Pelican Parts
Parts Catalog Accessories Catalog How To Articles Tech Forums
Call Pelican Parts at 888-280-7799
Shopping Cart Cart | Project List | Order Status | Help



Go Back   Pelican Parts Forums > Porsche Forums > 911 Engine Rebuilding Forum


Reply
 
LinkBack Thread Tools Rate Thread
Author
Thread Post New Thread    Reply
Registered User
 
tadd's Avatar
 
Join Date: Dec 2005
Location: Mount Airy, MD
Posts: 1,658
Port enlargement suggestions

No this is not an internet ad....

Ok, so I want to build a 906-oid spec clone but use some of the better tech porsche developed. Case in point the inproved 2.2 combustion chamber. Plus I get bigger valves than even the 906 by a mm. 'T' heads are pretty common and pretty cheap and have the same valve sizes as the S heads, just smaller ports.

So the question is what is the best way to enlarge to the 38/38 ports of the 906? I can easly use an indexable boring tool to do the first 'straight' 1/2 or so to give me a truly round hole. Combined with the truly round valve seat that gives a 'true' beginning and end to blend too. What I do not understand how to do is the roof (bowl) of the port over the valve.

When I played with volvos in another life (boy this post can go places!), there were templates that you would cut out in metal and attach to a long bolt that you would open open up the port to at a specific depth. This gave a profile to cut the port to. Some were used on the valve side for the bowl others on the opposite.

The 'T' heads need to open up 3mm on radius and that is a lot of material, so I am kinda concerned as to how to keep the well formed stock shape while just enlarging the port.

Any help would be greatly appreciated,

tadd
__________________
Building molecues or building cars... you do get more of first in every batch. A mol of porsches anyone?
Old 02-23-2006, 12:50 PM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #1 (permalink)
Registered User
 
jluetjen's Avatar
 
Join Date: Oct 2001
Location: Westford, MA USA
Posts: 8,595
Garage
Have you done a search on "porting" on the this and the 911 board. The subject of porting (although not necessarily 906 specific) has been discussed a number of times. It should give you some ideas.
__________________
John
'69 911E

"It's a poor craftsman who blames their tools" -- Unknown
"Any suspension -- no matter how poorly designed -- can be made to work reasonably well if you just stop it from moving." -- Colin Chapman
Old 02-23-2006, 01:43 PM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #2 (permalink)
Registered User
 
tadd's Avatar
 
Join Date: Dec 2005
Location: Mount Airy, MD
Posts: 1,658
Thanks!

I promise I did search. I thought I had read all 625 posts on 'porting' last night, but lo and behold a post with measurments...

Thanks John.

I would assume that most of the early ports are just round in cross section?

tadd
__________________
Building molecues or building cars... you do get more of first in every batch. A mol of porsches anyone?
Old 02-23-2006, 03:48 PM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #3 (permalink)
Registered User
 
jluetjen's Avatar
 
Join Date: Oct 2001
Location: Westford, MA USA
Posts: 8,595
Garage
Re: Thanks!

Quote:
Originally posted by tadd
I would assume that most of the early ports are just round in cross section?
Yup. As far as I know they're all essentially round. Some people have done "D" shaped exhaust ports though. If you read through all 625 prevous posts -- I'm impressed!
__________________
John
'69 911E

"It's a poor craftsman who blames their tools" -- Unknown
"Any suspension -- no matter how poorly designed -- can be made to work reasonably well if you just stop it from moving." -- Colin Chapman
Old 02-23-2006, 04:44 PM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #4 (permalink)
Registered User
 
BReyes's Avatar
 
Join Date: Feb 2005
Location: Tampa Bay, FL, Treasure Coast, FL USA
Posts: 1,475
Garage
I guess we all better reread as many as possible too.

Have you considered s heads?

Good luck.
__________________
Bernard
Old 02-23-2006, 11:02 PM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #5 (permalink)
Registered User
 
tadd's Avatar
 
Join Date: Dec 2005
Location: Mount Airy, MD
Posts: 1,658
OK, so it was only 610...

posts when you search 'porting' . My bad .

