Hello all,

Here are the specs for the upgrades to my 2002 FXD:

- 95", wiseco forged pistons
- S&S super stock 79 cc heads
- Andrews 55g cams
- S&S Grand National 2-1-2 exhaust
- Dynatek TC88 ignition

My question is simple, Mikuni HSR 42 or 45?

Thanks in advance

 

I don't see 100HP from that combination, so the CV40 or the Mik 42 are both adequate for the job IMHO.

 

Agree with the above, HSR42 gets my vote.

 

Thanks for your replies,

I have seen dyno charts of bikes with 95" and TW55 cams reaching well above 100 hp. What part of my combination is holding it back, in your opinion?

Pistons are +4.6 cc, static compression will be 10.5:1, ccp 194 psi according to big boyz calculator.

Thanks in advance

 

Definitely the 45. I don't know what the SnS heads intakes flow but they hopefully they are over 260@28.

The big problem will be the intake manifold.. If using an SE, it's too small IMO. What's the intake port size? IIRC it's about 1.7" You can use a Ultima manifold for the HSR45 but it will likely have a 1.8" spigot at the head. You'd have to match it..

Personally I'm not too hot on the Dynatek ignition but give it a try.. Some have been able to make it work.

 

I am not saying the combination won't hit 100HP but have not seen many 95"/96" builds that do; that's all, nothing specific about your combination. I hope you do hit 100HP; please let us know how it turns out.

Max makes good points about intake and port matching which may or may not have been addressed and will have an impact. SnS says the 89cc SS heads flow 264 but do not specify flow for the 79cc SS heads. Maybe the same but not sure; 79cc heads do have smaller intake. As for his comment about the 45, I don't see it hurting but don't see it gaining anything either at 95".

The DTT TC88 ignition would have been a better choice. JMHO

 

Thanks for your reply. I don't know any flow numbers for these heads, they have 1.940" intake valve, and the intake port is 45 mm where it meets the manifold, compared to 42 mm for my stock heads.

I have a matching S&S manifold that is 45 mm where it meets the head and around 51 mm at the carb side. I can fit both 42 and 45 mm carbs using different rubber seals.

 

Why ya thinking the 45, potential benefits without any drawbacks? I’ve had the 42 work well up around the 110rwhp mark for street. I pegged this setup as a bit under that but the heads seem potentially saucier as-cast than I thought.

 

What would the drawbacks be? The heads should flow more.. I doubt they will flow more than 300cfm at 28 tho..

The flow here is at 10 inches of carbs on different manifolds. Multiply by 1.67 ro get the flow at 28..

 

BTW, You really want the carb to flow more than the head as you want the head to be the limiting factor. AC also needs to flow well..