M20 B3x Naturally Aspirated Stroker build past, present and future

[digger]

6mm is fine, I would think I can get a idle speed close to 2000rpm or more not that you'd need to

[SkiFree]

Thanks for putting up those vacumm log pictures .... do you think 6mm was plenty big enough?

[digger]

What did they do to the 885 on this part marked by the smiley face? I can't tell if they completely removed it or just polished it.

What did who do ? looks standard to me

the head i got ported still has this, it has been sanded and the sharp edge blended over, some of the the pics don't show it well but some you can still see it

[ForcedFirebird]

That is part of the angled squish band to match the dome on the pistons.

[SNEAK413]

Just looking at optimal head design

[SNEAK413]

What did they do to the 885 on this part marked by the smiley face? I can't tell if they completely removed it or just polished it.

[digger]

Digger,what piston dome shape are you using with your head? I'm doing your build with an 885 head and I just got my Pistons from JE and they are pretty much flat.

I’ll be using OEM shape to match the 885, if you want these Steve from topend can get JE made to this style or Andrew at IE can do them to now by Mahle and maybe Ross.

[SNEAK413]

Digger,what piston dome shape are you using with your head? I'm doing your build with an 885 head and I just got my Pistons from JE and they are pretty much flat.

[digger]

Put the x-pipe near the drive shaft CSB.

Digger, because of 2mAn's post I read back and realized something. MM's intake with those "pulse tuned" manifolds are interesting. They would increase the runner volume without increasing length. Makes me wonder what kind of testing was involved to come to the conclusion of a "tuned" length with a various diameters.

given when i went to the RHD manifold i got the same sort of gains as others with stock manifold id say its much of a muchness over OEM, they did claim 20% more midrange torque. When i did some testing of it i had change to a different cam and a bunch of other stuff and there was noticeably more midrange but the contribution from the manifold alone could not be differentiated

[digger]

Sorry for digging this back up, but I wanted to ask your input on what I gathered from your experiments...

It seems like the staggered cats being equal-length from the exhaust manifold/ headers was the optimal setup and having a "x" pipe further back was the best way to go.

Any thoughts as to having a "Y" pipe instead of the "X" and keeping it ~3" from there back?

probably the Y and X behave much the same especially if the cross sectional area of the single pipe matched the dual pipe, i was very close to changing to a Y and single 3" and feel it be very similar. main reason i didnt was because i did want to get another muffler and with cats two cats flow better than 1 (not an issue if you get high flow cats tho)

[ForcedFirebird]

Put the x-pipe near the drive shaft CSB.

Digger, because of 2mAn's post I read back and realized something. MM's intake with those "pulse tuned" manifolds are interesting. They would increase the runner volume without increasing length. Makes me wonder what kind of testing was involved to come to the conclusion of a "tuned" length with a various diameters.

[2mAn]

EXHAUST

Did some exhaust mods a few years back, everything I did went backwards and by a lot….lol



Run 1 to run 2 was a catalytic converter change out where the new cats were moved closer and side by side as opposed to staggered

Run1



Run 2



Further investigation into this never found out what happened. I even put back a similar set of cats and used photos to position them as close to where they were but it didn’t do squat. Perhaps it was something to do with the dyno setup on Run1 and as such it is not real or there was another issue at play…..

Run 2 to run 3 was a x-pipe relocated closer to the engine...Exhaust from run 3 notice the x-pipe is closer to the engine
.... the real problem is the relocation of the x-pipe


I want to redo the exhaust before the new build so will be doling that over coming month or two though not 100% sure on what to do yet

Sorry for digging this back up, but I wanted to ask your input on what I gathered from your experiments...

It seems like the staggered cats being equal-length from the exhaust manifold/ headers was the optimal setup and having a "x" pipe further back was the best way to go.

Any thoughts as to having a "Y" pipe instead of the "X" and keeping it ~3" from there back?

[digger]

Where are you drawing vacuum? I have been running them behind the throttle plate on the ITB builds and haven't had any issues with assist (cams smaller than yours, I'm sure, though). With a vacuum gauge on a single runner and a 272 cam, it was pulsing from 7-11" or so.

i'm getting 8-10" at hot idle feeding off 3 runners which feels borderline, it still works ok for the main part but its worse than it was with OEM manifold especially when cold where its 4" or even less with ICV working alot.
at low speed when ive applied the brakes a few times but not had enough revs to draw vacuum back down sometime the pedal feels noticeably harder quite often so you really feel it at low speeds.

when you lift off at speed the vacuum is higher and it feels normal when you start to brake. new cam will have much more overlap so its more about looking to the future than anything.

[ForcedFirebird]

Where are you drawing vacuum? I have been running them behind the throttle plate on the ITB builds and haven't had any issues with assist (cams smaller than yours, I'm sure, though). With a vacuum gauge on a single runner and a 272 cam, it was pulsing from 7-11" or so.

[digger]

Anyone ever fitted an electric vacuum pump to supplement boost vacuum for the booster on a cammed m20 or similar? I’m only getting 8-10” at hot idle and much less when cold with fast idle. It’s been this way for years but it’s the reason I’m not happy with the stock brakes as the amount of assist I’m getting is marginal. When I build the engine this is likely to get worse with a little more overlap.

Hella make some good pumps that are compact, quiet as they are for OEM and electric vehicles but they don’t come with the relays and vacuum switch etc so implementation is a little more involved electrically

http://www.hella.com/microsite-elect...s_gb_druck.pdf

The UP28 is to supplement vacuum and UP30 can work as a standalone system. The UP28 is found on Audi’s etc so is OEM quality and can be had for cheap used.