4G63 Forge build, ring gap and running in questions

Good evening

Firstly i want to say hi my name is Karim and this is my first post and am excited to start using this forum.

I am currently building my 4G63 long rod engine for my evo 8. This is my first engine build and won't be the last. I have bought all of the necessary equipment to carry out the job properly and I am confident in carrying out the work.

My fall down in this build is having the knowledge on what clearances to run and how to correctly run in the engine.

I have Oliver xtream rods, weisco pistons, kelford 272 cams and ACL bearings.

The aim is to be running approx 450-550 max bhp and the car will be used for fast road and light track use.

When checking my piston ring gaps, it is clear they need adjusting. I have bought a manual ring file but what gap to use is bugging me. Wiseco have a chart in the ring packs with a formula to calculate the gap. Using that formula my gaps should be 0.016" top ring and 0.018" bottom ring.

Whenever I research this subject, people seem to use a larger gap than this. A theory from one person is that the top ring gap should be bigger than the second ring, as the compression passes the first ring, it opens it up creating the seal. Is this true? Others say the second ring should be bigger to prevent ring flutter.

Also can anyone offer advice on running my engine in? I have read that the engine should not be left to idle when started as it may damage the cams? And that it should be driven on and off the throttle to bed the rings in.

Any help on this would be excellent

Thanks

Karim

Hi Karim and welcome to the forums. With regard to ring gaps, we have seen a shift in the general trends over the last couple of decades. At the start of my career we tended to gap the second ring tighter than the top ring since the second ring isn't exposed to as much heat and won't expand as much. More recently though the trend has reversed and we gap the second ring a little looser. The reason for this is because we will always end up with some amount of combustion gas escaping past the top ring and we don't want this pressure building up between the top and second rings. if this happens it can destabilise the top ring which will affect engine power dramatically. I'd recommend you follow the recommendations from the piston manufacturer as those gaps are in line with what I'd personally use.

You may want to check out our practical engine building course as this has a specific module on engine break in. With a roller rocker cam such as those used in the 4G63 cam break in isn't a big concern like it is with a flat tappet cam in a pushrod V8. The main consideration during engine break in is the piston rings. To bed these we want to apply moderate load to the engine and vary both the load and rpm we use. As you've noted, we want to avoid periods of idling, particularly when the engine is hot.

Wow Andre thanks for the superfast reply!

Your information and advice has really given me confidence along with the courses that I have done.

I will now use the manufacturers figures as you have suggested above.

I just want to take this opportunity to tell you directly how excellent what you guys do at HPA do. I am a tech myself and before I found out about you guys I thought my learning was limited to the training of the manufacturer I work for.

I look forward to taking part in more of your courses in the future.

Thanks again for your help

Karim

Thanks for the kind words Karim! Great to get feedback like this :)