OK so I bought these heads. I am trying to find out if the springs installed on the heads now will work with the cam I am trying to run. I have narrowed the cam choice to a XE274 ( 0.487 int./0.490 exh. lift) or a edlebrock RPM cam (0.488 int./0.510 exh. lift). The springs on the heads are not stock. I took a quick measurement of the spring dia. and it is about 1.4 (I don't have any calipers handy). They are dual springs so I assume they could handle the rpm's but how do I measure for how much lift they can take?

I am still in the planning stages of this motor build and have only got the block machined (in progress), heads (ported 186's) and a Intake (RPM). I want to make sure that everything else I buy will play nicely with these other parts. I am planning on getting a eagle forged 383 rotating assembly headers, and am between getting a holley or a BG carb (money left over will decide that). If it matters then a 150 nos kit may be installed down the road (would need to change cam I am sure).

Any views on which cam? I will be getting a new TH350 with a new stall converter so I can get one to match the final setup. This car will be driven on the street and I would like to not have to shift the car into N at every stop light to keep it idleing. But, a rough idle would be ok.


Sorry for all the newb questions. I am just trying not to waste any more money than I have to.

 

The Comp cam will go faster - more area under the curve. For a 383, the next step up XE cam would be even better.

There are a few things you can do about the springs: 1) Get a real caliper so you can make accurate measurements; 2) take the springs to a shop that can give you installed and max lift force measurements - if they meet the cam requirements and don't bind, they'll probably be okay; 3) buy springs you know will be up to the task - cheap insurance.

You should also verify the valves have adequate travel for the lift you're planning. Although it would appear the springs are "performance" parts, you shouldn't make too many assumptions when building something significantly bigger than stock.

 

Thanks for the reply.

Ok here are a couple of more questions then. I can get a set of calipers. With the calipers can I measure this stuff my self? If so what am I measuring? If I just buy new springs what am I looking for to know they will work with my cam. I see the open load and seat load but I don't see a max lift on them. There is a coil bind at 1.150.
Like these for instance how do I know whether these will work or not? Obviously I will need to measure the exact outer diameter with some calipers but I am pretty sure this is the size.
http://www.jegs.com/webapp/wcs/store...10002_33272_-1

Also since the heads must have been machined to fit the larger dia spring do I have to run that size spring or could I still run a stock size spring? Would there be a noticeable performance trade off for a cam in the range I am looking at.

Here are some pics of the springs if it matters.

 

No you DO NOT want to go back to a smaller spring, if you can help it.

Likewise, DO NOT run that old POS "RPM" cam, if you can help it. Its design is 30-35 years older than the XE274. It is LONG obsolete and will either give less power, more "big cam" obnoxiouis behavior (bad idle, poor gas mileage, low vacuum, poor bottom end) than the newer design, or both. It is GARBAGE by comparison.

If you know the installed height of the springs, and since you do know the coil biond height, then max lift = installed height - (coil bind height + .060"). So for instance your coil bind height is 1.150", then that + .060" = 1.210"; if your installed height is 1.750", then you have room for about .540" lift, safely.

Yes the 986 springs would work fine with the XE274, set at the correct installed height. I've run that cam and those springs together before myself.

Another thing you can do, is measure the lift with the cam you have now; turn the engine to where one valve is fully opened, and measure the space between coils of the springs with a feeler gauge. Check the outers, the dampers (or at least you would if the springs had them), and the inners. Figure out how much more lift the XE274 will have than the cam you have now, and divide .060" PLUS the difference in lift by the number of coils, and make sure there's at least that much space between coils at full lift. Do a couple of intakes that way, maybe one on each side; and a couple of exhausts.

 

Ok so I tried doing this with the intake lobe on the number one cylinder first to make sure I am doing this right. This is what I measured:


Distance between inner valve springs (was the smallest) = .127
Lift of old cam= .387
Lift on new cam = .487
Coils on spring = 6

Is my math right?

.060 + difference in lift (.100)= .160 divided by 6 = .0266666

Since the measured distance between the springs is .127 I should be way good here right? The seems like I am off and the springs have room for tons of lift. Can you let me know if I did this right so I can go ahead and measure the other springs.

Thanks again.

Installed hieght of the springs I measured at 1.900 but not too sure I measure it to the right spot (since the bottom of the spring is kind of tucked under the machined parts. OD of large spring is 1.450.

these are the only springs on summit that match that discription but seem WAY too strong for my flat tappet cam. Am I way off with that assumption?

Crower Dual Valve Springs
Valve Springs, Dual, 1.450 in. Outside Diameter, 463 lbs./ in. Rate, 1.115 in. Coil Bind Height, Set of 16

 

It's almost impossible to "measure" installed height without the right tools.

However, it sounds like your springs have plenty of clearance for that cam.

The Crower springs are pretty typical. More likely though, the ones that are ACTUALLY on the heads, are Comp 986 or 987. Probably set up at 1.800", that being a very typical installed height for springs of that OD.

I'll let you in on a little engine building secret:

There's basically no such thing as "too much spring", within reason.

Reason, in this case, means, less than 1.55" OD.

And even that, big block springs are 1.550" OD STOCK, and the BBC uses the same lifters as the SBC. (apart from link-bar rollers, in which case the link bars are different) Meaning, even if you had hot-rod BBC springs, you're still OK with the SAME LIFTERS and the SAME CAM LOBE DESIGN, meaning you're still well within the design parameters for all of the critical parts. You gotta step up to the solid roller type suff before you exceed "reason".

Bottom line is, there are no 1.45" springs on the market, that are "too much" for a flat tappet cam. That's EXACTLY what they're made for. As long as the seat pressure and the installed height are adequate. Seat pressure should be 125-135 lbs MINIMUM (no maximum), installed height should allow .060" clearance to coil bind ABSOLUTE MINIMUM. As long as they meet those constraints, you're good to go.

At most, you'll need to pop them off when you go to break in the cam, and remove the inners; put them back on without the inners, leave the dampers in, just pull the inners. Run the motor for the ½ hour or so of break-in (whatever procedure the cam mfr is recommending these days... it's a kind of a moving target). Stay within a range of about 2000 to 5000 RPM during that time; then when the motor cools back down, put the inners back in.

Go with the XE274. You will LOVE it. It's a great cam. I had one for a while; people would just stand their and listen to it idle, and get wood. One guy said it sounded like the engine was "angry", "wanted to jump up out of there and kill something". That's what it ran like too. I really liked it.

The "RPM cam" is a POS; a true relic from the Stone Age. I've been beating that cam with ANYTHING ELSE I put in motors for about 30 years now. It's not "new" to Edelbrock, or "unique" to them, or any such thing; it's an old generic copy of a copied old generic cam they copied a copy of, that's at least 35 years oold that I know of. Don't put that stupid crap in your motor, you WILL regret it. If you just HAVE TO have it, get this other copy of the same copied copy of a generic copy of a copied cam instead. It's MUCH cheaper, or at least, less expensive. http://store.summitracing.com/partde...art=SUM%2D1107 Specs look familiar? You'll hate it just as much; the lesson in why you don't buy cams from the low bidder just won't be as expensive.

 

Ok thanks so much for putting my mind at ease with the lift and everything.

I decided to difenetly go with the xe274 because all of the terrible things I heard about the RPM (alot of those are from you in different threads by the way). I think the 284 will be a little to much cam for me after a little more research. The car is going to see alot of street use for the next year or so I think the 274 would be better.

Thanks again. I think I might have the spring pressure measured at a shop just to be sure since I have no idea how to measure that.

Also There aren't any dampers in the springs now, can I get some and throw them in or are these springs just designed to run with out them