Show full size 924Board.org
Discussion Forum of 924.org
 
 FAQFAQ   SearchSearch   MemberlistMemberlist   UsergroupsUsergroups   RegisterRegister 
 ProfileProfile   Log in to check your private messagesLog in to check your private messages   Log inLog in 
 Technical FAQ924 FAQ (Technical)   Technical924 Technical Section   Jump to 924.org924.org   Jump to PCA 924 Registry924 Registry

performance tuning literature for the heron style head?

 
Post new topic   Reply to topic    924Board.org Forum Index -> Performance Upgrades
View previous topic :: View next topic  
Author Message
MattN  



Joined: 25 Mar 2008
Posts: 34
Location: Manchester England

PostPosted: Sat May 17, 2008 9:55 am    Post subject: performance tuning literature for the heron style head? Reply with quote

Hello all,

I would like to start by saying what an imformative tool this webiste has been over the last few months. I would have posted sooner but every time I've had a question I've discovered that it has already been answered at some point by someone.

I have a 1981 924 N/A and have been doing a rolling restoration on it. It is by no means finished, but is reliable enough now that i want to start getting more power from it. For the moment I want to get more power from the original head by improving the rubbish shape of the inlet port. The pictures posted by Endwrench of a sectioned head really show what a poor design it is, but I'm hoping it can be improved. http://www.924board.org/viewtopic.php?t=6579&highlight=port
I have been getting my ideas from a book called Four-stroke performance tuning by A. Graham Bell (Third edition) this book has plenty of information on port design etc and a couple of paragraphs on modifying the heron style head.

My question for the members of the board is are there any other books that I should be reading? if there is a book with more specific information on tuning the heron style head then I would be really interested to know about it.

After some more research I will come up with a plan for modifyoing the head (and possibly fitting the Mikuni carbs) as and when this happens I shall post pictures and share my findings, until then if anyone can suggest some more back ground reading I would be most grateful.

Cheers

Matt
_________________
1981 924 N/A
Back to top
View user's profile Send private message
ideola  



Joined: 01 Oct 2004
Posts: 15505
Location: Woodstock IL

PostPosted: Mon May 19, 2008 11:26 pm    Post subject: Reply with quote

Matt, this is indeed a very interesting topic...

You might be interested in looking up a fellow by the name of Jon Mitchell (aka indi9xx), who runs 9xx.co.uk in Bournemouth. Jon claims to have developed some fairly significant improvements specifically for the 924 2.0L head, and there are at least a couple of UK members here who know him. Here are a couple of interesting threads from a few years back:
http://www.924board.org/viewtopic.php?t=11799
http://www.924board.org/viewtopic.php?t=11059

FYI, during that time frame, Jon had a run-in with one of our more nefarious former members, and basically packed his bag of tricks and went home. Jon was attempting to develop a market for the 924 2.0L, and grew concerned that the aforementioned ne'er-do-well was attempting to pirate and duplicate his R&D.

In any event, sarbirus apparently had a recent conversation with Jon, so it might be worth pinging him to see if he could put you in touch. In the above-linked thread, sarbirus indicated that Jon was amenable to contributing his knowledge to the forum because he had since determined that the 924 2.0L market was not viable enough to warrant any further investment. It would be fantastic if someone could persuade him to share what he knows.
_________________
75 Fiat X1/9 | 80 US 928 | 80 US 931 '941' | 78 D-Prod Replica | 78 Poli-Form
Back to top
View user's profile Send private message
MattN  



Joined: 25 Mar 2008
Posts: 34
Location: Manchester England

PostPosted: Tue May 20, 2008 9:41 am    Post subject: Reply with quote

Hi Ideola,
Thnaks for responding, I spoke to Jon a couple of weeks ago having already stumbled on the threads you mention.
The good news is that he is putting together a pdf file with instructions on how to get most of the benefits of the head he designed but with tools that the enthusiast can use at home.
The plan is to post these on this and other websites sometime this summer.
I am really excited to get this doccument, and want to do some more swatting up before it arrives. I can imagine what kind of changes will be made to the inlet ports as they are far too big in relation to the valve, I just wonder if there is anything that can be done to create some kind of squish area in the heron style head, the book I mentioned by A. Graham Bell suggest that recessing the valves can have a positive effect, and I just wonder if there are other ideas on the subject that you guys have come accross or even tried at some point.
_________________
1981 924 N/A
Back to top
View user's profile Send private message
Eturbo924  



Joined: 09 Nov 2002
Posts: 2187
Location: Londonderry NH

PostPosted: Fri May 23, 2008 1:42 am    Post subject: Reply with quote

I thought Johns work was on the 931 head?

Anyway funny talking about the recessed valves.

When I had my head ported and polished the guy working on it also "sunk" the valves. He did this because my (slight) performance cam was ground off an original 924 cam and thus had a smaller diameter. He had felt it would be hard to get follower screws to take up enough of the gap so he sunk the valves. Later I figured that this would actually likely lower the compression just a bit... but it seems to have worked out ok. The car definately had more power and revs much more quickly at the upper range.

Too bad I never took any pictures of the valve area before I put it all back together. Oops.

If you do get information on the head that is allowed to be shared I would be interested in seeing it. I had talking to John years ago and was going to buy one of his heads... but then all that crap about some one stealing his work came up and he disappeared.

Ah well.
_________________
1982 924
1987 928S4
Parts Parts Parts and More parts.
E-mail me for parts you need!
Drive Fast!
Back to top
View user's profile Send private message Send e-mail Visit poster's website
ideola  



Joined: 01 Oct 2004
Posts: 15505
Location: Woodstock IL

PostPosted: Fri May 23, 2008 12:14 pm    Post subject: Reply with quote

Eturbo924 wrote:
I thought Johns work was on the 931 head?

Nope, actually, all of his work was on the NA, although he claims there would also be some gains on the 931 as well, but not as much since it was already somewhat improved from the factory over the NA. The threads above are definitely worth a re-read...
_________________
75 Fiat X1/9 | 80 US 928 | 80 US 931 '941' | 78 D-Prod Replica | 78 Poli-Form
Back to top
View user's profile Send private message
MattN  



Joined: 25 Mar 2008
Posts: 34
Location: Manchester England

PostPosted: Mon May 26, 2008 4:07 am    Post subject: Reply with quote

Thanks ETurbo924 it's good to hear that someone has had some success with recessing the valves (even if the results are from the seat of the pants dyno)

I'm sure that Jon will make the information for the 924 N/A head readily available, and I will post pics etc of how I get on when I customize my head.

The drop in CR had occured to me, I might think about skimming 1mm or so from the block to up it a bit.

I'm still very interested in reading more about performance tuning, can anyone suggest any books or even other websites they have used?
_________________
1981 924 N/A
Back to top
View user's profile Send private message
Display posts from previous:   
Post new topic   Reply to topic    924Board.org Forum Index -> Performance Upgrades All times are GMT + 10 Hours
Page 1 of 1

 
Jump to:  
You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot vote in polls in this forum


Powered by phpBB © 2001, 2005 phpBB Group