[V8] Larger Valves?

[Scott Justusson]

LOL, there I was still in lurk mode drinking my coffee...  Tweeked v8s?  Done a few - years ago, including head mods beyond reason.  My .02 arbitraged through the peso.  First off Andy, the Euro v8 only uses a unique intake cam, the exhaust cam doesn't change.  The Intake Cam is not really that much 'larger', IIRC it uses a bit more lift and a slightly different tdc position (in relation to the exhaust cam), which gives the extra HP figure quoted in the euro 4.2 specifications.  Years ago, I was sourcing and selling matched 3.6/4.2 performance cams (intake and exhaust) from Germany, and I sold/installed/modified a few v8 heads with them here in the states.  The difference in these vs the euro 4.2 cam is the lift was even higher on the intake cam, and the exhaust cam changed profile and index, which yielded an even better torque curve vs the euro setup.  

To your question on valve sizing.  IME with valves, with N/A cars you want to increase the intake side maximally, which is exactly what ABT used to offer many years ago.  With turbo cars it's the opposite, you increase the exhaust side valve maximally, because you can always turn up the boost for effective intake valve sizing.  To what exactly you are going to 'gain', not much for the $ spent.  Tweeking v8 engines IME, is usually felt in the wallet at both the investment and the gas pump, more than it's 'felt' in butt calibration or numbers reflected at the dyno/acceleration.

If you have cheap access to the 32 valves and hardware, and flow matching port capability, it won't 'hurt', but you've already done the ABH motor, so the 'gains' are going to cost more than the return IMO/E.  With the price of 91 200tq these days, just the cost of your head work and attaching hardware on the ABH, is getting damn close to just owning a 91 200tq in addition to your ABH 5speed.  Which has much more potential in $/HP in a lighter chassis, than the v8 has in N/A trim.  BTDT2

I digress a bit, but in answer to your question...  N/A motors benefits the most from intake valve increases.

HTH and my .02

Scott J
92 v8 Auto 4.2 ABT Chipped
91 v8 Auto 3.6 stock for sale
91 200tq MTM 2.5
87 4ktq 20vt MTM 2.5
84 urq 20vt project
83 urq stock

 

 

 

-----Original Message-----
From: kyle leatherwood <kyle_leatherwood at hotmail.com>
To: Andy Rohrbach <acrohrbach3 at gmail.com>
Cc: V8 <V8 at audifans.com>
Sent: Thu, Mar 28, 2013 8:35 pm
Subject: Re: [V8] Larger Valves?


Andy, I am sure that Scott J can chime in on what you're wanting to do.  As much 
as I bust his balls, his 2 cents would probably give you some insight and points 
to ponder before you get in too deep, and he has had some pretty good experience 
with perfomance stuff on V8's.  

I had a friend who had his 4.2 maxed out with euro cams, but did not have larger 
valves, only ported and polished.  I think the only way we could have unleashed 
the full potential of that motor would have been to do stand alone on it with 
lots of dyno time, something we never did before he sold it.

Best of luck.  I miss my 5 speed, but I know Allen is taking good care of it!

Kyle

Sent from my iPhone

On Mar 28, 2013, at 6:57 PM, "Andy Rohrbach" <acrohrbach3 at gmail.com> wrote:

> Has anyone ever tried larger valves in the ABH motor?  If so please
> enlighten me on the subject!  I currently have a 91' ABH 5spd.  I was able
> to obtain the cylinder heads out of a Euro spec 6spd. V8.  The cams are
> much larger but the ports are equal to that of a U.S. ABH.  The valve sizes
> available are .5mm or 2mm larger for both the intake and exhaust.  Also
> available is a Ferrea valve train, manganese/bronze valve guides and
> adjustable timing chain sprockets.  Not sure about an adjustable timing
> belt cam sprocket.  Any advise?  -Andy
> _______________________________________________