There is some interesting info on this topic and some tends to run equal across the threads so I tend to lean towards that as 'true-ish'. Other tidbits are tossed out and go nowhere. For example, there was a comment about a 1.5% taper on the intake being optimum, but when numbers on real porsche heads are actually given, they tend to be slightly hourglass shaped as you go deeper into the intake tract then out to the valve.

One 'truth' that seems pretty solid is that porsche did a really good job on the ports in the first place. So in lue of actual 906 port dimention numbers I think I am just going to make a sillicone casting of the T intake and exhaust and then add 3mm in radius where ever I am measuring so I can drill out some go/no-go templates.

I am still worried about getting the bowl right. I figure I can go in on the head side with a template as well. THe other idea I am tossing around is to plunge cut into roof of the port bowl with a ball end mill of the proper radius and then just doing a linear travel on the table. This would be simply two slots, one on each side of the valveguide support boss. CNC would be nice, but I don't have one of those.

I wouldn't mind going with '69S' heads, but I don't have any and kenik seems to have been looking for a bit and I bet they would not be inexpensive. Armanjo (sp?) has some 935 heads for sale on his web page, but that is 6.5k. Becides, I have 2.4T heads in hand.

Oh, yea... jluetjen you have been at this for a long while and suffer the newbies well. THANKS! I'd be happy to mail you a sixpack of your favorite if you like.

tadd
__________________
Building molecues or building cars... you do get more of first in every batch. A mol of porsches anyone?
Old 02-24-2006, 06:52 AM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #6 (permalink)
Registered User
 
BReyes's Avatar
 
Join Date: Feb 2005
Location: Tampa Bay, FL, Treasure Coast, FL USA
Posts: 1,475
Garage
When you say 906 spec, how would 3.2 liter heads compare?

p.s. Aren't the differences between the s heads and t,e etc considerable. The 906 was a purpose built machine...
__________________
Bernard
Old 02-24-2006, 07:52 AM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #7 (permalink)
Registered User
 
jluetjen's Avatar
 
Join Date: Oct 2001
Location: Westford, MA USA
Posts: 8,595
Garage
No Problem Tadd. Thanks for the offer, but I've got at least half a case of Sam Adams in the basement that I never have any time to drink as it is.

What sort of engine are you spec'ing out? Are you familiar with this thread? I consolidated a lot of what I have learned into that thread. If I were you, before I'd worry about the porting specs, I'd make sure that you've defined the desired rev range, and then the resulting cam shaft. That will define how much air you need to pump through the engine which will give you an idea of your porting strategy.
__________________
John
'69 911E

"It's a poor craftsman who blames their tools" -- Unknown
"Any suspension -- no matter how poorly designed -- can be made to work reasonably well if you just stop it from moving." -- Colin Chapman
Old 02-24-2006, 07:59 AM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #8 (permalink)
Registered User
 
tadd's Avatar
 
Join Date: Dec 2005
Location: Mount Airy, MD
Posts: 1,658
Absurd street motor

at least that is the plan this time around. In a nutshell: I have a 67 912. Some engine parts are either no longer exist or are hard to find. Like oversize main bearings. No mo. On top of that a BASIC 616 rebuild typically runs about 6k. All for 90 hp. 125 is not unreasonable in a rebuild. I figure I have about 75 hp on my 70k orginal motor. It is slow. Momentum puzzles are great for the race track, but the cut and thrust of the asphalt jungle highway sucks.

Therefore instead of switching to VW type 4 power (which alot do), thou not bargin priced either, I picked up a 69 boxed 914-6 for $650. Decision made - even better it is really porsche and the stock bottom end is almost nuke proof.

That said, after reading BA book I was just going to go 'S' and call it a day. Then I read about a guy that redid a 906 for the steet to travel in with his wife and dog in the back of a PCA collection. Even worse I then found pelican and jluetjen posted that BMEP graph of the MFI 906E. It capivated me how it just destroys everything else. There have also been a couple of posts about people driving 911Rs or STs with retarted cams being quite acceptable on the street.

So, since this is a 'fun' car, think 4 wheel motorcycle since the misses wants me off the RZ, (I can always take the IHC scout) I figured why not and go all out. I've always bit the bullet and gone common sense (under, not over cam). Why not go over this time. Worst comes to worst, I have to drop the motor one weekend and drop back to S cams. I only got 75 on top now, so ANYTHING will be an improvement. I am therefore not scared of having a 'soft bottom end' below 3.5k. I would guess I have around 40 now.

