2017 SSR Motorsports Lazer 5 Sport & A Story

[190mech]

I agree with running it stock for now,glad to see a CDI that has a proper 4stroke curve going on it..Dont know if a roller setup would help much other than longer life on parts,the old Honda motorcycles had a similar head design and lasted a very long time with frequent oil changes..Heck just about any free flowing pipe will work as power increases are not near as great as an expansion chambered 2stroke!

[aeroxbud]

I enjoyed the video. Very insightful. And if the supplier ever gets asked those questions again. They can link them to your video.

[90GTVert]

I've been sitting here looking at all of the performance related books that I have for exhaust primary length and diameter formulas.

Performance Automotive Engine Math by John Baechtel and Performance Exhaust Systems by Mike Mavrigian both give the same formula for primary pipe cross section area. Both sound like they're based on formulas by Jim McFarland.

Ac/s = (cylinder volume in cubic inches x RPM) ÷ 88,200

Then to get the pipe size form the cross-section area, they give two versions of the same formula. The only difference is that Mike Mavrigian saves you one piece of math.

Pipe Diameter = sqrt(A x 1.273)
where A = cross section area

A. Graham Bell offers a slightly different formula for pipe size in Four-Stroke Performance Tuning.

Pipe ID = sqrt[cylinder volume cc ÷ [(P + 3) x 25]] x 2.1
where P = primary length inches (so you must know length before calculating diameter in this case)

Bell also mentions this one :

primary pipe Ac/s in mm2 = (peak torque RPM x cylinder volume cc) ÷ 2,240



It seems like there should be only 1 formula for primary length, but there are 2. This is where I am a little lost.

So, in Bell's book he gives this formula :

primary length = [(850 x ED) ÷ RPM] - 3
where ED = exhaust valve opening BBDC + 180

Then Baechtel and Mavrigian give what sounds like it's supposed to be the same as Bell's, because Bell is cited in an earlier version of the book that I have. It doesn't match though, and it gives different results.

Here is their formula directly over Bell's formula, just with ED in Bell's changed to what it means.

primary length inches = [850 x (360 - EVO)] ÷ RPM] - 3 (Baechtel & Mavrigian)
primary length inches = [850 x (180 + EVO)] ÷ RPM] - 3 (Bell)
where EVO = exhaust valve opening

They give a variation of Bell's diameter formula as well, but it's just done to use cubic inches vs cc. These formulas are not noted to be modified, but both are. As said, one is obvious. I don't know why they chose to change how EVO is dealt with vs Bell though. There is no explanation and it is stated as if it came directly from Performance Tuning In Theory and Practice, so I looked up that old version. It has the same formula that my newer version has.


I did the calculations for all of this stuff, with two different RPM. I used 8,500RPM and 7,500RPM. 8,500RPM is where I initially planned to tune for, based on the idea of trying to extend power either above or below the curve a little. 8,500RPM tuning may be able to help on the underside of the HP peak if I'm correct. 7,500RPM is roughly the peak torque of the engine. This stuff is all based on the dyno from a YouTube video that I found and posted a few pages ago. Some seem to say that the exhaust should be tuned for torque peak, so that's why I did those numbers as well.

I'll start with primary tube inside diameter. I got 1.0316", 1.032", 1.056", 1.0981", 1.0986", and 1.1242". So the whole range is roughly from 1" to 1 1/8" pipe ID or 26.2 to 28.55mm. The pipe that I initially chose and now have is 1 1/8" ID. Larger IDs may sway RPM tuning higher or favor larger engines. That's fine with me. I'm after a close sort of ballpark, and that should make whatever I end up with fine if I did go with a BBK or maybe it would just tune it a little nearer HP peak that initially intended. It sounds like 28mm is very common for aftermarket stuff. Plus, mine will taper, so it will start nearer 7/8" (0.875") to more closely match the port if I can get it right.


Then I started looking at length. There's much more of a range there. Using Bell's 180 + EVO version of the formula, I get 19.5 to 22.5" for primary length. The longer numbers being lower RPM tuning. Using 360 - EVO, I get 28.5 to 32.7". So now I've got a range from 19.5" to 32.7", or even using the same 8500RPM figure only, the range is 19.5" to 28.5". Hmmm.


