Oversized valves - SR20 intakes / exhaust

[madjak]

Has anyone other than Wozzah tried installing Nissan valves in a BP head?

Stock BP valves as follows:
Head Diameter: I 33.00 | E 28.00
Length: 102.00mm
Step Diameter: 5.94mm

SR20 Valves:
Head Diameter: I 34.15 | E 29.15 [ I +1.15mm | E +1.15mm ]
Length: I 99.70 | E 100.50 [ I -2.3mm | E -1.5mm ]
Step Diameter: 5.97mm

RB26 Valves:
Head Diameter: I 34.64 | E 30.15 [ I +1.54mm | E +2.15mm ]
Length: I 102.30 | E 101.60 [ I +0.3mm | E -0.40mm ]
Step Diameter: I 5.97mm | E 6.94

The SR20 valves are easy to pick up for free if you know any Nissan guys as they always have destroyed motors so there are heaps of them around. In fact, I'm picking up a set today. I'm not sure what the stock exhaust valves are made from but they don't have any issues with big boost levels and high temp so they should be fine in a boosted mx5. Other than being slightly to short, they should fit in with just a rehone of the valve seat and solid lifters.

[zossy1]

We have always used Supertechs. They are not too pricey and very good quality.

What sort of collets do the Nissan valves like? Do you use Nissan or Mazda retainers?

[Magpie]

Been done to mine, including SR20 springs.

[1600Dave]

My thoughts :

1. .03mm bigger diameter valve stem would need to be considered, is there still enough clearance, or will you need to ream the valve guides to suit ?
2. Bigger valve head without any porting - may actually hurt power ?? as you are putting a bigger "obstruction" in the inlet path.
3. Valve length not as important as "installed" length - ie how / where do the retainers grab the valve ? What does the cam / rocker operate on in both motors ?

[madjak]

This only applies to a few select people. Those wanting to port their heads so need larger valves and those trying to save some $ by DIYing it.

I fit the bill perfectly... tbh supertech valves are cheap enough but as most of you know I like to live on the wildside and experiment with new ideas. Plus you can't get cheaper than free!

I just picked up a set of valves from a SR20DET. The intake valves look great and I'm betting the stock collets will fit on as from memory they look identical. I'll compare the two valves tonight. I also think they are a bit meatier but they do have a nice radius on the outer rim and a small back cut scallop before the seat. This backcut could probably be a bit larger for better flow.

The exhaust valves are a thicker stem... 1mm extra by the looks of it. The top is still 6mm but it flares out below that all the way to the base of the valve. I think the SR20DE engines run 6mm shafts whilst the SR20DET engines run 7mm so maybe I need to grab the other type.

In terms of fitting these into a valve guide... if you are porting the head most likely these need changing and they will need to be bored to fit any valve. Those on the real cheap coukd probably fit them into a worn guide and make them a bit snugger... I'll try them tonight in my 200k protege head.

Magpie, I'll have a look at the SR20 springs and see how they compare.

[madjak]

SR20DET Valves

[manga_blue]

I'm struggling a bit to understand why you'd go to shorter stems. Invariably big valves go with big cams. Big cams on B6 and BP motors almost always mean reduced BCDs, either because of the necessities of regrinding or to get enough lift without fouling the tops of the bucket sleeves. You'd normally want to increase valve length in line with BCD reduction. Otherwise you'd have either shim overs that looked like poker chips with adverse stress and inertia impacts or tall shim unders with stability problems due to high slenderness ratio.

I'm with zossy here. Get Supertechs and match length to BCD.

[madjak]

Yeah the RB26 valves would probably work better given their length are longer than oem... but those valves are massive! Wozzah showed that they can fit in a BP head but it would be a very epic build.

I was hoping that they might work with two shims, one on the valve stem, one on the bucket but I won't know until I have everything together. With the cams in my race engine the cams have a very small BCD, and the two shims there are still fairly small. I figure it would easily move out a mm or so to fit the shorter valves.

Has anyone tried to retrofit hydraulic lifters into solid lifters?

[zossy1]

For a max effort build, you would want to back cut those valves for best possible flow.

By the time you stuffed around doing that... You could just buy Supertechs... Which are already back cut...

...but given this is Rick...

Have at it mate!

[zossy1]

Has anyone tried to retrofit hydraulic lifters into solid lifters?

Not sure I understand...?

[madjak]

You can pull the guts out of the hydraulic lifter, keep the shell and fit a solid shim instead. Basically convert them into a solid lifter. Maruha sell a kit.

