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Power thru 'special' upper cam shaft timing gear.
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newbie924  



Joined: 16 Mar 2016
Posts: 75
Location: EUROPE MALTA

PostPosted: Sat Nov 24, 2018 7:15 am    Post subject: Power thru 'special' upper cam shaft timing gear. Reply with quote

I do not have much mechanical knowledge therefore If I am writing something non existent please forgive my ignorance yet I read somewhere, not sure where though that there is some sort of camshaft timing gear which by itself in some way increases power .. does anyone have any idea about this or heard of it also. Cheers.
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Fifty50Plus  



Joined: 28 Feb 2008
Posts: 1013
Location: Washington DC area

PostPosted: Sat Nov 24, 2018 8:13 am    Post subject: Reply with quote

There are keys that allow you to advance or retard the cam several degrees. If you advance it, you have more low end torque and lose some top end. If you retard the cam, you gain top end power but lose on the low end. There is no free lunch that gets you both mechanically. (Hydraulics on some modern cars allow the cam to advance and retard while running)
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1979 924 NA race car
1982 924 NA race car - Sold
1982 924 Turbo almost a PoS
1981 924 Turbo a real PoS, new engine
1982 924 Turbo nice body, blown engine
1972 911 E race car - going to Vintage
Various 944s to become IT-S race car
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newbie924  



Joined: 16 Mar 2016
Posts: 75
Location: EUROPE MALTA

PostPosted: Mon Nov 26, 2018 10:28 pm    Post subject: Reply with quote

Do you have to have a 'special' upper cam gear that go with these keys or can this be done on the factory fitted cam gear? Im actually running DCOE Webers and to be fitting a Piper cam also.. would these adjustments effect the Piper cam timing when this is installed. Anyone? Thanks.
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Fifty50Plus  



Joined: 28 Feb 2008
Posts: 1013
Location: Washington DC area

PostPosted: Tue Nov 27, 2018 2:43 am    Post subject: Reply with quote

The key I was referring to is known as an offset Woodruff Key and fits in the stock camshaft and cam gear.
Another option I failed to mention earlier is an adjustable cam gear which allows you to advance or retard the cam timing by loosening bolts that hold the outer ringed teeth to the center of the cam gear.
If you can measure the performance differences by adjusting the cam gear advanced and retarded you can decide which option best meets your driving needs.
The offset Woodruff Key is non adjustable but will provide the fixed degree of advance or retard (it fits either direction in the cam slot).
Either would work with the Piper cam but you still need to make the determination whether you want some advance or retard - or neither.

Just slapping a cam and some Webers on a 924 won't necessarily gain you any performance or drivability without measurement, experimentation and tuning (carbs require knowledge of air correctors, mains, emulsion tubes, choke sizes and the affect they have on CO readings -you do have a wideband CO guage correct?)
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1979 924 NA race car
1982 924 NA race car - Sold
1982 924 Turbo almost a PoS
1981 924 Turbo a real PoS, new engine
1982 924 Turbo nice body, blown engine
1972 911 E race car - going to Vintage
Various 944s to become IT-S race car
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newbie924  



Joined: 16 Mar 2016
Posts: 75
Location: EUROPE MALTA

PostPosted: Tue Nov 27, 2018 4:54 am    Post subject: Reply with quote

As it is with the webers I kind of felt a bit of difference, better throttle response maybe(?). Obviously I am not trying to compete in or win a 24 Hr Le Mans, just want to have some weekend fun with it if possible. I will leave the fine tuning of webers , jets etc to my tuner/mechanic although he has already gone thru these after installation and some minor trials he done in the closed industrial area where he is located. I am sure that after the cam is fitted further experimenting and tuning will be a must. I think that the adjustable cam gear you mentioned comes with the Piper cam since without it the proper timing cannot be reached. Thanks for your advise Fifty50Plus, its much appreciated. The 924 is becoming a lovely little car to play around with, and I always look forward to those Saturdays so that I can do some body/paintwork on it. Hope it will keep me occupied for some time too.
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safe  



Joined: 18 Mar 2017
Posts: 21
Location: Sweden

PostPosted: Tue Nov 27, 2018 11:37 pm    Post subject: Reply with quote

Webers (or ITBs really) is nice for the throttle response and lower restriction from the air-plate.
But what these engines really need is a bump in compression (above euro) and to have their internals balanced. Then you get a pretty sweet engine that revs smoothly and doesn't feel like it's gonna go to pieces above 5500.
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newbie924  



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PostPosted: Wed Nov 28, 2018 5:08 am    Post subject: Reply with quote

safe.. during the last weekend I assure you we have revved the engine over 5500 rpm for many a time.but it never felt it was going to pieces. I'm sorry i don't agree with you on this one. Although i agree 100% any interior mods would definitely help. Unlike other engines I have hd modified, its a pity one has to completely dismantle the lower engine section to increase compression on these engines.
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CÚdric  



Joined: 27 Aug 2004
Posts: 1766
Location: Sweden

PostPosted: Wed Nov 28, 2018 6:14 am    Post subject: Reply with quote

The 924s I've driven have revs pretty smoothly aswell up to redline, not like an inline 6 but similar to man other 4cyls. The power drops of a bit at the top end though on the n'a with standard cam. How long are your total intake length with the webers? That affects the power curve significantly.
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Fifty50Plus  