So then I figure, why not check the specs based on info that John linked me to from KiwiBiker about the tapered header and see if they are obviously using the same formulas. Info there said 450mm length (17.7165") for roughly 12,000RPM tuning on a FXR150. I looked up FXR150 cam info and found someone that measured it at 24 BBDC EVO.

I came up with 11.45" and 20.8" for primary length, depending which of the formulas I used... so neither matches the 17.7" that they mentioned using. I'm not sure if there are changes based on the taper or what's up there.

I don't think it matters that much to be perfect for this, but it does bother me that I can't get a closer approximation of length. At this point, I'd probably just follow Bell's guidelines since he's the one credited for the length formulas anyway. I don't know if I'm done there or not yet.


Competition Engine Building by and the previously mentioned Performance Automotive Engine Math books both recommend PipeMax software as an affordable and trusted solution for exhaust design. Affordable is relative. It's $150 for the latest version here : maxracesoftware.com/PipeMaxPro400.htm It looks like older versions may be found for less, like $75-100, but I'm not sure how much you miss out on. I don't really want to spend much ATM and I'm not sure how much of a point there is to it so I doubt that I'll get it. Just makes me curious because multiple sources speak highly of it for exhaust design.

[woodini]

🤯

[190mech]

Here are a few calculators I just found,dont know anything about them..
www.nightrider.com/biketech/calc_exhaustlength.htm

www.mezporting.com/exhaust_length.html

[90GTVert]

The first calculator wants the center of the powerband. I used 8500RPM. That's before the HP peak area, but above TQ peak. It says 25.147" for short and 36.529" for long. They state this about short vs long; "Opinions differ as to the best exhaust pipe lengths for any engine. There appears to be two major "schools" of thought on the best exhaust system length. The "short" pipe and "long" pipe calculations performed below present both views. Short pipes seem to win from an esthetics point of view, but the longer pipes seem to produce a better power curve. The decision of which to use is up to you."

I've actually used the 2nd calculator before. It's supposed to be based on Bell's formulas and matches up in the range of results that I've got on my own. Using 8500RPM it tells me 20" for primary length and 1.112" for diameter.


I tried to look for more info on tapered headers last night. I searched KiwiBiker first, where the info that John passed along came from. The same thread that he linked came up and that was the only thread about tapered headers that I saw. I tried searching for posts, but just mentions of tapered headers without any info useful to me.


I found this site via google searching; rbracing-rsr.com/exhausttech.htm
There they say this; "The only duals we ever made was our LSR Nitro Duals (discontinued) which started out at 2” from our cnc machined turbo venturis and quickly tapered to 2.5” in the first 9” after the exhaust port by using a special seamless cone. The pipes were suited for large bore high compression motors where the customer, for one reason or another, did not want a 2-1 design. The taper or cone after the port is an attempt to broaden out the powerband and to smooth the transition with no internal steps from 2 to 2.5 inches. The length of these systems had been set at about 37.5" based on actual testing.".

I noticed that they're talking about Harleys, so the race-oriented stuff is doing roughly 6,000RPM and they've mentioned 37.5". That should mean that they aren't on the long pipe school of thought that the Harley calculator site mentioned or the pipe would be 5ft long for a 5000RPM middle of the powerband long pipe based on the calc. I found it interesting that they mentioned the taper within the first 9" of the pipe, which is 228mm, and the KiwiBiker info said to keep the transition within about the first 200mm. Similar info, with totally different RPM ranges.


ATM, I'm thinking I should stick somewhere closer to the numbers generated from Bell's formulas. Maybe aim for about 20" and if it works best for actual fit to go 1/2" shorter or 6" longer, I'm still in the range of results. A lot of this is about making sure I can explain this on video. As we know by now, YouTube comments tend to be more critical/negative or maybe I should say less understanding/forgiving. This sounds like a realistic plan, though the time figuring out cam specs feels wasted aside from passing on some info.

