Another day another question....
Thinking of putting bigger valves in my stock 2000 5.3l heads (862 if my research is right)
It seems the stock seats are 2.020" so without the price tag of swapping seats I can in theory run a 2.020" intake valve.
I'm going to run a comp cam with factory rockers which will give me 0.513" lift.
Now, both my head tech and comp tech support say that since its a small bore (stock 5.3l block) 2.020" valves might contact the cylinder and 2.000" would be a better choice...
This dosent seem right to me I believe I've seen a build or two ruining a 2.060" valve (re-seated naturally) with a more aggressive cam.
Perhapse bored out?
Or are the two techs being more conservative?
Would I be safe running a 2.020" valve?

 

Even if it doesn't hit the cylinder wall it will be damn close and you will start to see shrouding issues.

Richard a WCCH tested a set of 1.95 and 2.00 intake valves on a flow bench. You could see the 2.00 valve was starting to shroud by the flow numbers. At one point some one put them on a dyno and they only gained around 5 peak horse power towards the top of the power band but it made less power down low.

I guess the real question is what do you plan to do with the engine???

 

I have been wondering this too. Maybe when I get my heads back I will measure the valve clearance to the block, and post it along with some pics. FWIW, I was running the 2.02 heads on a 5.3 stock bore.

 

ons...

 

^^^f u moble site!!!! I click normal version but nothing happens!!!^^^
ok so what I'm going for is mild street performance, but, since I'm going thru the entire drive train any how I wanted to bump up the flow incase I want to add forced induction down the road.

 

Btw, called up comp. because my cam has mild lift and duration the tech said I'll have "miles" before interference is an issue

 

i looked into this same thing this past winter.

03regcab sierra was running a 2.02, but he also said he went F\I at the same time.
The smaller valve helps increase velocity into the cylinder (compared to larger valve) which helps low end torque (and I needed this since I am and plan on staying N/A)

I read a lot about mach index numbers and played with some calculators before deciding to stick with the stock size valve.

IF you a)increase the valve size or b) increase valve lift... velocity decreases.
I had already ordered my cam with .610 lift and increasing valve size was only going to hurt me more.

With a heavy *** truck, I didn't want to give up any already anorexic bottom end since I also wanted to stay with a stock converter.

Currently shopping for a converter.