Back pressure questions

Hi everyone, I have some exhaust questions. I have a 1986 vf 400 with the stock pipes still on it. Unfortunately the sound/performance from these pipes are far from the best. Now I'm considering either removing the baffles from the muffler or going to a metal shop and having and having some mufflers fabricated, my only question is back pressure?? Does this motor need any? If so how much?? The current pipes on there are in pretty good condition I suppose i just want a little bit more sound/performance. Like these pipes are so quiet that I can barely even hear the bike when I'm riding it untill about 7 grand. Any ideas/words of advice/warnings would be greatly appreciated.

 

the less back pressure the louder the bike will be.
try gutting the stocks or find ( or make ) a nice slip on.
you want proformance buy a header, if you can find one.

that is all, Hey Tink

 

Try the baffle thing first. Fabricating a muffler will cost you large loonies. If the baffle mod doesn't suit or work out there are aftermarket slip on's that are relatively inexpensive.

Try to be methodical in modding a can. There are all kinds. One dude I know tried punching some holes in some "fixed" baffles with a length of cold rolled. He knocked one loose and then couldn't get the muffler apart to fix it. Sure it rattled.

The dude was not from here of course, since we here are all perfect. Well almost..

 

Great link!

 

The stock mufflers have a lot of back pressure.
If you use after market exhausts You do not have to rejet but you may have to adjust the air mixture screw if it backfires on deceleration.

When you use after market mufflers they usually have less back pressure.
The engine runs a little cooler.

If you modify the intake system to breathe more easily AND you modify the mufflers,
you will have to rejet. But many people have done similar modifications and you can save a lot of money by asking what set up they are using.

Do not have a shop fabricate mufflers. You can go on line and get slip on after market mufflers and used performance mufflers online at Ebay,craigslist tc.,.

 

I read the thread and do not agree on everything said.
As far as dyno work it is very expensive and not necessary.
When you buy a "Dyno jet kit" you get a coupon with it and that coupon is worth $100 towards a dyno run on a DYNOjet dyno. See how it works?

Now the dyno jet people say even if you have the $100 dollar coupon and they have to do any adjustment then it can and usually will cost up to $300 dollars or MORE.

But all of that is not necessary because many people have all ready bought expensive aftermarket performance exhausts and the performance was already worked out on a dyno by the manufacturer of the exhaust and they have a better sound too. and lets face it . You wanted a better sound EVEN if it costs you 3 hp. RIGHT?

As far as negative pressure waves and all that i can assure you that if the factory had to get a little less power to stuff those exhausts and balance chamber under the bike and meet all of the EPA stuff they will do what it takes because they have to sell the motorcycle. Even if it costs a couple HP.

It is always a balancing act as far as torque VS HP and where in the rpm range you will get a power curve that suits the track and the rider.

And since the article was written by "LAZY IN AZ" I am sure all the work will be done by others.
He got good advice from experts and that is what he paid for.
But I am wondering.....Did he keep his stock exhausts? ...i don't think so.

One more thing.... I tune my bike by the seat of my pants. And I can tell you when the bike runs better and faster etc.,. I added two washers under my needles because the engine was lean and I got a LOT more power. I added one washer at a time and with two washers i called The experts in San Rafael CA. and they said two washers was max. Each washers about .030 thickness.
On the VF1000R or F model it will accept mainjets from 120 up to 150.
How much gas do you want to use up?

 

Can't speak to the VF400F but on the VF500F slip-ons do require re-jetting to get things back to (or close to) stock HP.

 

For the record, Don... I didn't do ANY work on my exhaust. She still has the same pipes that it came with back in '86 fully intact and no mods inside or out. The post wasn't me asking a question, but answering one that was posed to me. The advice is solid, the information concrete and as for the 'waves' that you are attempting to discount, point your ears in the direction of any of the motorcycle manufactures and ask them. You'll get the same answer.

Oh, and whats this crap about me having all the work being done by others? I've done everything on my bike myself aside from friends lending an extra hand when I needed 3 and my consulting this site for pointers and advice. I've also been paid to work on several bikes in my garage over the past few months including a complete top end rebuild and cam chain replacement on an '02 Vulcan Mean Streak.

