New modder
 

Hello! Up front I want to say thank you to all that have written posts over the years clear back to 2002? I have been reading like crazy and have just purchased a 1991 CRX HF with 193k on it, compression is good and runs and drives. Needs a few things...like an entire paint job and window seals. Right now I have 2 questions unanswered(I'm a google guru.)
Would putting a different, think si, exhaust manifold on and catalytic converter(further down the line) instead of replacing the expensive cat on the HF which is 2-4 times as much, cause loss of MPG?
What do you recommend for cheapest quality way to redoing all the rubber in the car including seals around the windows?
Last question, How legal and/or difficult would it be to add a front end dam? to front of my car using some kind of material like this guy 118mpg? do a google search as I can't post links! You guys/gals are awesome!

The new manifold generally wont help.
But if the converter is original it could be partially clogged, so gut it or put on a new one if required.
Same thing goes for the oxygen sensor, if you dont know how old it is or if it looks old change it.
If you want an air dam most of us use lawn edging made from ABS plastic.

air dam
 

I think gutting is a good idea. Thank you. I've got to replace my front motor mount(maybe inserts all the way around) first before I can do anything. Motor has so much rock I can barely take off on a hill. As for the lawn edging, I was thinking something bigger like the plexiglass used on that 118mpg car. I did see where one guy had cut the top of a 2nd bumper off as a air splicer and then used some rubber as front wheel spats. Something along those lines if this plexiglass idea never sees daylight.

Don't forget to increase psi in tires !

That plexiglass on the 118 mpg car was pretty "extreme". I suspect you'd attract the attention of the police with something like that. However, it looks like that thing is a combo air dam/grille block. So don't neglect the grille block strategy. They say on here that, within reason, the smoothness, or "streamlining" of the front end isn't as critical as stopping air from getting trapped/crammed under the car. So blocking the grill keeps it from going into the engine compartment, and then under the car. Of course, the air dam directly blocks it from going under the car, and the front wheel spats direct it to the outside of the wheel instead of - - - under the car.

So, going as radical as "118mpg" did with the nose extension probably got him only minor gains above just blocking the grille and any other "front openings" where the air has an opportunity to get underneath. Just covering the front of your car with clear packaging tape, for example, would probably get you 75-80% of the way there as far as improving the front aero is concerned.

aero
 

I plan on doing the grill/bumper block for sure. Waiting for my valve cover gasket, front motor mount, and new spark plugs to come in so I can drive this thing. Will try to post pics soon.

Check into the MPGuino so you can get real-time feedback on your driving. Changing how you drive will have a much larger impact than any other single mod you can make.

-soD

this!!!!
(or a scangauge) see link in sig

HF's have a smaller diameter exhaust(it's the smallest of all the CRX's),honestly I'd do everything I could to keep it as stock as possible.Honda had the HF figured out back then and IMO it was really ahead of it's time,they're wonderful cars.

OEM is always best(x10),
I'd rather have a gutted HF cat/stock exhaust vs a Si/DX exhaust with good cat,but I'm in a smog free state..YMMV

FWIW,my 287k OEM cat is still good albeit covered in rust and I wouldn't dare try taking any of the bolts out,but as they say "don't fix it if it ain't broke".

:turtle:

By the way,I get ~56mpg in my HF,which I am very pleased with.(seems pretty average from what I've seen)
What're you getting?
Oh and the 118mpg car was in the hands of a 'Honda Guru' I have a feeling there was a lot more done to that car than what was led on,but I could be wrong...
I've just never seen any other HF get close to what he got...
And he did it with the B6!?

Amazing.

Exhaust
 

Well I'm still torn about weather to A. Order the stainless still 2.25" exhaust I found for $110 catback or to take it to local shop and have them make a shorter one with thrush muffler so I can stuff the whole thing up in there and get a belly pan with a hole in it for the pipe for aero. Have a feeling doing a pan with stock exhaust isn't going to work out so well.