It Fits!!! As shown at right, the Rotrex fits snugly in the CRX chassis using the Kraftwerks K-Series supercharger kit. This kit basically comes with a mounting bracket to mount the Rotrex where the original AC compressor was plus some hoses, oiling system, and oil cooler. The rest is up to you. The picture at right does not show the front crossmember installed. If you are using an aftermarket bar, like the Full-Race, the clearance is fine for the Rotrex. If you have to revert to the stock member, like we did to comply with SCCA class rules, get ready to cut and weld ( see Front Crossmember ).

The major obstacles to be overcome are as follows: Supercharger/alternator belt setup, find home for Rotrex oil cooler, figure out how to get an intercooler and radiator in there, the piping and the intake/air filter, upgrading the injectors and fuel pump, and then tuning the sucker.

Choosing the Rotrex size and pulley

First, if you don't know about Rotrex superchargers, you should. It is very clever technology that combines many of the best advantages of both superchargers and turbochargers with few of the disadvantages. The key to the technology is a special gear technology that allows the supercharger to turn the compressor at turbo-like speeds, between 90-200,000 RPM. This means the compressor is more like a turbocharger in terms of efficiency. It is also a very compact and cool running package about the size of the K-Series alternator. I won't go into detail here, you can Goggle it and read all about it.

The main reason we choose to go this way was we were looking to increase our power across the entire rev range, critical for our application. If we built the NA motor, we would sacrifice things at the low end and decrease drivability and potential reliability. Turbo's are an option, but turbo lag is a killer when you are constantly accelerating and decelerating every few seconds like in Autocross. We felt this would be the ideal setup to meet our goals of a responsive engine with increased power over the entire RPM range.

Which Rotrex? The Rotrex comes in a variety of sizes and flows. There is basically the C15, which is very small and good for motorcycles and stuff up to about 200HP. Then there is the larger C30 and the even larger C38 suitable for automotive applications. Within each of the 3 model types are subtypes with different flows to match different power goals. For the K20, the 2 logical choices are the C30-94 for modest boost pushing into the 300-400HP range, and the larger C38-61 which would push up into the 500HP range with high boost. For our application, the smaller C30-94 was perfect, if you wanted to build a drag car, the C38-94 would be what you want to look at. In our application, since we were stuck using the stock front cross-member for SCCA compliance, we would not have been able to fit the C38-98 anyway, if you are using an aftermarket bar, like the Full-Race, it should be no problem.

The next factor is the pulley size. For maximum performance, you want to match the Rotrex pulley with the engine such that the Rotrex is spinning at it's max RPM at the engines max RPM. KraftWerks provides a simple Excel spreadsheet to calculate the pulley size. In our case with the K20A with a 130mm crank pulley, a 105mm supercharger pulley will drive the Rotrex to just about its maximum 100,000 RPM rev limit at 8500 engine RPM. If you didn't want as much boost, because say for example you didn't want to put in a large intercooler, or injectors, or you were just being conservative, you could run the Rotrex with a larger pulley and less boost.

So that's pretty simple. We think this setup with a reasonable intercooler should give us about 10lbs of boost and about a 100HP increase in power and substantial torque from about 3500RPM to redline. We shall see!

Drivebelt Routing

So, you know that nice AC/PS delete relocation kit you bought for the CRX swap, you can now remove it as the Rotrex mounts were the AC unit was originally located, which is where the alternator is now. The 2 reasons for using the delete/relocation kit is to get rid of the AC and PS that you don't need in the CRX, and to get hood clearance where the PS would stick through the hood. One simple solution is to just replace the PS with an idler pulley from an 02-05 Civic which just bolts right on (Thanks Brian at Karcepts for the info). Then you just go back to the standard setup with the auto-tensioner etc. Of course there are still 2 problems, one the pulley is still too big and sticks through the hood. This can be solved by going to a smaller 6 groove pulley available from a number of vendors (mine was a 59mm from Dayco) down from the standard 76mm 7 groove pulley. You need to make sure you space the pulley out right to align with the 7 grove pulley on the alternator and the 8 on the Rotrex. Then just find the right size 6 groove belt.

The other problem is the alternator interferes with the right headlight frame. But its not bad, just trim it like shown here, the headlight assembly clears just fine.

