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| Total Votes : 7 |
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78JDG87
Joined: 08 Jan 2009
Posts: 26
Location: Sedona, AZ
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 Posted: Sun Mar 08, 2009 6:45 am Post subject: New Camshaft? |
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I want to do some mild tuning on my 78 and i was looking at a Stage 1 Cam. Basically running everything else stock, except maybe throwing in some SS valves too. Any suggestions?
Stage 1 Cam Seat Duration .015" 268 degrees
.050" 232 degrees
Cam Lift .500"
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1978 guards red 924, stock... for now |
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Paul
Joined: 02 Nov 2002
Posts: 9491
Location: Southeast Wisconsin
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| Posted: Sun Mar 08, 2009 6:48 am Post subject: |
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If you are looking for more bottom end torque, a cam change will disappoint.
_________________
White 87 924S "Ghost"
Silver 98 986 3.6l 320 HP "Frank N Stein"
White 01 986 "Christine"
Polar Silver 02 996TT. "Turbo"
Owned and repaired 924s since 1977
Porsche: It's not driving, it's therapy. |
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ideola
Joined: 01 Oct 2004
Posts: 15548
Location: Spring Lake MI
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| Posted: Sun Mar 08, 2009 8:14 am Post subject: |
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Required Reading
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erstwhile owner of just about every 924 variant ever made |
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tuurbo
Joined: 08 Aug 2007
Posts: 1446
Location: East Windsor, New Jersey
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| Posted: Sun Mar 08, 2009 8:44 am Post subject: |
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Do you want to go faster or do you want to change when, in the accel of your car, you feel you're going faster?
Assuming limited funds and options, I wouldn't upgrade to a cam if going faster was my goal, personally. It's bucks and time and for a small output if you ask me.
I would do a port and polish on the head and maybe upgrade the exhaust. I'd consider carbs or MegaSquirt. Also, make it breathe better. Maybe lighten it up some. Dunno about NA cars so much, I've only had a couple of 924 NAs, but that's where I'd be heading.
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1980 924 turbo, MSD, Meth. Inj, otherwise stock. |
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Paul
Joined: 02 Nov 2002
Posts: 9491
Location: Southeast Wisconsin
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| Posted: Sun Mar 08, 2009 8:56 am Post subject: |
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Cliff notes of above:
HEAD
The next place most folks go to improve performance is the head. Unfortunately, the 924 head is the “Achilles heel” of our platform. It is widely reputed to be the major barrier that prevents all of the usual bolt-on improvements commonly used on other platforms from delivering any measurable improvements (such as cold air intakes, porting, polishing, etc.).
The turbo head is different than the NA, and is only marginally better. Putting a turbo head on an NA can be done, but complicates exhaust plumbing because the manifold ports and bolt patterns are different, and IMO is not worth the trouble. Jon Mitchell in the UK has purportedly developed some modifications for the NA head, but the details are not publicly available at the time of this writing. About the only commercially viable option I know of is the so-called “big-valve” head, available from European Motorworks (formerly Eurorace). Here is the required reading on the short-comings of the 924 head:
Heavy Breather
Cams
Choices
Stay with stock, regrind, aftermarket billet grinds
Evaluation Criteria
There are fairly good options available for cams, from reground cams to complete custom grinds on new billet stock, which can be had for reasonable money. The most important evaluation criterion is where you want the power band. For street use, a stock grind or hot street grind is widely considered to be the best option. For race use, it depends on your venue and where you intend to spend most of your time RPM-wise. Most of the cam grinders offer street, stage I (hot street), stage II and stage III grinds. While there are slightly different profiles available for NA and Turbo cams, the same principals apply. Basically, if you are not building a full-time track car, go with either a stock or hot street profile. Costs are typically less than $400. Be aware that new cams require new lifters.
_________________
White 87 924S "Ghost"
Silver 98 986 3.6l 320 HP "Frank N Stein"
White 01 986 "Christine"
Polar Silver 02 996TT. "Turbo"
Owned and repaired 924s since 1977
Porsche: It's not driving, it's therapy. |
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tuurbo
Joined: 08 Aug 2007
Posts: 1446
Location: East Windsor, New Jersey
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| Posted: Sun Mar 08, 2009 9:29 am Post subject: |
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Paul a port and polish with a good exhaust works to improve performance.
True, a cold air intake might not do the trick - but the port and polish DOES do the job nicely. As you said, the head is the Achilles Heel and porting it can improve performance. It's been done lots with good results.
