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Cam & Valve Spring advice .... 140-160

Hi all

I have the opportunity to buy (at a good price) a good 2nd hand Isky Z-322 cam for my 144 - plus a set of Isky lifters, pushrods & 625/626 double valve springs.

Anybody had any experience with this cam ? For reference, it's advertised specs are :

Intake 32/68
Exhaust 68/32
Lift 0.480
Adv. Duration 280

My car is running a B20 with slightly modified "E" head (basically just ports matched to manifold, & a little unshrouding of the valves ... no major port work) with a D cam. Standard integrated manifold (no secondary butterflies here in Australia !) with HS6 carbs & twin downpipes to 2.25" exhaust. Bottom end has been balanced. 5-speed Celica gearbox.

The engine is coming out for a freshen up in the next couple of months anyway (hopefully just a set of rings & valve stem seals - bottom end should be OK) so I was thinking it would be a good opportunity for a cam change if it was worthwhile.

Car is a combination daily driver / hobby car (I do a bit of rallying & dirt autocross in it). Not really chasing outright top-end hp, but a little more "urge" is always a good thing :o)

Ideally I would like the car to rev cleanly to 5500-6500rpm - which it won't do at present without "running out of steam" around 4500-5000 (although that may be largely to do with the fact that it is a bit down on compression in a couple of cylinders).

Also - regarding the valve springs ..... would I really need to use the double springs with this cam ? Given that the head would need to be modified to fit them, it would save a lot of hassle if I could keep the existing springs.

The valve springs in the car currently are not standard (although they are single coil). The are a "D51888" spring from Performance Springs here in Oz. Specs (from the companies website) are :

OD 1.080
ID 0.755
Seat pressure 1.530:65
Open pressure 1.130:190
Coil bind 1.101

Are these likely to be adequate for the Z322 cam ? Not sure how they relate to the specs of standard springs.

just as a side note, according to various receipts I got with the car when I bought it, it is running Datsun L20 valves - which at 44mm/35mm are the same size as late B20 ones !)

Interested in the thoughts/experiences of people with more knowledge on this subject than me !

cheers

Dave
Victoria, Australia








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    Cam & Valve Spring advice .... 140-160

    Its your choice whether you want an old design cam that is that "racy " in a car that will be street driven, but you really need to look at the valve and spring specs. The springs you have are actually weaker than the stock Volvo springs.
    Clearly inadequate for that cam and not at all what Isky would recommend.
    Also, if memory serves me, the Datsun valves may be a bit taller than the Volvo valves and have a different type of lock which sits higher on the stem. So check your actual installed height before chosing valve springs if you are keeping those valves.

    Regards,
    John
    Vintage Performance Developments








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      Cam & Valve Spring advice .... 140-160

      Thanks for the advice John.

      I'm not actively chasing a cam change really ... it's just that this package of stuff has been offered to me so I figure I should consider it !

      When you say "racy" .... what sort of characteristics would you expect a cam of those specs to have, in general terms ? From my - admittedly very meagre ! - understanding of cam specs, the Z322 appears to be fairly similar in terms of duration & valve timing to the Volvo D grind, but with a lot more lift ? Is that broadly correct ?

      Your comment about the valve springs is interesting ! I had just assumed that the springs in the car were an upgrade from standard - otherwise why would you do it ? All the engine work was done by the previous owner, so my understanding of it is limited to what he has told me + what I can glean from the various receipts for work that came with the car.

      I am thinking I might be better off leaving well enough alone for now ... just getting the engine freshened up and seeing what it's like then. It will be a good opportunity to get the actual valve opening etc checked anyway, & see whether the existing cam is excessively worn or not.

      cheers

      Dave








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        Cam & Valve Spring advice .... 140-160

        No time right now for a long cam disertation. But breifly, a race cam is designed for peak HP in a comparatively narrow power band at the top of the rpm range, most likely from 4,000 to 7,000 or 5,000 to 8,000. Low end torque was usually not important in the design and was sacrificed for high end power. ( try having to rev to 4,000 rpm to pull away from each stop ) I say "was" because these are old cam designs. More modern cams, even for racing, strive for a broader power band and the average HP over a specified rpm range rather than peak power.
        With modern changes in cam lobe design you do not have to have a long duration high lift cam to make decent power, and do not have to sacrifice low end power.
        In any case, a race cam is not what you want on the street. And any cam with that much lift ( .480 ) is going to require special valve springs, in fact stronger than the 625/626 that Isky shows as their dual spring for B20.

        Never assume that a previous owner did anything that was logical or reasonable.
        Do not consider this cam similar to the D cam. And remember that advertised cam specs tell you very little about the actual cam design as nothing about the lobe shape is specified. 2 cams with the same duration at .020 and the same max lift can have entirely different lobe shapes, and markedly different durations at say .250 valve lift.

        Last word. Everything has to be matched to work together.

        Regards,
        John
        V-performance.com








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          Cam & Valve Spring advice .... 140-160

          Thanks John

          I have have read through a few of yours (& others) dissertations on cam theory etc on the board, but admit that they make my brain hurt a bit ! So much information to absorb ....

          In any case .... sounds like the Z322 most likely won't be a good thing for my situation, so I think I I'll just stick with the "tried & true" formula (E head, D cam & twin SUs) that is in the car at the moment, rather than get on an upgrade/development merry-go-round.

          Dave








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            Cam & Valve Spring advice .... 140-160

            Don't want to discourage experimentation.
            You don't know what fun is until you've spent a couple of days trying different cams on the dyno with different jet and carb combinations. The fun part is finally findingt the best one. But unless you like doing that, have the time, and are doing it for the fun of experimenting, just installing a cam because its available and inexpensive, is not usually the way to go.

            I've got a better and easier suggestion.
            The actual valve lift in most of these engines varies by as much as .020 or more
            just based on differences between the stock rockers. This may not seem like much, but we can see a difference in power just by tightening up the valve lash a few thou. Rockers I tested last week varied from 1.43 to 1.58 ratio. Just swapping the same rockers around on the same shaft they came from to even up the intake and exhaust lifts and help the ones I thought needed help on that engine gained us 4 HP. So if you have access to a bunch of rockers, go through them and install the ones with the highest ratios, being careful to match up the ratios on exhaust and intake valves as much as possible. Then swap the highest ratio ones from intake to exhaust and vice versa, and see which way gives the best power. This gives the same effect as changing cams and is a hell of lot quicker and cheaper.

            Regards,
            John
            V-performance.com








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    Cam & Valve Spring advice .... 140-160

    i am using a similar Isky cam with dual springs and their lifters and pushrods in a b20 powered 122 wagon.the engine pull strong past 5000rpm even being limited by a restrictive dgv carb. the wagon has a 4.54 diff which helps acceleration but limits top speed. check that the valve spring retainer does not contact the top of the valve guide a at full valve lift.







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