ALEX P

I spoke to Steve Weiner who advised that:

1. If using 993 RS valves, larger seats need to be installed which isn't cheap.
2. If installing larger intake valves you should install the 993 exhaust valves & seats as well.
3. You will see no benefit from the valve change unless you use RS cams.
4. Together they are worthwhile doing but different software is also needed for the cams.

So - my cams definately need regrinding due to worn pitted lobes but not really sure which profile to go for - do the valves make a big difference or are they just a few extra HP if you increase their size?
I can't figure out if it's worth the extra cost or not?

Jimjacqmx5

I have standard sized valves and put a Dougherty DC21 camshaft.
This is ground on a standard lobe centre and gave me a 15kw increase at the wheels.
I am expecting more (hopefully another 10kw) once my new re-calibrated chip arrives.
FWIW, My car with these cams in a fresh engine, aftermarket chip,EVOMS pod intake, 100cell CAT and primary bypass made 215kw crank or @170kw at the wheels.
In this spec, it ran a mid 12 down the quarter.... 0-100 in mid 4's. One up with half a tank of gas.

johnsjmc

Intersting info from Mr Weiner. I am certain he posted somewhere here that he changed the intakes without the exhausts or the need for new seats. What did he say about the original issue about the cylinder and head gasket mods?

Jimjacqmx5

For parts, I have found EBS racing in the US also has great prices and their customer service is fantastic. I use them now as my first point of contact for parts as 90% of the time, they are the cheapest and the quickest. Speak to Troy Chapman.
As for the Cams. John at Dougherty Cams is a great guy to talk to and very patient, no matter how many silly questions you ask him!

johnsjmc

Your cams can be reground to RS specs; I use Webcam for that service.

I do stock RS intake valves since we do a lot of these conversions and the seats must be remachined to use these. Use the stock exhaust valve size.

Don't touch the ports! RS heads do have bigger ports but not needed for any street use. These are also different castings since the regular 993 versions are too thin to enlarge to RS spec.

Replace the lifters as you will soon do that anyway. I would recommend retaining the hydraulic lifters in anything but a dedicated race engine. New cams should get new rockers, too.

Hope this helps,
This was posted by Steve Weiner 10-21-2008 "Thread '95 Rebuild Options"
He also pointed out somewhere else that the relief in the piston needed to be altered to match the larger intake dia.

falcor

215 vs 170 ??

So you're loosing 45kW in the gearbox and between the wheels and the ground...? sounds like a too high amount of loss *confused*

ALEX P

Jimjacqmx5 - The Dougherty DC21 on a 114 lobe centre is the one that I'm leaning towards. How do you find yours at idle and at low speeds/RPM?

falcor - sorry I can't help as I'm not sure what the loss percentages are.

johnsjmc - I asked Steve about this and he replied that the stock sized exhaust valves are all you need unless it's a race engine, in which case the larger exhaust valves will help.

What I need to do is measure my valves to see if they are within limits or not. Same for the crank. The problem that I've got is that the Wayne Dempsey engine rebuild book has all the dimensions for engines up to 1989 3.2's but I don't know where to find out the information for 964's - Does anyone have this or have any ideas where I can get it?

ALEX P

I had a measure of the crank at the weekend using digital vernier as I don't have a micrometer that size. I put the results against the dimensions in the book but the main bearings and the rod bearings while being consistant, don't measure up as per the 3.2 crank unless mine is undersize?

On a seperate note - Does anyone know what the part number is for ARP rod bolts to replace the standard items?
I've had a look and think it's 204-6005 but want to confirm before I order the wrong ones!

Also - How much difference is there between steel and titanium valve spring retainers? (apart from about $300!)

ALEX P

I spoke to Ninemeister briefly today to try to get a rough cost estimate for refacing the heads, recutting the valves and replacing the valve seats. The advice I got over the phone was that I could quite possibly LOSE power if I enlarge the valves!!!

On their own manufactured heads the valves are actually slightly smaller than standard and are supposed to give good power increases.

Wow, it get's really confusing when you've got two completely different opinions from two different experts. Makes it tough to make a call either way - Very frustrating.

Greg964

Try this book;

http://www.bentleypublishers.com/por...guesswork.html

92silver964

I hear you - very difficult to figure out and move ahead. A big reason why my rebuild has taken so long. Good luck!

