4.2 40V engine Rpm increase

[daviesbike]

im just wandering what the max that the audi v8 can take rpm wise ?

have tuned rally cars added twin webbers,cat cams, titanium valve springs ect and removed the rev limiter altogether because of running launch controll with added rev limiter and have taken them up to near 9.000rpm

so was just wandering how the V8 would fair up to this kind of mod how well balanced is the engine and internals if the cams and valve springs were uprated would it take an increase of say 1-2,000rpm more ?

dont ask why i would like to know, im just intrested thats all and there seems to be nothing on the net with regards to this sort of thing,

i thought about getting an old 32valve engine and rebuilding it from the ground up just as a project no apparent reason other than i cant sit still too long or i will chew my own arm off

[Dezzy]

That is interesting Guy, buty got to be honest i'd quite like to see you chew your own arm off too.

Go on just rebuild one you know you want to, and then you can just find out what you can get to rev to, can you carb it? it would sound awesome snorting through weber 500's

[daviesbike]

haha i carb'd my rally car on twin webber 45's it dose sound fantastic,

i like tinkering with thinks like that when i have time so i would be intresting to see what the true limitations of the 4.2 are

[Nollywood]

The issue there is the crank and rods. Very heavy on the V8, you'll need to do a lot of lightening and balancing, with the flexi plate and torque converter. Oh, and an uprated torque converter would be a good idea.

A manual assembly is a lot easier to balance.

[ainarssems]

Not sure about crank/rods or 40V engine but on 32V engine S8 engines have solid cam followers with compensating piece for valve clearance adjustment instead of hydraulic ones on intake valves to save weight and to allow for higher rpm then A8. Exhaust are still hydraulic because of higher temp variations and higher change in gap due to temp change but use double springs. I still managed to get compensating pieces damaged on mine due to valve floating on high rpm.

These engines were not made with high rpm in mind. Even if you upgrade valve-train I don't think you can go more then 7500-7800rpm

Only way to know for sure what and how much needs to be done is to test, improve, test some more and again and brake a couple of engines in process.

[daviesbike]

MMM i see, was just curious as in the states there is a company that make H beam con rods and forged pistons the the S8 so thought that the diamiter would fit the A8 engine too

[adjuster]

It's been my experience that's is often cheaper, and more effective to force feed an engine, than try to spin one with this bore and stroke faster.

Now, add more stroke, and slow it down some? Or upgrade the rods/pistons, add more stoke, and keep the stock RPM the same?

Did that with a 7MGTE engine, added 6.5mm more stroke to an already "stroked" I6 by Toyota, and it changed the way the engine responded quite a bit. Pulls like a small V8, but sounds like a diesel. Weird, but effective, and at 18psi? No traction at all out of 295 wide Goodyear tires.

If I was going to build a race version of this engine, I'd follow what they have done with the RS6, get some custom forged billet rods made, custom forged pistons, coat the skirts and crown, replace the valve springs with new ones, clean up the head ports to remove any casting flash, and call it good Perhaps double up the head gasket to lower the static CR, and then feed it some more boost and larger injectors?

Have not played with the Audi V8's yet.

I suppose you could see if going to a smaller rod journal size might allow you some clearance with the block, and then have the crank welded up, and re-ground for more stroke? When I've done this, I go to common part sizes, such as 2" rod journals, and honda piston pin sizes, so you can get cheap high quality replacement parts and bearings off the market for Honda and GM parts. (The 7MGTE had small block chevy 327 2" rod bearings, this gave me some room for the rod shoulders/caps, but left the crank journals strong enough to handle the power I was building the engine for. The Honda piston pins were smaller diameter, so a longer rod could be used, and they are lighter yet tool steel and cheap due to lots of high performance Honda's here in the USA.)

Give Pauter Machine the specs, and they can build you custom rods easy, but even better, design a crank throw that allows for off the shelf parts, say 6" rods with 2" big ends, and Honda smalls, and they have those on the shelf. Then hit up ROSS and get some custom pistons, coat the skirts with molydisulfied, and the crowns with thermal barrier, and you are good to go.

Design the static CR at 10:1 get say 8mm more stroke, and on an 85mm bore, with say instead of the 92.8 stock stroke, you get 102mm.... That takes the 4.2L engine up to a 4.631 engine.. So it only spins up as fast as the stock RPM limit, but with the added stroke, you will have WAY more tourqe.

Add some force feeding? And it is a good guess that it would make more power, and power where you want it for a large sedan than the RS4 engine that is a high RPM spinner, but down on tourqe compared to the standard 4.2.

Tourqe is what moves you, but I suppose horse power numbers sound like more fun, and do give that top end rush. But 99% of the time, I'd take the added tourqe of say 100lbs at 3500rpm v/s 130hp at 6750rpm.