Porsche Enthusiasts Club Forum

Has anyone had any experience of carrying out a proper port and polish on a NA car? I have an 83' 2.5 8v and would be keen to hear from anyone and there experience and what outcomes they have achieved.

I have renewed most of the service items etc. and reconditioned the injectors. I am not expecting huge gains but a little more power would be nice and from what I have read most of the upgrade cams on the market are only any good at the top of the rev range?

Not an expert but I've read that Porsche did a reasonable job to start with and only very minimal gains to be had. In terms of bang for buck, poor value for money.

Stuart

Yeah, I was also told that on the 2.5 there weren't great gains to be had.
I asked as my head was off at the time so it would have been worth while doing if there were any gains

Yes, but unless you get a decent noticeable gain there's no point in doing it, and as with any N/A engine you'll have to spend thousands to get this.
I did just this and got +40bhp from a Camshaft (With low RPM gains - Web Cams USA) a displacement increase to 2707cc, a stage 2 Flowed rebuild
2.5 head from Lindsey Racing USA (+28% more CFM), honed Inlet Manifold, Zircotec Coated 944T Exhaust manifold and a smaller bore exhaust system etc..
Then 6 hours of Live Mapping!

There's really no point in touching it at all unless you want to have all the above and a rebuild with little change from 10K !

R
http://www.924srr27l.co.uk

I think Roger has put it very well although his car has the added bonus of little weight....you'll have to spend an awful lot of money for little gain. If you want real performance in the 'super car' territory I'm afraid that an N/A 944 is never going to fit the bill. Spend the same 10k that Roger mentions on modifying a 944 turbo and all of your wishes will come true. I have done it, have the T-shirt so to speak and yes it was worth every penny although, to be honest, 10k was spent on only the last round of mods 2 years ago. I have had the car for over 18 years and it has seen a number of transformations and developments during this time which has all added up to the car's performance today, you can add perhaps another 15k to that 10k. The end result is pretty spectacular and the smile that it puts on my face when I hit anything over 1 bar of boost can't be made in many other ways...first love, the birth of your first child....it's that type of a moment. If you do go the porting route be sure to get a company to do it who knows 944's well and don't go mad polishing the inlet side, you need some roughness to help mix/atomise the fuel for a good burn.

Pete

as I thought....

I am not expecting to leave hot hatches in my wake just a tad more power and driveability, I have tweaked the brakes suspension already ....

If you had £500-£1000 burning a hole in your pocket would you do the cam or the port and polish or swap the the afm for a MAF ( lindsey racing package)?

(I have done my driver training btw in case someone pipes up!)

Personally I would go MAF although I know little of what's available for N/A...Cam would be my last choice still having the original on my car....back in my fast Ford days I did fit a Kent cam to my N/A escort...a vernier spocket and big exhaust...this gained me 13bhp on the dyno from a standard car...not very noticeable in power terms but the driveability was better...

Pete

Yes for sure Turbo engines respond so much easier and cheaper with a Forced induction Boost hike than trying to
get more air and fuel to produce more power in a normally aspirated engine.

If it was me I'd consider:

Ignition refresh, New leads (Magnecour), Plugs (Nippon Denso Iridium), New Dizzy Cap & Rotor arm
- Head off, skim, new valve springs regrind valves etc..
- Camshaft (Webcam 274) which gives good power low and midrange and you'd not have to rev it high to feel gains
- live remap (Chip Wizards - Wayne Schofield)

That'll make a mess of a "Bag of Sand" !

R

Your Lump in my car would be something which I'd probably not relish being scared in, which is why 205bhp is enough for me
at the moment!

The roughness on inlet manifolds and inlet surfaces is a subject with great debate, most of it came from the Carburettor
era where a rough wall creates more turbulent flow and tumble when mixing air and fuel together, but for the Injection engine the Inlet is only carrying air which if this was increased with a faster flowing inlet manifold the CFM figure goes up and the air can enter more efficiently which when matched with fuel mapping creates more power.

Cylinder head inlet surfaces may be slightly different? as this is where the fuel is sprayed into the airstream but a rough
surface would slow the air speed so I'm not convinced and sure this would benefit?

Lindsey Racing did my 2.5 N/A head for me to their Stage II spec which produces 28% more CFM
(From 180 standard to 232)

https://www.lindseyracing.com/LR/Parts/LRHEADS.html

The Porsche 944 2.7 Head had Bigger valves, I used the 2.5 with smaller valves which I think is interesting how
I still got good power gains.

The Surface on my Inlets doesn't look highly polished but it has a grain



I modified my Inlet manifold chopping off the swan neck,



Then I had the internals Extrude Honed
which I think has made a difference as the extra 25% CFM is complimenting the head porting, as is
the smaller non restrictive exhaust bore scavenging and flowing the gases out much faster.

A typical Inlet looks like this inside, rough cast bobbles,



After an Abrasive putty is forced under pressure through the entire inlet manifold several times
it cleans the surfaces up to this..




R

It needs to be rough. Smooth will simply cause the fuel and air to separate.

This is what I call rough.....



And after CNC porting the surfaces are much smoother




R

Can we please stop squabbling, I hate having to moderate.

Any more and i will delete accounts.

I had Ford V6 and Cosworth heads modified by one of the best head fettlers in the country years ago. The results were as expected, more revs and top end power. I wouldn't substantially modify an 8V 944 head unless you were racing the car. In standard form it's not an engine that's built to take high RPM.

The large 4 cylinder 8v Porsche 2.5 isn't a high revving engine in stock form, it can be made to rev to 7000rpm for racing as you suggest.
But My modified ported 2.5 Cylinder head was also done by a very experienced and successful company but in the USA (Lindsey Racing) because I couldn't
find anyone on this country that offered the same confidence, expertise and cost that they did.

The Dollar was far better in 2013 and it cost me then approx £600, it's probably now more like £850.

Lindsey Racing also sell the (Californian) Web Cam 274 profile Camshaft and with these two combined in my engine I only rev up to 6000rpm
because peak power is at 5700rpm and peak torque 4500rpm.

The engine is 228cc more than a 2.5 @ 2707cc but the Torque is very impressive most importantly at low RPM, and it's all on stock Bosch Igntion, ECU and
fueling etc.. including the 30 year old AFM.


See link for power & torque figures. 190ft lbs @ 3000 rpm is very handy for road use !
The car will pull well and clean in 3rd gear from 30mph, but the car has 250kg less weight so a standard weight car would not perform as well.

http://924srr27l.co.uk/wp-content/uploads/2015/05/TEch-Spec-924srr27L-.pdf

R

[/quote]


The large 4 cylinder 8v Porsche 2.5 isn't a high revving engine in stock form, it can be made to rev to 7000rpm for racing as you suggest.

R[/quote]


As posted on PCGB recently I hit 7137rpm the other week...oops....I'll try not to do that too often but my engine can clearly handle it safely... Talking of heads, I have an LR stage 2 head, probably one of the first in the UK from some 10 years ago....with most of the extra goodies included....I have since changed the valves as LR's design was prone to failure which it did....

Pete