Help getting more power out of my Honda 400ex

[bodfper]

I have a 1999 400ex and would like to get more power out of it. It has works shocks, uni filter, nerf bars, 909 bars, DMC full dual exhaust, and thats about it.

I have some questions and would like to get an educated opinion. Im 17 so I dont have deep pockets but here is the list that I would like to do, tell me what you think. I have never worked on a machine like this engine wise, but I am good mechanically. Is this setup going to be reliable? Thanks and it will be greatly appreciated!

416 kit with 10:1 comp. (do I need heavy duty head bolts?)
stage 2 hotcam
port+polished head
450r carb (does this bolt right up or does it need to be modded?)
k&n with no lid (is the k&n necessary or will the uni do?)
crf 450 timing chain (any year CRF 450?)
geared 16/38
big gun rev box
RK racing chain/sprockets
Barnett clutches

[Scrap99]

I'm confused, I thought you said you DIDN'T have deep pockets.

[AgentSmith]

You're gonna need race gas to keep a 10:1 aircooled from pinging like hell...

The port and polish will accomplish very little without going +1mm on both intakes and exhausts.

The 450R Keihin will not bolt right up. Try and get one from a Yamaha that doesn't use the TPS.

[ninjamonkey_16]

buy a turbo and NOS.

should be a little faster IMO.

or you could buy a 2 stroke anything for cheaper than all those parts AND it will be faster.


like a cr500, then transplant the motor into your 400ex

[Kev_CR]

It's been a while, but I put the 450R carb on my 400ex. You have to hog out the boot at the engine side a bit to get it in there. The carb is a bit longer as well, so the airbox mount location will not line up, but a few wire ties work to mount it. You also need to plug the hole where the hot start goes into the carb make sure to plug it all the way down to the bottom where the air passage is. Just leave the TPS unplugged.

I had an 11:1 416 kit in there with the 450R carb and Hotcam stage 2 and it had a whole lot more power than stock. At 11:1 I ran 105 octane race gas, at 10:1 I would as well. I would highly recommend the heavy duty head studs. Mine pulled the stock studs out when pushing it hard at the dunes.

I had the UNI filter and it let sand through at the dunes. If you are dune riding I would suggest a K&N with an outerwear.

[bodfper]

Well is there a bore kit that i can get that just requires regular gas? If not can I put a 10:1 comp std piston in? What kind of job is it to put the heavy duty head studs in? If I can bore it do i need the 450 carb or can i jet the stock to fit the needs? What would i have to do to make a port and polish worth while? Will my headers still hook up if i add 1mm?

Thanks for all the help

---------- Post added at 11:10 PM ---------- Previous post was at 11:05 PM ----------

Also what kind of rev box, clutch, and chain do you recommend?

[Duran676]

i had a 2000 400ex and it was FAST i could line up in the desert and beat most other 400ex's out there. I had in it a 440 kit done by Duncan racing (not sure about the details but they dialed it in for me after the installed it, carb included), Fat Boy 4 exhaust, hot cams, K&N air filter and a rev limiter. It was fast enough for me

[Kev_CR]

Originally Posted by bodfper

Well is there a bore kit that i can get that just requires regular gas? If not can I put a 10:1 comp std piston in? What kind of job is it to put the heavy duty head studs in? If I can bore it do i need the 450 carb or can i jet the stock to fit the needs? What would i have to do to make a port and polish worth while? Will my headers still hook up if i add 1mm?

Thanks for all the help

---------- Post added at 11:10 PM ---------- Previous post was at 11:05 PM ----------

Also what kind of rev box, clutch, and chain do you recommend?

I'm pulling from the archive, because it's been a while since I built a 400EX. At 10:1 you'd probably actually be OK with premium pump gas and without doing the HD head studs (though the HD studs are good insurance).

The HD stud kit basically includes heavier duty studs with a longer thread for more bite into the aluminum head. It includes a tap and bit to install, or you could send the head to the supplier and they could do the work (I forget the 2 companies that make the kits).

I always recommend the 416 bore, because it gives you 1 overbore when you need it (426) and with the right combo of parts it runs very well. I was never beat by a 440ex that didn't have head work.

As I recall, most of the $100'ish rev boxes for the 400ex are actually made by the same company (Procom), just re-branded under different names. It's a decent rev box for the 400ex and I would recommend it when you run the Hotcam stage 2.

I ran my build for quite a while with the stock carb and then went with the 450r carb and it was well worth the price (used) and effort. This is a great budget build IMHO.

- 10:1 416 piston
- Hotcam stg 2
- Procom made (revmax, big gun, etc) rev box
- 450R carb
- Open air box
- Full after market exhaust

I also put in the oil cooler/block off kit that keeps cooler oil flowing to the head as an insurance. The stock clutch held up well for me, I wouldn't worry about that. I also ran the stock cam chain.

I went to a 406 bore 10:1 build when my daughter inherited my 400ex and I can say it definitly lost power over my 11:1 416. But we've ran it on pump gas with no issue, but she doesn't race it around like I did either.

[bodfper]

What is the oil/air cooler that you are talking about and how much do those run? Whatever I do i dont want to have to run race gas so try to be on the right track. THANKS

[Kev_CR]

[Only registered and activated users can see links. ] makes the secondary oil cooler kit. The way the oil flows to the head in the 400ex is up the side of the hot engine, so what you get is a small flow of already heated oil flowing over the cam. With this kit you basically block off the existing path and drill/thread in some fittings to have the oil flow through a hose and a small (transmission like) cooler and then over the cam. The cost is $110, but you have to do the install.. it's not horribly difficult if you have some mechanical skills and follow the directions closely.

