 has a larger inlet valve over the standard 998 casting, it doesn't flow a lot better due to the massively shrouded chamber design. Cutting back on the chamber wall around the valves will show a significant improvement.
Bear in mind this will increase chamber volume and you'll need to skim the head as required to restore the compression ratio.

Phil.