Unmodding my '91 Civic DX

[ohmycivic]

Hello everyone. Long time lurker, first time poster.

My '91 nissan NX died. As a replacement I found a track-modified '91 Civic DX. Got it insanely cheap, but the problem is that it's aimed at fuel burning a lot of fuel fast rather than economy (despite weighing only 1900 lbs). I've got a list of the modifications done, but not really knowing what means what results in me being afraid to make any changes. I'm great with a wrench and can pretty much DO anything, but not knowing what to do is limiting me here. I was wondering if you guys could help me un-and-re modify this thing into a daily driver.

Here's the list I got from the seller:

Engine not original is from a CRX SI -- no engine or tranny problems at all... Crane cams stage 2 (242@206 exh) 1500 rpm @ 7500 rpm, AEM cam gear, AEM alternator pulley Head Man header CHIKARA 4, 2, 1, Thermo Rap, 2 1/4 exh, Apexi racing muffler, cold air intake custom made, Holly fuel regulator, Hiper tech fuel pump, 16 gal fuel cel, fuel gage, (N2O) Nitrous wet system High Flow valve and blow of adapter with blow down tube, ZEX spark plugs, MSD 6AL, Two Step RPM limiter, MSD cap and rotor, Mallory coil, Accel wire set, Auto meter 5" tach with shift light, sunpro cages Oil and Air fuel mixture, Kurky's aluminum racing seat, 4 points harness, aluminum racing pedals and shift knob, B&M short shifter, Centerforce stage 4 dual friction clutch and throwout bearing, Matrix coil over strut bar front and rear, summit relocation battery kit.

[Andyman]

Probably the most important thing to do is to remove the high performance camshaft and install the original type camshaft. Lots of valve overlap will dilute the fuel mixture with too much exhaust gas and reduce effiiciency when using low engine loads.

Also try to get a warm air intake instead of a cold air intake. That could involve changing the location of the end of the pipe that takes the intake air.

[AndrewJ]

Engine ... is from a CRX SI

Overall, I'd try to ditch the motor and swap in an HF motor and tranny. I'm sure you could sell the motor and all the parts for way more than you'd pay for a HF motor and a complete rebuild.

That being said.

Crane cams stage 2 (242@206 exh) 1500 rpm @ 7500 rpm,
AEM cam gear,

Toss the cams quick!! They're probably terrible for FE, and probably don't idle worth beans.

AEM alternator pulley

Keep

Head Man header CHIKARA 4, 2, 1, Thermo Rap,

Keep, it probably won't hurt your FE, but I'd take the wrap off the headers, you actually want the heat in the engine bay.

2 1/4 exh, Apexi racing muffler,

Toss. Smaller diameter is better for torque/FE.

cold air intake custom made,

Toss. Get an OEM airbox or make an HAI.

Holly fuel regulator, Hiper tech fuel pump, 16 gal fuel cel, fuel gage,

It's fine to keep it all, but it's wayy overkill and you may be able to sell it for a handsome profit.

(N2O) Nitrous wet system High Flow valve and blow of adapter with blow down tube,

Toss. Nitrous is no good for FE.

ZEX spark plugs, MSD 6AL, Two Step RPM limiter, MSD cap and rotor, Mallory coil, Accel wire set,

It's fine to keep, but again, you could probably sell for a profit.

Auto meter 5" tach with shift light, sunpro cages Oil and Air fuel mixture, Kurky's aluminum racing seat, 4 points harness, aluminum racing pedals and shift knob, B&M short shifter, Centerforce stage 4 dual friction clutch and throwout bearing,

Keep if you like them, or sell for a profit.

Matrix coil over strut bar front and rear, summit relocation battery kit.

Keep. These will actually help your FE. The coilovers let you lower the car, which is good for aerodynamics, and the battery locate (assuming it's in the hatch-area) makes it easier to add more batteries for running your alternator beltless.

[ohmycivic]

Thanks guys. Especially AndrewJ. Going over it point-by-point is exactly what I needed. Off to the garage, then!

edit: You're right, it doesn't idle worth a damn.

