SF1 under engine Balance Pipe - Necessary?

R

RJS

New member
Location
Canada
I'm slowly (glacially slow) getting my 1973 SF1 together. I have a Rickey Racer 2 into 1 exhaust that I planned on installing but I can't seem to get it to fit. I had one on the SF1 I owned in the late 90s and it fit fine. Not so this time. I have a set of original down pipes and an under engine balance pipe which are in okay condition. I'm not a fan of the looks of the balance pipe and considered bending up some pipe to replace the balance pipe. Wolfgang tells me I shouldn't consider running without a balance pipe. That will ruin engine performance. I see photos of SF1s, 2s and 3s without the balance pipe, many using an extended set of down pipes with an extension like the ones Malcom Cox sells. Can anyone using standard mufflers and stock pipes (except for length) without an under engine balance pipe tell me their experience. I have also heard that the balance pipe makes the whole system stronger. Thanks
 
You will not undermine engine performance in any noticeable way, but it will be louder. Mine was noise tested as legal when I registered it in Norway The huge collector does make the system very well mounted. Without it, and just rubber mounted mufflers, over time things can crack or work loose. An idea is to fit a rubber mount forward of the muffler, it can fixed to the end of the frame crossover, then it will be fine.
 
Well, the SFC had a 2 into 1 system but it might have had a cross over system underneath, and I've read a 2 into 1 works well for these twins, but will probably require some jetting. Supposedly a 2 into 1 is good for top end, but the "experts" can chime in otherwise. My 74 750SF2 came w a Malcolm Cox system w/o a mid pipe, and I just spoke to Wolfgang who emphatically said the mid pipe affects mid range (which mine suffers from). The Cox exhaust is well made and the chrome has held up so far. I am looking into purchasing headers w/ the mid pipe. Wolfgang mentioned a system available in Italy and DAM Classic Racing in OZ offers headers w mid pipe. Someone on Seattle CL is selling Laverda headers w/ mid pipe for an earlier GT model that apparently uses a different flange mount.https://seattle.craigslist.org/see/mpo/d/seattle-laverda-headers-with-balance/7787194762.html
 

Attachments

  • Cox.png
    Cox.png
    598.2 KB · Views: 36
  • seattle.png
    seattle.png
    276.3 KB · Views: 31
Last edited:
I keep hearing about loss of midrange when the crossover is dumped? I'm baffled - truly. Have a look at the bike in my avatar. it's my stock (motor) SF1 with straight headers into std Contis (off a Ducati, but same same as SF Contis). I rode that setup for 160,000km before I SFCd the motor and exhaust. I raced it, toured on it, commuted on it, thrashed it. In my 2nd race it held a green frame on the Wanneroo straight (before outbraking it). People who saw it in action or rode it were always impressed at how quick it was. I would NEVER say it lacked midrange.

I just don't get it - anyone want to test the theory on a dyno? Cos I'm sick of hearing it. Another myth I came across was that the SF1 cam caused vibration ... I've ridden loads of SFs (I was a mechanic for the WA Laverda concessionaires in the mid-late 70s) and I'd rate my SF1 as one of the smoothest. Just bizarre some of this stuff. If you want to see lack of midrange (and bottom and and top end), fit a stock SF system to an SFC.
 
Given they're a 360degree crank, a 2 : 1 system with the join in the right place should be the best all-round solution.
It's effectively half of a 4 : 1 pipe for calculations. The length to the joint gives the torque peak rpm and overall length
sets the HP peak rpm.

Individual pipes require the overall length to be correct to give an optimal result. Think two singles for calculation purposes.

Separate pipes with an under-engine joiner can work - but put the joiner pipe in the wrong place and it can be an epic fail.
Again, the length to the joiner should set torque peak rpm. The waves see the extra volume at that point as the same as
a 2 : 1 junction.