Intercooler, oil cooler and Radiator

Now that we figured how to fit the Rotrex and dealt with the drive belt issues and the front crossmember clearance issues, we have some serious cooling issues to deal with. First, how to cram in an intercooler of sufficient flow and capacity and fit up the plumbing. So we got everything measured up carefully using foam board mock-ups. Seems like a lot of work but when you get a custom intercooler and radiator and it does not fit, you eat it. We wound up going with a custom unit from Bell Intercoolers. We have spent a ton of time researching intercoolers and we knew what we need, but the fitment was not going to work with any universal unit. Gerhard Schruf of Bell was a tremendous help in getting this right, he is truly a documented expert in the field. Do to fitment issues, the intercooler is just slightly under "optimum",the core is 24" X 9" X3" thick. 3.5" would have been better, but would just not fit under the stock bumper. What makes this intercooler work well is the inlets and outlets face back as opposed to out the sides as in most generic intercoolers. Not only does this make the fitment easier in tight places, it also makes for short, efficient plumbing. Here is a picture of the beast, Bell makes some nice stuff!.

You can see the inlet and outlet locations, and angles and the mounting tabs needed to hang it on the CRX. The small pipe is for the bypass valve. To mount it we had to first do some minor trimming around the front and seriously modify the stock bumper support. We welded some brackets off the front frame support member and used the EG radiator mounting rubber to support the bulk. We then fabricated some aluminum brackets bolted to the front bumper support points and used some rubber vibration isolation bolts to secure it in place, you can see how this was done best by looking at the pics.



Next we mount up the intercooler and see how it fits, not bad.

You can see how tight things are, the Rotrex plugs right into the IC inlet using a Treadstone 2 to 2.5 inch hump hose adapter. Makes for some pretty efficient plumbing.

The current half size radiator is just not going to do it. It already gives us problems on hot days in autocross without boost. The engine coolant temperature rises high enough on the end of multiple runs on hot days to trip the CEL light at 220 F (at the internal engine coolant temperature sensor (ECT)), not good. So we will go with a custom radiator from Griffin. It is a "full size" about 22" wide X 13" high, core size 18 X 13" with 2 row 1.25" tube. The radiator is a "Scirocco Style" radiator that is very popular do to it's compact size and cross flow design (sometimes double pass but this is a single pass). This radiator style was made popular when first used in the VW Scirocco, hence the name. It is really one of Griffin's stock racing radiators with a few minor changes. We specified the inlet/outlet locations for clearance, and we used the 8mm pin mounting system popular in Honda's. We used 2 on the bottom and 2 on the top sides. The other thing we will change is we will go from a pusher fan to a puller as they are more efficient and we have made some room for it but getting rid of the Hasport Hydraulic to Cable clutch setup in favor of a Sonem EF hydraulic clutch conversion from Suja One Motoring. This was an interesting adventure in itself, but it sure cleans things up nicely and we shall report how it works. By the way, Griffin Rad is a great company to work with, Pat, who I worked with, was always helpful, knowledgeable and responsive.

Too make room for everything the radiator had to sit back on top of the lower front frame support, and even at a meager 13 inches high, the radiator interfered with the hood latch and support, so we got rid of the support and used a stainless steel tube. We will have to change the hood latch to pin style latches to hold it down. To mount the radiator, we again weld 2 brackets to the front lower frame member to hold the radiator mounting bushings. At the top, we fabricated 2 stainless steel brackets holding the rubber bushings. You can get a better idea from the pics.

Above, you can see the final fit of the radiator and IC with the stainless brackets with rubber bushings supporting the upper radiator. Also shown is the support bar which replaces the hood latch member and is need to stiffen things up, and looks good as well. You can see the modification made to the front bumper support, a lot, and a lot of trimming was done to clear the IC inlet and outlet in the front end area. And of course, it has to fit under the stock bumper. We trimmed out the front grill and it is shown above with the IC just clearing. We will use some black mesh grill to fill it in and look good, although the IC looks pretty mean by itself.

Lets not forget the air intake has to go in there as well. A simple 3" aluminum tube 19.5" long with a K&N round filter 5 inch diameter 7 inch long filter (KNN-RX-2820). This is positioned right above a gap between the front of the engine compartment and the front cross member with the hope that it can suck in a lot of cool air from underneath.


Since we had to delete the hood latch, we used hood pins to secure the hood. But wanting to make it look good, we used a set of AeroCatch hood latches. These are pretty cool, work well, and look really nice. We did have to make some brackets up to bolt over the headlight securing brace to hold the pins, but, what else is new.


