Sport Compact Car - April '98
Project 200SX SE-R
By Mike Kojima
[Put into HTML format by Mike Mager]
In part eight of our SE-R project, we try an array of fine-tuning tricks in the search for hidden horsepower.
Whenever you make significant changes to an engine, chances are good that some fine tuning will be needed to get the most of your modifications. As many of you know, Project 200SX SE-R has been the recipient of extensive modifications--most recently including DPR headwork, Jim Wolf Technology cams, Stillen's intake system, GReddy exhaust and a custom-made header. The JWT ECU that we installed along with the cams was our first, and most critical fine tuning measure. And, now that DPR has ported the head and re-shaped the combustion chambers, we've returned to the ECU and other fine-tuning areas to see if there is more power to be had. Specifically, JWT tried some custom ROM tuning of the ECU and nitrous system to better match our new head. We have also experimented with cam timing and cold air induction to find if there is hidden horsepower left in the engine.Cam Timing
The fact that Honda and Acura motors respond well to cam timing tweaks has been well documented by many Honda/Acura tuners. We did this on Project Integra (see March '97 SCC) and found 17 horsepower. Note that this is not peak horsepower, but more power to a specific point. If the cam timing is optimized for top end power, usually bottom end power will falter. Likewise if the cam timing is optimized for bottom end power you will most likely lose power on top. As a rule of thumb, if the cam(s) of a modern twin cam engine are advanced, bottom end power is improved. If the cam(s) are retarded, top end power will be increased.
One nice thing about twin cam engines is that since the intake and exhaust cams are separate, they can be adjusted independently of each other. This also allows adjustments to the lobe separation angle or overlap of the cams. Generally, if the cam lobes are moved closer together, the engines idle quality is reduced because the amount of overlap is increased. More overlap means that both the intake and exhaust valve are held open at the same time for more degrees of crank rotation causing intake charge dilution, cylinder pressure bleed down and reversion (intake port backflow) at low rpm.
Then there is the eight-stroke misfire phenomena that we previously wrote about (see July '97 SCC). Eight-stroking is what gives high-performance cams that traditional rumpity rump idle. More overlap also produces more low-mid range power, less right off of idle power and less top end power. More overlap also reduces an engine's octane demand as plenty of overlap reduces cylinder pressure right off of idle and at low rpm, which is the place where engines are the most prone to detonation.
OBDII controlled engines do not like lots of cam overlap because the irregular idle is picked up as a misfire event, triggering a MIL light and storing error codes. With the new California Smog II laws, you may have to report to a government controlled smog station which might not allow you to register your vehicle if you have stored error codes in your ECU or an enabled MIL light. Needless to say, keeping the OBDII system happy gets more and more important all the time.
Less overlap generally gives a smoother idle and, if the engine has sufficient breathing capability, more top end power at the expense of mid range. Of course, there are many "ifs" attached to any discussion of cam timing. If the engine has restrictive intake and exhaust systems, or if it has short connecting rods, or if it has an oversquared bore/stroke relationship (bigger bore than stroke), the engine will tend to lose top end power with less overlap. But most modern, four-valve-per-cylinder engines, especially when modified, will gain top end to some degree. Due to the lack of low-rpm eight-stroke misfire, less overlap also helps reduce hydrocarbon emissions. Usually, stock cams are ground with minimal overlap or even sometimes no overlap for this reason. This is usually too little overlap for good breathing. That is why sometimes large gains can be found with stock cams (especially Honda/Acura VTEC engines) with adjustable timing gears. Many aftermarket cam makers will grind their more radical profiles on the stock lobe centers. The stock lobe spread is often too separated for these cam profiles to work well. Adjustable timing gears allow for the correction of this and hence a large gain in power.
For single cam motors you are out of luck if you want to change your lobe separation angle, but with a twin cam you can adjust the cams independently so lobe separation angle adjustments are a snap. To increase overlap you can advance the intake cam and retard the exhaust or just do either. To reduce overlap, retard the intake and advance the exhaust, or any combination of the two.
To assist in our cam timing adjustment endeavor we obtained adjustable timing gears from Jim Wolf Technology. Jim Wolf and company have been instrumental in the build up of Project SE-R, along with Dan Paramore of DPR Racing Development, who pitched in to help us wrench and volunteer the use of his Dynojet chassis dyno. Paramore has lots of experience tuning Honda/Acura motors and has gained plenty of power for his customers with DPR's dyno tuning service.
With years of experience behind him and after spending a lot of time investigating the proper lobe centers to grind street cams, Jim Wolf doubted that we could find much more useable power in our set-up. In his opinion, we could expect either an increase of top end or bottom end, which could be used to tailor the engine's powerband to our preference, but not much overall gain. Wolf went on to explain that big gains might be possible with stock cams or a different brand of cam so the adjustable gears would still have merit for other applications.
