Author Topic: Larger throttle body? Info? Power gains (Read 17006 times)

nomad · « **on:** June 06, 2007, 12:43:53 PM »

I have been reading through some books on E30s I picked up. The E30 Restoration book I have is written by some British guys. It has info on body and engine specs, just a few basic writeups on some hands-on work to the cars.

What cought my eye was where they mentioned the M42 engine was a detuned engine so as not to take anything away fom the upmarket 6cyl and M3 variants.

They mentione the engine does a lot better with a chip (we know this) and the stock header is good (we know this) and a good cat-back is a good addition (most agre on this). What they also mentioned though was that they saw good gains with an increased throttle body bore. Either have the stock one bored out with larger throttle plate or adapt the 6cyl throttle to it. I have not seen anything mentioned about larger TB's or adapting the 6cyl version or a later version to the M42.

Can anyone shed some light on this? It is mentioned that with chip/exhaust/TB they see 155bhp? Can this be all attributed to the chip?

Please enlighten me. I'm down for a junkyard TB finding mission.

kowalski · « **Reply #1 on:** June 06, 2007, 01:06:43 PM »

bigger throttle body = more air in so it makes sense. especially since the intake is the bottle neck on these things. I've never seen anyone go to the trouble of adapting an m20 throttle body to it. I know a few of us are going towards individual throttle bodies though. All you'd need for an m20 throttle body is a simple adapter plate made, i believe the TPS is the same on both.

Scumball · « **Reply #2 on:** June 06, 2007, 02:05:01 PM »

E30Zone here in the UK can source you one from their online shop... Not advertising, just advising.

Mine is the 4mm overbored stock item and I noticed a small gain, definately. I have the advantage of a chip that was written with the TB in mind though!

nickmpower · « **Reply #3 on:** June 06, 2007, 02:23:35 PM »

so did you notice a gain from the chip and tb together or the Tb seperatly?

Boyracer · « **Reply #4 on:** June 06, 2007, 02:49:46 PM »

I think it is advisable to have custom chip if you enlarge the TB diameter.

On part throttle engine measures how much air it is actually ingesting with the help of VAF (and lambda checks if engine is running rich or lean). So when the larger TB increases airflow it is compansated by injecting more fuel -> more power! :cool:

To my understanding on full throttle VAF and lambda are totally ignored and ECU is injecting fuel as it was programmed to do from the factory. The problem is that now it get's more air to cylinder but the same amount of fuel as when it was stock. This means engine is running lean which is dangerous! :eek:

You could avert this by fitting slightly larger injectors or preferable fitting adjustable fuel pressure regulator. So you could increase the pressure of fuel going to injectors. This is not a problem on part throttle, engine will adjust injetor duration to match the pressure. On full throttle it would inject fuel for factory programmed time but since the pressure is higher, there would be more fuel to burn on cylinder.

Best way is to get custom chip made for larger throttle body in my opinion.

Vladi · « **Reply #5 on:** June 06, 2007, 05:10:17 PM »

You could also get an M30 AFM case and switch your electronics. The M30 AFM has a bigger in/out diameter so you'll have more air going in. That's what i'm about to do.

tjts1 · « **Reply #6 on:** June 06, 2007, 08:34:14 PM »

You could probably use the M42 TB heater as an adapter plate for the M20 TB.

b318isp · « **Reply #7 on:** June 07, 2007, 06:41:17 AM »

Quote from: kowalski;27205

i believe the TPS is the same on both.

No, the TPS on the M42 is a potentiometer not a switch.

Alpine003 · « **Reply #8 on:** June 07, 2007, 11:56:06 AM »

I just can't see how a bigger tb on the M42 can benefit as long as there is the barn yard door ahead of it.

tjts1 · « **Reply #9 on:** June 07, 2007, 12:27:37 PM »

Quote from: Alpine003;27318

I just can't see how a bigger tb on the M42 can benefit as long as there is the barn yard door ahead of it.

+1
Has anybody megasqirted on of these engines yet?

Shift_Now · « **Reply #10 on:** June 07, 2007, 12:37:39 PM »

I was wondering if anyone has succesfully mounted a m30 AFM, as stated previously? If so, how difficult was it, and did it net any noticable gains? I ask this because many guys running the m20 motor perform this mod and they say it is rarely effictive.

rsafier · « **Reply #11 on:** June 07, 2007, 01:28:11 PM »

From my understanding the TB and a M30 AFM are both worthless mods. There really isn't much of a restriction on the intake side of things. If you were to compare opening surface area on the TB I am pretty sure its equal to the M20 TBody, just 2 throttle vales instead of one.
The M30 AFM on the M20 is a mild improvement, but nothing radical.

The AFM itself really isn't that bad as far as being a restriction, its biggest issue is the delay in throttle response.
I know there is at least one turbo M42 that is running MS. I know from my M20 experaince the throttle response on Megasquirt is much better. For the price if you wanted to remove the AFM just megasquirt it, will be cheaper and work better then any other MAF hack.

One thing I am working on is making a pulse manifold like Metric Mechanics sells for 1K. I have a spare intake and got the price from a guy to do a prototype, about 300. I might just do some of hte work myself for the 1st one. MM claims 15% increase in low and midrange torque

tjts1 · « **Reply #12 on:** June 07, 2007, 01:52:18 PM »

^^^ Good info. Thanks!^^^

Everything I've read about MS is from turbo volvos that seem to thrive on the system. I'm not really interested in turbo M42 but I suspect MS+S and cam adjustment (we have adjustable cam gears from the factory) could unleash a lot of potential from this engine. Sure theres all sort of chips out there but I like to tinker.

gearheadE30 · « **Reply #13 on:** June 07, 2007, 08:01:04 PM »

For anyone who has MS experience, how difficult is it to tune? I'm assuming that a dyno is necessary.

Also, instead of spending big bucks on the larger TBs, I have heard of people using a Dremel or something similar to grind it to a larger size. Not sure what they did about the plate size though. Any ideas how this would work? I have an extra TB in my garage right now, so I may give it a whirl.

Alpine003 · « **Reply #14 on:** June 08, 2007, 12:14:44 AM »

Quote from: gearheadE30;27364

For anyone who has MS experience, how difficult is it to tune? I'm assuming that a dyno is necessary.

Also, instead of spending big bucks on the larger TBs, I have heard of people using a Dremel or something similar to grind it to a larger size. Not sure what they did about the plate size though. Any ideas how this would work? I have an extra TB in my garage right now, so I may give it a whirl.

Some people taper the lip at the entrance to smooth airflow. This is different than porting the entire throttlebody since you're not changing the overall diameter and not using a larger throttle plate. This little mod has proven minimal gains in some cars/engines. But I suspect with our square and primitive barn yard door design, it would probably have very minimal or no noticeable effects. Also for the fact that we have oval tb w/2 stage butterfly plates sort of throws that idea out as well.