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04 400ex
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Discussion Starter #1 (Edited)
Hello all. Ive been doing a lot of reading on this forum and have found some great information- I would like to discuss my specific build and see where i can improve on it. Thank you in advance and look forward to reading what everyone has to say quad is an 04 400ex

Quad runs great, better than ever- extremely reliable, its got more power than when i originally picked it up, but i feel i should have come out with more power than i did when we put it on the dyno to jet the carb properly and see what kind of power it made. I will post the dyno sheet. I didnt want to goto a 416, i wanted to keep it reliable i do think i regret at this point not going to a 416- here goes...

.040 oversize 10.0:1 compression Wiseco prolite piston
Hot Cams Stage 2 cam (also replaced the cam gears)
Wiseco cam chain (did tensioners etc oem honda)
Cometic Top End Gasket Kit
Rebuilt Stock Carb (Dont know jet size, all i do know is the air fuel ratio is correct from being on dyno- plus plug looks textbook normal color)
Kibblewhite Valvespring Kit
Wiseco stainless steel valves (completely rebuilt head seals retainers etc the only thing I did not change were the original rocker arms)
I have a big gun rev box but it is not installed- We didnt see a need to install it because with the dyno results, there was no need to add any more RPM as the power was falling off before max rpm
EBC DIRT RACER clutch kit.
Lexx Slip on (could this be an issue?)
Stock Head pipe
-1 tooth on front sprocket
New chain, new sprockets
Lonestar Carrier
Stock suspension
Maxxis rzr2 rear tires
Open Airbox lid
KN FILTER with outerwear sock.

She pulls good through every gear power is solid, but i kind of expected A LITTLE more out of it. I am curious if i pull the head off and have the head and intake manifold ported and polished, put a head pipe on it (Recommendations needed!! FMF POWERBOMB? EBAY Also has a similar to power bomb head pipe for half the price) and rejet will this complete my mods and get the most out of what i have installed? I feel i made less than stock horse power (28?) where is the power being lost? Whats wrong? 26.32 BHP @ 85.20rpm and 17.96 ftlb @70.20 RPM
I ATTACHED THE DYNO SHEETS IN PDF FORMAT PLEASE LET ME KNOW IF THEY OPEN

Any input would be greatly appreciated. To add- I am an experienced rider- The quad is not much faster than a stock 400 ex with stock gearing. Everything from the piston up is brand new- if it wasnt replaced with a brand name part, it was replaced with honda OEM. The only ebay part on this quad is the Lexx slip on.
 

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I didn't see the stock engine dyno sheet - how do you know the stock engine was making 28 BHP? You are taking someone's word for it?

You have made so many changes and then dyno'd the wheeler (I presume you are reading HP at the rear wheels and not at the crankshaft?)

When you increase the bore it increases low end torque, but increasing the cam lift increases the top end at the cost of low end performance. You change the exhaust to low restriction to gain back some low end and allow the engine to rev higher and faster. Changes to the intake lean out the air/fuel mixture and you went to the extreme on reducing intake restriction. With a K&N keep it on the pavement and out of the dirt, or get a K&N pre-filter and a second K&N filter - that way you will have one to run with while the other is being serviced - it takes about 12 hours to properly clean and re-oil a K&N and they contribute to shorter piston and ring life as they flow more dirt than a foam filter.

Anyway........ The dyno charts (identical - only one dyno run?) do not indicate anything other than what the current set-up is capable of.

Why Kibblewhite valve springs and Wiseco valves?

Try degreeing the camshaft to piston position (requires machining the cam sprocket bolt holes about 1/8 inch in both directions from center.

What are you wanting to improve - acceleration, or top end speed or both? Are you wanting an improvement in mid-range for acceleration out of the turns on a flat track or do you want low end grunt for coming off the line? Maybe your goal was improved top end just to have the fastest terminal speed in comparison to other single OHC 400's?

When you start an engine build, you first determine the goal and then build toward that goal.

