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need some opinions on whether various mods will be worth it

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need some opinions on whether various mods will be worth it

Postby Andy69 » Tue Aug 20, 2019 11:07 am

1987 Si with D15a3. It's an SCCA Street Prepared autocross car. Right now the engine is basically stock with just a cold air intake and advanced initial timing. I'm trying to get a sense of what mods if any are going to make any extra HP.

I am limited by the class rules. Engine swaps and head swaps are forbidden except between 1984-1987 Civic and CRX models. Modification of engine internals are restricted. I can only bore up to .040 over, port match with a limit of 1 inch back from the opening for material removal, and balance the rotating assembly without removing material. Alternate cam timing gears are allowed.

Intake and exhaust are unrestricted, but turbocharging is not allowed. Stock ECU may be replaced with something like Megasquirt. Ignition and fuel injectors are unrestricted.

So basically, I can add a header and a high flow cat, and a later D series or B series intake using Chedda's adapter plate, larger throttle body, ITBs, etc., MS or similar, different injectors, different distributor, etc.

Ultimate HP is going to be restricted by the limitations on engine internals, but hopefully someone here has done one or more of the allowed modifications and gotten at least some HP gain. I realize gains are going to be small but that's what it takes in this class. The most I've heard anyone getting out of this engine under these rules is 115 HP or so.

Thanks in advance,

Lighter than stock flywheels are allowed.
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Joined: Thu Oct 04, 2012 8:36 am

Re: need some opinions on whether various mods will be worth

Postby CRXSWFL » Fri Aug 30, 2019 11:48 pm

How good of a driver are you? How well is the car set up as is? I'd think that getting the suspension dialed in would be your 1st priority. Is gearing unrestricted? IIRC the 2WD wagon has lower gears than the DX or Si. The '84 & '85 transmissions use narrower width gears for less friction.
Can you legally run a limited slip differential?

Can you legally run the HF wheel bearings, which are smaller for less rolling resistance. Repack the bearings with synthetic grease. Have you lightened the car to the lowest legal weight?

An adjustable cam gear doesn't add any power, all it does is shift the power band up or down some. Besides the 1mm overbore pistons, the match porting, HF or aluminum flywheel, exhaust header, 1teg injectors & ECU, the rest of the engine mods seem like a waste of time and money for what you'll get out of them.

Not sure how a 1st CRX could hope to compete with modern cars on the track, but I've never raced.
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Joined: Mon Jul 08, 2019 11:30 am

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