Therefore what I have in mind is:
- non-counterweighted T crank with precison ballance for +7.5k rpm and lighting spin up (My tach runs out of #s at 7k. How cool to shif when you run out of numbers!) I have never been able to dertermine if the crank is cast or forged. Several threads are on this, but nothing ever seems to get concluded.
- 2.0 rods w/ARP bolts
- DYI twin plug 2.4T MFI heads w/ enlarged 38/38 ports
- JE clone 906 pistons in LN nickes (although I hear Supertec has another option that is cheaper) Still on the fence about 10:5 or 11:1 CR.
- 906 grind cams
- shufflepins, timeserts, and turbo squirts for the case
- GT3 oil pump w/case clearencing
- Supertec 2.0 duel plug disty
- slide valve TBs (or mod TWM stacks)
- MFI run off the crankshaft nose (so its easy to play with)
- tilton low mass clutch

Did I forget anything?

Eventually the 912 will get its rebuilt 616 back the the screamer will go into a short wheel base 911R clone. But that is up the road.

Thoughts??

tadd
__________________
Building molecues or building cars... you do get more of first in every batch. A mol of porsches anyone?
Old 02-24-2006, 09:30 AM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #9 (permalink)
3 restos WIP = psycho
 
kenikh's Avatar
 
Join Date: Feb 2005
Location: North of Exit 17
Posts: 7,729
Sounds awesome, but I am still perplexed by the MFI off the crank thing. It isn't hard to get at the MFI pump where is is already engineered to fit. BTW, why not go with a more modern grind of the 906 cams (faster ramps).
__________________

- 1965 911
- 1969 911S
- 1980 911SC Targa
- 1979 930
Old 02-24-2006, 10:28 AM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #10 (permalink)
Registered User
 
tadd's Avatar
 
Join Date: Dec 2005
Location: Mount Airy, MD
Posts: 1,658
Man you are everywhere!

Kenikh:

Email and BBS, you must be damn uncertian! Maybe we should intergrate you over all space, that way we will at least know you are somewhere.

As for the 906 cams, I really like how 'gentle' they are. Even though the specs are a bit on the wild side for the street, Mechanically it should be quite long lasting even with full rpm 'burps' to 7.5-8k every now and then.

Yes I could get more area under the curve with a DC-60 cam, but then you need stiffer springs which means more wear on all the cam gear, ect.

Porsche made some fine stuff, so I am trying to stick with the best parts and upgrade the weak (rod bolts anyone).

Make sense? Maybe?

tadd
__________________
Building molecues or building cars... you do get more of first in every batch. A mol of porsches anyone?
Old 02-24-2006, 10:38 AM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #11 (permalink)
Registered User
 
tadd's Avatar
 
Join Date: Dec 2005
Location: Mount Airy, MD
Posts: 1,658
Whoops!

Forgot the whole MFI crank nose thing...

Well bottom line I just think it is in a damn goofy spot. If I had a 906 were I had a flip top car and had complete engine access I would leave it where it is. I had to change the fan belt on my 912 last week on the side of the road. I cannot imagine trying to do that with the MFI belt in the stock location.

Ok, fine. You got me. The truth will set me free: It just looks so wicked cool it is a shame to hide it in the back of the engine bay! Just so much mechanical goodness you just want to fondle it. Hell, I sleep with my 2.0 MFI unit under my pillow. Don't you??

Tadd
__________________
Building molecues or building cars... you do get more of first in every batch. A mol of porsches anyone?
Old 02-24-2006, 10:48 AM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #12 (permalink)
 
3 restos WIP = psycho
 
kenikh's Avatar
 
Join Date: Feb 2005
Location: North of Exit 17
Posts: 7,729
Didn't even think about having to change an MFI belt road side, BUT should it even be done? You'd have to ahve all of the tools to retime the pump to the cam. I'd rather tow it.
__________________

- 1965 911
- 1969 911S
- 1980 911SC Targa
- 1979 930
Old 02-24-2006, 11:22 AM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #13 (permalink)
Registered User
 
tadd's Avatar
 
Join Date: Dec 2005
Location: Mount Airy, MD
Posts: 1,658
More ignorance

Isn't retiming a pump easy? Its like line up the two dots. That gives two choices 180 out from each other just like a disty.

