TRX400EX vs. XR400R Head gaskets, Has anyone actually done the Math ???

[tri5ron]

Just curious,
I realize that the XR400R headgasket is thinner than the TRX400EX head gasket, and will therefore raise the compression, when used in our 400EX engines.

Ok,... thats a good, easy, safe, and cheap way to squeeze a little more power out of the entire powerband.
I like it.

But I'm just curious if anyone here, has done any actual Calculations, or Testing,...
to Accurately Determine,...
just HOW MUCH it really changes the compression ???

I also realize, that it in no way, is comparable to changing to a higher compression piston.

I am not trying to start a debate or argument of 10:1, 11:1, 12:1, Pistons vs. XR400R gasket.

I am simply asking the question of,
What is the amount of Gained Compression, by using the XR400R gasket vs. the TRX400EX gasket?

So come on all you Engineering Protege's, and/or Engine building Guru's...
Here's your Challenge...

Either by calculating the differences of thickness, between the two head gaskets.
(and No,... I do not know what the thickness of either one is at this point)
or,
by doing a compression check on the same engine, with the same piston and rings, changing ONLY the head gasket.

No speculations, and no guessing now !
We want REAL, ACTUAL , numbers here !
:D :D :D

[togup]

have you read this? Its really good.(quoting Mickey Dunlap)

I prefer to build a motor that pulls quick and hard through the RPM range and the piston with higher compression will build more cylinder pressure which develops torque and will rev quicker and run faster through the RPM range. On most after-market pistons, the pin to deck height is the same as stock. You should have a minimum of .040 clearance between the piston and head with everything torqued down. Right now the piston is about .043 too low and you are not getting a true compression ratio as advertised by most piston companies. For instance, a 440 11:1 flat top piston advertised is really only about 9.75:1 if you measured the volume correctly. In order to get the deck heights better, I use Honda HT silicone seal on the cylinder base and an XR400 gasket if you are running an 80 over piston or smaller. This will get you close to what your deck height should be. Keeping the squish clearance down to .040 gives a better quench area around the outside of the piston keeping it cool and less chance for detonation. You will be able to run an 11:1 motor on pump gas in most cases and have a more efficient flame travel and quicker burn rate across the top of the piston. I have read on the forums here how everyone thinks a 416 is faster and revs quicker than a 440 kit with the same compression. I think most people are not running as high a compression ratio with the 440 kits as they think they are and when you put a cam with it, you end up with lower cylinder pressure making the machine rev slower than the higher compression 416 motor. Just my thoughts anyway. Without talking to each individual, it's hard to figure out why people think the 416 is faster than the 440. Any time you put a longer duration cam in, you have less time to build cylinder pressure. This is why it's important to put a higher compression piston in when you install a longer duration cam. You can get more torque the higher you go on the compression ration and your cam will give you the mid-range to top-end without losing low-end.

[tri5ron]

Originally posted by togup
have you read this? Its really good.(quoting Mickey Dunlap)

No, I've never read this before. Who's Mickey Dunlap?, and what is the source of the info being presented?
Is this ALL a quote of his?, or is some of it also your thoughts?
[i] You should have a minimum of .040 clearance between the piston and head with everything torqued down. [/B] Where is that Spec from?, what data is available to support this ? (I'm not trying to be a smart-***** here,... I'm trying to determine actual tested, supported data.
Originally posted by togup
Right now the piston is about .043 too low and you are not getting a true compression ratio as advertised by most piston companies. For instance, a 440 11:1 flat top piston advertised is really only about 9.75:1 if you measured the volume correctly. .043 too low????, are you saying it needs to be raised .043?, or .003? to bring it up to the above stated .040 clearance ?
[i][QUOTE][i] For instance, a 440 11:1 flat top piston advertised is really only about 9.75:1 if you measured the volume correctly. [/B] If this is a accurate statement, alot of people here are not going to be too happy. where is this shown to be accurate info?
[i] In order to get the deck heights better, I use Honda HT silicone seal on the cylinder base and an XR400 gasket if you are running an 80 over piston or smaller. This will get you close to what your deck height should be. [/B] OK, I'm good with that, and you have apparently measured these deck heights when using the sealant, and thinner gasket. So what did it raise the compression ratio , on the stock piston to?, also,does this create any issues with the cam chain tension?
[i] Any time you put a longer duration cam in, you have less time to build cylinder pressure. This is why it's important to put a higher compression piston in when you install a longer duration cam. [/B] so what are your thoughts on putting a stage 1 or 2 cam,... on a stock piston,... while doing the HT seal, and XR400 gasket?

or in other words,...

