[V8] cam clearence- big cams vs-heads

[Sean]

The Biggest factory cams I can get my hands on are the S8 which have 12.5mm rough of lift.  These require of 3mm of machining to fit in the PT castings.  This isn't something I would do with a dremel as your removing allot of material around the lifter bores and if you nic one of those your in trouble.  I do heads as a means of paying for the cams so I've seen the results.  Stock 16v VW heads are clearanced for larger cams from the factory so the 16v boys don't have to clearance anything till they are in the 12mm range IIRC.

Vw cams fit in the PT/S8 heads, but like mentioned You can not use them.  Also you can not use most of the 16v blanks as they are cast with rough lobes so Your looking at welding and regrinding then hardening the cam (very important) to get above ~10-10.5mm of lift.  I have ~50 hours into this research so I am quite aware of what will and will not fit.  I have a complete set of S8 32v heads which have HUGE solid lifter cams and they don't even come close to spinning in a PT.  You can set them in the castings and every thing lines up, but the cams lobes hit in the lifter bores 3.2mm down.  So if you want to dremel your heads and weld the cams feel free, but I have been down this road with multiple cam grinds all say that you need ~.5mm of clearance to be safe.  That means for the S8 heads your looking at ~4mm of material.  that puts the lobes into the valve cover gasket area almost.  I have pictures Here <http://www.tdif.com/phpBB2/gallery2.php?g2_itemId=1022> That should show you some of the work Audi did.

Larger cams can be had if you want to spend the money going rate is ~60-80 a lobe for welding.  that means your looking at 1900-2600 for welding the lobes.  The regrinds are cheap, but the welding since you are welding cast iron that is heat treated is expensive.  I have a cam guy lined up if any one wants to get billets made which have enough material for 13mm of lift on stock base circles or 14mm on reduced base circles cost is dependent on amount.  The V8 has many similarities, but Audi did cut corners on them, the heads only got minimal machining the cams sucked, the injectors were to small, the intakes suck, all add up to losses in power.

Sean

Message: 4
Date: Wed, 21 Mar 2007 14:09:12 -0500
From: "Tony and Lillie" <tonyandlillie1 at earthlink.net>
Subject: Re: [V8] cam clearence- big cams vs-heads
To: <J123fs at aol.com>,	<v8 at audifans.com>
Message-ID: <001b01c76bec$69b2ae00$0900a8c0 at tfh5lqoxlbb5rh>
Content-Type: text/plain; format=flowed; charset="iso-8859-1";
	reply-type=original

<SNIP>

>> All the VW racers I know (including myself) do not pay for  "machining" we
>> just clean the edge up with a high speed dremel or die  grinder......no 
>> fancy
>> machining required!
>> As the V8 heads are the same as the 16 V VW motors I can say with 
>> certainty
>> that very little needs to be clearanced with larger cam lobes- just a 
>> couple
>> MM's.....pretty straightforward.....though it should be done prior to 
>> doing
>> the  valve work (you are going to port and change seals- valve job 
>> right?), so
>> you  can hot tank and clean any fillings out.
>> Jack
>  
>
<SNIP>

Well, not exactly the same. But, the bore spacing, valve angles, etc are the 
same. Everything important with respect to the larger cams, anyhow. So, how 
large of cams can you put on the VW motors. And, more importantly, what's 
the timing spec on those cams. Another thing to consider is what the lobe 
center is. As there is much more of a market for VW 16V cams, I'd say they 
grind new ones with the same specs as stock, other than lift and duration.

As for VW cams directly in a V8 (to answer Dave's question) the firing order 
is significantly different in a V8Q than VW 4-cyl. Running 4-cyl cams, you 
would in essance have a "flat" 8-cyl, much like a Ferarri. That's what Audi 
did with the DTM ,cars, but I doubt you are going to get one of those cranks 
for cheap  ;-) 

Tony Hoffman 



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