4-Tec "Cold Air Intake" ...pros and cons?

[rcarp64]

I have a 2008 RXT 215 and a 2003 GTX 4-Tec SC. I have done most every inexpensive mod to increase speed/performance (no engine/supercharger mods) and it's given me a little more speed and rpm's. RXT hits 7950+/- RPM and about 72-73MPH on the stock speedo with a full tank of gas and two adults on board. GTX hits 63MPH and about 7300+/- RPM with a full tank of gas and two adults on board. The only thing I haven't done is replace my stock air intake. I have replaced both stock props with Solas, covered ride plate bolts with epoxy, blocked OPAS in the up position, put in new plugs, new Rotax oil/filter, free-flow exhaust (RXT only), and new wear rings. I'm not interested in a pump wedge or scoop grate because I ride in mainly flat/small chop water. My question is about the pros and cons of replacing the stock air intake with a custom (build it myself) 4" air intake with a K&N cone filter. Is it safe? What about water ingestion? With my current performance is it worth the risk to the engine to add the intake for maybe a 1MPH gain? If I do the mod, do I route the air filter so it sits just above the fuel tank (under the steering column)? What do I do about the smaller hoses that feed into/out-of the stock air intake near the battery? Do I completely remove the stock air box/breather that's up by the fuel tank? Can I expect significant gains in top speed/throttle response from this mod? This looks like a fairly easy and cheap mod to do. I'm looking for advice from those who have done it. Thanks!

By the way...the free-flow exhaust I added to the RXT made a HUGE difference in throttle response and it sounds awesome! I made my own exhaust pipe out of 2.5" automotive exhaust tubing bent at 90 degrees. I coated the inside and outside with galvanizing spray and then metal spray paint over that. I used adhesive style window caulk on the ends and three hose clamps on each end to secure the rubber exhaust tubing to the pipe. This ensures no water leaks and no chance of the pipe slipping out of the hose. I also made a rubber support brace to go between the metal pipe and the inside of the hull. This mod only cost me $20 and it made a big difference.

 

[red2blue]

Okay....this should go into the performance section....

First off...dunno how you're hitting 72-73mph...on a stock speedo...(especially in what I assume to be brackish or salt water flats)...w/o a bigger wheel. You need to invest in a gps if you're gonna go down the mod road.

As far as diy air intakes...up front 4" kana-flex...(no filter...filters are restrictive...self defeating in an air intake mod)are relatively safe re water ingestion. It's not until you go rear(cold) air intake that water ingestion is a threat.

A 4" front instead of the restrictive oem intake will typically net 100rpm. A rear air will typically net another 100rpm over a front. When you bump up to a bigger wheel...results are even better.

You aren't saying what prop you're spinning up to 72+mph @ 7950 rpm...(with 15gals of fuel and two adult riders)so....really can't offer you an educated guestimate of your future results.

Your ecu's rev limiter is 8300 I believe...so you're already down rpm....a better air intake will increase those r's where you should see immediate results...regardless of your current prop.

You run a 4" front in the same place as the oem. In fact...you'll need to address the slop in tank bungie length when you remove the oem. Only thing to be wary of is to make sure as you route around the motor you don't press down on the carbon seal boot.

If you keep the length of the 4" front to about 7'...about the same as oem...you'd rest it on the tank...about where the oem ended. Why?...when you roll your ski the air intake will be outa the water...you hope. If you run it to the glove box/seat opening...then water ingestion could be a worry.

 

[rcarp64]

red2blue...you are right, I have a GPS and I need to use it. I know the factory speedos are inaccurate. My RXT impeller is the Solas recommended one for a stock engine...13/18. It has great hole shot and top end performance is good too. It is definitely better performance than stock impeller. I have hit 8,000RPM a couple times, but I haven't gone WOT too many times with a passenger. I've hit 72MPH on my RXT once going with the current and with the wind on flat water with a passenger on board. I have never tried my new mods riding alone on my RXT or my GTX. Both skis are new to me and the mods were just completed. The free flow exhaust pipe gives me excellent throttle response that is particularly noticeable at higher speeds. I can just blip the throttle at any speed and the thing will lunge forward much more so than before the exhaust mod. Sorry for my post in this section...I didn't realize there was a performance section on this forum (I'm new here). I may try the free flow intake on my RXT. Seems easy enough and relatively cheap to do. You didn't address my question about the small hose that connects to the intake pipe near the battery. What do I do with that small hose? Also, will changing the intake cause any error codes or require a remapping of the ecu? I didn't mention before that both superchargers on my skis were just rebuilt to factory specs with new washers, etc. so they are at peak performance.

 

[red2blue]

. You didn't address my question about the small hose that connects to the intake pipe near the battery. What do I do with that small hose? Also, will changing the intake cause any error codes or require a remapping of the ecu? I didn't mention before that both superchargers on my skis were just rebuilt to factory specs with new washers, etc. so they are at peak performance.

Sorry 'bout that...I miss sht sometimes...old age creepin up on me.

The blow by hose...

One of two things...simply cut it into your new intake...what I did way back when...or install a catch can. The ecu can more than handle the increased air on your set up.

Instead of a filter on a front air...I used fiberglass window screen zip tied over the end. Lil to no restriction yet small enough to keep out any misc styrofoam balls from hull flotation.

 

[rcarp64]

red2blue...I found some 4" diameter flexible plastic gutter material at Lowe's for only $13 for an 80" piece. Can I use that for my intake tube? Does the engine get hot enough to melt the plastic tubing on the side where the tube will be routed? What is the actual O.D. of the intake port on the supercharger? I bought a 3" to 4" adapter by Spectre, but the thing actually measure 3"O.D. to 4"O.D.. It works fine for the gutter tubing, but I don't know if it will mount onto the supercharger on the 3" side.

 

[red2blue]

red2blue...I found some 4" diameter flexible plastic gutter material at Lowe's for only $13 for an 80" piece. Can I use that for my intake tube? Does the engine get hot enough to melt the plastic tubing on the side where the tube will be routed? What is the actual O.D. of the intake port on the supercharger? I bought a 3" to 4" adapter by Spectre, but the thing actually measure 3"O.D. to 4"O.D.. It works fine for the gutter tubing, but I don't know if it will mount onto the supercharger on the 3" side.

You talkin about drain tile?

The sc opening is 3" so your specter reducing bend will work. You will need some kind of a "coupler" to join the bend with the "tube". Don't forget some ss clamps.

Now...one of the reasons folks use kana-flex....WD620 I believe...it's smooth bore...so you will get a better flow as opposed to the corrugations in others.

 

[JoeZ]

Moved to performance section. Great suggestions in this thread.

 

[Bierbreth]

Has anyone ever tried or heard of someone trying 'Shieldsflex' hose for higher-flow intake tubing? I came across this on eBay: http://www.ebay.com/itm/4-ID-SHIELDSFLEX-RUBBER-MARINE-EXHAUST-HOSE-WITH-WIRE-BY-INCH-/161515009769?hash=item259b0b76e9&vxp=mtr