I may try to check out the intake and see how long it is and if the 28mm carb fits it. If I need a new intake, I may see if there are options that put me in the range of tuned length there. Can't hurt I guess. It would be something like 5.5-7.5", depending exactly what RPM I was aiming for. My understanding is that it doesn't have to match exhaust tuning anyway, unless you are trying to go for the strongest peak point vs creating a wide powerband. Any intakes that put me in that ballpark estimation should be close enough. Again, if nothing else maybe I won't leave a bunch of power on the table from a randomly tossed together setup, even though it doesn't feel terribly scientific with all of the variations and ranges.

[aeroxbud]

I guess a lot of applications, even if you have a correct length in mind. Must be a compromise. The way it fits round an engine, shock, frame might ultimately dictate the final length.
It's also funny how most sports bikes are going to under engine pipe designs.
There is no way you could get a reasonable bore size of any length to fit under an engine.
I wonder if there is a new way of thinking about exhaust length?

[90GTVert]

They're definitely guessing at temperature and velocity, among other things, to come up with exhaust numbers.


I was just messing with this taper calculator : www.magafor.com/841/uk.htm

Going from 7/8" to 1 1/8" in 200mm would give me a 3.175% taper. I'm not clear on what the FXR header dimension were, but someone did mention steps from 32mm to 38mm and if those dimensions are what they used for a tapered primary then the taper would be 2.997%. The RB Racing site said 2" to 2.5" over 9" length, which is a 5.5565% taper. Sounds like I should at least be in the ballpark there.


1.25" pipe circumference should be 3.93" so if I start at 3/4" out of the circumference and draw a cone 200mm long, that should put the header roughly at the desired diameters I think.

[190mech]

You could make a 'trombone' sliding aft section to tune it to length...Then make a 'hard copy'!

[90GTVert]

Feb 22, 2021 12:59:30 GMT -5 190mech said:

You could make a 'trombone' sliding aft section to tune it to length...Then make a 'hard copy'!

If Bell is correct and it makes maybe a 3% difference as long as it's not totally wrong, I don't know if I could tell for sure. Interesting idea though. Could be an option if however it fits lends itself to such a thing.

[90GTVert]

I also downloaded the Four 4 Stroke Exhaust Calculator app on my PC since it's free. It tells me 495.3mm (19.5") for 8500RPM, so it seems to use Bell's formula. It says 28.551mm (1.124") for diameter, so again it's right on with my calculations from Bell's info.

[190mech]

A 2stroke tapered headpipe is usually around 1.5 degrees(3 degrees total),anything more than that over scavenges the incoming charge..I would think the same would apply with a 4stroke depending on port layout and cam profile...

[90GTVert]

I got the tapered section of the exhaust done today. Didn't worry about trying to totally hide all evidence of welding the U-bend to the tubing and welding the pipe back together where it was cut to make the taper, but I did clean it up a bit. It wasn't as bad as I thought it was going to be trying to reform the pipe after cutting a 200mm long, 0.8" max width wedge out of it. Tapers from ~7/8" ID to 1 1/8" ID.






Not much progress. I've mostly spent time since the last update trying to make the first part of the vid, about planning the pipe. The majority of that time in trying to animate 720 degrees of rotation with moving valves, mixture, exhaust particles and exhaust pulses. It's simplistic and it still took me forever. During that process, I stopped sleeping very much. Averaging about 3 hours per night currently for unknown reasons. I actually had the beginning section of the pipe done and welded before now... but I welded it on backwards and ruined it. Normally that kind of thing may show up in a video, but I've already deleted that. I was pretty irritated about it, and doing it because I can't think straight ATM. I dropped what I was holding and started to fall asleep standing up the other day. Ridiculous and not confidence inspiring while using a bandsaw, angle grinder and about to mess with the lathe. Anyway, figured I'd at least let you know the project wasn't ditched or something.


BTW, the bandsaw has been very nice for pipe cutting. Thank you once again John. I'm enjoying having it around. I figured out to draw some reference lines on the table since I'm really bad and eyeballing a straight cut. That seemed to help me cut where I wanted to a bit better.

[aeroxbud]

Any progress, is still progress. 👍

I'm suffering terribly with insomnia at the moment. I feel your pain. Just leaves you feeling wiped out, and nothing is getting done.

[Kenho21]

The fabrication on this bike is coming together nicely, regardless of the amount of sleep involved.

The band saw and insomnia may end you up with a missing digit or two, but this has been such an entertaining build so far, it may be worth it for us. Haha