Early vs. Late Cam

[loftygoals]

Just realized that the early and late cams are different.

 

 

I confirmed this looking at the cams out of my 1983 944 and my 1987 924S.

 

The 1983 was stamped: 155.05

The 1987 was stamped: 155.09

 

Since we can update and back date, I can throw the late cam on my early motor. Interesting!

[cbuzz]

You want the late cam for all 944 motors.

[Spec944#74]

You want the late cam for all 944 motors.

 

Does the late cam work ok with the early ECU?

[cbuzz]

Yes, the ECU does not care what cam is there. The late cam has a better profile.

[loftygoals]

Yes, the ECU does not care what cam is there.

 

He's right. Guy run late motors with early DMEs all the time.

 

The late cam has a better profile.

 

Yep. I was surprised to find this out. I had never seen anything about this on the Spec forums.

 

So the best spec legal motor would be an 83 factory cross drilled and forged crank, 88 pistons, and a late cam.

 

I still need to research what's the best DME/AFM/injector combo. I'm guessing it would be early DME/early AFM/late injectors. This would lean the mixture out a bit. It might make a few more ponies. I'd need to do a little more research to see if the impedance is the same, though. I would also need to do some dyno runs to ensure it doesn't make it go too lean.

 

-bj

[944-Spec#94]

I have never quantified any difference in the output of each cam profile.

 

So don't expect a big change if you change cams. That said I can only guess the late cam is better.

[cbuzz]

Be careful you may end up with more than 135 rwhp!!!!!

 

Then you can be called a cheater for maximizing your car.

 

We will welcome you to the club though.

[loftygoals]

I have never quantified any difference in the output of each cam profile.

 

So don't expect a big change if you change cams. That said I can only guess the late cam is better.

 

I'm not expecting a big change. Maybe a horse or two, maybe nothing. The fact the later cam has a little more lift and duration is probably worth something, though.

 

If found this that breaks it down a bit: http://members.rennlist.com/951_racerx/CamProfiles.pdf

 

 

Be careful you may end up with more than 135 rwhp!!!!!

 

When I first built the car, I did nothing to the 160k motor except reseal the front, change the belts, and add an oil cooler. That motor was good for 134RWHP. I'd be happy just to see that number again.

 

My current motor is the same 83 block with the nice crank, new rod bearings, and all the matching 83 DME/AFM/injectors. I'll be installing a late cam with all new lifters on to a freshly rebuilt head with a stock valve grind and the steam vent. So it's almost a full rebuild, minus the crank bearings, new rings, and balance bearings.

 

Maybe I'll look for a set of 88 pistons for 2012. I think that would be a motor built to the full extent of the rules.

 

Of course I still need to do the early vs. late fuel injector testing... Man I wish I could afford to buy a dyno for the shop! I do like having a 83 DME, because the 1983 DME doesn't have a replaceable chip. At least that keeps someone from accusing me of having a custom tune.

 

-bj

[kbrew8991]

maximizing your car

that kind of maximization is why you see $30k Spec Miatas fwiw.

[Sterling Doc]

There are also early and late heads. The late head has a bit less shrouding of the valves, but again, the significance is clear.

 

The late computers allow a few more revs: 6640rpm vs. 6480rpm. This allowed the 944, on stock tires, to reach 60 in 2nd gear, which was good for magazine 0-60 quotes. . It allows about 2 more MPH in 3rd gear, for example.

Lots of subtle changes through the years.

[loftygoals]

There are also early and late heads. The late head has a bit less shrouding of the valves, but again, the significance is clear.

 

Hmmmm... Hadn't checked the casting number on my heads yet. I believe I have a late head going on the car. Thanks for the info!

 

The late computers allow a few more revs: 6640rpm vs. 6480rpm.

 

That's interesting, too. This makes me want to do even more dyno testing. I have a 87 924S I can swap the electronics from.

 

This all makes it sounds like best 944 Spec candidate isn't a 944, but a 924S. It's a little more aerodynamic, has a short 5th & LSD, late motor, and early suspension (can use cheap control arms and cookie cutter wheels). Just add some 88 pistons and an 83 crank and you might have the ultimate 944 Spec car. Too bad the 924S doesn't look near as cool as the 944.

