SPD Tuning Service

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What modifications should I do to my 2.5 to get more power?

Rule No 1. "Unless you alter the breathing ability of your engine by changing the cams, anything you do to your normally aspirated engine is just buying presents for your car. Spend it on your girlfriend or wife, the results are more rewarding" -anon. Spoken by some mechanic last seen standing under a large sign in the back of his garage that said "Speed costs money, how fast do you want to go?"

Rule No 2. Subaru EJ series modular motors have a high performance version called the EJ20G. It is a purpose built turbocharged motor. It has a hardened crank and a closed deck to the upper end of the cylinder block and a couple of other tid-bits that make it an effective hot gas generator for the attached turbine. It is the turbine that makes the power. It weighs 364 lbs. all up and is generally considered bullet proof up to 300 very effective horsepower. As a result there are no takers in the after market for Subaru cams.

Rule No. 3 See rule number 1. There is just no current interest in development of the 2.5 Japan or England. Not when EJ20G will put out 300hp all day long.

What if I want it use my 2.5 as a hot gas generator?

We see two trends developing. Superchargers and turbochargers after market kits for the 2.5. The 2.5 DOHC engine is a "stretched" design engine and is not recommended for more than 235hp. The cases of this engine are strong enough to run for ever at 165hp, but are not designed for 300hp. So, until proven otherwise, we are recommending that the DOHC 2.5 keep its stock pistons and compression ratio and be limited to about 240hp on pump gas. Supercharging is idea for this low pressure boost, 5-7 pounds scenario.

The weakest link in the 2.5 motor is the crankshaft connecting rods. The end caps are too thin to take a lot of stress. The stress can be rotational or due to high power output. We recommend miving the red line down to 5200 rpm when going to 220hp output levels. This will keep the bottom end out of harm's way. As many of you know a 2.5 engine running flat at 130pmh+ lost a rod bearing this spring. Like, what did  we say about this before, guys?

For those wanting the "Big Power", as a friend of mine calls it, these US engines need a change of pistons to lower the compression down to 8.5:1 or so. Then is is fairly easy to get 300hp from the the 2.5 SOHC engine with some hope of reliability. We are holding our breath on the reliability of the 2.5 DOHC at these higher outputs. As I said earlier, lower your red line and install an oil cooler. Do not get greedy with the boost. All boost junkies suffer the same fate: engine damage sooner or later.

There are, as of July 1999, projects coming into place. Several customers report satisfaction with  Minnam's turbo kit. I have been told the fit and finish is good and aftersales service is not as good as some would like. The motors sometimes "code" and Minnam is working on fuel and timing tricks to keep this to a minimum. Rimmer Engineering has a kit that now fits under the hood of an Impreza and is shipping kits slowly. These run flawlessly at about 220hp.

Please stand by..... as the saying goes in the Navy. More news is sure to develop.

Send mail to mshields@spdusa.com with questions or comments about this web site.
Last modified: May 23, 2000