home register FAQ memberlist calendar

Go Back   Turbobricks Forums > Mechanical > performance & modifications

Reply
 
Thread Tools Display Modes
Old 09-17-2020, 01:21 AM   #1
blakemcelroy2000
Board Member
 
Join Date: Oct 2017
Location: Portland OR
Default Mikuni HSRs worth all the fuss?

So Im running two SU HS6s with DX needles on a slightly built B20 (F head, nice header, slightly hot cam) and Im wondering whats the truth on Mikuni HSRs. Big power gains + efficiency gains? Or just efficiency? 42 vs 45 vs 48? I know they’re a lot easier to tune and have a far better overall design. Just wondering if worth the cost to upgrade, or to just get the old SUs professionally tuned and deal with the quirks.
blakemcelroy2000 is offline   Reply With Quote
Old 09-17-2020, 07:45 AM   #2
fatcatbestcat
Professional Hack
 
fatcatbestcat's Avatar
 
Join Date: Oct 2019
Location: Mississauga, ON (Canada)
Default

If I'm remembering right, the HSRs are for motorcycle and other small engines... I've seen the dyno charts from v-performance on these, and honestly doesn't look like it's worth the money for a proper kit.



This one was a direct comparison between stock SUs (green) and the 42mm mikunis (red). They didn't specify what the blue line was, perhaps larger mikunis.

Wasn't a B20 being dynoed though. I think in their tests it was a B-series BMC engine with a hot cam and a mega-ported head, so I'm not sure you'd see the 13 hp difference in a lightly done-over B20. Also consider that peak power in the 'road test' condition for the dyno was 105 mph, so I'd assume they were revving this engine pretty hard.

EDIT: For what it's worth, assuming you're running a pretty stock head (not super shaved or ported or with big valves), you'd probably be better off sticking with the SUs.
__________________
Doing the wrong thing the right way.

-------------------------------------------

Quote:
Originally Posted by redblockpowered View Post
Will you do $14.99 shipped?
Quote:
Originally Posted by IansPlatinum View Post
please no more prying things with screwdrivers and bashing things with hammers!
Quote:
Originally Posted by Cwazywazy View Post
my balls have more wrinkles than my brain
--------------------------------------------

-1967 144S

Last edited by fatcatbestcat; 09-17-2020 at 09:39 PM..
fatcatbestcat is offline   Reply With Quote
Old 09-17-2020, 10:22 PM   #3
blakemcelroy2000
Board Member
 
Join Date: Oct 2017
Location: Portland OR
Default

Thanks for the advice! Definitely don’t want to spend money if it isn’t worth it. Ive learned to not exactly trust V Performance after some of the stories Ive heard about the shipping on their supercharger or carb setups. Guess Ill put the money into maybe putting a P1800 rear axle and disc rears later.
blakemcelroy2000 is offline   Reply With Quote
Old 09-24-2020, 08:53 PM   #4
TimS
Board Member
 
Join Date: Dec 2017
Default

there is a book " tuning bl A series motors" about mini motors by Vizard. There is one chapter just on air cleaners and bellmouths. The important one to you is s chapter just about getting SU's to flow more, almost as much as a weber sidedrafts. There are a lot of little cheap mods, like cut the throttle shaft in half and use buttonhead screws. Most of the data was for 1 1/4 or 1 1/2 sus but would still apply any of them.
He air flowed everything he did to show any improvement.
Well worth the read.
TimS is offline   Reply With Quote
Reply

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is On

Forum Jump


All times are GMT -4. The time now is 05:47 AM.

Powered by vBulletin® Version 3.8.11
Copyright ©2000 - 2021, vBulletin Solutions Inc.