Twenty-five exhausting dyno runs later, we determined that Wolf was correct. No matter what combination of advancing, retarding and lobe center shifting we did, we could not glean much more useable power out of the SR20 motor. In fact when we increased the overlap by eight degrees the good old OBDII system barfed up a MIL light, just as we predicted. We were able to get two-to-three more top end or bottom end horsepower. However, as Wolf had predicted, when we gained two-to-three more top end horsepower, we lost four to five more horsepower on the bottom end and also one to two horsepower in the midrange. When we adjusted for more bottom end, the converse effect happened. We determined that it was not worth losing power over such a wide range to gain it over a narrow range, so we gave up.
The only worthwhile adjustment was advancing the intake bye two degrees. This gave a nice snappy feel to the bottom end, which allowed for rolling burnouts with no clutch fanning! This setting might have some merit for a person driving on the street only, or an autocrosser who regularly accelerates out of low speed corners. The engine was definitely flatter above 6700 rpm so we reverted back to the stock setting.
Wolf was right when he explained that JWT ground the cams to their peak performance, making adjustable gears unnecessary in combination with them. In Paramore's experience, the adjustable gears should be able to produce good results with stock cams or other brands of cams.
Air Flow Meter
In looking for other easy tweaks we turned our attention to the airflow meter. The airflow meter on an SR20 is the bottleneck of the induction system. Although the throttle body is a whopping 60mm (bigger than a 5.0 Mustang) the airflow meter necks down to a mere 50mm inside. It doesn't take a brain surgeon to look into the air flow meter and see a restriction. We decided the airflow meter was the next logical place to upgrade.
We purchased an airflow meter from a 95 Maxima to replace our wimpy stock meter. The Maxima's airflow meter is a huge 80mm, and doesn't neck down inside. We obtained a silicone reducer hose that necked from 3.25 inches to 2.5 inches, and then used a piece of 2.5 inch pipe and some hose clamps to fashion an adapter.
Of course, you can't just go swapping air flow meters and expect things to work. To run an airflow meter of this size it is necessary to reprogram the ECU. A larger airflow meter has a lower intake air velocity and develop less input voltage for a given flow. An airflow meter of this size is beyond the stock ECU's ability to compensate, thus making reprogramming a necessity.
Clark Steppler of JWT reprogrammed our ECU for the big Maxima airflow meter. In his experience, a bigger airflow meter is not necessary until more than 200 hp is produced. Steppler doubted that the airflow meter would give us a substantial, if any, increase, but we were convinced that the small was a restriction. While reprogramming our ECU, Clark also retarded the ignition timing slighlty. Since we increased our compression ratio while porting our head in the last installment, we noticed a little pinging during hot weather and while on the Dynojet. Since our Nissan has a knock sensor that aggressively retards timing when detonation is detected, we felt that elimination of the pinging might produce a little more horsepower. Steppler took some advance out of both the nitrous and normally aspirated timing maps, and our pinging was gone. After the reprogramming, Steppler hooked up JWT's Horiba air/fuel ratio analyzer to confirm the correct mixture. We tested the engine on JWT's Clayton chassis dyno, and tested the driveabilty on the street with the Horiba. After a few minor corrections, Clark perfected the program.
Driving home from JWT, Project SE-R had a little more low end punch, but did not seem quicker. To confirm the seat-of-the-pants judgment, we returned to DPR the next day to test the airflow meter on the Dynojet. Project SE-R put out about 1.5 more horsepower below 3000 rpm and none anywhere else. JWT was right again. For some reason the big airflow meter made more bottom end, the converse of what big usually gets you. We theorize that since the airflow meter did not neck down drastically like the stock airflow meter did, it acoustically lengthened the intake pipe, lowering it's resonant frequency, and improving a resonance-driven ram effect at low rpm.
Considering the cost of doing this conversion, we feel that it is not worth the effort and expense for a typical street engine. Since it didn't hurt power anywhere, though, we didn't bother to undo our work.
Cold Air Intake
So far we have been zero for two in our quest for more power. The fact that easy tweaks are not getting us gobs of increased power is testimony to the thoroughness of JWT's development. JWT's stuff seems to already be set to extract the most useable horsepower, as is.
While investigating the Internet as to what other SE-R owners were up to concerning engine modifications, we stumbled across a major site for SR20 hop-up information. This excellent, comprehensive web sight (managed by Nissan aficionados Searl Tate, Ken Pratte, Kurt Sussman, Mike Mager, Ron Chong and Pat Griffith) contains a wealth of information on the 200SX SE-R, the late great "classic" Sentra SE-R, the NX2000 and Infiniti G20. To visit the SE-R site go to http://www.se-r.net.