So what, now that I've learned a bit more from actually going to school you feel the need to bust my chops because I'm offering advice and helping out? Bite me.

OH, and if you need a set of stock pipes for an '86 VFR750 I just so happen to have an extra set in my garage that I got just in case my stock pipes ever went out.

 

Awesome. You should market your ass, it would put all of the A/F sensor manufacturers out of business. Hello 1960's.

 

I restrained from making a rebuttal concerning the dig on Mark Salvisberg and the Factory Pro folks.......

 

Keep on posting Lazy.

I for one very much appreciate your tech posts. It is obvious from reading them that you put a lot of thought into what you are writing.

You’re a welcome addition here!

 

I was not out to bust your chops. I am sorry if you were offended. Seriously.

As far as Factory Pro, I like them and they have given me excellent advice.
I live near where their shop is located.

The " Lazy in AZ" was me just having a little fun with you and your on screen name.
Next time i will add on the LOL.

I just do not agree with all that was said in the thread written by "Lazy in AZ"

I see nothing wrong with anyone wanting different exhausts for styling reasons or they want a different sound etc.,.
As far as bikes subject to the new 2008 smog rulings I think that as long as the bike meets the smog criteria there is no reason to keep people from changing the looks of their bike or the sound if it is not excessive. Also if the bikes get too quiet more riders will die just like the death rate has climbed for children and older people who cannot hear these new hybrid cars in parking lots. And that is a known fact.

Some people see things first , some hear things first, so sound is important.

I will not get into all the stuff about negative pressure waves etc.,. but I was on the scene when all of those things were being discovered. I was around when the first expansion chambers were developed for two stroke engines.

I was not out to ruin you, I just disagreed about some of the assumptions.
And i know the factories have sophisticated equipment to do their design work, but if it was not for the "hot rodders" who did not have engineering degrees and developed many new modern innovations it would be sad. I believe in creativity.

 

I've got my pencil and notepad on the ready.

Totally say go for it. It's Mechanics' Garage after all.

 

Okay, firstly I was never really considering messing around with the pipes, just the mufflers. Now my reason for asking this question was that recently I removed both of the mufflers and started her up. I noticed that it was a little quicker off the bottom end, but I noticed a signifigant difference between 4-7 grand. I didn't go any higher because I was worried that the high rpm's might not be good for the motor without the mufflers on. (hence my original question). This is where I was curious about the performance improvement possibilities. (I've been riding dirtbikes since i was 3 and I've found that usually one has to pull out the air intake baffles and sometimes the muffler baffles to get the bike to perform how it should) Now I have to admit although I'm not a harley fan, I sure wouldn't mind a little bit more sound, I kid you not when I tell you that my little brothers 02 XR 80 is louder than my vf untill around 5-6 grand. I think part of my problemis that my father has a 1999 honda CBR 900 RR that he has had piped with a yosh exhaust system and then jetted with a dyno jet jetting kit (as well as dynoed on a dynojet dyno) I love the sound of that bike and since then, I have always been a sucker for a little low rpm noise. Also making my bike a little louder would be good for me since I havn't managed to get my horn working, (it's on the bike and wired I'm just missing the button it seems) so a little engine noise might help others notice me in the parking lot and in turn help keep me safe. Also thanks to Lazy in AZ for his thread I've found it really informing (perhaps just a little much to take in all at once but good all the same) . Now onto decesions, so right now I'm leaning towards drilling out the rivets wich hold the face of the muffler in, then either drilling holes into the baffles (i'm sure they're welded to the inside of the pipe) or maybe just cutting them out altogether. Unfortunatle slip ons aren't really an option for me since slip ons for a 4 to 2 converter are hard enough to come by in the first place and then my VF is so rare it's almost retarded. Anyways, thanks for all the advice so far and don't be afraid to comment further I really appreciate the help since everybody who I normally fall back on for bike advice know little or nothing about this bike so this site has been a real help.

 

It appears that Lazy in AZ isn't the only one here who gravitates towards longwindedness, haha.