Will putting a stage 1 or 2 cam, on a stock piston, be beneficial or detrimental to, the OEM performance envelope, when installed in conjunction with a XR400 gasket and HT sealant on the cylinder and head?

I.E.- Does the installation of the HT sealant/XR400 gasket, compensate for the lost cylinder pressures, with the installation of a longer duration cam?

Thanks.

on edit here,... I have no idea why some of this above reply came out in bold, and some did not. It was not intentional on my part, so please disreguard the discrepancy.

[gtt416ex]

mickey dunlap owns FST(four stroke tech). i am also wanting to know the exact difference. ive got a XR400 gasket on the way so i'll measure the difference between it and a stock one. but i don't know the formula to calculate how much it raises compression.

The XR400 head gasket will raise the compression to the factory spec 9.1:1 compression.

The XR400 has 9.1:1, and with the 400ex, due to the thicker head gasket, the compression was slightly lower. But instead of changing the specifications, they simply just took them from the XR400. A stock 400ex is probably about 8.8:1, or around that range. The XR400 head gasket would bring it up to the true 9.1:1 that Honda claims.

No real math needed, just some research;)

[tri5ron]

Originally posted by DMC-4OOEX
The XR400 head gasket will raise the compression to the factory spec 9.1:1 compression.

The XR400 has 9.1:1, and with the 400ex, due to the thicker head gasket, the compression was slightly lower. But instead of changing the specifications, they simply just took them from the XR400. A stock 400ex is probably about 8.8:1, or around that range. The XR400 head gasket would bring it up to the true 9.1:1 that Honda claims.

No real math needed, just some research;)

so by that, I'm assuming the XR400 engine, and the 400EX engines, have exactally the same crank, rod, and piston,...
therefore having the exact same stroke and combustion chamber volumes ?

I realize this may be a dumb question, ...it's just that I am not THAT familiar with the XR400 engines, and/or, any specification differences between it and the 400EX engine.

I also realize that they are ESSENTIALLY the same engines, but obviously there are some minor differences,...
the different head gaskets, being one of them, as an example.

Originally posted by tri5ron
so by that, I'm assuming the XR400 engine, and the 400EX engines, have exactally the same crank, rod, and piston,...
therefore having the exact same stroke and combustion chamber volumes ?

I realize this may be a dumb question, ...it's just that I am not THAT familiar with the XR400 engines, and/or, any specification differences between it and the 400EX engine.

I also realize that they are ESSENTIALLY the same engines, but obviously there are some minor differences,...
the different head gaskets, being one of them, as an example.

I believe so. The XR400 also has an ever so slightly more aggressive camshaft, and different flywheel set-up which is also lighter. And a kick-start, of course.

But I do believe the crank/piston/head is the same, thus having the same combustion chamber volumes and just different head gaskets.

[fauxamish]

The xr400 crank is the same length in terms of stroke, but the flywheel side is not as long since the xr400 does not have the starter gears. The transmission gears are also a little taller. The swingarm mount is also slightly higher. Not sure that this is 100% relevant, but I did not want anyone getting the wrong impression about being able to drop in an xr400 crank and expecting to be able to still use electric start.

[honda400ex2003]

I have also heard along with the cam being more aggressive, the gears being higher, and different mounts, that the clutch is a little different with thinner plates and a smaller basket. I have read that it was beefed up for the ex to help with power and the drag of added weight from both tires.
heres the info from mickey.

http://www.atvriders.com/articles/askmickey1.html

http://www.atvriders.com/articles/askmickey2.html

steve

[F-16Guy]

Enjoy:

http://www.exriders.com/vbb/showthread.php?s=&threadid=8316&highlight=have+you+decked

[tri5ron]

F-16, Thanks for the link. EXCELLENT info there. I'm only into page 4, and am reading every word.
I may have to read the entire 21 pages a few times, and take notes along the way, LOL!... but I'm confident that some excelllent detailed info can be obtained there, that I do not normally see in most of the threads lately.
Thanks again,
Ron

[F-16Guy]

Yep, those were the good ol' days!:D

These days, there just aren't very many threads like that popping up.

[400exrider707]

Originally posted by F-16Guy
Yep, those were the good ol' days!:D

These days, there just aren't very many threads like that popping up.

I miss those days...


It's pretty widespread knowledge that the 400ex is designed weird with the piston sitting down in the cylinder .043" at TDC.

This is why a lot of people get away with putting high compression pistons in and running pump gas still. I always ran 87 octane in my 11:1 EX with a thin head gasket.


Also if you guys are going through the trouble to put the XR gasket in... Cometic sells a gasket that's even thinner than that. Colby from C&D sells them and when I bought mine it was $20.

I'd recommend getting the CRF cam chain if you guys are already tearing into the motor anyways.