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To carb or to FI


tinkwithanr
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I'm having an internal crisis. I've decided to dive into an m20 swap while I'm fixing up the rest of my car. This means I need to fuel the m20 and proceed to blow up said fuel in a timely manner. I already decided and ordered the Ford EDIS parts and coils, so I'll be running a 36-1 trigger wheel ignition (either megasquirt or megajolt).

So now I have to decide how to get the fuel in her. I've always had a soft spot for the 32/36 that was on my m10, and for that matter carbs in general. I can't help but feel like there is just something right with a properly carb'ed '02. But at the same time going with megasquirt and FI would really let me adjust things and tune it precisely, something I feel like carbs wouldn't let me do. FI would also let me go turbo down the road if I choose to do so. Hence my dilema...

So what is the FAQ's opinion on FI vs. Carbs?

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Guest Anonymous

Hi Tink, weird, I had to logout to reply to your post otherwise got an error. Anyway, I am also someone who LOVES carbs, and will rebuild them for friends just for the fun of it. Nonetheless, for your application I would vote for Megasquirt. For a more-or-less stock car that's a daily driver, the 32/36 is probably just too good to beat. But for the more custom setups, such as your motor swap and since you'll be using EDIS anyway, I think it makes more sense to squirt it. Another plus for Megasquirt is that it is really fun to tune/play with also, in my opinion. A few tips from my experience:

- Use a wideband O2 sensor

- Relocate your battery out of the engine compartment before you even start

- Don't forget to run a GOOD ground between the frame and the block

- Worst part of EDIS is getting the tach to work properly, and each tach seems to need a slightly different fix.

Feel free to email me with any specific questions and/or any pics of my setup, always glad to talk induction!

-Carl

ceichel02 at gmail

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Guest Anonymous

Stupid error messages lol.

But thanks for the reply, I'm slowing coming around to the FI side of things. Like you said it just seems to make more sense, especially when I wanna run a hot cam etc. As far as the other stuff you mentioned:

-Already planning on a wideband

-Tray has already been removed, just need to weld in the new brace in the trunk

-Hadn't though much about it yet, but definitely will do

-I'll keep that in mind. I feel like a working tach is something I'll worry about once she's actually running lol

Glad to see i'm not way off in my thinking with this so far. I'll most likely be in touch in the future, I'm sure I'll have some questions. What setup are you running now?

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Guest Anonymous

If you weld? think about putting the battery under the back seat on passenger side not in the trunk. It will fit nicely(saw this in another car at an auto-cross) if you build in a little pocket tray. Great for protecting the battery plus very good for weight location, polar moment or something.

My battery is located there but than I removed 15 pounds of back seat bench so i didn't have to weld anything to get it to fit.

Have fun

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On the FI front, any reason you don't want to do a m20 with stock ECU (as opposed to aftermarket ie megasquirt) I've been through it all, and the most I drove my 02 was when it has a chipped m20 in it. It was a blast and was dead simple. The more gadgets and mods you have, the more of a pain in the ass it becomes. I'm a geek and addicted to modding (anything) but there is always a price to pay. Just something to think about.

Matt

www.tinyurl.com/02m20/

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I did consider that option. For starters I just have a long block, so I would need to go an purchase an stock ecu, wiring harness, etc. All that for just the stock performance (not that it's to shabby). That combined with the other modifications I want to do - itb, hot cam, programable ignition - it just makes more sence to be able to control each aspect instead of being locked into one program.

I also have always been intriged by tuning a completely custom FI setup, so this seems like a great opportunity.

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That a good point. Are we talking the m20b27 or the m20b25. Frankly the 2.7 is a bit of a dog. Now the 2.5, that's a fun engine. I had a chipped 89 325i and the motor was great. Just a BMP chip, minor intake and exhaust work, and it could almost keep up with a WRX. Had an amazingly flat torque curve and revved to 6.5k.

Unless you are talking about doing some work, go FI. About the only reason I could see for carbing the M20 would be a big cam, nice header, and a trio of sidedrafts. Honestly FI would probably still be better even in that situation, but wouldn't sound anywhere nearly as good :)

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That a good point. Are we talking the m20b27 or the m20b25. Frankly the 2.7 is a bit of a dog. Now the 2.5, that's a fun engine. I had a chipped 89 325i and the motor was great. Just a BMP chip, minor intake and exhaust work, and it could almost keep up with a WRX. Had an amazingly flat torque curve and revved to 6.5k.

Unless you are talking about doing some work, go FI. About the only reason I could see for carbing the M20 would be a big cam, nice header, and a trio of sidedrafts. Honestly FI would probably still be better even in that situation, but wouldn't sound anywhere nearly as good :)

It's going to be a b27 block, crank and rods with 'i' pistons and an 'i' head. The block will be decked ~2mm to get the compression back to where it needs to be. CR should be around 9.5-10. This should give me the flow of the b25 but the extra displacement and torque of the b27. At least that's the plan.

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err, don't you run into piston height problems with that setup?

As in, the pin's too low on an i piston?

I'd run efi, btw- you can use a lot of the existing efi hardware

even if you don't use that humongous manifold.

Of course, 3 dcoe's would be neat, too. But not as practical for a DD>

t

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Shouldn't be any piston clearance problems. The 'eta' rods are 130mm while the 'i' rods are 135mm. the 'i' (2.5L) stroke is 75mm and the 'eta' (2.7L) stroke is 81mm. So:

'i' height = (75/2) + 135 =~ 172.5mm

'eta' height = (81/2) + 130 =~ 170.5mm + 2mm decked block = 170.5 mm

Of course I'll triple measure everything before actually decking the block, but there are a few people already running the same basic setup ('i' and 'eta' combo w/ decked block) so I know it can work. I'll also need the adjustable cam gear to get the valve timing back in line with the crank, but that's not a huge deal.

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