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Old 11-04-2012, 11:49 PM   #1
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Questions about devac-ing a 87 CRX

Hi,
Please excuse my ignorace, but I've been sculling about the dark corners of the internet as I work on rescuing a 87 CRX that snapped the timing belt. And while I almost have it running, swapping in a HF head, and tranny, I've started reading about how (mostly) tuners will take off all the extra vacumn hoses. Which is almost all of them. Now, it seems that results in more power, but does will it hurt FE? is the best setup I should be trying to use invlove a HF intake and carb? with or without the vacumn system?
Thanks
Jonathan
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Old 11-05-2012, 04:41 AM   #2
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If you are using a carb that came from an engine that used an oxygen sensor (a 1.5 liter engine), then you should leave the vac hoses/emissions connected (the 1.5 carbs are jetted a little bit rich and then there is a little intake manifold vacuum bleed valve in one of the black boxes that allows fresh air to enter the manifold and lean the mix out if the oxygen sensor is reading rich).

If you are using a carb from an engine with no oxygen sensor (the 1.3 liter- these carbs were jetted to run just the right mix), then you should not need the black emissions boxes from a car with a 1.5 liter.
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Old 11-05-2012, 06:16 PM   #3
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If you are using a carb that came from an engine that used an oxygen sensor (a 1.5 liter engine), then you should leave the vac hoses/emissions connected (the 1.5 carbs are jetted a little bit rich and then there is a little intake manifold vacuum bleed valve in one of the black boxes that allows fresh air to enter the manifold and lean the mix out if the oxygen sensor is reading rich).

If you are using a carb from an engine with no oxygen sensor (the 1.3 liter- these carbs were jetted to run just the right mix), then you should not need the black emissions boxes from a car with a 1.5 liter.
Well, should I find a 1.3L carb so I can get ride of the vacumn box? or should I rebuild my HF 1.5L intake/carb and fix all the vacumn leaks? should I try both? see where I end up in the final FE? Thanks for the reply, I'm pretty sure you helped me when I was looking for a HF cylinder head. And you will also have to stay around when I get set up to install a fuel cutout switch.
Thanks
Jonathan
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Old 11-06-2012, 05:04 AM   #4
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Are you using the HF ECU/emissions system? Or a DX emissions system?

The HF oxygen sensor is multiwire and an odd smaller size and is really expensive. If you have the HF ECU/emissions, then I'd say that you may as well swap to a 1.3 carb and ditch that whole system. If you have a DX emissions (with the cheap 1 wire oxygen sensor), you might try to rebuild the carb.

You will also need an HF transmission in order to keep the rpms down and take advantage of the torquey cam in the HF head.
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Old 11-06-2012, 06:07 PM   #5
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Are you using the HF ECU/emissions system? Or a DX emissions system?

The HF oxygen sensor is multiwire and an odd smaller size and is really expensive. If you have the HF ECU/emissions, then I'd say that you may as well swap to a 1.3 carb and ditch that whole system. If you have a DX emissions (with the cheap 1 wire oxygen sensor), you might try to rebuild the carb.

You will also need an HF transmission in order to keep the rpms down and take advantage of the torquey cam in the HF head.
As equiped now, I have an HF tranny and cylinder head installed on the car, which I'm currently not driving yet.

I own, to be installed when I get around to it, an HF carb and intake, and ECU. I plan to rebuild the carb somehow, and then find out what I need to do to make the wiring and emissions work out. I don't know if I can find a way to trick the ECU into thinking I have a 5 wire O2 sensor installed, or if I'm going to try to find a good one and make it back to stock.
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Old 11-07-2012, 05:13 AM   #6
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It is really good that you are using the HF transmission.

You will also need the HF wiring harness, HF distributor, alternator control box, barometric pressure sensor, HF speedometer (the HF ECU needs a VSS signal) and and spark timing control box to make the HF emissions system work correctly.

If this is a DX, it would probably be much easier to just find/install a 1.3 carb.
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Old 11-07-2012, 06:34 AM   #7
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Great to have you as a resource Erik! As an owner and daily driver of an '87 CRX HF I am so glad that I pushed through and got mine running good after I first towed it home instead of ripping out the complicated vac system. I still haven't put my HF transaxle in, yet with the Si transaxle I'm averaging 46mpg. I just got all the seals last week to install before the swap. Hoping to prioritize that soon... anyway, just wanted to encourage Jonathan6229. Obviously do what you need to do to get it running so you can save on fuel but if you have most everything to keep it stock I hope you'll push through. Let me know if I can help you locate anything... kind of my hobby to research and locate.
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Old 11-09-2012, 03:00 AM   #8
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Great to have you as a resource Erik! As an owner and daily driver of an '87 CRX HF I am so glad that I pushed through and got mine running good after I first towed it home instead of ripping out the complicated vac system. I still haven't put my HF transaxle in, yet with the Si transaxle I'm averaging 46mpg. I just got all the seals last week to install before the swap. Hoping to prioritize that soon... anyway, just wanted to encourage Jonathan6229. Obviously do what you need to do to get it running so you can save on fuel but if you have most everything to keep it stock I hope you'll push through. Let me know if I can help you locate anything... kind of my hobby to research and locate.
Wait....how did a SI transaxle get into an HF?

As it related to my CRX, I got the HF transmission in and it running, and it runs so smooth compared to my rattle trap Geo metro. (Geo for sale. cheap!) I'm going to fix the DX emission system, which seems mostly ok, just a choke valve that needs to start working, and I plan to install a vacuum gauge. and then drive for a few thousand miles or so. But I'm excited about it. If it's tuned right with DX emissions system, should I still put in a DFCO cutout? is that going to be worth it?
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Old 11-09-2012, 07:19 PM   #9
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[QUOTE=Jonathan6229;168472]Wait....how did a SI transaxle get into an HF?

Previous owner put the Si transaxle in to get some "peppy" acceleration. I've learned there is a different final drive ratio for SI, DX, or HF {CA HF differs from 49 state HF too} I'm looking for mpg's, not acceleration, so I'm back to the sluggish gearing.
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Old 11-10-2012, 04:43 AM   #10
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Since you have a carb, you really can't use a DFCO switch to control fuel like ppl with fuel injection. Your emissions system has a DFCO type device on the intake manifold (top of driver's side) which automatically bypasses the carb and allows filtered air from the air cleaner into the intake manifold when you are decelerating in gear.
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