[ohmycivic]

Overall, I'd try to ditch the motor and swap in an HF motor and tranny. I'm sure you could sell the motor and all the parts for way more than you'd pay for a HF motor and a complete rebuild.

So, um... what's an HF motor (google is being ambiguous), and what does a "complete rebuild" entail? I'm aware that this is probably a dumb question, but everyone has to learn sometime, right? The best I can come up with is that the HF thing refers to select D series honda engines. Also, what's an HAI? Any suggestions on where to look online for these things?

The suggestions seem to contradict in some parts. Keep the alternator pulley but go to a setup with no alternator? Ditch the engine but only remove certain parts? I'm willing to follow complete instructions in turning this thing into a gas sipper (I put on roughly 40k miles per year and need a project for this summer) so long as the cost of changes can be offset by the price I could sell the current parts for (so knowing whether to sell the engine as-is or unmodify and sell in pieces would be a great help). I'd also like to know how exactly the changes would help -- Andyman's post:

Probably the most important thing to do is to remove the high performance camshaft and install the original type camshaft. Lots of valve overlap will dilute the fuel mixture with too much exhaust gas and reduce effiiciency when using low engine loads

is great. It actually taught me something, though I only have a tenuous grasp of what it means (I know the operating principles of an ICE, but that's about it. Practical experience is what I'm lacking, so to me "valve overlap" means that the next valve opens before the first is shut).

I know how annoying it is for a newb to come into an established forum and be utterly clueless. I'm willing to come at this project with 100% humility and willingness to learn and work hard. I also promise I'll not be a jackass even if someone flames me.

With a little guidance I'd like to become more wise in the ways of ecomodding (and automobiles in general), so where do I start? I'll take/post any pictures that're requested -- would a snapshot of the extra parts I got with the car be helpful?

[SVOboy]

Don't worry about being a newb.

The HF was the model of CRX that got wicked good fuel economy, engine code of d15b6, in case you want to look that up. If I were you I would look for a d15z1 engine, like the one I'm about to buy tomorrow.

HAI = hot air intake, but that's debatable on its merits and is very car specific, so I won't comment now (I'm too tired to think with my whole brain tonight).

Welcome to EM

[AndrewJ]

Yeah, an engine from the CRX HF would be best, but if you want to keep the one you have, go down the list and toss/keep all those parts.

If you get a HF motor, it'll very likely be used, and you'd probably want to do a rebuild, new gaskets, inspect all the bearings, seals. New timing belt, plugs, etc...

The alternator underdrive pulley is better than the "stock" pulley, but inferior to removing the alternator belt entirely. It depends on how far you want to go.

EDIT:
Oh, and remember, if you get a HF motor, get the HF transmission too. The motor will be next to useless without the transmission.

[Duffman]

I would bet that if you got on a honda board and said that you wanted to trade engines (+ cash diference) with someone in your area, you would have people lining up. Changing cams and striping components is a lot of work and you need to know what you are doing when taking engines apart and timing cams.

I would keep the MSD ignition stuff, they give multiple sparks so you will get less misfires statistically.

[ohmycivic]

Originally Posted by SVOboy

Don't worry about being a newb.

The HF was the model of CRX that got wicked good fuel economy, engine code of d15b6, in case you want to look that up. If I were you I would look for a d15z1 engine, like the one I'm about to buy tomorrow.

HAI = hot air intake, but that's debatable on its merits and is very car specific, so I won't comment now (I'm too tired to think with my whole brain tonight).

Welcome to EM

Why would you suggest the z1 over the b6? I currently have the d16a6, and I read somewhere that you could put y8 headers on it. Now, I'm not entirely sure what that means, but would it be worth it to keep my current engine and do that (which seems like less work) considering the engine I've got only has about 35k miles on it?

Also, thanks for the welcome. Most forums groan at newbs.

[SVOboy]

The z1 has about 30 more HP than the b6, is newer, and I would say returns better mileage in the same car with the same gearing than the b6.

Headers are the pipes running the exhaust from the exhaust ports into a collector to the cat and out the back of the car, I would say there's no point in swapping headers, and the y8 headers were made for a performance engine, so they're prolly tuned for higher RPMs anyway.