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Tiny
Joined: 10 Apr 2006
Posts: 502
Location: London, UK
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 Posted: Tue May 25, 2010 11:32 pm Post subject: |
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Hi RC and thanks for posting,
Yes that was the idea to get a new cam too, and I thought I could - but enquiring with Piper, and got a flat NO. They said they don't do any new camshafts for an AUTO 924 as they are apparently totally different - he said AUTOs are different because something to do with vacuum. I can't remember exactly.
So I was thinking perhaps changing the lifters lone might take up a bit of wear and quieten the top end - but now I see your point re worn cam surface.
Tiny
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*****1981 - 924 - Auto - London, UK****** |
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Rasta Monsta
Joined: 12 Jul 2006
Posts: 11723
Location: PacNW
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| Posted: Tue May 25, 2010 11:36 pm Post subject: |
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Tiny, Integral Cams has a replacement stock profile.
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Toofah King Bad
- WeiBe (1987 924S 2.5t) - 931 S3
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ideola
Joined: 01 Oct 2004
Posts: 15548
Location: Spring Lake MI
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| Posted: Tue May 25, 2010 11:45 pm Post subject: |
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There is no mention of a different cam profile for an Automatic 924 in PET. In fact, the NA and 931 have the same profile.
I have a very good condition, very lightly used (only 10K miles) stock camshaft available if you're interested.
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erstwhile owner of just about every 924 variant ever made |
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Tiny
Joined: 10 Apr 2006
Posts: 502
Location: London, UK
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| Posted: Wed May 26, 2010 4:45 am Post subject: |
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Thanks - I only looked here in the UK, due to shipping costs on that weighty lump...
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*****1981 - 924 - Auto - London, UK****** |
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ideola
Joined: 01 Oct 2004
Posts: 15548
Location: Spring Lake MI
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| Posted: Wed May 26, 2010 4:51 am Post subject: |
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Can probably be shipped via USPS to the UK for ~$60, will have to double check on exact weight...
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erstwhile owner of just about every 924 variant ever made |
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RC
Joined: 25 Mar 2007
Posts: 2636
Location: Australia
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| Posted: Thu May 27, 2010 2:15 am Post subject: |
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| Tiny wrote: | | Yes that was the idea to get a new cam too, and I thought I could - but enquiring with Piper, and got a flat NO. They said they don't do any new camshafts for an AUTO 924 as they are apparently totally different - he said AUTOs are different because something to do with vacuum. I can't remember exactly |
This is one of those cases where all the info given you is correct, although it appears contradictory. Will try to explain.
First off, yes the same cam is used in auto & manual NAs as well as the turbos, well except the very early 76 - 77.5 USA motors, but dismiss that. IIRC duration @.040", 1mm, is 222* and lift 11.9mm. Anything "hotter" has more duration, and more overlap. This moves the powerband up the RPM scale, at the expense of low & mid range, and may produce more maximum HP. However like most things in life it is a compromise, nothing is free and no cam will increase torque everywhere. Not talking VVT, just fixed timing.
IIRC Piper has 2 grinds, both with more duration. Without looking it up, they estimate something like 5Hp gain & 8Hp gain respectively. Unlikely to even get that without other mods, head, CR, exhaust headers. Anyway you will lose low - mid torque to gain some at higher RPM. Torque X RPM = power.
I know there is a stock torque curve posted here somewhere but search and impatience have failed me. Bugger it, wait for an upload. waiting ....
See how max Tq is around 3.5K and max HP at 5.8K. Torque is fairly flat and very close to max @ 2.5K. Few different torque converters for various MY but they range between 2400 - 2800 RPM stall speed. They also hydraulically multiply the torque by 2.1 - 2.5 times, however easiest to just think of them as a hydraulically coupled clutch. Below stall they have some slip but not sufficient for much drive. So at idle in D the car slowly creeps forward. Say you`re at the lights, go green, right foot down, RPM increases, fairly quickly approaching stall speed, drive connection becomes much more positive at say 2.5K and off you go. Keep foot down and car accelerates as revs increase. The cam and torque converter are designed to work in harmony. You NEED the torque from 2.5K to accelerate the fastest. A stock trans will change at 5800 - 6000 RPM, same as maximum power.