I could buy Supertech valves, solid lifters, supertech dual springs, get it all ported and machined proffesionally but where is the fun in that? Plus its a BP05 head anyway...

This is a complete DIY performance (I hope) build... the challenge I set was to do as much as possible myself for as little as possible snd learn lots in the process. I'll never get it as good as my existing race head, but for a DIY rotrex build, it only needs to get to 75% and it will be awesome. My end build is somewhere around 11.5:1 compression, 270 - 280 deg cams, E85, 8300rpm, c30-94 Rotex for around 400whp. It's going to need to flow well so bigger valves will be required.

Btw the valves in my race head aren't miata valves. When I pull it off next I'll have a good look but they are either fully custom or machined from a Nissan valve. So someone out there has more info!

[madjak]

Ok update: the intake valve slides right into the valve guide nice and snug. It actually fits better than the stock valve probably because the valve guide is worn from use. The exhaust valve doesnt fit so I'll need to source a SR20DE one or get the guide bored out.

The intake valves are very close in length, with the SR20 one being slightly shorter... less than 0.5mm. The retainer collet slot is narrower on the SR20 valve so I'll need to see if the nissan collets fit into the stock retainer washer.

With the exhaust valve they are essentially identical in length. If they were the same shaft size as the intakes they'd drop straight in to.

Left: BP05, Middle: 1998 Protege, Right: SR20DET
Intakes:




First things to note is the differences between the two BP valves. The BP05 has a much larger back cut but also a square edge on the outer rim. Whilst the Y2 (Protege) has a smaller backcut but a nicer chamfer in the outer rim. The SR20 valve has the smallest back cut but a nice radius on the outer rim.

Left: 1997 Protege, Right: SR20DET
Exhaust:


Exhaust valve is much bigger... pretty much 2mm oversize. I think the SR20DE valve will slide right in if the shaft size is smaller than the SR20DET valve I have.

I think these SR20 valves might be a good option for anyone with a damaged seat. Simply get the seat machined to suit the larger valves and run the nissan springs and retainers (if they fit). It would be a cheap option and equivalent to the Supertech +1mm intake and +2mm exhaust. If you have some nissan mates you should be able to get a complete valvetrain set for free given they tend to hole so many motors. Add $300 for seat machining and apply a bit of DIY porting and you have an upgraded head.

I think I'll give it a go!

[zossy1]

Most of Gary Stewart's engines run converted HLA solids.

Deckspeed uses converted HLA solids too.

They work fine but are heavy compared to Supertech/Mazdaspeed solids.

[madjak]

You can't back cut the SR20DET valves because they are sodium filled. Is there any value in trying to fit them over the non sodium filled 6mm valves? They probably restrict the flow more due to their thicker stem. Maybe they would be useful on very high boost motors due to the exhaust temps.

I'm getting a complete SR20DE head so I'll see if its worth running the nissan springs or not. I have a set of Eibach evs singles I can use too.

I may as well go full frankenstein on this head and try lots of craziness. Give the HLA conversion a go too.

[madjak]

I started porting the combustion chamber last week and it's actually quite awkward to get in around the valves and smooth it out. I'm going to struggle to get them all the same, so given I have the CNC machine setup in the workshop and I do 3D modelling for a living I figured I'd take it high tech.

First step, I photoscanned the head. I took around 30 photos with my mobile phone in a few orbits around the chamber and then run them through AGI Photoscan to make a high detail model. It's amazing how well phone photos work! You get a better result with no-reflective surfaces so it's handy the combustion chamber is pretty dirty and the valves are covered in carbon. I can average the ups and downs when I model it so it doesn't matter if the scan is noisy, as long as it is accurate.



I scaled the model to match the dimensions of the head which is around 81.4mm diameter. I then 3D modelled over the top of the existing surface. Here you can see the larger SR20 valves in position with the valves unshrouded out to the 84mm diameter mark. This then gets blended back to the original chamber profile.



Before:


After:


Note: you can see the big ridge where Mazda bored in the valve seats. Even with stock valves this ridge obscures the valve a lot. It's really hard to remove though without damaging the seat so thats where the CNC machine comes in.

Lastly, here is a shot showing the intersection of the two models. When I machine this on the CNC machine I can slowly work this down to clean up all of the chamber.


I'll load the head up on my CNC machine tonight and get it cutting. It will be interesting to see how it goes!