From the SE-R web page we found the SE-R mailing list. This is one of the best, most active automotive lists on the web. Most of the subscribers are knowledgeable, and simply downright nice and helpful. NX2000 owner Larry Weeks is the attentive volunteer moderator and owner of this great news group. To subscribe, go to http://www.se-r-list.org. Don't forget to check out the list archives and FAQs (Frequently Asked Questions) while you are there.
On the advice of SE-R.net editor Mike Mager and list member Justin Choi we decided to experiment with a cold air intake from Place Racing (PR). Mike's 200SX picked up two tenths in the quarter mile when he installed PR's air intake. From a table of list members, quarter-mile times and listed modifications on se-r.net, we determined that other list members have had substantial improvements in quarter-mile times with this intake as well.
PR offers two different types of cold air intakes. The first uses a K&N cone type filter, and the second is designed for use with JWT's POP charger air filter system. We opted for the second because the POP Charger has a much bigger filter than PR's K&N cone. In addition the POP charger had the aluminum air horn filter base, which we felt could produce a flow advantage. The PR cold air intake is a 3-inch mandrel-bent steel duct which goes from the throttle body to the airflow meter, and then through the inner fender to the filter, which is located in front of the drivers-side front tire. The filter takes the place of a huge resonator box was used by the stock intake.
The filter is shielded from splash and dust by the plastic inner fender liner, so water ingestion should not be a problem. For extreme wet weather, you can remove the pipe from the airflow meter to the filter and attach the filter directly to the airflow meter. When installing the cold air intake, the hole in the inner fender which goes from the stock airbox to the resonator box must be enlarged so the intake pipe can fit through. PR supplies a template with each air intake to make locating the hole a snap. We used an air-powered die grinder to make quick work of the sheet metal but an electric drill and a hole saw would work fine.
The PR air intake increases power in three ways. First, it reduces the restriction of the stock intake. The stock plastic intake pipe is full of places were the inside diameter goes from almost three inches to as little as two inches and back again. Also, the plastic intake pipe is full of ribs and convolutions, which can cause turbulent air flow. The smooth mandrel bent tubing of the PR air intake has none of these potentially flow-impeding restrictions.
Secondly the PR intake only picks up cold air from outside the engine compartment. This air can be up to 50 degrees cooler than the air in the engine compartment. Each 10 degrees of temperature-drop generally produces a power gain of 1.5 percent. After driving Project SE-R, the tubing of PR's air intake is cool to the touch even when everything else under the hood is baking hot.
Finally, since the ducting of the cold air intake is a long, single-diameter tube, a resonance builds up in the tube similar to that of an organ pipe. This resonance can result in improved power at a certain rpm range. This is a gain just like the one we experienced with the AEM air intake, and to a slightly lesser extent in the Iceman intake during our Honda Civic intake test in the September '97 issue.
Going back to DRP's dyno we were amazed by the results. Project SE-R recorded a gain of eight horsepower at approximately 5000 rpm in the fat part of the powerband. Peak horsepower was increased by about two hp. Horsepower was increased even right off of idle. The seat-of-the-pants feel was much improved, with the engine feeling much more torquey with more punch. Overall, the motor feels bigger, almost like it gained displacement. While driving, the PR intake makes a neat sound. When the window is down a throaty roar can be heard at WOT. When the intake produces the maximum power gain you can hear the resonance effect, which is similar that of the AEM Honda air intake.
We were unable to do the rolling test with the Vericom like we did with the Honda intakes in our intake comparo, so our gain may be off by a few horsepower. However, the gain was large, and obvious enough by the seat-of-the-pants estimates that we are confident it is real. In addition, we tested the car on a hot, humid day with the temperatures in the dyno room way over the 90's, so some of the cold-air benefits were lost, meaning much of that gain was from the smoother pipe and resonant effects. Temperature effects are not reliably measured in a stationary dyno room, but pipe diameter and resonance effects are.
While strapped to the dyno we decided to try a nitrous pull. To our amazement, project SE-R belted out 235 horsepower and 220 lb-ft of torque. JWT's re-tuning combined with the new intake gained over 10 hp on nitrous! This equates to roughly 270 hp at the crank, an impressive amount for a clean burning, catalytic converter equipped, daily driven car.
On the motor, Project SE-R now pumps out 151.7 hp and 133 lb-ft of torque at the wheels. This equates to about 175 hp at the crank. While this gain might seem mild by some of your standards, remember that our original objective was to build the ultimate daily driven, clean-emissions engine. That goal has been achieved nicely.
According to the dyno results, Project SE-R has lost no bottom end power, has a smooth idle, gets 28-30 mpg and will still pass a tail pipe sniffer emissions test with ease (it will not pass a visual underhood inspection in most states, but not all states require one). This is a lot more than can be said of most of the fast, but pipey emissions spewing street machines out there.
Stay tuned to future issues as we are now working on building a new bottom end for Project SE-R using oversized flat-top pistons for a total displacement of 2045cc with a streetable 11:1 compression.
Reprinted with Permission