My 05 TRX400 was totally screwed up when I got it - I restored it to the factory exhaust and air box, replaced the worn out and broken rear brake and axle carrier. Now that it runs right and out performs the acquired POS, it will never out accelerate, out pull or have the terminal speed of my 05 LTZ400. The LTZ with dual cams has less reciprocating mass and is more precisely tuned than the 400EX. The EX is lighter (being air cooled), lower and shorter than the LTZ and therefore has better handling, will turn shorter and is less prone to flipping in the turns.

If you decide to have the head ported - it will decrease low end performance slightly and enhance top end performance slightly. Only the exhaust port gets polished to reduce carbon build up. More importantly is increasing the size of the ports to flow more air, but an increase in volume is offset by a decrease in velocity which will require decreasing the size of the jets in the carb.

One thing you did not mention was the changes made to the carb (if any) - the top end power may reflect a loss due to being too rich. Too lean has a tendency to just flatten and taper off - too rich usually results in more loss of power with an increase in RPM, which is what I'm seeing, but there are no comparison charts to refer to.

Study the carburetor and reveal the current jetting - re-jet accordingly and re-dyno to see the resultant change.
 

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04 400ex
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Discussion Starter #3
I didn't see the stock engine dyno sheet - how do you know the stock engine was making 28 BHP? You are taking someone's word for it?

You have made so many changes and then dyno'd the wheeler (I presume you are reading HP at the rear wheels and not at the crankshaft?)

When you increase the bore it increases low end torque, but increasing the cam lift increases the top end at the cost of low end performance. You change the exhaust to low restriction to gain back some low end and allow the engine to rev higher and faster. Changes to the intake lean out the air/fuel mixture and you went to the extreme on reducing intake restriction. With a K&N keep it on the pavement and out of the dirt, or get a K&N pre-filter and a second K&N filter - that way you will have one to run with while the other is being serviced - it takes about 12 hours to properly clean and re-oil a K&N and they contribute to shorter piston and ring life as they flow more dirt than a foam filter.

Anyway........ The dyno charts (identical - only one dyno run?) do not indicate anything other than what the current set-up is capable of.

Why Kibblewhite valve springs and Wiseco valves?

Try degreeing the camshaft to piston position (requires machining the cam sprocket bolt holes about 1/8 inch in both directions from center.

What are you wanting to improve - acceleration, or top end speed or both? Are you wanting an improvement in mid-range for acceleration out of the turns on a flat track or do you want low end grunt for coming off the line? Maybe your goal was improved top end just to have the fastest terminal speed in comparison to other single OHC 400's?

When you start an engine build, you first determine the goal and then build toward that goal.

My 05 TRX400 was totally screwed up when I got it - I restored it to the factory exhaust and air box, replaced the worn out and broken rear brake and axle carrier. Now that it runs right and out performs the acquired POS, it will never out accelerate, out pull or have the terminal speed of my 05 LTZ400. The LTZ with dual cams has less reciprocating mass and is more precisely tuned than the 400EX. The EX is lighter (being air cooled), lower and shorter than the LTZ and therefore has better handling, will turn shorter and is less prone to flipping in the turns.

If you decide to have the head ported - it will decrease low end performance slightly and enhance top end performance slightly. Only the exhaust port gets polished to reduce carbon build up. More importantly is increasing the size of the ports to flow more air, but an increase in volume is offset by a decrease in velocity which will require decreasing the size of the jets in the carb.

One thing you did not mention was the changes made to the carb (if any) - the top end power may reflect a loss due to being too rich. Too lean has a tendency to just flatten and taper off - too rich usually results in more loss of power with an increase in RPM, which is what I'm seeing, but there are no comparison charts to refer to.

Study the carburetor and reveal the current jetting - re-jet accordingly and re-dyno to see the resultant change.
hello! I appreciate the response!
Let’s take this question by question,

there was several dyno pulls made with different jets. These were the finals and the only print outs I was given. The dyno tech told me this was the best AFR for the build “more fuel will just give you dyno numbers that will not translate to the rear tire”

I had purchased a dyno jet jet kit and quickly learned that one jet companies “170” is not the same as another jet companies “170” the dyno jet kit was thrown in the garbage and we started swapping “oem” jets. I believe the main is a 155 mikuni. I can’t remember what the pilot is and the needLe is set at the stock spec.

