2.4 CIS rebuild

[ljowdy]

Hello and thanks in advance. So far, I haven't been able to find any answers via the search engine so,,,

I'm getting ready to rebuild my 1973.5 CIS 2.4 engine.

What if anything can I do to increase performance without sacrificing efficiency or longevity

The car is strictly a weekend driver and won't see any track time but I'd like to have a little more power.

Any help will be greatly appreciated.

[Bobboloo]

Considering this will be a street motor I would suggest just a bump in displacement from 2.4 to 2.7. Everything else would stay the same on the motor inre: the cams and port size. Basically you would then have a 2.7 normal CIS motor. (as opposed to the more common 2.7S CIS motor) Any other mods short of converting to EFI will not improve street performance in my opinion. Installing carbs would improve throttle response but at the cost of fuel economy and cold running performance.

With a bump in displacement horsepower would increase from 140@5700rpm to 150@5700rpm which is not a lot but that's not really the important figure here. The important figure is in the torque which will increase from 148.5@4000rpms to 175@3800 rpm. This is a substantial increase that will put a smile on your face during your weekend drives. If you notice the peak torque has moved down the RPM band which is good for a street motor.

This mod will require boring your case spigots out to 97mm to fit the larger P+C's. This will be no problem for the longevity of your motor considering you have a 7R magnesium case which were the strongest mag cases made. The mild cam and small ports limit your usable upper end HP which will only help with the longevity of the motor considering there will be no reason to rev the motor above 5700 rpm because the motor looses power above that range.

The most important thing for longevity of these motors however is control of the operating temperature. Realistically you could use this motor with out a front oil cooler but if you want the motor to last a long time you should put one up front.

I believe you may need to replace the fuel distributor with one from a 2.7. It might also be necessary to change out the WUR (warm up regulator) to one from a 2.7 motor or atleast modify your current one for the displacement increase. More research is needed to be sure if you decide to go this route.

The easiest and most cost effective way however to increase performance would be to swap your motor for a 2.7 or 3.0 CIS motor. It's something you might want to consider. Swapping could be done in a matter of hours and your costs would be virtually cut in half as opposed to rebuilding and modifying your present motor. This way you could just put aside your matching numbers 2.4 motor and keep it original.

[ljowdy]

Thank you for that comprehensive reply.