Scalloping Intake Valves High HP/boost built NB2
 

Hey all,

So I have a high hp (404 whp) on E98 EFR6758 build. This was a TSE built block that was bought from a local guy that Ive been running at mostly track events for the last two years and some street driving. This block had the supertech double heavy springs and I believe only stock valves in the head.

Earlier this year on the second day of a HPDE event when I started the car in the AM the car was running on 3 cylinders. Did a compression test and figured cylinder 1 was down. Pulled the head at home and checked my valve lash, and had a zero lash situation on the intake side. All of my exhaust valves were in spec. I was able to order a new mazda shim, i think their 3rd thinnest shim and was able to get this back into spec. Seems that I am scalloping the valves on the intake side.

Fast forward a few more events and now the car when cold sounds like its losing compression in cylinder 1 again. When fully hot i guess things are stretching/expanding and the lash comes back. Thankfully the season is about over and its time to pull the head and send over to the machine shop. A few questions...

• What is the current best spring option for a high boost build?
  • VS855s arent available anymore correct?
  • Just go double heavys again?
• Valves, best option here again?
  • Are oversized or any other cut options on the seat better at preventing scalloping?
  • Coatings or Stainless? Does grinding the valves for seating negate this?

It seems Greg @1993z32 miatadad has gone through this and most information has been moved to other formats such as instagram/youtube and FB pages. Was hoping to get something back into this forum (unless there is something and i missed it).

Greg if you see this we talked at MATG and you mentioned a spring with a higher seat pressure and length you were going to try. Would love that info ;-)

Thanks all,
Zack @muthagoose00 on instagram

I feel for you bud.

https://www.miataturbo.net/race-prep...ing-out-82462/

Oh dang nice.. sorry missed this thread in the Race Prep sub forum.

Seems like info on ST valves is all over the place depending on what year the info is from. What is the latest on ST valves? What is the best/

Valve seat angle width and condition seems to be a big concern as well.

Volvo springs can still be had
https://vp-autoparts.com/en/artiklar...20_b30e_f.html

I've had this problem twice on my 14psi turbo BP6 engine. I'm currently running SuperTech double heavy springs and +1mm SuperTech Inconel intake valves. After about 15K miles, the intake valves and seats are in great shape.

Careful. Those are made in China. You should probably ask your USA engine builder to find you some replacements made in USA.

Some really good questions there. I have the same concern. I had to tear down my race engine after 3 hours of running, (lash was separate to why I opened it up) found that I had to re-shim halve of the valves again, cupping was very slight but the valve job was only 3 hours old. It's back together and I'll be checking the lash again soon. My thoughts are the Supertech valves after being ground loose (some of ) the hardened surface? I could be wrong.
Subscribed

The intake valves overheat and deform. The cause is not enough seat pressure. The ST inconel valves are in stock at FM. It’s a bummer that there are only a few spring options. Better springs are not the solution if they are not installed correctly. The installed height is often overlooked.

If you dont have a catalytic converter you can try a lead additive for your fuel or run leaded race fuel.

There are probably more springs options than most people know about. Most people just jump on the ST train because its a known brand name. For my track build I found a set of PAC "PACALOY" springs that Kelford offers. Their off the shelf offerings are 66lbs, but they can do custom springs.

I'm sure there are a few manufactures that will make custom springs for a price with a long lead time. It just seems that the options are relatively low for the popularity of these engines. The ST springs are not my favorite design because of the spacer. I'm actually having a slight issue with this myself. I'm running the manely intakes and the ST inconel exhaust with the ST med doubles. I have a set of the inconel intakes but before I pull the head I'm going to make a set of taller spacers to increase the seat pressure and switch to sub's.

When you say "scalloping" intake valves are you referring to the valve seat face getting worn to a slight concave shape where it meets the valve seat causing it to sink slightly in the head? If thats what you are seeing I have always considered that to be valve recession. Valve recession can be due to wear at the valve face, valve seat, or both. Is it possible you did not have stock intake valves and maybe they were replaced at some point? if so, maybe the replacement valve material may be a little softer than oem? Lead fuel additives add some lubricity which can help mitigate valve recession. That is actually whats its for.

Oh didn't realize FM sold those valves... weird that they don't list ST as the producer for the valves or the double spring kits.

Had issues for several years with intake valves.
Started using the Manley intake valves and a set of really heavy intake valve springs and have had zero issues since.

Went from putting ST valves in the motor 2 times a year to the same set living in the motor for 5 years.

One of the many issues with the OS ST valves is they are longer, and they place that length below the valve keeper. This reduces the compressed height of the valve on the seat reducing seat pressure. I found,and have tons of dyno data to back it up, that every time we went up in MEASURED spring pressure, we made more power and the valves lived longer.

Also keep in mind that high pressure valve springs on high RPM motors are a wear item. They will lose seat pressure over time.

Measure your valve spring height, and then buy a valve spring pressure gauge and test your seat pressure. If it's below 85, you need to make some changes.

and the Volvo springs are junk. I've seen them drop MEANGFUL amounts of pressure in very short run intervals.

The ST Doubles are a good off the shelf offering, but you will need to shim them up to get the advertised seat pressure out of them.

Do you have specifics on the Manley valves used? Coatings size etc?

Details on the "heavy intake valve springs" make/size/ final pressures?

The Manley Valves I uses are just their off the shelf high flow 1mm os Stainless valves. You can order them from Summitt.

The intake springs I am using right now are some that Kelford made to work with the most recent set of cams they did for me. I'm running a ridiculous amount of lift with very aggressive ramps, so what I am using for springs would be way overkill for most motors.

I have used ST Doubles in the past, but like I said, you really need to measure your spring height and then the seat pressures and shim them up to about 85 PSI.

And if you are on stock cams, they should last a while, but I'd still check them every off season just to be sure they havent moved...which I have seen....but again, my setup is a bit outside the box.