Thanks in advance if you can help me with this...

I want to go bigger on the cam and I'm trying to figure out how much lift I can run with my current heads... they are the MTI S2e. Valves are 2.02 / 1.56 and I was told the head was milled .007. Not sure about the thickness of the current head gasket, but I would replace that anyway. I've been running the X1 with .591/.571 lift.

Would a big off the shelf cam such as the TRex or MS4 fit, or should I have something custom ground with big duration but lift around or under 0.600? I don't have the expertise to measure PTV myself... so I'm trying to capitalize on the knowledge out here to get my expectations aligned correctly.

 

You cant fully rely on what someone here will tell you because every setup is different, you should measure your PTVC, it is very easy to do and if you google "piston to valve clearance" you will find a bunch of writeups on how to do it.

By the way duration and LSA, which determine overlap, will have way more of an effect on PTVC than lift does. This is because closest PTVC occurs at piston TDC where both valves are almost completely closed (minimum cam lift). Max lift happens when the piston is well down into the cylinder.

 

I hear you... I guess I was initially just looking for a "yeah, it may work - but you'll have to check" or the "no way man, it will never work!"

I've looked at the DIY PTV measuring threads... still a little intimidated by it. Maybe I should look again. Good to know on the duration & LSA impact, I had always assumed lift was the primary factor. Obviously I'm a newb at this!

 

I wouldnt run a Trex or MS4 with those larger valves for sure without at least measuring, but i can promise you it would be too close.

 

OK, good to know. Would it be too close for a thicker head gasket to compensate? And on a somewhat related note... is the old adage of the TREX being designed for stock heads primarily because of these PTV clearance issues?

 

Since you are pulling heads to change gaskets search the clay method to check PTV if you've never done it before. It is less technical than using a degree wheel.

 

Lift has liitle to do with PTV at the durations we run on our hydraulic cams.
To answer your question, NO WAY; you'll have to flycut with a cam the size of MS4 or TREX

 

Thanks - what type of ballpark specs should I be considering if I want to avoid flycutting? Something the nature of the low 230s in duration (and high lift), perhaps the TRAK cam (231/234 .640/.590 112 LSA)? And would switching to this cam be worth the trouble over what I've got?

 

The Trak will fit, if 10>15 rwhp worth it to you then yes.

Also, I would look at a custom cam, like 230/232, .612/.595 111+2 LSA

 

OK, so is 234 on either the intake or exhaust side (with a 112 / 111 lsa) about the max duration you would try with my PTV clearance - or would even that be pushing it on the intake side? Did you give those custom cam specs primarily to play it safer on PTV clearance, or was there a performance angle I'm unaware of at play? Would the specs you gave result in a nastier lope that the Trak because of the 111 lsa?

Thanks again for the insight.

 

I just used the clay method when I installed my Dart 205's with my 233/233 595 595 112+2 TSP cam. I also used a Cometric .040 head gasket and I just had enough clearance. I was going to used the degree wheel method but I ran out of money and also lost my job.

It would be nice to have a chart that would give you an idea on what the PTV clearance is with certain cams/heads,etc.
Bill

 

Yes it would be nice to have a reference chart such as you speak for issues like these...

What cc are the Dart heads? When you say "just enough" what was that - 0.070 or so?

 

Heads are 62cc. I do not rem exactly but they were close to the .100/.080 spec I was using.
I still have the clay. I will have to go measure them again.

Bill

 

Good info... your valves are the same size, combustion chamber slightly smaller... so it sounds like I could get away with 234/234 or so.