does timing matter for a BLT?

[1Gina2G]

I was setup to do a boost leak test earlier today and I heard air reaching into the head. I was thinking the PCV valve since I also felt air coming through the open hose from my catchcan (from having the turbo intake pipe off)

then I also remembered about the timing and the valves, some people on here say the timing does not matter for a BLT but apparently 40* BTDC has all the valves shut for best results.

Does it matter?

and I read this link already http://www.dsmtuners.com/forums/art...st-how-boostpro-net-tester.html#post152554139

I don't understand the diagram at the bottom, what does 40 degree BTDC look like?

 

[92AWDHX40]

I never paid attention to that i just ran my blt.

 

[xtotek]

http://www.dsmtuners.com/forums/newbie-forum/443149-intake-pressure-test.html

 

[NHerron]

I set my engine to roughly 30* ATDC, so the valves aren't in overlap and air cannot leak out the exhaust. I also marked the pulley with a red paint marker, so it makes future tests easier.

30* ATDC would be about 2 inches counterclockwise from the mark in the crank pulley, lined up to the 0* mark on the plastic cover.

The PCV, that is easily solved with the very popular USplastics check valve
They can be bought on eBay. I just bought one a couple months ago and works great, no more leaking.
3/8" Kynar Check Valve

 

[1Gina2G]

http://www.dsmtuners.com/forums/newbie-forum/443149-intake-pressure-test.html

thanks I'm glad this was already asked about and solved.

 

[NHerron]

thanks I'm glad this was already asked about and solved.

Ha -If only it were easier to search, there wouldn't be 'merged' threads.

 

[TSIturbo91]

The PCV, that is easily solved with the very popular USplastics check valve
They can be bought on eBay. I just bought one a couple months ago and works great, no more leaking.
3/8" Kynar Check Valve

I just got some from them. But used my FedEx account for payment and it rang in at $18 and change! For just 4 of them. I got it 2 days later but I would have been ok with a delay.

 

[1Gina2G]

One last question regarding the 40* BTDC postion, you have to take off all the external timing to get a view of the crank sprocket mark correct?

Or is there a mark to use on the crank pulley? what mark is at 40* BTDC?

 

[NHerron]

Picture attached. The marks on the pulley is two small notches

Look at the number 10 on the cover. Measure the distance from the 10 to the 'T'. Now, quadruple that measurement. With that measurement in mind and looking at the pulley timing mark, go behind that crank mark (counterclockwise from the notch) and make a new mark on the pulley. This is roughly 40* ATDC, when lined up with the 'T' on the plastic cover.

And make sure not to turn the engine backwards, always go clockwise.

I didn't realize you had stock cams. This trick doesn't seem to work on my setup with my cams, so all I can do is make sure I'm not in overlap (30*ATDC)

I just got some from them. But used my FedEx account for payment and it rang in at $18 and change! For just 4 of them. I got it 2 days later but I would have been ok with a delay.

I must be a sucker, I paid 5.49 for just one so I think you got a better deal for 4 of them @ 18! They work pretty good though huh? I think I'll just do away with the OEM one when I get a proper valve cover setup

 

[1Gina2G]

Okay so this is what I still haven't figured out after alot of re-reading.

Is 40* BTDC any better than 30* ATDC? what's the differemce? Is it the intake or the exhaust valves that we are trying to close?

I guess what's really bothering me is I don't know how dead-on your supposed to be with an invisable timing mark

 

[NHerron]

Setting it to roughly 40ATDC just makes sure the valves arent in overlap. Overlap is when both the exhaust and intake valves are open at the same time in the same cylinder. Since a BLT pressurizes the intake system it would end up going straight out the exhaust and not pressurizing anything. Most of the time the engine rotates out of overlap on its own though, when you shut off the car. Not sure why on that one though.

So basically no theres no deal with 30 vs 40*.

Look up "BLT ATDC steve dsmtuners" and you'll find lots more good info.

 

[1Gina2G]

But the test can still be done as long as you are between the 51 and before the intake valve opens up? What would be different about doing the test at the half way mark on the left side?

 

[NHerron]

Sorry I am not 100% on that. Steve's posts make sense though, maybe you can find the answer there? Just Google "BLT steve dsmtuners" and it bring up lots of BLT notes from steve (Good Wiseman)

 

[1Gina2G]

so would the halfway mark on the left side be a bad spot for the boost leak testing?

 

[NHerron]

Not sure but why would you want to? Just go past the timing scale...

 

[WES_393]

Serious question here: Why not just pressurize the intake and spray it with soapy water to check for leaks? Unless your serious about checking pressure drop or the valve overlap leaks all the pressure, then there's no point to messing with valves IMO. I personally just pop on the tester, turn on the air compressor, and spray down the intake while watching for bubbles. If your concerned about the PCV system or blowby then check those things separately.

 

[NHerron]

I like to make sure it out of overlap because I don't have an adjustable regulator on the compressor that I could set to 30psi at the moment so it's a PITA to keep pressurizing over and over. Keeps pressure in longer to check for leaks...

 

[1Gina2G]

Well if air is going through the exhaust it'd seem to me that your boost leak test would be inaccurate. Not really sure what you mean by pressure drop, so does the compressed air still leak out eventually WITH the BLT still attached to the hose? I thought it's supposed to hold the air in untill you take the air hose off and the BLT itself.

My setup is completey new & rebuilt all the way around so I need to make sure everythings tested for a while. Deffinatley no major leaks yet, but somewhere. I wonder how it'll work next time I start up and and after the rings get warm.

 

[WES_393]

What I mean by pressure drop is the amount/speed of pressure lost out of the intake, just like they show in the "How-To" link you posted. For this you would want valve timing to be correct to minimize pressure lost through the engine. But you run into one problem: How are you going to find leaks that don't make noise?

So what I'm saying is to pressurize the intake and spray the intake with soapy water. Anywhere that pressure is leaking out of the intake will be surrounded with bubbles. Simple as that. You could still set valve timing and measure pressure loss if you want. But the soapy water method alone works great, so why complicate things?

 

[1Gina2G]

How do you just pressurize the intake , do you mean testing right at the elbow before the throttlebody?

So you're saying you only line it up to 30 ATDC if your trying to check pressure loss?

 

[007jimmy]

i get what he is saying.. he is trying to minimize pressure lost into the cylinder and out the exhuast valves if they are in an overlap state but its a 1 out of 8 shot in doing so. when you do a boost leak test one day and something like this happens to you youll understand why he is asking. if you have the engine rotated in a way that all the intake valves are supposed to be closed then it makes it easier to do a leak down test as well..

 

[WES_393]

Sorry, when I say intake I mean the entire intake system. So you would still put the tester on the turbo inlet. And yes, if your not measuring pressure loss then a little air leaking past the valves doesn't matter. You just need to maintain the testing pressure while watching for bubbles.

I simply hook up the tester and pressurize the intake system about 5psi higher than I plan to run. Then spray the entire intake system with soapy water and watch for bubbles. Check the gauge and add air if needed, then spray everything down again. Large leaks will be very obvious while smaller leaks might take a few rounds of this to grow a noticeable amount. I use an air compressor with a regulator so this might be easier said than done depending on your equipment. But regardless, if you keep the intake around the testing pressure and continue spraying and searching for bubbles, you'll find all your leaks in no time.