The quad went to the dyno for the sole reason of i couldnt jet the jetting right. 165 -170 dyno jet main it ran rich and bogged a lot. Went to 155 the pipe glew cherry red

I am looking to improve mid to top end power (bottom end is pretty ballsy pulls wheels into third and I’m sure if I purposely did it she will come up into 4th). I’d like to improve the acceleration and if I can gain some top end speed that would be great.The “28 hp” I saw that Honda400ex made stock was thenumbers I have seen posted throughout several forums- but I also know dyno numbers are variable from dyno to dyno and climate to climate. How different? I don’t know.
As for the springs and valves- that is wht motosport had available at the time of the build - my buddy had said it’s fine order them. Should I have gone +1 on the valves? Will a +1 work with my piston?

did I make any mistakes? And can you also elaborate on machining the cam gear? What that would do? Also what about these timing keys I read about.
 

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hello! I appreciate the response!
Let’s take this question by question,

there was several dyno pulls made with different jets. These were the finals and the only print outs I was given. The dyno tech told me this was the best AFR for the build “more fuel will just give you dyno numbers that will not translate to the rear tire”
He was correct - more fuel is not more power - just the opposite - more air is more power, but you have to keep the mixture rich enough not to burn the motor up.

I had purchased a dyno jet jet kit and quickly learned that one jet companies “170” is not the same as another jet companies “170” the dyno jet kit was thrown in the garbage and we started swapping “oem” jets. I believe the main is a 155 mikuni. I can’t remember what the pilot is and the needLe is set at the stock spec.
Even Mikuni jets are not the same between hex jets and round jets - some are sized by flow and other are sized by hole size, but if the jet is for the application whether K&N or K&L or other manufacturer should be sized accordingly, but I know there are a lot of complaints when it comes to Dyno-Jet kits. I don't use them and just buy packages of known quality jets. One example is a company that made an adapter to change the Keihin long hex jet to accept the Mikuni round jet. Nothing wrong with the concept, but a 155 Keihin does not meter the fuel the same as the 155 Mikuni.

The quad went to the dyno for the sole reason of i couldnt jet the jetting right. 165 -170 dyno jet main it ran rich and bogged a lot. Went to 155 the pipe glew cherry red
A red pipe is not abnormal - steel glows red at about 900 degrees F - the exhaust gas may be as much as 1200* F - growing up on the farm, I did a lot of plowing - one night I noticed the bottom of the muffler was red hot, but only while turning the soil, raise the plow out of the ground to make a turn and it quickly cooled - later I noticed no only was the muffler glowing, but the entire cast iron exhaust manifold was glowing from the side of the head to the exit on all 6 cylinders ans it was brightest in the middle where it was connected to the muffler - on 1/2 mile pulls, the muffler would glow all the way to the middle.

My CRF has a stainless steel head pipe and it glows at night or in subdued light, bur only when running hard and at high RPM - stainless glows funny compared to carbon steel.


I am looking to improve mid to top end power (bottom end is pretty ballsy pulls wheels into third and I’m sure if I purposely did it she will come up into 4th). I’d like to improve the acceleration and if I can gain some top end speed that would be great.The “28 hp” I saw that Honda400ex made stock was thenumbers I have seen posted throughout several forums- but I also know dyno numbers are variable from dyno to dyno and climate to climate. How different? I don’t know.
If it wheelies that easy, you could change the gearing for more top end, but if you want brute pull in the higher RPMs, you could gear down some more, improve the HP number, lose a little top speed, but gain top end torque. Horsepower is a work number - it is directly convertible to watts, BTU's, calories and a couple more thermal definitions. Torque is turning force - a higher torque number could be more impressive than a HP number.