 

-bj

[cbuzz]

No go on the cookies. The 924s has to use the late offset phone dial wheels.

 

I currently drive the 924s and there is definitely no disadvantage to this car.

 

You do want the late head. The early head has a minor disadvantage. It has sharper edges in the chamber and is a little more shrouded.

[loftygoals]

No go on the cookies. The 924s has to use the late offset phone dial wheels.

 

Really? Is it because with the cookie cutters exceed the maximum track width or because they won't fit under the fenders?

 

-bj

[cbuzz]

Won't fit under fenders without mods.

 

My car has the phone dials and it works just fine. The narrow track and body does seem to provide a better aero package on long tracks like Miller.

 

It does not lack any corner speed either.

[loftygoals]

Won't fit under fenders without mods.

 

That's too bad, because I understand the cookie cutters are lighter than the phone dials. I have a set of both for my early 944. I haven't weighed them, but by hand the cookies feel much lighter.

 

-bj

[loftygoals]

That motor was good for 134RWHP.

 

Doh, I was wrong. Just looked it up: 131 rwhp / 136 rwtq. Still, not bad numbers for a high mileage motor. I hope to make a little more after the rebuild.

 

-bj

[cbuzz]

Mill the head to within .007 - .010 of the minimum thickness according to the new rules.

Use the late cam and head. Be sure the valve job is done by someone who understands the 944 valve train. With fresh rings and head you should easily be able to reach the 140 rwhp mark.

 

A note of caution though. If you are using the 9.5:1 piston motor then the minimum thickness for the head is too thin. It does not allow for the lack of adjustment of the cam belt.

[loftygoals]

A note of caution though. If you are using the 9.5:1 piston motor then the minimum thickness for the head is too thin. It does not allow for the lack of adjustment of the cam belt.

 

 

So is it just a timing issue or an interference issue? If it is a timing, I'm guessing it's probably off by half a tooth--meaning I'd either have to advance or retard the timing half a tooth.

 

-bj

[Sterling Doc]

BJ timing is not adjustable legally at this time. We're working on gathering some data on this, but no changes this year.

 

Yes, an '88 924S makes a very good starting point for a 944 Spec car (it has the '88 piston motor). It does have the smaller, steel tank, and the early electronics. I never got a chance to try fitting late offset wheels under the 924S fenders when I had my '87 924S. It's not illegal to run cookies on them, but fitment appears to be an issue, as Charlie mentioned. The cookies are both lighter and stronger than the phone dials, but not large differences.

[cbuzz]

The problem is that there is not enough adjustment on the early cam belt adjuster to accomodate the minimum thickness stated in the new rules (unless this was changed recently).

 

The 87 and later blocks have a different adjuster and are fine. I do not know what the mimumum head thickness is for the early blocks. I will check around to see what I can find out.

 

The best possible cam timing is factory stock. Porsche had already maximized this. By shaving the head it does retard the cam timing slightly changing the power curve. The benfit of the increased compression is still worth the trade off.

 

It may be possible to put the Cookies under the 924s but I have never tried it either. It would require bulging the fenders a little and running more camber. If you have a set give it a try. Not sure if this violates any rules.

[Sterling Doc]

Here's the applicable rule:

 

924S models may increase stock width by use of updated suspension components or adding

spacers providing that the tires do not touch the fenders or springs at any point in the

suspension travel.

 

They are of course still subject to the maximum track width rule.

[loftygoals]

The problem is that there is not enough adjustment on the early cam belt adjuster to accomodate the minimum thickness stated in the new rules (unless this was changed recently).

 

The 87 and later blocks have a different adjuster and are fine. I do not know what the mimumum head thickness is for the early blocks. I will check around to see what I can find out.

 

The best possible cam timing is factory stock. Porsche had already maximized this. By shaving the head it does retard the cam timing slightly changing the power curve. The benfit of the increased compression is still worth the trade off.

 

As I remember, a tooth is worth about 6 degrees. Assuming a retard of 3 degrees, that wouldn't be bad at all. That would move the torque curve north in the RPM range yielding a little more top end power. Edit: But, it provides slightly less exhaust valve clearance for the shaved head.

 

 

It may be possible to put the Cookies under the 924s but I have never tried it either. It would require bulging the fenders a little and running more camber. If you have a set give it a try. Not sure if this violates any rules.

