bcrx7

iTrader: (5)

This have come to mind after seeing recent talks about stock head and higher RPM. Now I have not done anything to the valves or the valve train. The head is definitely ported. An associate of mine that knows more than I will ever know about engine design and modified engines (he has been building funny car 5000hp+ engines since the 80's) recommended I don't go with bigger valves. But with that big turbo I am thinking I will need the higher RPM. Would you guys recommend changing the springs over?

The head is a 99 head, heavily ported and polished. I have an EFR 8374 and looking to run ALLOFIT race only. No street use. This thing will only see under 4000rpm when it is spinning tires out of the pits!

I know the stock valve-train will most likely be fine a few times at about 8000 rpm. But continuously pushing it at 550-600hp might not be the best idea. Do I go all out with springs or something in the middle?

Twibs415

iTrader: (8)

springs to help seal the valves with all that boost you'll be running. go big or go home!

cjsafski

iTrader: (2)

I would do stiffer valve springs. My 99 head had +1mm valves and here is the result of 14 psi and the motor's first track day. 70% cylinder leakage is acceptable right?

bcrx7

iTrader: (5)

The springs collapsed???

slmhofy

iTrader: (5)

Yeah. I'm not sure what I'm seeing in the pic, other than a mess. Is that oil or water?

Twibs415

iTrader: (8)

hammered valves. the folks at supertech say valve float. how was the valve lash after that event.

bcrx7

iTrader: (5)

what are the chances of both valves having been hammered? What RPM? Of course you can replicate that at 8,500. Just curious? I do not over-rev my engine. I have been racing for over 10 years and never have and not planning to do it!

Mobius

iTrader: (2)

This has been discussed. Dual valve springs & subs recommended. Emilio has posted numerous times what is required for 8k+ rpm and will sell you the parts.

Leafy

iTrader: (1)

How much are the SUBs worth. I'm going to be checking my valve clearances this off season and installing the inner springs to my supertech duals. And if I need the change the shimming on more than a couple valves I might as well just get the SUBs. I've been spinning to 8.5k with just the outer springs of the supertech duals on the VVT head. If I can turn that up another few rpms I gain another mph for every ~125rpms and I've been hitting the limiter a few times lately while still down 200hp from the competition.

iantboyd

iTrader: (11)

why not shimless lifters?

cjsafski

iTrader: (2)

This happened to every single one of my intake valves. Rev limiter was set to 7K with no over revs. No idea on what the initial lash was since it was built by a reputable shop.

Twibs415

iTrader: (8)

what kind of valves? im starting to think supertech valves are junk.

bcrx7

iTrader: (5)

Good to know! I guess I am shopping for springs!

m2cupcar

iTrader: (5)

That would be ideal IF it exist for the B engine- does it.

If not, shim-under-bucket is. It's a significant reduction in valve load, reduces wear and improves action.

NiklasFalk

iTrader: (1)

Ford Zetec also use 30mm lifters.
https://www.miataturbo.net/build-thr...2/#post1068251

Leafy

iTrader: (1)

shimless lifters sound expensive since you have to buy new lifters to adjust clearance.

It looks like the zetec are 32.6g for 17.35mm height while the supertech subs are 34.2g + shim weight.