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Tech / General EngineIs your car making a strange sound or won't start? Thinking of adding power with a new combination? Need other technical information or engine specific advice? Don't see another board for your problem? Post it here!
I had a XR270HR cam in my 400SBC x24 build which had a cheap roller lifter screw it up, so I've bought a forced-upgrade replacement to a Comp Cams XFI20HR13.
The problem is, the springs I had for the XE270HR were slightly too soft so the shop putting the heads together for me put some shims in to up the pressure, and I just bought a set of 986-16 springs to find out I should have bought the 26986-16 beehive springs.
Comp 987 shimmed slightly will handle that cam to 5500-5700 rpm. Maybe 5800 before it may start to float. Ran a similar spring that was slightly less pressure and it lost control at 5600-5700 rpm
That spring recommendation for a XFI cam doesn't look right somehow. Looks like WWWWWAAAAAAAAAAYYYYY too little tension, ESPECIALLY on the seat. Looks almost like it was looked up for some other cam, like some MUCH less radical flat-tappet one or something. Just doesn't look right. (even if it is? ...)
Note that the 986 & 987 are 1.45" OD and will not fit in stock spring pockets without machine work; and that some stock heads (Vortecs in particular) are VERY THIN in the place that needs to be cut for that, and you can hit water. Whereas, the PAC springs are 1.29" OD and will drop into unmodified stock pockets, and the 787 retainers match their beehive upper end to the SBC valve stem diameter. OTOH if your heads have larger spring pockets you will need to use OD type locators. Which are also available from PAC. And you might also need them with 1.45" springs, if your pockets are already all the way to 1.55". But then, if they're 1.55", use 1.55" springs, with due care, instead of any of the smaller ones.
As said above you may need new locators and such. They will fit on the heads but idk what you have on the heads now.
Most 195 eliminators came with the 8017 springs which are good to 5500-5800 with most aggressive cams and higher with softer lobes. They are 1.29” i believe. The 8019 drop in as they are 1.27”
I would not use the 986. I would go 987 bare minimum and check your bind height
I would suggest staying away from AFR's springs. Last I knew, they just were reselling K-Motion. Pretty much bottom of the barrel.
I don't see anything in Comp's catalog that's really a comfortable match to that cam. Odd though that may sound. Time to look elsewhere.
Get something GOOD. The BEST you can realistically afford, that has the right characteristics. I would be looking for 130 - 140 on the seat, 275 - 300 rate, at least .625" to coil bind.
No, springs will not cause idle problems or anything of the kind. All they do, is restore the valve to the closed position when the cam/rocker is no longer pushing on them. Most importantly a GOOD spring choice will prevent the valve from bouncing off the seat when it's supposed to close; aka "valve float". Valves rarely "float" as the cam goes over the nose at max lift; we call that condition "toss". However, inadequate push rods can cause a somewhat related phenomenon known as "pole vault", wherein the push rod bends under the stress of operating the valve, and when the cam withdraws the pressure, the push rod straightens back out and sproioioioings the rocker a few extra kicks. VERY hard on parts, almost as much so as bouncing off the seat, which literally HAMMERS the closing ramp of the cam to death. Very easy to spot during an autopsy.
I also just noticed your comment about "shop shimmed up the springs...". I can think of FEW BETTER QUICKER OR MORE EFFECTIVE WAYS to produce a BASKET OF DESTROYED VALVE TRAIN PARTS along with metal chips in the main & rod bearings that REQUIRE tearing the motor down ALL THE WAY and cleaning all the shavings out of the oil passages with rifle brushes. Good thing you're researching the topic.
So, just for the halibut, I went and looked up the specs for that cam. Comp recommends the 26986 which is a beehive. Here are the ACTUAL catalog specs:
Seat Load: 123 @ 1.750"
Open Load: 284 @ 1.175"
Spring Rate: 280 lbs/inch
Coil Bind: 1.040"
I would consider that the ABSOLUTE BARE MINIMUM, given that they call out for the same spring for some MUCH smaller cams.
