If I had a dollar for every time someone asked me when I was going to swap in a SR20DET engine into my 240 I would be a rich man. Okay, I'm exaggerating but the point is that everyone thinks that if you own a 240SX you need a SR20 in it...the faster the better. And can you imagine the reaction of these people when I tell them that I plan on building the stock KA engine and turbocharging it? It is as if I am performing a sacrilegious act on my car and I shouldn't be allowed to own a 240.
Don't get me wrong, I will be the first to tell you that the SR20DET is an awesome engine. But I feel the KA24DE can be an equally powerful engine with some work. The last time I checked, an SR20DET changeover cost anywhere from $2,000 to $2,500. With that money you get about 200 to 220 flywheel horsepower, which equates to about 170 to 180 horsepower to the rear wheels. Most SR20DET enthusiasts will often times add an upgraded downpipe, high-flow air filter, exhaust and a piggy-back fuel computer. With those upgrades the engine should generate around 250 to 275 horsepower to the wheels. If you want to generate any more power beyond that you will need to upgrade the head gasket, fuel system and turbocharger, which can add up to a couple thousand dollars. We felt instead of spending money upgrading to an SR20 engine we could fully build a KA24DE engine from the ground up to withstand boosted duty.
We decided to add some performance upgrades to Project Silvia while we searched for products for our boosted engine. Our first avenue for more power was to increase the exhaust flow. Although future plans are to turbocharge the KA engine, we found a used GReddy tubular header at SP Engineering. It came from one of the employees who installed a SR20DET power plant and no longer was using it. Although GReddy no longer offers the header, we wanted to check out how well the header works. We expected the long tubular runners and 4-1 collector to increase mid- to top-end power of the engine. On the dyno, the GReddy unit performed like a champ pushing the power output of the KA from 136.3 to 141.1 horsepower. Peak torque also rose from 145.6 to 152.2 lb-ft. The GReddy manifold produced power exactly where we thought it would, from 3750 rpm to redline. The largest power increase we witnessed was at 5200 rpm with an increase of 7.8 horsepower.
Anticipating the future turbocharger, we wanted to find an exhaust system with large diameter piping to expedite the increased exhaust flow from the turbocharger. Our search ended by selecting the Blitz Nur-spec polished stainless steel exhaust system. The Nur-spec piping measures in at a behemoth 80mm (3 inches) in diameter. If this system doesn't take care of our exhaust needs, nothing will.
We were worried, however, of how loud the system was going to be with the 80mm piping diameter. Fortunately, the exhaust system comes with a silencer and it does a great job of quieting the exhaust note without sacrificing too much power (see dyno chart).
The two-piece exhaust system is constructed from mandrel-bent polished stainless steel piping with a robotically TIG-welded muffler canister and large diameter tip. The system bolts up to the factory downpipe and retains factory the catalytic converter. On the Dynojet the KA posted 146.6 horsepower and 156.1 lb-ft an increase of 5.5 horsepower and 3.9 lb-ft. From 5700 rpm to redline the Blitz system generated 6 to 7 horsepower over the stock system.
Our last power product is an Unorthodox Racing lightened front pulley. We had great success with Unorthodox Racing pulleys in the past and felt the KA engine could benefit from one too. Constructed from billet aluminum the UR pulley is substantially lighter than the stock cast steel unit. The UR pulley tipped the scale at a feathery 1.5 lbs while the stock unit weighed 6.5 lbs. Besides being lighter the UR unit also slightly underdrives the accessory units (A/C, P/S, alternator and water pump).
Installing the UR pulley is a straight R&R affair with the only difficult part being the removal of the 24mm front pulley bolt. Once the bolt is loose, remove all the belts. The UR pulley will require new, shorter belts due to the under driving. The instruction sheet lets you know what belt lengths you need. Once the UR pulley is installed, pop on the new belts and it's party time.
The key to power production is to not over-tension the new belts. Too much tension on the new belts will increase drag causing a lower power output. Trust us, we checked it out and you will lose power if the belts are too tight. Once we adjusted the new belts to the proper tension it was time for another dyno run. With the new pulley in place we recorded an increase of 1.8 peak horsepower and 3.7 lb-ft of peak torque. We figure once the new belts wear into the grooves of the pulley we should see an even greater power increase over the stock pulley.
Peak output now stands at 148.8 horsepower and 159.9 lb-ft of torque. Pretty impressive numbers considering a stock 1994 to 1998 240SX only makes about 125 horsepower to the wheels. We are now generating 20-plus more horsepower than a stock engine.
Just for fun we thought it would be interesting to see how much power the Blitz silencer, if any, would rob compared to the un-silenced system. To our surprise, with the silencer installed the Nissan made nearly identical power numbers, losing only 0.1 horsepower and 0.3 lb-ft of torque. Our guess for the identical power numbers is that the 80mm piping diameter flows much more than what the naturally-aspirated 2.4-liter can produce.
Now the Nissan has more grunt off the line and instead of falling flat at the top-end it pulls to redline. Although the 240 is nowhere in the performance range where we ultimately expect it to be, it is, however, a start in the right direction. If we are lucky maybe we can even break the 200 horsepower barrier in N/A. Dare we say, SR20 owners beware.