Rotrex Oil Cooler Setup

Finally, we must find a home for the Rotrex oil cooler. The Rotrex has a separate oiling system with a canister, filter, and radiator. We fit the cooler behind the front bumper on the right side in front of the wheel and cut out the hole in the bumper from the unused fog light location for air. The Rotrex reservoir and filler are mounted above as shown.

Crankcase Ventilation

Since the car will now run under boost, you can no longer run the standard PCV valve to intake manifold setup as the crankcase preassure has to fight against the boost pressure in the manifold. In a NA seutp, the one way PCV valve is between the crankcase and the intake manifold. Since the valve allows crankcase blow-by to vent out the valve and the gases (oil vapor and fuel) are recycled through the engine. The PCV valve prevents any fuel vapor from the manifold from entering he crankcase.

One way to address this, and the most environmentally friendly way is to vent the crank to the intake side of the supercharger. What we don't like about this, is you are introducing oil and fuel vapor through the Rotrex and intercooler and it accumulate over time as well as contribute to engine knock. A slightly less environmentally friendly way to do this is to vent it through an oil catch can open to atmosphere. The catch can is simple a baffled aluminum tank with a filter on top. You remove the PCV valve (not needed now since we are not venting to the manifold) and connect a large hose to the catch can. Most, but not all, fuel and oil vapors condense in the can and you must periodically drain the fluids from the can. We used a Moroso unit # 85470 and some Earls Super Stock -8AN (1/2") oil resistant hose and some adapter fittings to connect the can to the crankcase vent.

This is the simplest setup and works well. Note that you don't get a manifold vacumn "pulling" on the crankcase but this still does the trick of allowing blow-by to vent. An added advantage is you don't muck up your intake manifold (NA) or intercooler (boosted) with oil and fuel gunk. More sophisticated setups include using a pump to pull a partial vacumn on the crank to reduce windage and increase power.





Tune Time

We finally finished the Rotrex build just in time for our first AutoX of the season. We had it tuned at Kinetic MotorWorks in Hampstead, NH by Rick. Rick's good, if you live the the Northeast, he's your man. They now have a 4WD dyno so all you Subu and Evo freaks should check it out. Below is the dyno run, an AutoX run, and the dyno plot. We made 340WHP and 215 lb-ft of torque at 10lbs of boost, better than we thought. We are definately restricted by the exhaust plumbing now, as you can see and hear in the video, and Rick feels we could easily get anothe 20-30 HP out of it. At our first 2 Autocross events we did pretty good taking 1 and 2 in our class and 1st overall in modified, and we have a lot of room to grow as we learn the new car, it is a completely different animal now.


Oil Cooler Setup

In all our hurry to get ready for the Autocross season, we did not get the oil cooler hooked up. With all that power and heat, an oilcooler is a good idea. We used a Mocal unit which was about 13 X 6" and just about fits, with some clever bracketry, behind the left bumper. Air is feed in from the newly created hole in the not used fog light location, similar to the right side was for the Rotrex oil cooler. Mocal was also the source for a take-off plate from the current filter location. Stainless steel -AN10 teflon hose and fittings from Pegasus were used to route the oil to the remote filter located now on the left shock tower and then to the oil cooler. The cache can for the crankcase vent was relocated to make room (see pics). The oil lines ran behind the header and were carefully cushioned with 1" rubber heater hose and some high tech insulation and all carefully secured in place.

The oil cooler was mounted by welding some stainless washers to the frame and then fabricating some supports from lightweight stainless tubing. It was bolted up using rubber grommets for vibration isolation. It just barely makes it behind the bumper and the cooler mount tabs had to be trimmed.

This was a challange to figure how to get it all in, but the results look good and our engine temperature seems down as well.


AeroCatch install done, in locked postion, nice.
Latch in pin in place in unlocked position.
The latch pin has to be offset back for clearance via a bracket.
To install the AeroCatch hood pins, carefull measure and cut a hole in you hood.
Oil catch can for crankcase ventilation.
The oil line run through the hole in the rear motor mount and behind the headers (well insulated). You can see the -10AN lines running to the shock tower mounted oil filter and to the oil cooler.
The front on the oil cooler is mounted to the frame and the back held off by support rods.
The Mocal oil cooler just barely tucks behind the stock front bumper.