Muckman

iTrader: (2)

I have a DART head with +1mm intake and +1mm exhaust valve. I decided to run the Skunk2 Tuner1 cam but have found I need 5 degrees of cam seperation to maintain .030" v2v @ .000" lash. That seems a little ridiculous! What do you guys do to run really aggressive cams with big valves? Does anyone have similar experience with dual oversized valves?

Here is my v2v table


Cams at 0/0 = .005" v2v

eDm cRxXx

Did the cam gears line up properly when you put the cam belt on?

Maybe you should try and degree them on the engine to see where they end up.

koczeka

It does not make any sense using 1mm oversize on both intake and exhaust resulting very limited camshaft selection and degree settings.
What you win with the big valves U loose with the small cams and restricted settings.
For a big power turbo setup your combination would work... not smart for NA.

BTW I like the chamber... show pics of the ports too!

Muckman

iTrader: (2)

No I didnt degree the cams. I dont have any dial indicators.

Actually this is a turbo application. I posted in the all motor forum bc you guys have more experience with oversized valves. You can still run alot of lift with big valves just cant have alot of overlap.

As requested

EG1834

I would think your best options are either sinking the valves or accepting the safe range of settings and seeing what it does. You may be surprised.

Muckman

iTrader: (2)

You may be right. But I can't run the cams even close to 0/0 to compare.

What do you guys think about the .030" v2v safety margin plus the .000" valve lash safety margin? Is the double safety margin nessecary or are those two seperate requirements?

Im trying to understand where the .030" v2v came from. If the lash is at 0 thats the closest the valves will ever get, right? I would think any positive v2v clearance is enough in that situation. Has anybody run less than .030" v2v?

SP GARAGE

iTrader: (1)

Any reason why you went with +1 on the exh?

JDogg

I have seen guys sink the exhaust valve in order to gain some clearance... but rarely does anyone use big exhaust valves

SP GARAGE

iTrader: (1)

Most head I've used we done os intake vales and stock exh valves works Great and still have great v2v

Fink29

I also run a 34mm intake valve and stock exhaust. With the custom cams I got from Rocket my v2v @ 0,0 is 0.030

Muckman

iTrader: (2)

How much can I sink the valve seats? Are there any negative effects of doing that?

97mm_EH3

Unless you actually degree in the cams, your cam gear #'s mean nothing. Plus the centerlines for a turbo are different than NA on the same cams. Intake closing and EX opening numbers ( the two most important) are different for turbo/ NA motors. Plus you gain V-V and V-P with the proper valve lash, which is 10-11 intake and 13-14 thou when done correctly "I will let you figure that out".

hYbRid_Eg6

iTrader: (2)

What would the clearance be if you went +.5mm on the exhaust side, instead of the +1mm? Would you get the .030 clearance that you needed?

97mm_EH3

That should increase the clearance by .010 thou.

Muckman

iTrader: (2)

I found that +1mm of valve diameter was worth .025" v2v when comparing the same cam.

4piston

The DART head was a pretty good head. That port doesn't look like the darts I have seen, but its been a long time. Put a new VJ on it for a stock size exh valve and put stock size exh valves in there.

GhostAccord

If you want to run larger valves you should find yourself an engine with a better valve angle. My 2¢

97mm_EH3

It should be .020, and the guy above me was talking .05mm or .010 cl. As the pro series cams from Skunk seem to want the EX. advanced, so when you actually degree them the V-V will be different, plus add the increased cl. when you adjust the valves, you do not even have a question yet, until you do it correctly to start with.
A battery powered drill, belt sander, and caliper will allow you to remove .05mm and you can radius the leading edge of the margin.

93supercoupe

can you cut in smaller valves after youve already cut in +1mm?

Im in the same boat.

EG1834

You might be able to, but it may hurt the performance of the valvejob. It depends on the size of the venturi (aka the throat). Many head porters like to open up the venturi to as much as 92% of the valve, so going to a smaller valve may not leave much room for the bottom cuts, or even the seat in worse case scenarios.

4piston

It really just depends on the port and how the head guy set it all up. If it was my motor I'd put new seats in if needed and run the smaller exh valve. With the popular cams out there, I think the extra cfm you got there will not make more power than having some flexibility with moving the cam. Also, sinking the vj can eat up more cfm than you gained going to the bigger valve...so be careful with that.

We run stock size valves on B heads and our customers who opt for that seem to have more success than the guys that insist on me using a larger valve. That is on my port...I'm not speaking for anyone else. I have customers running 10s AM in street class cars on stock strokes and around 300hp and some running very low 11s in daily drivers AM...stock stroke, intake manifolds, basic small cams. It seems to work well on the bigger motors too, and it keeps it simple for guys that always seem to skip checking clearances HA HA.

hYbRid_Eg6

iTrader: (2)

Question? I kind of have the same thing, but I have +1mm intake and +.5mm exhaust, my question is after you get the clearances my cam card(Brain Crower 2 stage NA cam) tells me to set at 0/0 for best results then adjust while tuning. Now do I start the car at 0/0(.015) or do I go with my measurements?

4piston

You need to degree the cams and not go off of suggested gear settings. Set the head up on the bench assembled with some test springs and rotate it over at various settings and measure your valve to valve. Map out where you can and can not go on a piece of paper and keep those notes with you when you go to the dyno.

spoolinvtec54

4 pistion racing you talking about a stock stroke b series making 300 hp if so that's really good numbers.

hYbRid_Eg6

iTrader: (2)

I already have my measurements, what I'm asking is do I keep it 0/0 for the first initial start up with my base map so I can check for leaks or do I start with the cam gears adjusted already then check for leaks and then head to the dyno?