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Discussion Starter #1
1987 CRX Si with a D15A3. Some of the questions here will overlap with the engine management forum.

It's an SCCA Solo car in F Street Prepared. Class rules put severe limitations on what I can do to the engine internals and head. Basically, allowed modifications are as follows:

Overbore, with an absolute size limit including cylinder wear of .0475 over standard bore.

Port matching between the intake and the head with removal of material no more than 1 inch from the opening.

Milling the head with an absolute limit of .010, or what the manufacturer recommends, from stock.

Standard factory service valve job

Any flywheel can be used.

Rotating assembly can be balanced but not lightened.

Alternate cam drive gears can be used on engines that don't have variable valve timing.

So this means no head work to increase flow rates, no performance cam, no high compression pistons, forced induction, etc. Basically, all the normal easy stuff you would do to increase power is not allowed.

Also, engine swaps are not allowed except between a limited number of models. In the case of the CRX, I can swap in any engine from any US market Civic 1984-1987. But I already have the most powerful engine offered of those models.


What IS allowed is as follows:

Carbs, fuel injection, and intake manifolds are unrestricted.

Exhaust is unrestricted except it must be quiet and terminate behind the driver

The ECU is unrestricted.

Engine management (eg MegaSquirt) can be added.

Injectors can be replaced with anything.

So, with all that said, I am limited to changes in intake, exhaust, ECU, injection, and air filter.

It already has a cold air intake, and I had the initial timing advanced. The old engine dynoed at 93 HP (91 is stock). The replacement is a $100 CL engine and I have no idea what it makes, but the old one had over 300k miles on it when it spun a bearing.

I guess I'm looking for suggestions on bolt on mods - intake, header, MS, etc. Perhaps some suggestions I haven't thought of as I am by no means an expert on the D series. What kind of HP increase can I expect? I'm thinking intake, headers, and MS or similar would give me maybe 15 extra HP.

I realize that there is close to zero aftermarket support, and I'll need to be creative. Any help will be appreciated.
 

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I would hit the ECU you could easily pull 5-10hp or more with a tune alone on the stock engine.
Which if you think of that in percentages that is a large gain for that engine. (10% increase)
 

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I would hit the ECU you could easily pull 5-10hp or more with a tune alone on the stock engine.
Which if you think of that in percentages that is a large gain for that engine. (10% increase)
I guess that would fall under installing something like MegaSquirt. The stock ECU is not tunable, but I can replace it with something that is. Like everything else, I'll have to get creative given the lack of aftermarket support.
 

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I would hit the ECU you could easily pull 5-10hp or more with a tune alone on the stock engine.
Which if you think of that in percentages that is a large gain for that engine. (10% increase)
Poking around, it looks like Cheddas adapter plate for later D series intakes is the way to on that side of the engine. It opens up a whole range of options for bringing in more air given that the stock intake is highly restrictive. I want to say the stock throttle body is somewhere in the neighborhood of 22mm, which is puny.
 

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Between intake, exhaust, and ECU you could be in the 20+ range for additional HP. While not great, my particular car with it's weight reduction would show a pretty good benefit by having 110hp vs 91 in stock form (the old engine was 93 whp according to the dyno)
 

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