As said, PAC 1218 would be a better choice. http://www.texas-speed.com/p-6431-pa...-pac-1219.aspx They are used on LS motors with aftermarket cams which in general have CONSIDERABLY more aggressive ramps than any SBC setup, but of course they don't damage stock valves seats etc. There is also a kit http://www.texas-speed.com/p-6443-pa...-pac-ks13.aspx KS-14 which has locators, retainers, seals, etc.; except that you can't use those retainers or seals because your valve stems are a different diameter, you have to use the Comp 787 retainers and matching keepers, and of course, 11/32" seals instead of the 8mm. To get the right installed height you might need offset keepers rather than the "standard" ones.
Last edited by sofakingdom; 03-26-2018 at 11:42 AM.
The hyd roller small springs are PAC and are very good
The springs that are already on the head are triple springs. It looks like dual springs with a 3rd design specifically to set coil bind, but I don't know what they were from because I bought the heads 2nd hand.
Would this mean the locators would already work for the 986-16's?
As I said I'm not looking for the most hp or high end power right now. I just need to get the motor running comfortably and back in the car. I can upgrade the springs later relatively easily.
I can get the cylinder head shop to test the current springs and let me know the specs and see if they'll be better suited to the XFI280?
Yes! Have a shop that has a good spring tester test the springs! Find out what diameters they are, the current install height on the head, get pressure of spring at current install height and find what is true coil bind and also measure pressure at .050” from that true coil bind
Do not use the 986-16 spring, it does not have enough lift capability. The valve lift .576 and you will be under .050 clearance with a 1.75 installed height. Near or at coil bind.
Do not use the 986-16 spring, it does not have enough lift capability. The valve lift .576 and you will be under .050 clearance with a 1.75 installed height. Near or at coil bind.
Hi,
Sorry can you explain the clearance bit for me, is that piston to valve clearance?
If I increase lift that would mean opening the valve further pushing it closer towards the piston yes?
If I don't have as much lift, I won't flow as much but it won't have clearance issues, which is what I want. At the moment, more power is not the goal. A working engine is the goal, once I have that, then I can look at power.
Sounds like you have some different springs then what came on those heads but if not...
When I got my afr heads last fall I upgraded to afr 8019 when I purchased them knowing I was going to use a 235-245 minimum dur at .050 hydro cam. but most 195s come with 8017. Which are pac springs. 140@1.81 and 356@1.21 .600 safe lift with 6300-6500 rpm max.
Not sure how old your heads are or what springs you have in them but if it is the no stripe 8017s then I don't see why you need more spring then that for a xfi280 cam as it's not
A terribly big cam. If you just use 1.5 rockers that's .570. .576 lift.
Thanks guys.
The builder is going to take a look at the springs and let me know the specs.
I was also going to ask with the cam rpm range and requirements...
Do they rate based on a 350?
So essentially for the 400 the rev range drops about 500rpm yes?
I'm trying to determine if the car is going to bog right down using 2.77 gears and a stock convertor with this cam, or if it's more so that it just won't have "as" much power as it can.
I'm going to put 3.45 gears and a 2400rpm stall behind a built Turbo 700 transmission, but I'd rather do that later once the car is driving again than have to try and save more and get it on the road later.
Transmission and stall change will be easy enough to do in-car, and the diff I'll just take to a shop to change the carrier and gears.
In a 400 the 280 xfi will peak nearer 5800 if heads are big enough. It will be very strong in the 5000-6000 range. In a 350 it goes to 6400-6500 peak if head is sized right and ofcourse a short enough runner intake manifold.
You can run on those stock gears for now but it will be abit of a slug until 3000 or so. I have tuned that cam on stock converter in a 360 sbc aka 60 over 350 block but it did have 3.73 gears
In a 400 the 280 xfi will peak nearer 5800 if heads are big enough. It will be very strong in the 5000-6000 range. In a 350 it goes to 6400-6500 peak if head is sized right and ofcourse a short enough runner intake manifold.
You can run on those stock gears for now but it will be abit of a slug until 3000 or so. I have tuned that cam on stock converter in a 360 sbc aka 60 over 350 block but it did have 3.73 gears
Thanks for that.
Yeah I've got to change the rear end anyway as it's only an open series 2 9 bolt at the moment, I think 3.77 is meant to be a good match for the cam, but I still want some punch and economy on the highway.
I can live with a bit of slug down low for a while, it'll be nice to see them money make a difference when the new bits go in.
03-25-2018, 11:22 PM
