EVO7 pistons

I have seem some people just dropped in evo 4-9 pistons into dsm/evo1-3 and running just fine but also have seen some people hitting and bending intake valves.
Back in the 90s and early 2000s, that was a very common upgrade for EVO1-3 guys in Japan. If strictly speaking about the right way to use evo 4-9 pistons in dsm/gvr4 or evo1-3, you have to follow the evo rotating direction due to piston offset and trimming valve reliefs and set all piston top dish volume equally. Most of performance shops in Japan were doing this way.

Thanks. I'm still getting different answers from different sources so far. As for the hitting valves, I think that may happen when you're running milled block decks and heads, including thinner headgaskets or MLS. Mine are all stock, unmilled and using OEM-style composite gasket. The valves are also stock and barely poke from the head surface. Valve lift duration and height is also a factor to consider, but again in my case it's all stock, so I'm not worried about that.

I've already installed them with the arrows pointing towards the timing side, which should also be in the same direction as they come in the EVO blocks (clockwise crank rotation).

I think I'm just gonna roll with these and try to hit my power goals. They shouldn't *technically* be any weaker than the EVO 8 combo, or so I'd think...

I have seen a evo3 guy bent valves due to hitting evo 9 pistons without trimming valve reliefs. I am not sure what caused that but valvetrain was all stock. (Just FYI, evo combustion chamber approx. 43cc, DSM 47cc and IIRC the pin height is a bit different, I am not sure about evo7 piston though)
The safest way is you degree cams to check the piston to valve clearance or at least clay to see the minimum clearance.

@DSMPT is correct on being concerned about the valve clearance. DSM intake & exhaust valve are flipped in our heads from the Evo's heads. Intake valves are larger diameter & when installed, the Evo pistons in our DSM blocks, the piston exhaust releif is under the DSM head's intake valve & vice versa. The fix is to get the reliefs for the exhaust side in the Evo pistons cut deeper to match the reliefs on the intake side of the pistons.

Right, so I did some measurements with the calipers, zeroed properly by using a straight edge from the top of the block deck. I measured from the block deck to the deepest part of the intake and exhaust valve reliefs. My point of reference is the 2G N/A 10:1 compression ratio flat top piston. I ran that up until now without any issues; it sits flush with the block, just like the turbo pistons from a 2G turbo DSM.

I will attach a simple diagram (made in Paint of course). It shows both pistons (2G N/A and EVO7?) in relation to each other within the 7 bolt DSM block. The EVO 7 piston is shown sitting slightly lower in the bore, as it is the case. Thus it adds an extra bit of clearance. However, you will notice that for the EVO 7 piston, the valve reliefs are shown to be flipped. That is because I am keeping the EVO standard orientation (arrow towards cambelt) and utilizing the benefits of the offset wrist pin.



Right off the bat, we can see that in a DSM block, the EVO 7 piston will have enough clearance for the DSM exhaust valve. However, the intake valve remains a consideration. Those 0.05mms (0.001") are questionable. It's possible my measurements are not 100% accurate. It's also possible that a valve which has been lapped/machine enough could have less margin material and never even reach the actual valve relief. In fact, I'm 100% sure that valves never get so close to their reliefs, unless some serious modification has been done.

Upon this evaluation, I would consider proceeding and using this combo. I guess the real conclusion can be done after firing it up for the first time and checking for bent valves... I will update this as necessary, but feel free to add any more information related to this. I am still not 100% sure if these are in fact EVO 7 pistons.

Kryndon said:

Right, so I did some measurements with the calipers, zeroed properly by using a straight edge from the top of the block deck. I measured from the block deck to the deepest part of the intake and exhaust valve reliefs. My point of reference is the 2G N/A 10:1 compression ratio flat top piston. I ran that up until now without any issues; it sits flush with the block, just like the turbo pistons from a 2G turbo DSM.

Click to expand...

Probably you are fine with Evo pistons, this is just if you want to make yourself feel secured.
No offense, but you can't check the deck or piston to valve clearance by a caliper in hand. You can't know the accurate numbers until you check it with a dial gauge w/ a degree wheel or at least clay to know the minimum piston to valve clearance as I mentioned earlier.
Degreeing cams is a little bit complicated if you have never done before (and need adjustable cam gears) but clay is easy, why don't you just clay while the engine is disassembled?

Kryndon said:

I guess the real conclusion can be done after firing it up for the first time and checking for bent valves...

Click to expand...

To be honest, this is not right. if you clay you can get the answer that you have been waiting for and can get rid of the concern. Even no need to fire up with taking a risk.
Even valves don't hit the pistons while you are rotating crankshaft by hand or at idle, it doesn't mean that you don't hit while you are driving at higher rpm.

Kryndon said:

I am still not 100% sure if these are in fact EVO 7 pistons.

Click to expand...

I said those piston are from EVO7 because I have physically seen the pistons from Mitsubishi when I was in japan. IIRC, if it shows "E7" that is from EVO7, if it shows "E6" that is from EVO 5/6. I am not speaking of my guesses but this is from my old memories, so it could be wrong. If you would like to be 100% sure then ask Mitsubishi motors dealer in your city to bring one EVO7 piston to compare.

Thanks. I trust you and I also trust Mitsubishi Engineers when setting up and more or less keeping the same geometries between 4G63 blocks. I'll run her like she is. The clay testing looks too complicated for my dumb brain and I also don't have solid test lifters anyway. The head is already assembled and ready to go. Also I just realized I could check CAPS for part numbers and the part number for the EVO 7 does in fact show these exact pistons.

The only last question that remains (which I cannot for the life of me figure out) is if they also have the offset wrist pin design. Or was that adopted from 8 onwards? I'm shocked how little info there is about just the EVO 7s...

Long time ago I was taught by performance shops guys in japan that evo pistons have offset. I am not sure exactly which evo pistons have offset, but if I remember correctly, they were saying that before mitsubishi started to sell evo 8. So which means it is not only for evo 8 or 9. At least evo 6/7/8 pistons are not symmetric as you can see it. Most of shops they were doing the same way with evo 7/8/9 pistons, so I trust their way since some of them have worked with mitsubishi engines since 70s 80s. and I believe there is a reason why they do that way.
As for the rods and the wrist pins. the newer model's rods are better, because not only they are reinforced a bit, the newer has higher accuracy. Especially the small end weight. That is easier to match the weight /balance. The older 4g63 rods such as DSM/EVO1-3 don't have it unified well. And the wrist pins, the older has thiner wall (less material/less weight) the newer evo has thicker wall (more material/ more weight). When they told me about this they compared between evo 3 and evo 9, so I am not so sure if this is totally applicable to evo 7.
As well known that evo 9 piston is the best to use and have better oil rings. An another tip, I was told that there is no much benefits to use evo 4/5/6 pistons.
Good luck,

Looks like I never came back to update with results, but ever since assembling the engine in May 2019 it has ran with this EVO 7 rod/piston combo without any issue. I have it all documented in my build thread. Again many thanks to Hiroshi for confirming the specs!