19 replies to this topic

[mailman]

I am nearing the end of the rebuild of the engine to go into my mini.

998 +0.040"
12G940 head with 35/29 In/Ex valves
266(ish) Cam
Sintered Rockers
9.75:1 CR
Aldon Yellow Distributor
3.44 FDR

I have rebuilt a pair of Twin HS2's only to realise the manifold is not what I thought it was. My initial thought was to rebuild the HIF6 I have with the kit I also already have. However recent search results tend to lean away from HIF44/HIF6 on 998 engines.

WinSU suggests either HIF44 with needle BDL being within a few % mid and top, or twin Hs2's which are not as close.

What are the recommendations currently?

I did run an HIF44 on a very similar engine I built (but with smaller inlet valves) which drive beautifully, but leaned out at 4.5-5k RPM. Unfortunately I had to sell that car to fund a house purchase before I could investigate further.

[imack]

Personally I like the twin hs2 set up, even if only for looks. Whats wrong with the manifold?
I wouldn't rely on Winsu's needle selection guide, I tried it to choose a basic running in setup for my twin hs4's before I could get it on a rolling road and the needles it chose were so far out that it would barely run on them, miles too weak.

[whistler]

BDL is the needle for modified 1275 with HIF44. HIF44 too big for a 998 is the accepted advice.

[Anthony30]

twin hs2.

[28hodge]

I might have a pair of twin hs2's coming up for sale as they came with a car I bought that really needs twin hs4's rather than the hs'2's or a single hs6.

If you decide to go with the twin hs2's drop me a pm if interestwd

[mailman]

Thanks for the input guys.

Any thoughts on the choke vs valve/port size? The HS2 choke size is slightly smaller than the port size and 3mm smaller than the inlet valve size. I don't have high lift cam or rockers.

[mailman]

Thanks for the input guys.

Any thoughts on the choke vs valve/port size? The HS2 choke size is slightly smaller than the port size and 3mm smaller than the inlet valve size. I don't have high lift cam or rockers.

[mailman]

Personally I like the twin hs2 set up, even if only for looks. Whats wrong with the manifold?
I wouldn't rely on Winsu's needle selection guide, I tried it to choose a basic running in setup for my twin hs4's before I could get it on a rolling road and the needles it chose were so far out that it would barely run on them, miles too weak.

Thanks Imack.

WinSU suggests that the hs2's will be lean off the bat. Would you expect that to be true from your experience?

[dotmatrix]

I have a very similar engine and it is mounted with a single HIF38 on a standard cast iron metro manifold. it made 65bhp at the crank on the rolling road.

[mailman]

I have a very similar engine and it is mounted with a single HIF38 on a standard cast iron metro manifold. it made 65bhp at the crank on the rolling road.

What cam and head do you have? And what carb needle?

[imack]

Personally I like the twin hs2 set up, even if only for looks. Whats wrong with the manifold?
I wouldn't rely on Winsu's needle selection guide, I tried it to choose a basic running in setup for my twin hs4's before I could get it on a rolling road and the needles it chose were so far out that it would barely run on them, miles too weak.

Thanks Imack.
WinSU suggests that the hs2's will be lean off the bat. Would you expect that to be true from your experience?

I don't remember where in the rev range that they were too lean, I didn't persevere with them as they were so far off the mark.
I haven't got winsu loaded anymore to compare them with my current needles.
Winsu suggested AAC x2 for my twin hs4's, these were way too lean. I ran it in switching between my own needle selection, AAR which appeared to run well but I wasn't sure if it was running lean at any point, and AAM which I was sure was safe but was too rich at 4-5000rpm causing severe misfire caused by over fueling if you opened the throttle too quickly. Set up on rolling road by Peter Baldwin, he selected AAU needles.
Don't think I ever compared the Winsu selected AAC profile with the correct AAU needles on the profile overlay to see how they compared.

[Icey]

Have you reached the limit of a single carb (e.g HIF38)? If not, theres no need for a larger or more carbs.

My preference is always a single carb over twins and anything over a Weber. The HIFs are simple, work well and can be fettled with to make them better.

[mailman]

It's a new build that hasn't yet run. I don't have access to any HIF38's so far.

I have the twin HS2's, an HS4 and a pair of HIF6's. I just want to optimise the fuelling as best as possible without limiting the performance potential.

[dotmatrix]

 

I have a very similar engine and it is mounted with a single HIF38 on a standard cast iron metro manifold. it made 65bhp at the crank on the rolling road.

What cam and head do you have? And what carb needle?

 

 

MD266 cam and Mg Metro head. I can't remember what needle I started with, but it was modified afterwards

[carbon]

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.