Now imagine a warmer (hate these BS terms hot, warm, etc but easier for general communication) cam that moves the Tq curve to the right, say 1000 RPM, from 3.5 - 6.8K In reality though it wont be the same curve as it will be much less down low and hopefully a bit more up top. With the torque converter connecting at the same 2.5K theres hardly much power available but you move forward, loading the engine. Slowly at first, bit faster, 3K now, eat lunch, coming, coming, 3.5K ooh here we go. Exaggeration of course but thats what happens. A little more power at 6K is irrelevant since the auto just changed gear, but it took an extra second or two to get there. With an even hotter cam the acceleration becomes even worse.
Presuming acceleration with drivability is the goal? Yes, a hot cam may give a slight increase in top speed but where can you do 200KmH in the UK? With a "hot" cam in a manual, the engine can be revved to 3K, 4K, 5K, and the clutch dropped or slipped, all depending on the particular cam`s profile, the driver, the situation, etc. A kamikaze N to 1 or D @ 4 or 5 K will spin the wheels but not for very long.
A high stall converter will really help acceleration, on a stock cam, and is really a necessity for anything warmer. Nothing however will compensate for a bad decision on a hot cam with practically unusable high powerband.
Besides all that there is also the vacuum issue. As most know, a hot or "lumpy" cam will result in a more erratic idle and a loss of manifold vacuum. The vacuum will also be lower throughout the whole rev range. (well higher MAP actually as vacuum is displaced air pressure) This is no drama for a good EFI but is for a carby and absolutely detrimental for the CIS. Less vac, less AFM plate movement, less fuel, less air, less power. Certainly can be tuned around somewhat but will never be as efficient as a stock cam with stock CIS, as Porsche designed it.
A cam suitable for a stock auto will not have much more duration than stock but individual in & ex timing will be changed, generally advanced slightly, and possibly less rather than more overlap. Sort of "colder" than stock. My best recommendation is to contact Steve Gruenwall (don`t think thats spelled right) at Integral Cams USA. Among many others, I am running one of his cams. It is a "modified stock" that has 225* duration, a negligible increase over stock that is primarily for a smoother ramp, better durability, with a decreased lobe centre spacing. Selected for a supercharged auto, ran very well NA for a while before boost was added. Definitely noticeable get up and go from the butt dyno. Smooth idle, revs over 7K with head, springs, headers, but perfect to 6.5K redline on an otherwise stock engine. Not sure of your intentions or budget but would also suggest a higher stall torque converter for the most benefit. To give an idea, stock ROW NA A/T 0-60MPH is 11 secs, and my high stall converter brought that down to around 9 secs, and cam much closer to 8. Having a read through the Integral Cams thread will give more particulars.
Have BTDT with a few different cams and A/T so speak also from experience. Sure I have the world`s fastest 924 2.0L auto to show for it. Might put that in my sig line, and waiting for anyone to prove otherwise.  |
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ideola
Joined: 01 Oct 2004
Posts: 15548
Location: Spring Lake MI
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| Posted: Thu May 27, 2010 3:08 am Post subject: |
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Awesome stuff Roger!
And yes, you should change your sig 
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erstwhile owner of just about every 924 variant ever made |
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peterld
Joined: 10 Dec 2006
Posts: 946
Location: Noosa Heads QLD Australia
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| Posted: Thu May 27, 2010 5:50 pm Post subject: |
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+ 1 to Dan's comments.
Rog... a splendid, concise and informative synopsis...as usual. Wish all the newer, younger guys on the Board get to see it.
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Tiny
Joined: 10 Apr 2006
Posts: 502
Location: London, UK
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| Posted: Thu May 27, 2010 8:33 pm Post subject: |
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Well....what a truly great explanation. I take my hat off Rog, and agree with Peter too. Brilliant!
Thank you very very much.
