CAI geeks II: CAI on the cheap

[Bman98SL2]

Hi folks,

After reading some articles in the web magazine Autospeed (http://www.autospeed.com/), I bought some Dwyer magnehelic gauges on EBay (0-0.5" H2O, 0-5" H2O, 0-30" H2O). I put taps on the passenger side fog light blank on my '98 SL2, and on the intake hose just before the throttle body.

I've taken readings at highway speed, but am finding at least 0.4" H2O as low as 35 mph. On a previous flow bench experiment, I found that simply putting a short 45 degree flare in the end of a 2.5" tube gained 27% flow at the same backpressure. So, I've replaced my driver side foglight blank with a black plastic replacement and poked a flared 2.5" pipe through it. I welded mesh to the back side. This certainly hurt peak flow (2.6" H2O at 230 cfm to 5.2" H2O at 230 cfm), but I didn't want my K&N filter to have to contend directly with hornets, dragonflies, and the chipmunk that keeps leaving nut shells in my airbox. Behind that I've routed 2.5" ID flex hose along the side of the radiator and into a hole I punched into the passenger side of the air box (sealing all other holes, of course). I've found that peak flow does not like the flex hose (11.2" H2O @ 230 cfm stright, 13.2" with a gentle 90 degree bend), but pressure does not seem to mind. With my current set-up, at light throttle cruise I actually see the same positive pressure in front of the throttle body that I see at the nose of the car. It will be interesting to see if this is the case at highway speeds and if this equates to any mileage boost.

In the mean time, my next revision will be to replace the flex tube with mandrel bent stainless (I can piece it together with scrap pieces from work) and use the flex pipe only to hold the pieces together. This way I should accomplish both positively pressured ambient air at cruise and low restriction at full throttle.

Such is the project so far...

Bman

[Bman98SL2]

Here's my rev. 2 intake. I used various bends of 2.5" OD stainless to route the air form the fog light blank out to the airbox. I am now only using short segments of flex pipe for the joints.

I was under pressure to get this together and get off the lift, so I have been unable to run flow bench numbers on the new inlet. The butt dyno says that I have more top end now (an a neat raspy honking sound).

I did run a mileage test over the weekend. I made a trip to Mid-Ohio sports car course and back this time last year and averaged 37.7 mpg. As I recall, I stayed around 60-65 mph. I made the run this year with my magnahelic gauge in hand and saw some interesting results. At 60 mph, I see a consistent 0.6" H2O (all measurements in the intake, just before the throttle body). Pulling light grades this dropped to 0.3" H2O. At 70 mph, I consistently saw 0.8" H2O (with spikes to 1.2" when there was a headwind). On light grades the pressure dropped only to 0.6" H2O. Above 70, the pressure actually started to drop because of the increased load on the engine to maintain the speed. So, I figured 70 mph was the "sweet spot" and cruised at 70. I also got snarled in a lot of stop and go getting out of the event Sunday. All told, I got 39.1 mpg, my best ever. Without stop and go and dropping back to 65 mph, I bet I can finally break 40 mpg.

The next goal will be an undertray up to the front sway bar. We'll see what that does.

Bman

[Leadsled Coupe]

Go Bryan... GO Bryan!

Nicely done. Any close ups of the SS pipe and the front facia? Kudos! I am jealous of your mileage!

I saw 40mpg when I got mine two years ago, but haven't seen it since. Don't know if the gas has been reformulated around here or what, but I dropped significantly soon after I got it.

[Bman98SL2]

Thanks, Chris.

[sc2dave]

Bman98SL2,what about using a bellmouth on the bumper?http://www.velocity-of-sound.com/com...egory=+++GO!++ also,the lower the number on the reading the better?Is 2.5" the tb diameter?

[sl_don]

Originally Posted by Bman98SL2

Here's my rev. 2 intake. I used various bends of 2.5" OD stainless to route the air form the fog light blank out to the airbox. I am now only using short segments of flex pipe for the joints.

I was under pressure to get this together and get off the lift, so I have been unable to run flow bench numbers on the new inlet. The butt dyno says that I have more top end now (an a neat raspy honking sound).