Exhausts have been a pet subject of mine for years. I've lost count of how many systems I've built over the years for bikes,sidecars
and speedway cars
 
Piranha,

Good point about dyno data, just relaying what Wolfgang claims. But have to wonder why they came stock w mid pipe? Guessing the true test would be comparing both on the same bike- anyone before I spend $500 plus to find out-
 
TeddyG said:
Piranha,

But have to wonder why they came stock w mid pipe?
Click to expand...
Quite probably to quieten them down? I only got rid of mine because it scraped when cornering with gusto - and had a tendency to lift the rear wheel when it did, because it didn't have any 'give'. You can chase this for all its worth but I will happily bet you real money that your lack of oomph in top gear over 50mph has nothing to do with the lack of a crossover. A better view of my avatar bike ... no crossover.

QF-SF1-1976-Wanneroo.JPG
 
piranha-bro2 said:
Quite probably to quieten them down? I only got rid of mine because it scraped when cornering with gusto - and had a tendency to lift the rear wheel when it did, because it didn't have any 'give'. You can chase this for all its worth but I will happily bet you real money that your lack of oomph in top gear over 50mph has nothing to do with the lack of a crossover. A better view of my avatar bike ... no crossover.

View attachment 92671
Click to expand...

Yeah - that were the days!
(y)



Lee and Quentin mentioned already two of the key points: the pre-silencer supports the exhaust system in the middle and it’s much quieter than the stock exhaust systems that were used before.

According to "La Diva", new noise regulations had to be taken into account.

The disadvantage of the pre-silencer is the limited ground clearance. My SF1 has levered me out more than once ...

I’m with Quentin though that it has nothing to do with your performance lack.
 
Last edited:
There were two versions of the under gearbox crossover pipe from moto Laverda, the later one had the ends "tipped up" to a steeper angle and many dents/flats on the inside to achieve this, but they both had internal baffles and direction inducers, left cylinder (sort of) feeds to right silencer, and versa vice. Aftermarket types very rarely have the internal sheet metal work, (at least in the 70's maybe not so now) so will affect just about everything. I rode my SF1 for years without this item fitted |(at the time you could buy 6" long bent and swaged pipes to replace it with) and never sufferred at all, it was the same with my SF3 much later on (now sadly sold on) the SFC 2 into 1 didnt help performance over much, but its interesting to note that it DOES HAVE bracketry to enable the system to be bolted to two of the sump plate stubs, giving lots of additional supports, but remember this is a 24 hour racer and come what may if cracking or seperation occurs thewn you want to be able to carry on, even if that is only to the pits.
CLEM
 
CLEMTOG said:
There were two versions of the under gearbox crossover pipe from moto Laverda, the later one had the ends "tipped up" to a steeper angle and many dents/flats on the inside to achieve this, but they both had internal baffles and direction inducers, left cylinder (sort of) feeds to right silencer, and versa vice. Aftermarket types very rarely have the internal sheet metal work, (at least in the 70's maybe not so now) so will affect just about everything. I rode my SF1 for years without this item fitted |(at the time you could buy 6" long bent and swaged pipes to replace it with) and never sufferred at all, it was the same with my SF3 much later on (now sadly sold on) the SFC 2 into 1 didnt help performance over much, but its interesting to note that it DOES HAVE bracketry to enable the system to be bolted to two of the sump plate stubs, giving lots of additional supports, but remember this is a 24 hour racer and come what may if cracking or seperation occurs thewn you want to be able to carry on, even if that is only to the pits.
CLEM
Click to expand...


Hi Clem,
on my SF1 the under gearbox pre-silencer / crossover pipe was designed as shown in my little drawing:
49991591117_c7cd693656_c.jpg
 
Very refreshing to hear from people who've 'been there, done that' with crossover removal. i think the dyno test would be a waste of good money :cool:

I've still got the sump bracket for my factory SFC 2/1 - never fitted it, never had a break. As Clem says, 24-hour's racing produces a different set of demands.

The brand new 1200s collector didn't last 3 hours in the 4-hour proddy race i rode it in ... possibly a mounting issue - but the gearchange crossover also broke at 3 1/2 hours, so the vibes were taking their toll. So I finished the race on a noisy mongrel stuck in 3rd gear! I don't recall feeling like it was a bad shaker at all though.
 
Here is Teddy putting up a picture of a pipe joining the headers in front of the engine, and discussing the "banana" crossover collector under the rear of the engine that the mufflers attach to. This is going nowhere.
 
You must log in or register to reply here.
Back
Top