1991 honda CRX Daily Driver Rebuid....Open for Suggestions/Comments... - Fuelly Forums

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Old 09-27-2010, 01:49 PM   #1
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Thumbs up 1991 honda CRX Daily Driver Rebuid....Open for Suggestions/Comments...

Ready to spend some money on my 91 HF and been doing some research. If im correct a D15Z1 would give me hopefully in the high 50s with its current weight specs. Switching to a carbon fiber hood and fenders also to reduce weight. Also a possible turbo/supercharger for added air intake volume. Besisdes the obvious ignition componenets (wires, sparkplugs) and a aluminim flywheel what do you guys suggest? Reason Im asking is I want to do this right the first time without screwing myself out of time and money. Oh and will the D15Z1 be a direct boly up to the 5 speed HF Tranny? And what about the motor mounts? Just making sure...

Thanks!
Paul
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Old 09-27-2010, 03:01 PM   #2
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Re: 1991 honda CRX Daily Driver Rebuid....Open for Suggestions/Comments...

carbon fiber hood/fenders and aluminum fly wheel will not likely yield enough return(if any) to be cost effective. turbo/super charger will negatively affect FE(fuel economy/efficiency) w/ possible exception of WOT(wide open throttle) . motor mounts have no effect, but you could go w/ long life polyurethane if you desire. stay w/ stock(OEM) plugs/wires.

keep researching(here) and welcome to the site. FYI: best gains are achieved via driver mods(the WAY you drive).
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Old 09-27-2010, 03:15 PM   #3
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Re: 1991 honda CRX Daily Driver Rebuid....Open for Suggestions/Comments...

If I leave everything stock on the D15z1 that will work. I should have explained myself a bit better about the motor mounts. I was wondering if they would need to be changed with the engine swap and if the motor would directly bolt up to the HF tranny.
What/how do you feel about a cold air intake for th Z1 along with a catback exhaust system? Thanks for the info yo!!

Paul
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Old 09-28-2010, 06:11 AM   #4
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Re: 1991 honda CRX Daily Driver Rebuid....Open for Suggestions/Comments...

Quote:
Originally Posted by pwjuggernaut View Post
What/how do you feel about a cold air intake for th Z1 along with a catback exhaust system?
Avoid a cold air intake, if you are going for fuel economy.

Cold air intakes are for racers, or others that want maximum power. They do increase power a small amount, but that comes at the expense of using more fuel (which is the opposite of what you want for fuel economy).
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Old 09-28-2010, 06:18 AM   #5
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Re: 1991 honda CRX Daily Driver Rebuid....Open for Suggestions/Comments...

What are your goals and what are your motivations? That will make a big difference in what you should do.

It sounds like you're really looking for performance and willing to spend whatever money it takes.

If you're trying to invest to save money, none of the things you have described will ever pay for themselves in fuel economy. Exception: If your engine and transmission are severely broken then choosing the most efficient replacement probably would pay for itself.

If we know your goal (what you want from the car) and your motivation (why you want it) then we can provide much more effective guidance.
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Old 09-28-2010, 07:44 AM   #6
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Re: 1991 honda CRX Daily Driver Rebuid....Open for Suggestions/Comments...

Actually Im trying to balance between mpg and power. I live in the mountains of Western North Carolina and do a to of interstate driving which is never completely flat. Mountains (steep at times) are a must for me to deal with. The stock D15 currently in my CRX produces about 67 hp at at 4000-4500 rpm with torque around 83lbs per ft. The D15z1 has about 93 hp at 5500 with 97lbs of torque at 4500-5000 rpms. I think this will help out tremendously with hill acceleration/maintaing speeds but would like to increase my power without sacrificing mpg...(Yea I know good luck with that one)

The reason I was asking about cold air intake is that they provide less resistance for air intake consumption.
Example-Its easier to get air into the motor with a hole the size of a softball vs the size of a golfball which to means less work load for the motor to pull/suck it in = less power used to accelerate via combustion off gas=less gas used=better mpg.