_________________
1980 924 turbo, MSD, Meth. Inj, otherwise stock. |
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Paul
Joined: 02 Nov 2002
Posts: 9491
Location: Southeast Wisconsin
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| Posted: Sun Mar 08, 2009 9:34 am Post subject: |
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| tuurbo wrote: | Paul a port and polish with a good exhaust works to improve performance.
True, a cold air intake might not do the trick - but the port and polish DOES do the job nicely. As you said, the head is the Achilles Heel and porting it can improve performance. It's been done lots with good results. |
That's been tried by me and many famous tuners including several well known car magazines with very poor results.
If you have found a way that works, please share with the rest of us.
I've been building motors since the 70s.
_________________
White 87 924S "Ghost"
Silver 98 986 3.6l 320 HP "Frank N Stein"
White 01 986 "Christine"
Polar Silver 02 996TT. "Turbo"
Owned and repaired 924s since 1977
Porsche: It's not driving, it's therapy. |
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Rasta Monsta
Joined: 12 Jul 2006
Posts: 11724
Location: PacNW
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| Posted: Sun Mar 08, 2009 10:41 am Post subject: |
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In light of the fact that Integral cams are computer-profiled and flow tested, and the stock cam was drawn on paper in the days before computer assisted design, you have to think there is some improvement over stock.
The other good part of a cam swap is getting rid of your worn out lifters, but the bad part is paying for new ones.
CW around here would be to spend that money on suspension and brakes, where HUGE improvements are quite easy to attain.
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Toofah King Bad
- WeiBe (1987 924S 2.5t) - 931 S3
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tuurbo
Joined: 08 Aug 2007
Posts: 1446
Location: East Windsor, New Jersey
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| Posted: Sun Mar 08, 2009 11:18 am Post subject: |
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Paul I don't have a track record building engines but do I need one to contribute? We're not rebuilding the engine we're just porting and polishing. But since you've said so, perhaps if you did your ports and polish at the same time you rebuilded you couldn't evaluate the results of the port and polish alone as they would be confounded by the fact that you've just rebuilt the engine so you didn't isolate the job? I don't know why yours didn't work. I just can't say.
| Quote: | | That's been tried by me and many famous tuners including several well known car magazines with very poor results. |
I'm sorry I can't account for these results from famous tuners. Did they preserve the stock exhaust? Or change it? Perhaps there were other restrictions after the port and polish that confounded the test? Maybe a poor exhaust setup? Or maybe they tried a bunch of changes at once. I truly don't know because I don't have the articles of which you speak. Like, even famous tuners can fail to control in the need to save labor.
I could see the results in my case because I ran a straight pipe with a big glass pack muffler before and after the port and polish. No cat. It wasn't a bad test.
I acknowledge the real restriction is at the valves, but that doesn't mean flow can't be improved post valve.
I've ported and polished the 1978 unit I used to have, and a '79, and both responded favorably to deburring, porting (mildly making wider) and taking off any rough spots both at the exhaust ports and at the exhaust manifold. I compared before and after and the breathing was markedly improved. This is one of those things where I don't have the cars anymore or I'd show you. BTW I'm not saying it'll work on the turbo and you'd see or feel any difference. I'm just talking the NA.
_________________
1980 924 turbo, MSD, Meth. Inj, otherwise stock.
Last edited by tuurbo on Sun Mar 08, 2009 11:35 am; edited 1 time in total |
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Paul
Joined: 02 Nov 2002
Posts: 9491
Location: Southeast Wisconsin
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| Posted: Sun Mar 08, 2009 11:28 am Post subject: |
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No issue, I never try to argue with anyone and try to state facts.
How did you measure the improvement? In repeated tests in the 80s that involved flow benches and timed runs by Car and Driver and others, led to the conclusion that port and polishing, headers, exhaust did little.
_________________
White 87 924S "Ghost"
Silver 98 986 3.6l 320 HP "Frank N Stein"
White 01 986 "Christine"
Polar Silver 02 996TT. "Turbo"
Owned and repaired 924s since 1977
Porsche: It's not driving, it's therapy. |
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tuurbo
Joined: 08 Aug 2007
Posts: 1446
Location: East Windsor, New Jersey
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| Posted: Sun Mar 08, 2009 11:41 am Post subject: |
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Paul I guess I'm going by what I felt and by what I think were appraisals of how hard the car moved from A to B before and after my single change of that one variable.
Here's someone that did one on our car and found 4% improvement.
http://jenniferandjon.com/ABRacing/index.php?option=com_content&task=view&id=25&Itemid=39
I can't vouch for their work but they tested P&P alone.
