Help-PONTIAC 400 Springs

2889 Views 6 Replies 3 Participants Last post by doogank, Sep 24, 2003

doogank

Discussion Starter · Sep 23, 2003 (Edited)

I am having a head assembled to use the SBC valves and read that a pontiac 400 springs is a good combo.

Is there certian spring type/model I should be using?

Also how much material can be machined off the intake valve seat to get proper pressure?

I am currently using a cam with .425 max lift.

Any help would be appreciated

Thks
kel

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Mach1Tom (R.I.P.)

· #2 · Sep 24, 2003

Hi Kel,

I checked my reciepts & parts list from my recent rebuild at my friends machine shop. I used Crane valve springs # 99893-8 and Crane V-spring retainers # 99953-8. (I believe 1.44 dia springs)

As for the machining of the intake valve spring seat, your machinist will need to figure that out. It depends on valve seat depth & each head will be different. (roughly .050" or so)

Send me an email & I can send you more info on my machine work & parts used. I'll also have it at the OAA gathering at Allen & Vickies house. Hope to see you there.

Tom C [email protected]

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doogank

Discussion Starter · #3 · Sep 24, 2003

Thanks for the info Tom.

the other concern is the amount that can be machined off the int valve seat. looks like there needs to be alomost .090 that needs to removed to get proper installed height/open/closed pressure.

We did test using a std chevy spring. to get some comparison on open/closed pressure. 238lbs/113lbs. Binding is also a concern, but it looks alirght so far. that is again at max lift of .427

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RallyBob

· #4 · Sep 24, 2003

Head castings vary somewhat, but generally they're .220" - .250" thick under the spring seats. What retainers are you using? I ask because generally I have had to mill .050"-.055" from the intake seats only.

Watch for high spring pressures too, if you are running a hydraulic cam you need very low seat pressures to avoid lifter collapse. You didn't mention the cam duration (more critical than lift for spring pressures), but if you're not gonna rev it about 7k or so, keep seat pressures down to 95-105 (max), and about 200-225 open. The 'open' number is subject to change depending on valve sizes, retainer type (steel, ti), max rpms, and cam duration.

There's a photo of a cutaway 1.9 head in the 'Opel Roller Cam/Roller rocker arms' thread.

Bob

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doogank

Discussion Starter · #5 · Sep 24, 2003

Thanks for the reply's!!!!!

I p/u'd a solid lifter cam from Bob D.

It's .250 dur @ 50. max lift s/b .425. Thats all I know. do not know lob sep or if Ext is different? offset etc...

the springs we are looking at right now are std. chevy sbc springs, end cap and retainers. for both Int/Ext.

With this combo, the Ext seat will need to be shimmed and the Int needs to be machined.

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RallyBob

· #6 · Sep 24, 2003

I think you are using aftermarket SBC retainers then, standard are 1.25" and won't fit the 1.44" Pontiac springs.

With that much cam duration, you'll need more spring pressure...about 105 seat pressure is still good but you'll want to bump the open pressure to around 240-250. So you'll need to use a relatively short inner spring which is largely 'inactive' or under minor loading at seat pressure, but increases the open pressure substantially by about .400", as your maximum lift is not too great....only around .405" after valve lash is taken into consideration. With this much pressure, you can safely run to 7800-8200 rpms without valve float or valve bounce.

Another alternative is the Crower spring/retainer combo I usually use with 11/32" valves. I mentioned it in the thread for the 1.5 litre head. http://www.opelgt.com/forums/showthread.php?s=&threadid=1992&perpage=20&pagenumber=2

Bob

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doogank

Discussion Starter · #7 · Sep 24, 2003

Yes the SBC std springs and retainers were the ones we were testing with. that is were we got the numbers of 113lbs/238lbs seat/open pressure.

Reason I asked to look at the SBC springs is B/C I was worried about how much maching would need to be done on the int valve seat with the Pontiac 400 springs. Again looks like there needs to be a ton of machining that would need to be done to fit those springs.

So I read it as this-with the cam at .250 dura/solid lifter I need a spring no matter make or model or size that gives me a 105lbs of valve seat pressure and a quick open pressure at max of 250lbs open.

The combos that have been able to give this type of load/pressure is Pontiac 400 or the other, that I will read more on, is crower spring/retainer.

If i can accomplish this then I should be good up to the 8000 rpm range if the spring/retianer/etc are better quality liek the crower.!

Whew!

Sounds great to me.

thanks a bunch guys.

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