 

From the rules:

 

14.2 Track Width

The maximum track width for all cars shall not exceed the stock 944 width front and rear. The

924S models may increase stock width by use of updated suspension components or adding

spacers providing that the tires do not touch the fenders or springs at any point in the

suspension travel.

 

and

 

14.9 Rims

Only 15 x 7 inch ATS (Cookie Cutter) or “Phone Dial” stock wheels with offsets of 23.3 or 52.3

mm are allowed. Steel lug nuts must be used. Wheel spacers are allowed as long as the

maximum track width is not exceeded.

 

and

 

16.1.2 Fenders and wheel openings shall remain unmodified. The front fender liners may be

removed or modified. Front and rear wheel fender opening lips may be rolled inward to

maximize tire/wheel clearance. ADVISORY: This may be necessary for the 924S to achieve

its maximum track width.

 

My race car is a 83 944. I do have an 87 924S street car. I'll throw the cookies on sometime to see what it would take to make them fit.

[loftygoals]

Finnally have my top end all ready to go. Thanks for all the information in this thread. It was really help full.

 

 

Early vs. Late Cam

 

Early - 155.05 - Stamp located on the cam between intake and exhaust lobes for #3

Late - 155.09 - Stamp located on the cam between intake and exhaust lobes for #2

 

Late Cam. You can see the end of the number (5.09) in the pic.

 

Early vs. Late Head

 

I noticed several difference. Note: The early head is a from very early 1983 head stamped 82

 

Intake pocket:

The early head has an indentation opposite of where the injector sprays. The late does not.

 

Early head - Notice the pocket at the bottom.

 

Late head

 

 

The early head has an intake pocket volume of 109cc. The late head has an intake pocket volume of 117cc. These are approximate, but there is definitely a big difference. I measured with water and a syringe.

 

Exhaust pocket:

 

I didn't measure, but the late look larger. The early head has a small pocket that the late does not.

 

Early head - Notice the light gray area: that's the exhaust pocket.

 

Late head

 

New Head Thickness Specs

 

I used the new published head specs to deck my head. I had the head decked to .893" (22.68mm) using the factory measurement point. This is 2 thousandths from minimum spec. I wanted 8 thousandths, but I messed up when I had it decked. I knew the measurements in mm, not in inches and screwed something up when I converted it at the shop.

 

 

 

It makes a very noticeable difference. Take notice of the spacing from the decked surface to the intake valve on the two heads:

 

Head removed: 24.15mm

 

New head: 22.68mm

 

 

Oh, I also added a steam vent.

 

Steam Vent

 

-bj

Edited January 12, 2011 by Guest

[loftygoals]

Just wanted to add my costs for my motor freshening...

 

In 2008, I resealed the front of the motor. I didn't see a need to do this again, yet.

 

2011 Freshening Costs

• Late head with stock valve job - $380
  
• Late Cam & Tower - From Spare Motor I paid $300 for - ~$100
  
• Decking to minimums - $70
  
• Head Gasket Set - $100
  
• Rod Bearings and Pan Gasket - $100
  
• Oil Baffle Kit from eBay - $60
  
• Oil Baffle Aluminum Welding - $40
  
• 8 New Lifters - $600
  
• Steam Vent Kit - $100

 

Total: $1550

 

Not bad for a near complete motor rebuild.

 

I had enough good lifters between my original motor and my spare motor that I didn't have to buy new. But when I pulled the the cam tower, three lifters had cracked. One of the three was in split in pieces and chewing up the walls of the cam tower bore! This made me decide to go with new lifters before any others exploded.

 

-bj

[cbuzz]

I am assuming based on your head measurement that you are using a 9.5/1 block and pistons.

 

There are two potential problems you may have created by shaving to near minimum if you are using an 86 or earlier block.

 

The first is not having enough cam belt adjustment for that measurement if using an 86 or earlier block.

 

The second is that you head may measure too thin when torqued down and run through some heat cycles.

 

Please let us know how this works out.

 

My personal measurements on my car indicated that the squish is .007 of the head gasket. After I had run the car at the track. I did not measure before use. Si I do not know if there is a difference between freshly installed and heat cycled.