I'm trying to state facts too but I have no numbers. I have had, in the past, the disadvantage of not having these articles around to discourage me. Instead I just sorta tried it and liked it. Believe me, I'm more than willing to eat the cost when I do something and it doesn't work or is marginal somehow (e.g., ZMax spent $50 not much good, KN filter $ not much good, MSD no noticeable perf improvement admittedly just feels good).
Unfortunately I don't have a flow bench.   I didn't do timed trials. And now I wish I did - it might be a good writeup. As I said, I can only give you what I did and that it worked. I don't doubt my own subjective evaluation because it was 'noticeable'.
| Quote: |
How did you measure the improvement? In repeated tests in the 80s that involved flow benches and timed runs by Car and Driver and others, led to the conclusion that port and polishing, headers, exhaust did little. |
Oook so I don't know whether changing headers, cat, muffler and pipes at the same time is a good control, but ok. They threw the kitchen sink and a few products they thought would work at it and drew their conclusions. Fair enough. I just don't know which products they put on so it kind of complicates things. Anyway, arguing isn't good, and if it's a matter of degree then, alright. I can accept that. I don't propose that it grabbed my ass and hauled it to the end of a 1/4 mile in 8 seconds, but it worked where 'worked' is defined as 'noticeable'. No argument. Someone else did a different test and found small improvement. I did a controlled one shot (well actually two shot) test and found it improved things to my liking. And I paid zero dollars. To me that's a deal. Maybe the best way to view it is this: What good are burrs and casting marks or imperfections doing for your performance? How are they adding to your efficiency? Just turning the point on it's head. For me it's like repotting your computer board connections if it's 30 years old - you don't need reliability data to know it's a good idea.
YMMV
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1980 924 turbo, MSD, Meth. Inj, otherwise stock. |
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leadfoot
Joined: 11 Dec 2002
Posts: 2222
Location: gOLD cOAST Australia
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| Posted: Sun Mar 08, 2009 6:47 pm Post subject: |
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that's applebits website, he gave up trying to get performance out of an N/A and converted to an LS1.
Best performance mod is weight reduction followed by overbore high compression pistons or forced induction.
Stu
_________________
1981 ROW 924 Turbo -
carbon fiber GT mish mash
LS1 conversion in progress... |
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Cedric
Joined: 27 Aug 2004
Posts: 2616
Location: Sweden
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| Posted: Sun Mar 08, 2009 7:10 pm Post subject: |
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A correct port job will do difference in any car, if you do it rigth, wich isnt easy.
If i had a us engine the first mods i would do is to get hold of euro spec pistons for example. Not that expensive and guaranteed performance increase 
_________________
1980 924 Turbo
www.instagram.com/garagecedric/ |
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RC
Joined: 25 Mar 2007
Posts: 2636
Location: Australia
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| Posted: Sun Mar 08, 2009 11:26 pm Post subject: |
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Will agree with Cedric`s statements and also back Paul`s stance since i`ve BTDT on a 924 and have much experience on other engines.
The installation of a longer duration cam in an otherwise stock 924 will at best be good for a few HP, like 0-5, and only at high RPM. Expect to sacrifice all low and most midrange torque (hence power) where you need it for acceleration and practically all street driving. If you run on a circle track at > 5KRPM there MAY be some minor benefit.
The OP has not specified his year/model/spec, so will lie between the 95Hp (US, Ca) small valve smog engine and the 125Hp 9.3:1 Euro/ROW spec. IMO it is a waste of money even considering a cam change in any less than a well tuned 125Hp motor.
Having tried various cams, intensive headwork and installed headers with 2.5" exhaust would only give a COMBINED power increase of 10% maximum. As recorded by my butt dyno. Gains from any individual modification is negligible and only of any benefit as a package. The CIS system and AFM restriction then becomes the major impediment.
Unless you are prepared to watch your bank balance decline faster than your 924 goes, spending less money than a cam on maintenance and a thorough tune is your best move at this early stage. |
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Scorpio
Joined: 05 Jul 2007
Posts: 1957
Location: Brisbane, Australia
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| Posted: Sun Mar 08, 2009 11:46 pm Post subject: |
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waste of money...dont do it unless youre rich...which you cant be otherwise you would have just bought it tested it then thrown it out when the toyota camry takes you out at the lights.
If you want an extra few horsepower top end, remove all your sound deadening rubber and wear 20 cent earplugs
TURBO stop causing trouble... everyone knows a port and polish is a waste of grinding stones, sand paper and time on a stock engine...  couldnt help it...hahhaa
_________________
1979 NA
MS1..EFI..
GARRETT T25 TURBO
BILSTEIN SHOCKS
GT BASED CUSTOM BODYKIT
Brisbane , Australia
Think mean think fast
all youll see is
my Porsches Arse!!! |
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