325i vs. 318i throttle body for FI conversion

[mp1k3]

I have all the required parts to convert the 2002 to fuel injection and will commit within the next week or so. Question is with the stock 318i setup what noticeable benefits will I notice with the 325i throttle body vs the stock 318i throttle body and will there be an affect on fuel economy? Thanks.

[Zorac]

im in a similar boat! no answers though, just morequestions...

do you know if the swap is a direct bolt on for the throttle bodies? does the 325i throttle body have a tps? might be worth it for the tps alone.

edit::

this answers my questions, but not yours!

http://www.bmw2002faq.com/component/option,com_forum/Itemid,0/page,viewtopic/p,833604/sid,8dac13c2ab2a1c3ca45ea32791938759/

[valentine02]

I am also just finishing the final phase of parts collection for the same swap. Hope to begin the actual swap within the next month or so.

The 325i TB is not a direct bolt on to the 318 manifold. You will need to fabricate an adapter bracket, or contact Tom at 02again and purchase one of his. It's a very nice part (all his parts are nicely made and reasonably priced).

Post up with your progress and results.

[bluedevils]

use 325i TB for better low end torque.

[///mChris]

The tricky part of the throttle bodies is that the butterfly isn't the same size as the inlet or outlet of the throttle body.

I took out several butterfly's to measure them

http://mybmw1600-2.blogspot.com/2011/08/throttle-bodies.html

Typically you can estimate throttle body size by Horsepower. The MegaManual has a calculator for this.

http://www.megamanual.com/v22manual/minj.htm#throttle

[Guest]

use 325i TB for better low end torque.

I don't think you'll see better low down torque, but it will make the throttle a bit twitchy. You'll be getting more airflow with less throttle movement so it may feel more powerful but really it's not.

I'll be going MS very soon now that I have to rebuild my motor, I've got all three but I'll probably be using the 325e throttle body. 318i TB would be good for just a DD with very mild upgrades while a 325i TB isn't really necessary until you really build the motor. I'll be going with a 292, 10:1, 3-angle valves, dual springs, HD rockers, 7k redline, AL flyhweel, and possibly a few other small things. The 325i TB is going on my turbo motor and for what it's worth a friend ran an M30 TB(63-65mm iirc) on an M10 turbo and hated it. He said the power up top was great but the drive-ability was terrible, he switched back to the 325i TB.

[TKMad]

I'll second what Manimal said. I have had my engine to 6000rpm with no 'choking' effect from the stock 318 TB.

If you are going turbo or stroker you may need to consider the larger one, but I see no reason to switch for a close to stock engine.

[Zorac]

are the 325e and 325i throttle bodies interchangable? 02again has the nice adaptor plate for the 325i, which would be nice if it worked for the 325e too.

happens to be a 325e at the junk yard currently too, might have to stop by.

[///mChris]

The 325e and 325i are interchangeable. They both are 4 bolt. I've got the 02again adapter. It makes it very easy.

[valentine02]

Ok, so now i'm not so sure any more (as if i ever really was). I've done a lot of reading and searching, and up to now was under the impression that the 325i/is TB was the way to go.

manimal - I hear what you're saying about what will work for each particular engine, but it's difficult for me to say what's going on inside my engine as i have never had it apart. I have both throttle bodies (318 and 325 is). I am also a "first timer" with megasquirt. Am i blowing it if i go with the 325? I haven't really commited yet, so it's not too late for me to change my mind.

I respect the opinion and input of those here who have gone down this road before.

[///mChris]

Honestly it makes very little difference.

According to the megamanual the drawbacks to a oversized throttle body are:

However, there are some drawbacks to a too large throttle body:

At low rpm, you go from low kPa to 100kPa with very little throttle movement, making driveability 'worse'. For example, with a very large throttle body you may get 100 kPa at 20% throttle at 2000 rpm. This means if you want to hold it at 40 kPa for cruise, you have to be very steady on the throttle, as small movements may produce large changes in engine output (so it's harder to be smooth), and

A small throttle movement (and a small V/sec TPS signal change) can result in a very large change in MAP (as mentioned above) at low rpms. The result is little (or no) accel enrich when the engine needs it most. However, you can usually tune around circumstances like this by richening the VE table at low rpms and higher kPa (say < 2500 rpm and> 70 kPa) by about 5-7%. This has a negligible affect on fuel economy, since you likely never see 70 kPa while cruising.

The bmw progressive linkage throttle system keeps the throttle from opening too quickly. It seems to me the 325e throttle body is ideal.

In the end, do which ever is easiest. I'm very guilty of overthinking this stuff. At the end of the day, just get it running. You can change stuff later.

Are you doing MS2 or MS3? Which coils?

[Guest]

I don't think using the 325i TB will be bad necessarily, just given the choice I'd do a 325e TB but don't sweat it too much. You'd most likely only notice a difference when trying to pull away slowly since it would require less throttle than using the smaller TB. It's something you'll most likely get used to. I just like to point out that bigger isn't always better, especially with overly large intake/exhausts like the ITB's w/larger diameter runners than the intake ports or stupid big exhausts on NA motors.

For what it's worth, I was going to use the 325i TB before I got a 325e one for free. The 325i TB is now going on my turbo project.

[valentine02]

Thanks for the advice guys.

Chris: I'm planning on running MS2 and will probably go the Ford EDIS route. Your name was just one of several that Tom from 02again mentioned as being a wealth of knowledge on this subject. This may not be the last time I "pick your brain"

mp1k3: sorry if I sort of hijacked your thread...

thanks again, guys

[Zorac]

does it matter what year of 325e?

[///mChris]

According to realoem.com all 325e's and 528e's used

Part 13541285467 (Throttle Housing Assy) was found on the following vehicles:

E28 528e Sedan, M20, AUTO (4083) : Throttle Housing Assy

E28 528e Sedan, M20, MANUAL (4073) : Throttle Housing Assy

E30 325e Coupe, M20, AUTO (1264) : Throttle Housing Assy

E30 325e Coupe, M20, MANUAL (1254) : Throttle Housing Assy

E30 325e Sedan, M20, AUTO (1564) : Throttle Housing Assy

E30 325e Sedan, M20, MANUAL (1554) : Throttle Housing Assy