Valve spring selection help (boosted)

[zep]

Hey everyone,

I am trying to sort the valve train for my engine build, but I am getting conflicting information from different parties. I'd like to see where the OS opinions lay.

This is for an Isuzu 4ZD1 with a 4ZE1 open chamber head.

Exhaust valves are 36.9mm
Inlet valves are 44.2mm
Boost will be 30psi max (I think)

First the cam specs - this is a regrind I had done by Kelford:

Kelford have supplied some of their valve springs with the following specs:

• 90lbs, 225lbs @ 11mm lift
• coil bind @ 26.5mm
• Install height 41mm

The Kelford rep assured me that these springs will be stiff enough, stating that they are the same as they use in their 650+hp big cam RB25DET builds.

However, I am also in contact with an oldboy outfit who sells upgraded valve train parts for Isuzu engines, as I was looking at buying larger valves. He also sells valve springs and has heavily suggested that the Kelford springs will not be stiff enough and will drop valves, and that I should buy his valves. I don't think he is trying to pressure me into buying his parts, but appears legitimately concerned. Some of the communication I've had with him is below:

Quote

It will drop valves and destroy valve train parts with that little of pressure, with 30 psi it will only have 60lbs on the seat under boost, our 4 valve 4 cylinder has 120lbs on small valve head size, my Gemini 35 years ago had 160lbs on the seat, I listened to a so-called camshaft specialist 30 years ago about the spring pressure and dropped it back to 110lbs, and it didn’t get past 7500rpm and dropped a valve, I thought it was my parts getting old, so I put all new stuff in it and fixed the damage, strangely enough it did it again straight away, I put my old stuff back in, and it didn’t have a problem ever.

[Fast Gemini drag man] had a problem with destroying valve train gear in his Gemini when he started running his car hard, he told me what pressure he had, I instantly told him to take it up too at least 160lbs, and he did and his problem went away

My turbo valve springs I sell are 140lbs on the seat, I can’t remember the over the nose pressure

I told him that I would still probably stick with the Kelford springs and the response was:

Quote

Your choice, 90lbs on a 35mm and 28mm valve is different to 90lbs on 44mm and 39mm valve, I call bullshit on running them in an rb25 also, diameter is different and they don’t use a rocker setup which they haven’t even got that right on your cam sheet, they say it is 1.5 ratio, they are incorrect again, it is closer to 1.7 ratio, a shim over bucket is different to a rocker setup

Anyway, I am totally unsure on what to do with this conflicting information. One the one hand, Kelford have been working with a guy in the Gemini community to develop new cam profiles - I sent them a head of mine to help test (so I assume they measured the rocker ratio?) and they sent me these springs as a thank-you gift. On the other hand, the oldboy has been building turbo Isuzu engines for a long time and so I assume he knows what he's talking about.

I would appreciate any input or thoughts on this. Obviously the end goal is not to destroy my valve train!

Cheers

[440bbm]

the only thing i do know, and somewhat experienced was kelfrds used to be good a long number of years back, and then a number of years back it went not so good.  when i got my cam and hyrdaulic lifters from them i also experienced some conflicting data but trusted them over alot of research.

they talked a big talk and sounded to know but i think there was an element of baffle with bullshit. 

well honestly i wish i never did and just got everything from the states and followed my own research results.  

 

sorry its not really relevant info to your actual question  #spam as usual

[dwlee]

The specs are just for the springs, not how they are installed.

With an install spring height of 41mm they generate 90lbs of force and when compressed by 11mm (spring height 30mm)the generate 225lbs of force. This gives a spring rate of (225-90)/11mm = 12.27 lbs/mm.

Lets say, for example, you install the springs with a height of 38mm, you will have a seat force of 126.8lbs. The valve lift from the cam datasheet is 0.363" (9.22mm). So at max lift the spring will be generating 240lbs of force. At 9.22mm lift and install height of 38mm the spring length will be 28.78mm, which is above the coil bind height of 26.5mm.

If you want 160lbs of seat force with those springs the install height would need to be 35.3mm, but then the spring height at max lift would be 26mm and you would have coil bind.

I think you should be asking Kelford what the install seat force should be for your application (30psi boost on a 44.2mm valve). Other useful information that may be helpful in getting a better answer is the standard spring install height on a 4ZE1 open chamber head and max rpm you intend to use.

[zep]

11 hours ago, dwlee said:

The specs are just for the springs, not how they are installed.

With an install spring height of 41mm they generate 90lbs of force and when compressed by 11mm (spring height 30mm)the generate 225lbs of force. This gives a spring rate of (225-90)/11mm = 12.27 lbs/mm.

Lets say, for example, you install the springs with a height of 38mm, you will have a seat force of 126.8lbs. The valve lift from the cam datasheet is 0.363" (9.22mm). So at max lift the spring will be generating 240lbs of force. At 9.22mm lift and install height of 38mm the spring length will be 28.78mm, which is above the coil bind height of 26.5mm.

If you want 160lbs of seat force with those springs the install height would need to be 35.3mm, but then the spring height at max lift would be 26mm and you would have coil bind.

I think you should be asking Kelford what the install seat force should be for your application (30psi boost on a 44.2mm valve). Other useful information that may be helpful in getting a better answer is the standard spring install height on a 4ZE1 open chamber head and max rpm you intend to use.

Thanks mate, this is a useful explanation. When you speak of installing the springs at a particular height, does this mean that they are shimmed to that height?

I'm going to do a bit more investigation around this. Always a new can of worms to open with these projects eh?!

[dwlee]

8 hours ago, zep said:

When you speak of installing the springs at a particular height, does this mean that they are shimmed to that height?

Yes, shimmed to give get your desired height. 

[zep]

On 27/02/2025 at 17:33, dwlee said:

Yes, shimmed to give get your desired height. 

So that means that the spring is now more compressed at the installed height. And I assume the binding length remains the same, so does that mean that shimmed springs reduce the lift potential?

[dwlee]

Yes, shimmed spring can reduce the lift potential. The binding length stays the same. You just have to make sure the compressed height at full lift is above the coil bind height with a bit of margin for safety.  

[ajg193]

Probably not relevant for OHC engines but some old Barries reckon to use softer springs for the cam break in period (obviously with no boost) to give you less chance of eating a lifter.

[cletus]

Yes I had to do that with mine, run in with just the outer spring, then fit the inner ones after

[RUNAMUCK]

^I've done this heaps of times with my engines too. 

I'd ask @BobbyBreeze what he reckons. He's not only a cam Barry, but hes also a former employee of Kelfords. 

I won't personally deal with them again. Every time I've gone In, they've rubbed me up the wrong way. Buying performance parts should be a happy experience. (Like buying a new toy when you're a kid) but this has never been the case. I'm not giving my $$$ to people who treat me poorly.

[zep]

I've had a good experience with them so far - perhaps partly because they were already working with another dude who is doing the full gamut of designing new cam profiles and rockers, etc, for Isuzu engines, so I kinda just jumped on the back of that.