Thats why I assumed a turbo would work and not a supercharger. Since a supercharger requires belts and pulleys to be attatched to the block/motor it means more drag/work on the motor which=more combustion of gas=less gas mileage. Turbos work on exhaust and require no outside power sources (attatchments to the motor) except what is produced by the car and forces more air into the motor=less combustion of gas=better gas mileage.

Now I do wonder about if a turbo would actually accomplish this because I can see it from both sides of the discussion. The cold air intake while producing more hp still leaves less drag on the motor which yes does give it more hp but if you adjust you driving habits it might be a win-win situation..

Just explaining my thought process guys so feel free to correct me where Im wrong. Be gentle though, Im a noob who is at least trying...
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Old 09-28-2010, 08:09 AM   #7
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Re: 1991 honda CRX Daily Driver Rebuid....Open for Suggestions/Comments...

you can't use an HF transmission because it's a cable actuated transmission and not a hydraulically actuated one.
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Old 09-28-2010, 08:10 AM   #8
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Re: 1991 honda CRX Daily Driver Rebuid....Open for Suggestions/Comments...

Do you know how to tune with a management system? CROME,Neptune etc.
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Old 09-28-2010, 08:27 AM   #9
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Re: 1991 honda CRX Daily Driver Rebuid....Open for Suggestions/Comments...

sorry pgfpro Im not familiar with that. I grew up as a mechanics son so im a shop rat so im willing to learn if you will send me in the right direction!

************* I was reading las t night and thought I read about a conversion cable...any ideas??

Thanks guys!

Paul
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Old 09-28-2010, 09:45 AM   #10
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Re: 1991 honda CRX Daily Driver Rebuid....Open for Suggestions/Comments...

A more free-flowing (whether cold or warm) intake could free up some restriction, if there was a restriction before the throttle. Usually the throttle or RPM is the restriction. A closed throttle flows a lot less than any intake. At low RPM, no amount of throttle opening will make the engine want more air. The only time better intake flow may help is if you're running at high RPM with wide open (or nearly so) throttle...and that's only if the engineer who designed the car had a reason to compromise on intake flow.

A turbocharger is less lossy than a supercharger, but the energy used to shove more air (and therefore fuel) in doesn't come for free...it's just harvested more efficiently and at different speeds. Additionally, it is common to need to go rich with a turbo. The use of a turbo for fuel economy is if you choose a more efficient engine that has less power and need to be able to make the extra power on demand.

In your case you're looking at putting in a more powerful engine. A turbo would be counterproductive to your fuel economy goal.

The D15z1 doesn't automatically come with all the fuel economy of a VX, even in a car as light and aerodynamic as a VX. It must be accompanied by the tall gears and wide ratios of the VX transmission, as well as all of the things it needs to use its lean burn mode (wideband O2, proper ECU, etc). There's another thread right now where someone put a similar engine in and is not getting worse results than his original engine; his transmission is almost certainly to blame.

I'm not sure how to reconcile all of that with your mountain driving. It probably still all applies the same.

Here's the best modification you can make, and one of the only modifications that will ever pay for itself: Your driving. The usual advice about slowing down applies, but I've found it unnecessary...there are plenty of techniques you can practice, most of which work at whatever speed you want (though you still do better with lower speed). Before you begin, though, you need to start a gaslog to get a baseline average that you can compare and measure your progress against.

Also don't overlook the free car modification that almost always produces results: Increased tire pressure. Never exceed the tire's maximum, nor go below the car's recommendation. Somewhere between those two is a pressure that is still comfortable, handles better than stock, wears the same or better, and improves your fuel economy. I drive heavy cars and usually run the tire's maximum but I imagine your CRX may ride harsh/handle badly at maximum pressure. OTOH the tires are probably pretty small and may be good at the max. You can experiment carefully to find out.
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