Tiny
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Lizard
Joined: 03 Nov 2002
Posts: 9364
Location: Abbotsford BC. Canada
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| Posted: Fri May 28, 2010 12:19 am Post subject: |
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Keep in mind with the stock cam profile from that 222 duration and .475" lift makes for a VERY sharp nose on the cam.
Now does anyone know what the LSA of the stock cam is?
There is power to be had if the LSA is around 110-114. If it is 114, you could get away with around a .460" lift and 230 duration @ .050" which would give much better breathing, and with a 114 LSA would produce only around 1-1.5 deg of overlap. With that type of a profile it would also be easier on the valve springs and stock springs could be used.
The thing to realise is that overlap does hurt getting a perfectly smooth idle. But it does actually lower the rpm of the torque peak (as does a lower LSA). But overlap tends to increase peak TQ. The caveat on that is that you do need a decent exhaust to take advantage of it.
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RC
Joined: 25 Mar 2007
Posts: 2636
Location: Australia
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| Posted: Fri May 28, 2010 9:03 am Post subject: |
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Cheers Pete & Dan.
| peterld wrote: | | Wish all the newer, younger guys on the Board get to see it. |
ROFLMFAO. Most are too lazy or stubborn to search and think this board is full of parrots who like continuously repeating themselves. Particularly the above post which is bordering on O/T in a thread on buying lifters, will not magically pop up. Then these noobs just post something like "gona put a hot cam & turbo in my auto", so no one bothers replying or if they suggest to use search only get verbally abused.
| Steve Gruenwald, Integral Cams wrote: |
Hi Roger:
Yes, I agree. I wouldn't go any bigger than a stage 1 cam with an automatic transmission.
Also, I would like to grind it on the wider lobe separation angle that we do the turbo cams on.
I checked with the Post Office and the cam is too heavy for first class mail. The cheapest
route is through the US Post Office via Priority Mail International which takes 6 - 10 days and
costs $72. The costs for the cam would be:
-$330 for the new cam
-$72 for shipping
-$402 total.
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| Quote: | Hi Roger:
We grind the NA cams on 110 lobe centers and the turbo grinds on 112 and 114 lobe
centers. The improved stock cam is designed to be a modern design upgrade to the stock
cam so it would be a good pick especially if you want the most low end torque. I would
recommend grinding it with 112 lobe seperation. Generally, you want less overlap with a
forced induction application because there is less blow through at TDC and you get a gain at
every rpm. I think going to 114 lobe separation will probably be a little too much because the
intake valve will close later and this will shift the power band up which isn't what you want. |
| Quote: | The cam will have the
stock base circle diameter so its no problem to set the lash.
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Tiny
Joined: 10 Apr 2006
Posts: 502
Location: London, UK
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| Posted: Fri May 28, 2010 8:31 pm Post subject: |
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ah you beaut. this thread spoils me. why?
because my toofah is worth it!
thanks RC
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Rich H
Joined: 10 Jun 2007
Posts: 2665
Location: Preston, Lancs, UK
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| Posted: Fri May 28, 2010 8:48 pm Post subject: |
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Tiny,
Got a couple of usable stock cams here somewhere if you need one.
Rich
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1994 Lotus Esprit S4 - Work in progress...
1980 Porsche 924 S2 DITC Turbo - Original spec
1978 Homo-Sapiens - Tired spec
1953 Landrover S1 - Pensioner Spec |
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RT40Corona4AGTE
Joined: 08 Jun 2010
Posts: 1
Location: Rockhampton North, QLD, 4701, AUSTRALIA
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| Posted: Mon Jul 05, 2010 2:16 pm Post subject: |
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| are these still available? even if not as a group buy, but can someone get these as a single set for me at the normal price? |
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ideola
Joined: 01 Oct 2004
Posts: 15548
Location: Spring Lake MI
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| Posted: Mon Jul 05, 2010 11:22 pm Post subject: |
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No, as far as I know, all the sets were sold and accounted for, unless one of the original buyers hasn't installed them and wants to re-sell them.
Newman requires a minimum purchase of five sets to do another production run. However, in the meantime, I have a local company (to me) looking at making a solid lifter. Hope to have more information this coming week.
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