As for the springs and valves- that is wht motosport had available at the time of the build - my buddy had said it’s fine order them. Should I have gone +1 on the valves? Will a +1 work with my piston?
I just prefer to match springs to valves as the spring is designed for a specific valve weight (reciprocating mass) - the higher the recip-mass is the less HP that can be extracted.

did I make any mistakes? And can you also elaborate on machining the cam gear? What that would do? Also what about these timing keys I read about.
Everyone makes mistakes and not every build turns out as expected. Machining the cam sprocket allows you to advance or retard the cam timing to increase the accuracy of valve timing in relation to piston position. The offset timing keys allow you to advance or retard the spark timing to compensate for fuel and other timing requirements. If you want to run higher compression and higher octane fuel, you need to advance the timing to start the ignition of the slower burning high octane fuel to realize more power in the higher RPMs. Typically you cannot run higher than 94 octane at below 11:1 compression without experiencing a loss of power. My stock CRF250 starts to lose power at appx. 94.5 octane (that octane number is derived by experimentation of mixing 100 octane non-ethanol with 89 non-ethanol and trying to find what mix worked best and trying to calculate the octane by percent of mix) - I run my CRF pretty hard and although it's liquid cooled, I like to run a cooler burning fuel to reduce engine temperature, but doing so raises exhaust temperature (which doesn't hurt anything).
 

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Discussion Starter #5
Understood.

Sounds like if i want to continue running pump gas (93) i should leave the timing alone. As for gearing do you recommend touching the rear sprocket to find these gains? I certainly agree with torque may just be what i am looking for- but i dont want to run out of mile an hour.... 75mph would be a nice target speed. 5th gear seems very long as ive held it wide open for quite some time and i have never heard it hit the limiter (in fifth). Getting to 75 as fast as possible would be even better. do i achieve this by sprockets only (i would assume this would be torque multiplication) or would I need some more supporting engine modification and accompany it with a head pipe. I reached out to a company in Pennsylvania Advanced Machine Services- He said since my head was rebuilt, he would disassemble port, polish and reassemble with new valve seals. He would also port the "Intake manifold"- This would require a new head pipe. He suggested an FMF Powerbomb- not sure if this will marry up with my Lexx Slip on. I also see powerbomb knock offs that look identical on ebay- not sure if they would achieve the same outcome. Then, I'm back to the dyno playing with jets.

Then the question is what would, or could I expect from doing that? Is it worth say $900... port and polish roughly $350 with shipping, pipe 250ish, tuning 350 or should i just keep on riding and put it behind me?

Or can this issue be resolved with gearing and timing (if i can keep running pump gas) adjustments?

Your opinion is valued. Thanks again

PS- So you get an idea of the main area i ride. It is a melting pot of all kinds of riding from your standard trail riding trails, crazy woop trails, Hill climbs, berms, Flat sandy straight roads, bowls, you name it- its out there id say everything under the sun but jumps and tabletops lol. i can get all the power i need out of it to go fast in the trails, its the straight lines when we all drag race that i want to come out on top all the time LOL. or close to it. im not going up against 450's or banshees... Theres a nice 87 250 r thats out there- we have gone nose to nose until they kick 6th gear and they pull off on me.
 

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If you are not bumping into the rev limiter and the end of 5th gear and you want a higher top speed, you need more top end power or lower gearing - of course lower gearing will get you to top end quicker (drag racing), but if you want higher terminal speed, then you need to make changes to extract the power in the higher rpms.

It's a trade off because for more top end power you are going to sacrifice low end power and some acceleration. I suggest you port the head, go to a larger diameter head pipe, and perhaps a 2mm larger carb or a more efficient carb - a friend of mine is running a Keihin FCR carb on his 400 flat tracker, but he NEVER goes into the woods, sand or mud - it was built strictly for flat tracking and it does that well.

If I were you, I would seriously think about giving up on the 400 and get a TRX450, but it's not my choice. Beat on it some more and you will achieve what you are looking for - maybe consider a stage 3 cam for the ultimate top end power.

OH yeah! Forget about the 'look alike' power bomb head pipes - that's exactly what they are; look alike. Get a full system FMF exhaust. The engine will perform better with an engineered exhaust vs a 'increased noise' exhaust. I chucked an HMF slip on for the stock muffler and got better performance than the cheap POS HMF.
 
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