We aren't talking about setting all the little pesky linkage rods.

Color me slow.

tadd
__________________
Building molecues or building cars... you do get more of first in every batch. A mol of porsches anyone?
Old 02-24-2006, 11:27 AM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #14 (permalink)
3 restos WIP = psycho
 
kenikh's Avatar
 
Join Date: Feb 2005
Location: North of Exit 17
Posts: 7,729
It is the 180 degree isue. PIA by the side of the road.
__________________

- 1965 911
- 1969 911S
- 1980 911SC Targa
- 1979 930
Old 02-24-2006, 11:30 AM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #15 (permalink)
Registered User
 
tadd's Avatar
 
Join Date: Dec 2005
Location: Mount Airy, MD
Posts: 1,658
But...

Between the where the disty is pointing and the timing marks on the crank nose, shouldn't it be unambigious which cylinder is at spark on TDC? Then just line up the dots....

Its not like the disty timing case where you have only the crank to go by.

tadd
__________________
Building molecues or building cars... you do get more of first in every batch. A mol of porsches anyone?
Old 02-24-2006, 12:42 PM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #16 (permalink)
3 restos WIP = psycho
 
kenikh's Avatar
 
Join Date: Feb 2005
Location: North of Exit 17
Posts: 7,729
Ah yes, if yoy have a disty. You have a point; replacing a belt is a PIA.
__________________

- 1965 911
- 1969 911S
- 1980 911SC Targa
- 1979 930
Old 02-24-2006, 12:44 PM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #17 (permalink)
Registered User
 
tadd's Avatar
 
Join Date: Dec 2005
Location: Mount Airy, MD
Posts: 1,658
Now returning to the regulalry schedualed program...

Back to ports.

So after taking a hard look at the 2.4T heads (which have 30mm intakes! - didn't see that one coming), how important are the teardrop shaped 'islands' that the valve guide protrudes thru? Back from my Volvo/MG days we would just knock the guides back and grind those suckers away leaving the guide naked... I ask because by the time I get out to 38mm there isnt going to be much left and if I leave them as is, they will be sticking quite a was into the port.

tadd
__________________
Building molecues or building cars... you do get more of first in every batch. A mol of porsches anyone?
Old 02-27-2006, 06:57 AM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #18 (permalink)
Registered User
 
tadd's Avatar
 
Join Date: Dec 2005
Location: Mount Airy, MD
Posts: 1,658
Head Refurbishment Options

Ok folks, after only having to drill out two exhaust studs and only send one off for EDM...

Can anyone tell me if I should take a beauty pass off the cam tower sealing surface (I have a 6", 8 bit cutter itching to be used)? They don't look too horrible, just a few dings and nicks. The exhaust gasket faces are another story and will be getting a swipe of the cutter.

Also, would glass bead blasting be useful on the fins (outside of the head)? They leave a real nice texture on aluminum and the extra surface area seems like it would be a nice thing to have.

And finally on the head front... I have broken down and bought a set of neway seat cutters (I am a sucker for carbide) but what size ream do I need and instead of grinding the valves, can I turn them on the lathe with a carbide insert tool instead?

Ok, not quite heads, but would there be any advantage to drilling the crank throws like the 906 type cranks? I can't figure if that was to ballance the Ti rods or if it was done to actually lighten the crank.

thanks in advance,

tadd
__________________
Building molecues or building cars... you do get more of first in every batch. A mol of porsches anyone?
Old 03-06-2006, 05:59 AM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #19 (permalink)
Reply

Thread Tools
Rate This Thread
Rate This Thread:

 


All times are GMT -8. The time now is 01:08 PM.


 
Powered by vBulletin® Version 3.8.7
Copyright ©2000 - 2019, vBulletin Solutions, Inc.
Search Engine Optimization by vBSEO 3.6.0
Copyright 2018 Pelican Parts, LLC - Posts may be archived for display on the Pelican Parts Website -    DMCA Registered Agent Contact Page
 

DTO Garage Plus vBulletin Plugins by Drive Thru Online, Inc.