Compatible engines & economy

[Cap'n J]

So I have heard that the 16valve non-vtec engine will work in my 1991 crx hf without having to swap ecu's. Would this work and if so what kind on difference would it make on economy?

[suspendedhatch]

The 1992-95 Civic CX 8 valve head is the same as the HF head. If you want to swap the DX 16 valve non VTEC engine, I strongly suggest you convert your CRX to OBD1 and run the P06 ECU.

[Cap'n J]

the guys at rising sun engines out of chico say that you can run a 16valve with the same ecu and it should still get similar gas mileage.

[GasSavers_Erik]

Will you be using the HF intake manifold and injectors?

I only know a little about FI, but it seems like your HF ECU would at least have to be running the same size injectors and all the same sensors as it was made for.

The 16 valve cam will likely be different than your HF cam so you may lose much of your low end torque.

[dkjones96]

The fact that it is 16v instead of 8v will account for most of the losses.

When swapping engines like this and wanting to use the same ECU as long as the injectors and mass air flow sensors are appropriately larger there shouldn't be an issue. Mass air flow can be difficult to work with though.

When we used a Chrysler 318 ECU for a 460 EFI conversion we just made sure the injectors were 45% bigger than the 318 and the ECU was oblivious to the extra displacement. MAP sensor is unaffected by the extra displacement.

[suspendedhatch]

Originally Posted by Cap'n J

the guys at rising sun engines out of chico say that you can run a 16valve with the same ecu and it should still get similar gas mileage.

So you're inclined to believe them? Don't be silly. They're salesmen. What kind of warranty do they offer on that claim? Will they put it in writing? I didn't think so!

Up until 1991 Honda used Peak and Hold injectors that require a resistor box to interface with the ECU. After 1992 they switched to Saturated injectors. Not insurmountable... but I'm curious whether Rising Sun even mentioned that.

Originally Posted by Erik

I only know a little about FI, but it seems like your HF ECU would at least have to be running the same size injectors and all the same sensors as it was made for.

The 16 valve cam will likely be different than your HF cam so you may lose much of your low end torque.

The HF injectors and the CX injectors are both 190CC, but they're not the same type of injectors.

The 16 valve motors make more horsepower and torque than the 8 valve motors.

Most of the sensors are actually interchangeable. The plugs are different but if you wire them up the actual signal coming from the sensors (with some exceptions) are compatible with either ECU.

Honda doesn't use mass air flow sensors to measure load. They use manifold air pressure combined with intake air temperature to calculate it. The IAT and MAP sensors are compatible between OBD0 all the way up to OBDII ECUs.

[dkjones96]

Originally Posted by suspendedhatch

The 16 valve motors make more horsepower and torque than the 8 valve motors.

PEAK torque, yes. But low-end torque suffers when a multi-valve head is used.

I'll explain.

Exhaust and intake gas velocities are what makes or breaks torque. In a multi-valve head there is more surface area to breathe, yes, HOWEVER, because of the larger valve area there is more port. More port = slower gas speeds which = less torque. Now, this holds true at low engine RPM (under 4000-4500).

The flip side of this is you get more torque higher up where the larger port reaches the same velocities of its single valve counterpart. More valve area and smaller valves means the engine can rev higher and therefore more horsepower.

Now, it IS possible to design an engine that can do both. Take my Tacker for example, it has a 16 valve 2.0. This isn't a vtec engine or anything like that but it has two torque peaks.

The engine begins making over 100ftlbs at ~2050-2100 rpm. First torque peak is at 3000 rpm where it makes 117ftlbs. This is the peak created by very long intake runners, cam timing, and a properly sized exhaust system that scavenges well. While it's between tune areas torque falls to around 108ftlbs @ 3750 then climbs again. The second peak happens at 5000 rpm and is 120ftlbs. This is the port peak. Gas velocities at the ports have raised to a point that we get maximum head air flow. After this torque drops off fairly quickly, I blame this on the intake manifold's long runners that help the low-end so much. But, torque still stays above 100ftlbs until around 6400 rpm.

According to the dyno, this car should be an awesome drive, but it weighs too much.

[Cap'n J]

Well I am not sure what to believe because from what I'm gathering I would just have to use all the same sensors and injectors. I am always skeptical about what salesmen say that's why I ask you guys and do additional research! The difference for me as it stands is half the price for a 16v as for an 8v and supposedly rising sun will put it in writing that the engine is warranted for 6mos unlimited mileage. I still have to look around though. Just trying to figure out how much work is involved swapping in the 16v and what the mpg difference is if i'm saving 500 bucks on the engine. If the difference was 10+ mpg then at these prices it would pay off in a little less than a year to get the more expensive 8v motor.

[FritzR]

upon more study of stormin matt's post I withdraw my info as complete BS

It sounds to me like the only good choice is to do the VX swap

[StorminMatt]

Originally Posted by Cap'n J

So I have heard that the 16valve non-vtec engine will work in my 1991 crx hf without having to swap ecu's. Would this work and if so what kind on difference would it make on economy?

You have to understand that there is a difference between working and working well. And while the car would probably run if you eep the HF ECU, it will not run to its full potential (when it comes to either power or economy). Also remember that the 16 valve engines have no provisions for EGR. And if you do not run EGR, you WILL get a check engine light. This will DEFINITELY reduce mileage.