Joined: 28 Feb 2008
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Location: Washington DC area

PostPosted: Wed Nov 28, 2018 6:27 am    Post subject: Reply with quote

I race a '79 924 in SCCA and raised the compression ration one half point, installed an MSDS header and modified the fuel flow to get 12.8 CO while running. I turn this engine quite often between 6000 and 6500 and have done so for the past several years with no issues. Unfortunately the stock cam becomes pretty much torqueless above 5800 and the induction really sucks (pun intended). I use the higher revs pretty much to avoid a shift mid-corner.
The bottom end of the engine is pretty much bullet proof if you don't suck air into the oiling system while cornering.
_________________
1979 924 NA race car
1982 924 NA race car - Sold
1982 924 Turbo almost a PoS
1981 924 Turbo a real PoS, new engine
1982 924 Turbo nice body, blown engine
1972 911 E race car - going to Vintage
Various 944s to become IT-S race car
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newbie924  



Joined: 16 Mar 2016
Posts: 75
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PostPosted: Thu Nov 29, 2018 3:54 am    Post subject: Reply with quote

CÚdric wrote:
The 924s I've driven have revs pretty smoothly aswell up to redline, not like an inline 6 but similar to man other 4cyls. The power drops of a bit at the top end though on the n'a with standard cam. How long are your total intake length with the webers? That affects the power curve significantly.

I will have to measure them up Cedric on saturday when I go do some work on the car, the inlet manifold was bought from the USA. Trumpets are short. Do you want to know the length from trumpet end to cylinder head side? I have another set of longer trumpets also but these were removed from another set of webers.
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newbie924  



Joined: 16 Mar 2016
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PostPosted: Thu Nov 29, 2018 3:57 am    Post subject: Reply with quote

Fifty50Plus wrote:
I race a '79 924 in SCCA and raised the compression ration one half point, installed an MSDS header and modified the fuel flow to get 12.8 CO while running. I turn this engine quite often between 6000 and 6500 and have done so for the past several years with no issues. Unfortunately the stock cam becomes pretty much torqueless above 5800 and the induction really sucks (pun intended). I use the higher revs pretty much to avoid a shift mid-corner.
The bottom end of the engine is pretty much bullet proof if you don't suck air into the oiling system while cornering.

If I understand correctly from posts here, the bottom end is strong enough to withstand a certain amount of turbo /supercharger boost.. something some other engine types dont handle and sometimes require balanced or hardened race parts.
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Fifty50Plus  



Joined: 28 Feb 2008
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Location: Washington DC area

PostPosted: Thu Nov 29, 2018 8:14 am    Post subject: Reply with quote

The bottom end of the NA and Turbo are identical internally and strong like bull. Same block, same crank, same rods, same bearings. Pistons and head are different for the turbo version. If you want to boost an NA, you must at least change the pistons to a lower compression ratio over stock.
The turbo pan has an extra hole for oil return from the cooler.
_________________
1979 924 NA race car
1982 924 NA race car - Sold
1982 924 Turbo almost a PoS
1981 924 Turbo a real PoS, new engine
1982 924 Turbo nice body, blown engine
1972 911 E race car - going to Vintage
Various 944s to become IT-S race car
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nickthompson  



Joined: 26 Mar 2013
Posts: 863
Location: Central Georgia

PostPosted: Thu Nov 29, 2018 1:14 pm    Post subject: Reply with quote

The stock compression at it's highest in a 924 is 9.3:1. I'd say that's pretty boostable. The 1.8t VW/AUDI has 9.2:1 and people run 16 PSI boost in those engines.
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safe  



Joined: 18 Mar 2017
Posts: 21
Location: Sweden

PostPosted: Thu Nov 29, 2018 8:40 pm    Post subject: Reply with quote

newbie924 wrote:
safe.. during the last weekend I assure you we have revved the engine over 5500 rpm for many a time.but it never felt it was going to pieces. I'm sorry i don't agree with you on this one.


I have too, but it really feels like the van-engine its rumoured to be (I know its not), not the sports car engine that it can be. Properly balanced its effortless to well above 6500.

Maybe I'm unlucky I'm only tested 2 cars with 4 different engines.

Cedric: I know we disagree on this, but I think they are next to horrible in stock form. Not saying they are slow or gutless, the engines are pretty good power vice, but they are too rough for my taste.
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safe  



Joined: 18 Mar 2017
Posts: 21
Location: Sweden

PostPosted: Thu Nov 29, 2018 8:47 pm    Post subject: Reply with quote

nickthompson wrote:
The stock compression at it's highest in a 924 is 9.3:1. I'd say that's pretty boostable. The 1.8t VW/AUDI has 9.2:1 and people run 16 PSI boost in those engines.


I agree!
I have an NA engine that's going to be boosted, if I can find some usable pistons or a solution for worn ring grooves...
Worst case (which is only worst for the wallet) I buy new JEs, but then it will be delayed for other projects.

I think that a reduction to 9:1 would be good, but that is achievable with a thicker head gasket.
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