19 replies to this topic

[Minigman]

Running twin HS2 on my 998 with 266 and 295 head. Far better throttle response than a single SU. Also tried a Weber DCD which I found to be awful despite setting up properly on a rolling road.

[mailman]

With a 998 using the larger 35.6mm inlet valves you may lose out on low-mid range torque even with MD266 type cam and low lift rockers.

 

If you're looking for best torque at higher rpm with MD266 you may need more valve lift than you get with A+ sintered rockers. These sintered rockers were definitely the weakest link on my 1293, and just going to 1.25 ratio (measured as 8.0mm valve lift on MD266) made a massive improvement in mid-range and higher rpm.

 

With a well tuned 998 you may also see a difference in top end performance when using valve lifts of less than 8mm. I would be interested to hear other's experiences, as I am putting together a 998 and was thinking about using 9.5 - 10mm lift at the valve, probably using 940 head with 33mm inlet and 29mm exhaust.

 

 

I am using the sintered type as I have not pocketed the block and I installed the larger valves as I plan to use the head again in the future on a 1275 build. Thus my specs. Hopefully it doesn't lose too much low down! Perhaps with what you are suggesting, and what others have mentioned, twin HS2's will be best as they will provide some additional air speed and help maintain throttle response and low down behaviour?

[Retroman]

I have used a HIF44 on a 998 with a 12g940 and got 78hp with a 544

and recently got 80hp on 1117cc (998 at 68mm bore) using a single vizarded HIF38 and a 270 cam, pulls from nothing really nice smooth motor with plenty of torque.

  I am about to use a vizarded HIF38 on Petrols 998 screamer build.

http://www.theminifo...rebuild/page-90

 

  Twin HS2's are not good on a standard manifold, its a complete myth about keeping the gas speeds up with 2 of them. For years I have been going to do airflow calculations to prove they are asthmatic....I now have and they are pretty chronic when compared to a single HS4, HIF38 or HIF44.  

  I will sort the figures and post them.

[mailman]

I haven't been able to source an HIF38 at all so far. Not even eBay.

One plus to the HS2's on this engine is I don't think I'll be making 70bhp. I'll be happy if it's in the 60-65 range as I don't think the cam is a high revver.

That build is awesome Retroman. I need to give it a more detailed read. Do you have any engine build specific threads?

Edited by mailman, 06 December 2017 - 01:43 AM.

[Retroman]

I don't have any threads as such, its not my thing, do have a HIF38 and manifold pm me