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[GMR-PERFORMANCE]

The stock cam is a short overlap. Keep that in mind as you read this.


The stock head pipe is longer in the front so the harmonics are better suited for low RPM. The rear head pipe is short so the harmonics of that pipe are better suited for high rpms. So with the low rpm you ride in under normal street instead of suction you get reversion or stand off in the rear cylinder as the rear pipe is out of sync with low rpm. That is one cause of the rear cylinder running hotter than front under street use. Where as the front pipe is better suited for that rpm range and it will run cooler.

Now the new stock cams for the 07 ( I will find the specs and post them we degreed one a few months ago) are under 10* of overlap. This small amount of overlap is an issue. As it is a very short period of time. The overlap cycle aids in cooling down the head. Previous t/c had 35-40 * of overlap in the stock cams. ( not all stock cams are the same)

Since the harmonics are off you do not get as much scavenging to cool down the heads with that short overlap.

Now onto header pipe length, The front cylinder head pipe length is longer so it works better under lower rpms so it will cool the head down more than the rear, but as you move into high rpm ranges the rear will start to cool more than the front as the harmonics are suited for the higher rpm range. As the front cycle harmonic cycle is out of tune in the higher rpm range.

315/405 that is the degree that a common runner use's to run at.

When the front cylinder is firing at 35* BTDC the rear piston is at 10* ATDC so your rear piston has only 315 to fire from the front cylinder firing.

Now the rear cylinder is firing at 35* BTDC your front pistons is at 80* BTDC so for it to fir again it has to go 405 again to fire. Add those up you get 720*

So what you get is a different bounce back wave on the intake runner and get uneven cylinder fill from front to rear.

This is where correctly ported heads shine. Our head is ported differently from front to rear to compensate for this different timing event. The old trick that was used was to skew the intake manifold from 1.5 -2.0 degrees to try to alter that and have a close cylinder fill. It does not work as well as using math to make the changes to the port. Where a head that is ported to compensate for this will balance out cylinder fill and run cooler. AS well tightening the port up will result in better atomized fuel resulting in less chance for ping, as you have lower head temps and then you can add more compression in there as well with no ill effects.

You have a wave that is bouncing off the intake valve. Now as that valve is opening the short pipe on the rear under low rpm is out of tune with the intake valve. SO when the valve opens instead of the ex sucking the intake charge in to purge the chamber and cool it down for the next cycle you get reversion and lack of scavenge this equals excessive heat build up in the head.

As well the overlap cycle is so short on the stock 07 cams your tune needs to be spot on. I am not saying that with a spot on tune you will fix all of this, what I am saying is that there is almost no degree for error. AS before you had a much longer overlap cycle the head pipe legnth was not as critical, so you had better cooling as they work hand in hand. So adding a cam with a longer overlap will help you out in that area. But you are still dealing with the 315/405 timing events and stock heads.

Now the front cylinder head pipe is much longer it is more in tune with lower rpm ranges. SO it is more likely to come into tune with a stock cam. Do not forget that you are battling the rear cylinder at low rpms. So they are fighting each other with the stock head pipe, short overlap, and stock heads.
All of this adds up to the hot running that is seen in the 07 models.

If you look at a head pipe that has a large legnth difference from front to rear it is going to be hard to tune it as the harmonics are way off from one to another. That is where a pipe with front and rear head pipes that are equal legnth perform so well.

I hope this sheds some light on the subject, I tried to keep it simple as there are 4 harmonic waves you are dealing with I listed one. But it keeps it simple and you can see what is going on with the stock bikes.

That is why using a package that is set up to work together makes so much sense. There are some fixes for poor exhaust pipes like adding a washer and skewing it to help with the scavenge cycle. If you get it so out of tune withthe harmonics you are fighting a uphill battle the entire way. This goes for improperly ground cams, incorrectly ported heads, improper exhaust systems.

I know that in our world that many times you cannot have it all but if you know what you are up against going in you are more likely to have a winner as a final build vs one that does not live up to what you where looking for.

Lunch is over gotta go.
__________________
02 Deuce
640 stick
White Bros E-Pipe
54MM TB
159/163


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[Talon]

GMR-P good info, do you think an AR cone in the rear cylinder would help at all. Although I don't like the look the Bassani true duels, but they might help with the rear cylinder situation. 

[skreminegul07]

How the factory crossover or lack affect this situation with stock cams?
Also what about the SE 110 stock cams SE-255?

Thanks

[rednectum]

trust what gmr says!! changing cams is as necessary as a good tune to correct the 98 inch heat and pinging.

[Vosselman (NL - Europe)]

Last week, a customer brought his 07 nighttrain.
He was at the point to sell it. He hated the bike!
He went to France but returned after just a couple of days, he could not even ride a mountain or the bike got so hot it turned off.
Even here in a flat country it was turning very hot. Dealer could not change it.
The bike was completely stock. Stock aircleaner and stock HDI exhaust.

We tuned the bike with DirectLink. Added a SE aircleaner, still used stock HDI mufflers, and gained a little over 10hp at the rear wheel.
Bike is much more responsive and pulls much better. And it keeps cool (just like another HD).

Customer loves the bike now.

I'm not saying GMR is wrong as the stock cams are EPA cams, so don't do any good other than for emissions, just saying a good tune will make a '07 run cooler and much better. So a good tune and a better cam would be ""

[rednectum]

Last week, a customer brought his 07 nighttrain.
He was at the point to sell it. He hated the bike!
He went to France but returned after just a couple of days, he could not even ride a mountain or the bike got so hot it turned off.
Even here in a flat country it was turning very hot. Dealer could not change it.
The bike was completely stock. Stock aircleaner and stock HDI exhaust.

We tuned the bike with DirectLink. Added a SE aircleaner, still used stock HDI mufflers, and gained a little over 10hp at the rear wheel.
Bike is much more responsive and pulls much better. And it keeps cool (just like another HD).

Customer loves the bike now.

I'm not saying GMR is wrong as the stock cams are EPA cams, so don't do any good other than for emissions, just saying a good tune will make a '07 run cooler and much better. So a good tune and a better cam would be ""

yep, allowing the bike to breathe, and a good tune really help. BUT, they are still running hot. a cam change finishes the curing process. the tw37 works great for this. our geographic location allows riding year round and summer temps are in mid and high 90's with high humidity as well. barometric pressure is usually around 29. yes, we see lots of detonation and overheating. add the paraders (beach riders, boulevard queens, bar hoppers) and we also see cooked engine oil, cracked exhaust, blown head gaskets and all sorts of problems related to heat.

all that said, after cams, and tune, typical o7 bike temps are around 230 head, less than 260 oil, on even the worse days.