NineMeister

Here's my opinion for what it is worth:

1. Leave the engine standard unless you intend to upgrade the engine management. Stock engine on Motec makes more hp & accelerates faster than a cammed engine on 964 motronic.

2. Larger valves increase the "curtain area", which means that you potentially get more flow for any given valve lift - so in theory you could gain power with a stock cam and larger intake valve. In practise you won't unless you address 1.

3. 964 exhaust valves are large enough for the displacement and performance that you will likely achieve. In fact, they could do with being smaller.

4. If all the valves have to be replaced due to wear you could consider fitting a 993 set which will fit the existing seats. Intake would be 50mm, exhaust 42.5 - the major advantages are narrower seats, thinner 8mm stems & lighter weight.

5. Looking at your engine photos, I would buy a brand new set of OE pistons & cylinders before you think about any "tuning" options. The heads would have to be machined to fit these - but they need machining anyway....

6. If budget is then running out, fit a pair of used stock 993 cams rather than having yours reground.

7. When you later decide that you want more power, fit Motec to your perfect engine & you will gain 10% over the stock Motronic.

ALEX P

Hi Colin, thanks for the detailed reply :

1. I do intend to get the car live remapped when the engine has been run in - is that what you mean or is it a physical limitation of the motronic system?

2. Does this mean that if I change the cams and inlet valves to the RS spec/size and remap the motronic there should be a useful gain?

3. Ok - the exhaust valves will remain stock dia, the question now is about the inlet valves and whether it's worth increasing to the RS size.

4. I hadn't really considered the lighter 8mm 993 stock dia valves as an alternative. Could be a good compromise, thanks.

5. Why would you replace the P & C's that I have? The bores in the cylinders seem fine, as do the pistons - the only real issue I know of is that they are the earlier type with no sealing gasket?

If changing the P&C's why would you go for OE rather than the seemingly more popular JE / Nickies type route?

If replacement is required (and from my wallets point of view I seriously hope not) then surely it would be worth considering a 3.8 conversion compared to brand new OE.

6. I hadn't really considered using 993 stock cams. Again, it could be a good compromise. I presume it would also involve resurfacing or replacing all of the rockers to suit so may not be a huge difference in cost when all put together.

Thanks again for the advice Colin, it is much appreciated.

Jimjacqmx5

The DC 21 Cam is fine at idle and low rpm.
And the 215 crank vs 170 crank. I was advised by Porsche cars Australia on their dyno-dyamics dyno that they use a 1.32 multiplication factor to calculate crank kw from rwkw.

NineMeister

1. Easy answer, based on actual tests on our dyno (numbers obviously vary between dynos, but differences will be the same).
Max power of perfect standard engine running remapped 964 Motronic = 300-305hp.
Max power of modified engine with cams + ported heads on 964 Motronic = 305-310hp
Max power of 3.8 engine on remapped 964 Motronic = 305-315hp
Max power of perfect standard engine on 9m Motec = 330hp.
Max power of modified engine with cams, ported heads, 993 valves on 9m Motec = 350-355hp.

In my view it is a completely pointless doing to do any modifications from standard unless you have future plans to address the bottleneck in the system, irrespective of whether you remap it or not.

2. Depends if you deem 5-10hp useful.

3. Worthwhile gains will be made on the flowbench, however to date I have never seen a flowbench make power on a dyno.....

4. Need 993 valve guides, stem seals & of course keepers and retainers to match. All parts lighter than the 964.

5. You need to replace the cylinders because they will never seal effectively to the head due to the design causing distortion on assembly. Since you will also need rings it makes sense to buy a new set of everything and have a zero risk solution.

JE & Nickies are ok for racing but do not have the optimum tolerances & materials for road use, nor will they make more power. Again, for reasons explained in 1. the most efficient engine (power/economy/longevity) is to keep the engine stock and get the best from it in other ways.

6. Whilst definitely not ideal, when looking for economic solutions for customers I have often run used 993 cams with used 964 rockers and have seen no longterm problems. For stock(ish) engines £225 a pop 9m billet rockers are definitely overkill; since new stock cast rockers are now £70 each we considered refacing & rebushing stock rockers, however we do think the optimum solution is to make a lower cost, lightweight forged & bushed rocker to our own design which will sell for around £80-100. These would be ideal for RS, Cup & all fast road and race engines running below 8000rpm & with 13mm or less lift, only problem is that I need to save up the funds to have the forging tools made....