TB Boring - BMW Forum

Kevin325i · 07-07-2004, 12:31 AM

Well I'm gonna head over to a couple machine shops and talk to them about throttle body boring. Anything I should be thinking they'll ask me? Should they be able to measure everything up for minimum clearances?

Autotechnica, I know you've had this done. How long does it take them, how much did it run you?

Kevin

Kevin325i · 07-07-2004, 02:36 AM

Bumpity bump bump....... bump

Autotechnica · 07-07-2004, 10:59 AM

Do you have any idea how much larger you want to bore it or are you planning to just bore it to it's maximum size? That's the only thing you should know before bringing it there. I would check Dinan's website for specifications. I did mine according to Dinan's site which was +3.5mm.

The M42 TB is a little more complicated as it has 2 throttle body plates (dual stage) rather than 1 on the 6 cyl models. Anyways, my machinest charges only $150CDN for labour and the installation of the new larger butterfly plate. Most shops will charge anywhere between $250-$400CDN. If the plate is not made to fit perfectly, you'll have some rough idle issues, so make sure you bring it to a good shop. My machinest completes a TB the next day. However, I guess it would depend on how busy the shop is that you bring it to. I have spare 318 throttle bodies so I never have any downtime.

I wouldn't get this modification done if it costs you anymore than $200. If you think about it, no matter how big you bore the TB out, the restriction is still in the intake manifold and/or intake ports. You'll get the most power gains when you start matching parts up after you port out the intake ports.

Bry

Kevin325i · 07-07-2004, 01:07 PM

I checked Dinan's site for specs but they don't say. I'll see if I can look some more but I don't know if I'll find anything.

What's the core charge? Does that mean if I buy their new TB and send them my old one they'll give me back like 250 bucks for the core charge?

Kevin

Autotechnica · 07-07-2004, 02:05 PM

I have no idea how Dinan deals with core charges. I would just bring the TB to a local shop and ask them how long it'll take. If you can afford a couple days of downtime find someone to drive you there. If you have another car, even better!

I just checked for you from my catalouge. Dinan bores out the 325 dia. from 64mm to 67.3mm (increase in 3.3mm). Tell your machinest this is the exact specs you want.

Bry

Kevin325i · 07-07-2004, 02:11 PM

Perfect, where'd you get themagical booklet?

Kevin

Autotechnica · 07-07-2004, 05:01 PM

Quote:

Originally posted by Kevin325i@Jul 7 2004, 02:51 PM
Perfect, where'd you get themagical booklet?

Kevin

Got it at a local Toronto Autoshow. There was a Dinan booth there last year.

Bry

FruityOne · 07-07-2004, 07:56 PM

dinan will charge you the core charge if you dont give them your old one when you buy a new throttle body from them...its an exchange basis. so it works like this...if you have no throttle body to give them they charge you the core charge...if you have it they waive the core charge no discount nothing.

wulley1 · 07-07-2004, 08:34 PM

any seen any dyno graph of the before and after? A 64mm throttle body isn't large, but it's not small either. Your average V8 has a 63-65mm stock from the factory. On a V8, most guys with headers/exhaust/CAI only see a 4-6hp increase when stepping up to a 70mm or larger.

Kevin325i · 07-07-2004, 10:11 PM

So if I tell Dinan the core is in the mail, they'll wave the charge? Or do they have to have the core in their hands to give me the discount?

Kevin

Autotechnica · 07-07-2004, 11:00 PM

Quote:

Originally posted by wulley1@Jul 7 2004, 09:14 PM
any seen any dyno graph of the before and after? A 64mm throttle body isn't large, but it's not small either. Your average V8 has a 63-65mm stock from the factory. On a V8, most guys with headers/exhaust/CAI only see a 4-6hp increase when stepping up to a 70mm or larger.

It doesn't really matter how many cyl's you have. V8 doesn't equal a certain gain. You have to look at engine design and find out where the bottleneck is in your motor. You're motor can only take in so much air, so find out if the airflow is the restriction or if the motor is even capable of sucking in more air. The restriction is usually in the intake ports, so without further headwork you're not doing very much in terms of increasing airflow. If you're motor (literally) runs out of breath, you may think of getting some higher duration cams.

According to Dinan, their dyno plots show a gain of 8 peak HP (engine dyno). However, I have a feeling that Dinan's dyno's are sometimes fabricated.

Bry

Kevin325i · 07-07-2004, 11:13 PM

The peak numbers sound about right. With a chip, cai, exaust, and TB they say like 210 or something. And the '92 got an extra hp over the 93+ which jives with the higher lift cams in the '92.

Kevin

P.S. I'm taking it over to rice-o-rama tomorrow to see if they can do it for me. They've got a machine shop out back and they're like the only tuner anywhere near me. They deal more with the Honda scene but they should be able to bore my TB. The Dinan one looks rediculously expensive.

Autotechnica · 07-08-2004, 01:10 PM

The 325 TB is very easy to work with. It's no different than a Honda TB. If you have problems I can get my machinest to bore one out for you.

Bry

Kevin325i · 07-08-2004, 01:50 PM

Well this idea has fallen through. I realized I'm building up WAY to many projects for this car going on right now so I'm saving up so I can do my tranny mounts guibo and SSK. I'm also going to knock the cats out cause they're starting to go bad.

Then after that I need numbers for autocross and a harness. THEN I'll bore the throttle body.

Kevin