[bodfper]

Alright so Im new into this like I said and dont have a clue what the piston compression ratios mean. What burns hotter a 416 with 11:1 or a 416 with a 10:1? Which ever is cooler is the one i want also correct? Will I have a reliable quad if I run premium gas from a normal gas station with this build? Also, can a machine shop do my boring and heavy duty head studs? Another thing I need to know is what honing is. Do I need to re-sleeve with the 416? And one last thing is the port and polish, what is it and what do I have to do to make it worth the time and money with my dmc dual full exhaust system?

Thanks alot and I appreciate all of your time!

[Kev_CR]

Originally Posted by bodfper

Alright so Im new into this like I said and dont have a clue what the piston compression ratios mean. What burns hotter a 416 with 11:1 or a 416 with a 10:1? Which ever is cooler is the one i want also correct? Will I have a reliable quad if I run premium gas from a normal gas station with this build?

Compression ratio is the amount the air in the cylinder is compressed at the top of the stroke compared to when it is at the bottom of the stroke higher compression with the right gas means more power. The 11:1 is going to burn hotter with pump fuel than the 10:1. The higher the compression and consequently more engine heat generated will cause the wrong fuel (too low of octane) to ignite before it's supposed to. This is called "ping" and it is a very bad thing. With the goal of running premium pump gas I would definitely go with the 10:1 piston. Of course how hard you push the engine and outside temps also have an effect on engine temps and could cause ping. I'd say go a head and run premium at 10:1, but if you notice significant power fade and hear funny sounds out of the engine you might have to step up to a premium/race blend.

Originally Posted by bodfper

Also, can a machine shop do my boring and heavy duty head studs? Another thing I need to know is what honing is.

A machine shop should be able to install the heavy duty head studs no problem, the alignment is critical, but they shouldn't have a problem with it. Honing is basically taking the glaze off of the cylinder wall and putting in some fine scratches in a cross hatch pattern so that the new piston rings will seat with the cylinder correctly. A machine shop should be able to do that as well, but if you are getting it bored for a bigger piston they'll do it at the same time anyway.

Originally Posted by bodfper

Do I need to re-sleeve with the 416?

Nope, 416 doesn't use a sleeve, just a bore.

Originally Posted by bodfper

And one last thing is the port and polish, what is it and what do I have to do to make it worth the time and money with my dmc dual full exhaust system?

Port and polish basically modifies the intake and exhaust ports in the head to allow more optimal air flow through them. As AgentSmith mentioned, a port and polish doesn't buy you a whole lot on the 400EX without putting in oversized valves. I did my own port and polish, but I don't know that I'd pay anyone else to do it.

[gravelfreak]

If you put in an aggressive hotcam, I'd say you can up the compression even more. More aggressive cam, the less compression You'll have.

[Kev_CR]

Originally Posted by gravelfreak

If you put in an aggressive hotcam, I'd say you can up the compression even more. More aggressive cam, the less compression You'll have.

That's true, but with the 400EX and a Hotcam stage 2 with an 11:1 compression piston you will no doubt get pinging when you push the engine to hard. Voice of experience..

A few other things I did was eliminate the base gasket and use high temp silicone instead, as well as just used one layer of the 3 layer head gasket. This helps get the compression ratio up as well as get the squish and deck height set more optimal for the 400ex. But it sounds like reliability is a big concern, so I wouldn't recommend these mods.

[bodfper]

Well thanks alot. Would I be alright without the port and polish because I dont think that I want to got that far, Im already out of my budget. Another thing I have a question on is the secondary oil cooler. Can you install this after everything is put together or is this something that is installed at the same time as the piston, hot cam, hd studs, and timing chain?

---------- Post added at 07:37 PM ---------- Previous post was at 07:25 PM ----------

Another thing ive been hearing is to take the choke off of the carb. what does this accomplish and will it make my 400ex bog down or cold blooded?

[Kev_CR]

Originally Posted by bodfper

Well thanks alot. Would I be alright without the port and polish because I dont think that I want to got that far, Im already out of my budget. Another thing I have a question on is the secondary oil cooler. Can you install this after everything is put together or is this something that is installed at the same time as the piston, hot cam, hd studs, and timing chain?

---------- Post added at 07:37 PM ---------- Previous post was at 07:25 PM ----------

Another thing ive been hearing is to take the choke off of the carb. what does this accomplish and will it make my 400ex bog down or cold blooded?

The secondary cooler needs to be drilled and tapped into the head cover and oil pump housing. It'd be easier to do while it was apart, but it's not hard to do down the road if you wanted to do it later on. From what I've heard the choke removal doesn't gain you much if anything. I'd prefer have it on there for cold weather starting.

[bodfper]

Alrighty well then what is a good price on the 450r carb and what years will work on a 99 400ex. Also how much work is it to do this, I need detailed instructions as well please. Another thing is the crf 450 cam chain that I want to get. How do I time my 400ex after taking everything apart and putting this new chain on and does it matter what year of crf450 it is?

[Kev_CR]

Originally Posted by bodfper

Alrighty well then what is a good price on the 450r carb and what years will work on a 99 400ex. Also how much work is it to do this, I need detailed instructions as well please. Another thing is the crf 450 cam chain that I want to get. How do I time my 400ex after taking everything apart and putting this new chain on and does it matter what year of crf450 it is?

It's been about 4+ years since I did the mods on a 400EX, so I couldn't tell you current prices on parts or even give you accurate instructions on doing the work. Setting the timing is easy, but I would HIGHLY suggest you get a shop manual if you are going to do this work. Perhaps someone here is fresher on doing 400EX builds? Another option is [Only registered and activated users can see links. ], do a search in the 400EX section and you'll get a plethora of information since the site specialized in the 400EX for a number of years. It was my favorite stomping ground until I found ATM

Good luck with the build.