I did run a mileage test over the weekend. I made a trip to Mid-Ohio sports car course and back this time last year and averaged 37.7 mpg. As I recall, I stayed around 60-65 mph. I made the run this year with my magnahelic gauge in hand and saw some interesting results. At 60 mph, I see a consistent 0.6" H2O (all measurements in the intake, just before the throttle body). Pulling light grades this dropped to 0.3" H2O. At 70 mph, I consistently saw 0.8" H2O (with spikes to 1.2" when there was a headwind). On light grades the pressure dropped only to 0.6" H2O. Above 70, the pressure actually started to drop because of the increased load on the engine to maintain the speed. So, I figured 70 mph was the "sweet spot" and cruised at 70. I also got snarled in a lot of stop and go getting out of the event Sunday. All told, I got 39.1 mpg, my best ever. Without stop and go and dropping back to 65 mph, I bet I can finally break 40 mpg.

The next goal will be an undertray up to the front sway bar. We'll see what that does.

Bman

all that is left is to do some sort of insulated wrap on the new pipe, the original intake pipe and air box and you will have a really solid CAI that works better than anything you can buy

[Jim Dunlop]

Awesome!

I had a very similar setup, only with corrugated tubing instead of your nice smooth stainless!

What's the pad with the wires running to it in the other fog light blank?

[Bman98SL2]

Originally Posted by sc2dave

Bman98SL2,what about using a bellmouth on the bumper?http://www.velocity-of-sound.com/com...egory=+++GO!++ also,the lower the number on the reading the better?Is 2.5" the tb diameter?

Wow! Those are neat, if expensive bellmouths! I've bookmarked the page - thanks! Yes, the lower the inches of H2O, the better, as resistance to flow is dropping. This means more air in the engine on the intake side or less work to get the exhaust out on the exhaust side (usually read as backpressure). In both cases there is a limit, because if you make the pipe(s) too big, velocity suffers, especially at low throttle / rpm. And yes, the stainless tubing I used was 2.5" OD (0.065" nominal wall thickness).

Bman

[Bman98SL2]

Originally Posted by sl_don

all that is left is to do some sort of insulated wrap on the new pipe, the original intake pipe and air box and you will have a really solid CAI that works better than anything you can buy

Good point. I actually have a preofessional connection to Design Engineering, Inc. They make great reflective / insulating materials. I'll try to get some intake vs. throttle body temperatures to see if this would make much difference.

Bman

[Bman98SL2]

Originally Posted by Jim Dunlop

Awesome!

I had a very similar setup, only with corrugated tubing instead of your nice smooth stainless!

What's the pad with the wires running to it in the other fog light blank?

Very cool! I know that not everyone has access to nearly free stainless mandrel bends. My rev. A version used flexible tube (now holding the bends together). I ran this on the flow bench. It does fine for ducting the pressure into the intake, but WOT flow rates do not like the ribs at all (I was seeing stock " H2O levels again). If the tube is rubbed on the outside and smooth on the inside, you should be fine.

Thanks for the complement!
Bman

[Bman98SL2]

Originally Posted by Jim Dunlop

Awesome!

I had a very similar setup, only with corrugated tubing instead of your nice smooth stainless!

What's the pad with the wires running to it in the other fog light blank?

Sorry, I forgot your question. That is actually a small hose, now removed, that I was using for some pressure test readings. I used a magnehelic gauge (reads small pressure changes) to compare the pressure on the foglight blank to the pressure in the intake just in front of the throttle body. I saw that at light throttle openings around town and up to 70 mph cruise on the highway, the pressure in the intake is very similar to the pressure on the nose of the car (efficient capture of the positive pressure). I have a PT Cruiser that generates a much bigger pressure wave (aerodynamic brick!) and I'm working on a CAI / ram air system for it as well. I learned about the gauges and pressure readings from the Autospeed on-line magazine. Search the archives.

http://autospeed.drive.com.au/cms/archive.html

Bman

[Bman98SL2]

Hi folks - an update on the performance of the intake.

I now average ~30 mpg on my urban commute (stop & go, 5 miles, 40 mph max.). My highway mileage at 60-70 is now 38-40 mpg, and I've yet to add any undertray to the car. I run synthetic oil, +4 psi over factory in the tires, have a 2.5" free-flow exhaust, and my custom intake.

I've seen a 10-13% improvement in mpg (urban and highway), just from the intake.

Bman