port and polish

[northeast400]

I am installing my 426 kit. I was wondering if porting is worth the time.

Worth the time???




You plannin on doin it yourself:confused:

[northeast400]

I should let everyone know I run a auto performance repair shop. thats how I get all my stuff done so cheap. I have somone to port it in the shop, but yes i have the stuff and know how to do it myself. I was just wonding if there is any real gain.

[03400EX_Nacs]

i dont think it is that bigadeal i heard it was awhile back but i am sending mine off in a couple of days to get a 416 and they said it wouldnt matter enough to do it, but you still might want to check it out..

[K_Fulk]

It helps quite a bit with a full pipe and a carb.

[skemp]

If you have enough air coming into the motor through a big enough carb, and into a big enough exhaust, it is worth it. There is more to it than that, but you get the picture. And like any car, don't open up the ports too much or you will kill your power. Basically just enlarge the intake and exhaust a bit. Keep the intake rough, and polish the exhaust.

[Derrick D]

While you have it off I would get some bowl work done along with a valve job.

[markk]

i think that it is worth it, if your gona spend money on a full system pipe, jets, and an overbore.

i have heard that it pretty much helps out the most in high end r's




(i have heard of guys that port the heads to get the air to SPIN into the cylinder making it burn a litte more even!

[400exdad]

I say DO IT! I'm running stock bore with high comp piston and the "right" gaskets to take advantage of the piston and an XR400 cam. I can definately tell a difference. Even though I did all the mods at once, I still believe the porting made a difference. Last year at Loretta Lynns, the motor just did not make the power for the long uphills and some of the fire roads. This year, it was awesome! Pulled the hills great and would fly on the fire roads. I was extremely happy with the changes that I made. Porting that was done was minor. I port matched the intake and cleaned out the casting marks and did a general smoothing... but not too smooth. Cleaned up the bowls and removed some high spots where the charge comes into the valve opening as well. On the exhaust side I just opened up the outlets to almost match the gaskets. It was a big difference in area when you compare the before and after on the outlet circles. Now, IMHO, I think, with a big bore, the portwork is really REQUIRED! Some of you may argue with that, but, from my car days, I learned it was the little things that made the big difference! My mild little 350 whipped its share of big blocks and hotter small blocks. All because the extra little things added up. Porting takes time or money or both.

[AndrewRRR]

If you have a good porting person at your speed shop, you know what a difference head porting can make. Quads are no exception. After "bolt-on's" like intake, exhaust, ignition, porting is the next step (along with internal work) to unlock power. Plus, as long as you have your motor apart, you might as well do it now. You can unlock some serious power with porting. Make sure your porting guy knows what kind of riding you are going to do with it and ports it accordingly (ie- you don't want a top-end port job if you are gonna ride woods). Do you have a flow bench?
You also might look into oversized valves, a cam, and valve springs and retainers.

[xc400ex]

ah boys....if you guys could only see my intake ports......and put my bike on a dyno....my intake ports are 35% smaller......and after the decrease it felt like 35% more power

[400exdad]

xc400ex, I could prolly say that my ports were 35% bigger and it felt like 35% more power too. :) I ran up on some guys talking about decreasing port size and it makes sense to a point when you are increasing velocities and maybe improving volmetric efficiency at lower RPM's. Since you are reducing port size, are you also reducing the carb size too? I'd love you see the two quads on a dyno. I imagine the throttle response is awesome, (the seat of the pants feeling) but also think its over at 3000-4000 rpm.

[RAPTORAZ]

Originally posted by xc400ex
ah boys....if you guys could only see my intake ports......and put my bike on a dyno....my intake ports are 35% smaller......and after the decrease it felt like 35% more power


Sounds like you should find a dyno in your area and report back. Make sure you find out what type of dyno they're using and get the air temp and humidity readings while it's on there as well. That way we can see how well your bikes numbers compare to one that's been ported.

[go_chrisg]

some info here about smaller ports

http://www.mototuneusa.com/think_fast.htm

[xc400ex]

Yeah its got great throttle response but really after the porting it was just starting to pull at 3-4 thousand rpms....this thing really pulls up top but is not slow on the bottem end either..yeah ill try and find a dyno I doubt I have any luck though. Im using the stock carb. Im running keihn jets smaller than stock...I get better gas mileage than stock and yet I have much more power. It simply runs more efficient. By making the ports larger you can actually mess the timing up by when the air/fuel ratio enters the combustions chamber becuase its slows the velocity.

[howboutchaw]

Originally posted by xc400ex
ah boys....if you guys could only see my intake ports......and put my bike on a dyno....my intake ports are 35% smaller......and after the decrease it felt like 35% more power


How did you actually make the ports smaller?
Thats a damn small hole to fill with the tig!

Anyhow head flow is just about the most important aspect of building a hot motor. Hell we did tests on small block chevys running dart heads. When we dynoed the out-of-the-box heads to ones with just bowl work it was good for 60 horse. On the 400ex there is alot of room for improvement, especially in the bowl and the short side radius. As soon as I get the time I thought about setting the ex head on the flow bench just to see exactly how many percent gain I can get out of it. But one thing is for sure, I wouldn't even consider putting an EX together without at least doing the bowl and short side radius work.

[xc400ex]

JB weld...works perfect with the aluminum.......

[Derrick D]

They would probably use a stick welder to weld the cast aluminum. Seems like the only way to get in there to add material.

[xc400ex]

Man no stick welder will ever be weldin on an aluminum head............:huh

[skemp]

It is interesting stuff guys, and it does make sense. That Mototune website sure does make a lot of hype about it though with all the flashing words and different colors. Doesn't make much sense to me why he can't just come out and say that smaller ports can lead to an increase in power. Geez. He has so much BS leading up to it that I can't even read through it all.

[400exdad]

I went to the link and that was the one that I had seen in the past. I really liked the bread joke/comparision at the bottom (of the very long) page. I have a hard time believing some of it, like most I guess and am skeptical. Why? If it were true, single exhaust and low profile intakes would be all what was sold. Smaller carbs would dominate the market. Every racing team and manufacturer would be utilizing this "downsizing" technology. Just my .02. Everybody probably told the Wright Brothers they were crazy. The Wright Brothers showed them!

[xc400ex]

95% of the racers out there when they have there motor built want the most possible peak horsepower out there. Enlarging the ports will increase power, but it will make the power curve smaller. On a dyno larger ports probably do make more PEAK power but thats not the point. Smaller ports make more useable power. That doesnt mean they take away power and make it easier to ride its just smoother more horsepower throughout the entire rpm range. And like I said early smaller ports run more efficient, better gas mileage, cooler motor temps, and more POWER.

[hondafox440]

Yep.

The trick to getting a great power curve is small ports, but a lot of port area. This is the reason behind having 2 (or 3) intake ports. The small size of each individual port gives the motor better bottom end power and torque, and the multiple ports allows the total port area to be larger, thus creating more top end. Porting will be a trade off, just remember that. If you shrink the port size, you probably will lose some top end, but gain a fair amount of low end. If you increase the port size, you will lose some low end but gain top end.

Oh yea, this is referring to intake ports.

[northeast400]

I talked to the "porting guy" he recommended that the ports be cleaned up with minimal "porting". just enough to get the rough stuff out and to smooth the intake to valve seat ridge for woods riding.

Originally posted by northeast400
I talked to the "porting guy" he recommended that the ports be cleaned up with minimal "porting". just enough to get the rough stuff out and to smooth the intake to valve seat ridge for woods riding.

ya that is exactly what we did to my bike:D