I managed to get my hands on a comp cams hydraulic roller cam with .502/.520 lift made for nitrous. Can I get this cam to work with my L98 heads? I know I can change the springs out to change the max lift, but how high can I go? What springs should I use to get about .560 lift?

I want them to work with my heads because they have been heavily ported and flow just fine for what I'm looking at doing. Plus they are aluminum so the weight savings nice. I know everybody will say get new heads but, I've already got the cam and don't have the cash to buy new aluminum heads.

 

If you had stock heads you'd have to get the spring pockets milled to allow for the extra valve lift. Stock heads are only good to about .480 or .490 lift before they coil bind. If they bind the springs will self destruct...

You say that you have Aluminum Heads? If so, they are not stock, and probably are good for for at least .520 lift! Check the lift specs for your heads.

 

They are off an 87 corvette. Yes they are aluminum.

 

You'll need to change the springs and maybe retainers, depending on whats on there now. Cant say if there's going to be enough retainer-guide clearance (dont forget to account for the seal) but its possible. I was running a .497/.517 on L98 AL heads and had just about enough space, there wasnt a whole lot more left. Neither the guides or spring seats had been machined... but check your heads as they may be slightly different, you never know with factory stuff.

 

comp 981's are the common ones for that type of application. Use .050" offset locks, and new retainers. Positive seals if you don't have them.
You'll need a pack of shims. Using calipers, measure the spring height with valve on seat, and measure clearance with valve open all the way, etc. Shim as needed. That setup should be good to .550" lift. Just using the 981's will be good to ~.600" lift, but you may have guide boss interference (usually the first point of interference, before coil bind), so that's why I said use the offset locks ($20), and shims. That'll bring the assembly up higher, so you shim it to bring it back to a decent spring pressure.

 

one main concern should be piston to valve clearance DONT assume or things could get real ugly. i destroyed an engine that had 0.005 clearance!! be careful

 

Well I was told wrong about the cam. It's a hydraulic flat tappet but the specs are .488/.510. With my 1.6 rockers this becomes about .520/.544. Can I still achieve the lift I'm looking for? Can anyone give me a complete setup with all the parts I need?

 

EEEeeeeewwwwwww..... the "RPM" cam, or some other copy of the same generic relic that it's a clone of...

http://store.summitracing.com/partde...art=SUM%2D1107

You're about to spend a couple hundred $$$ in parts, and no telling how much in labor, to put in a $50 cam that you'll HATE.

Don't do it. Give that pile o' junk away. Nobody in his or her right mind will buy it for enough to make it worth the trouble, unless they're an even greater idiot than me, which there probably aren't many of in the world, so don't bet on being able to sell it, and certainly not for very much (see price on link). Get yourself something better.

 

I used the specs off that cam on my desktop dyno. The results were pretty goodwith and without nitrous. Why do you say that I will hate this cam? What would you reccomend. I like this cam simply for the extra exhaust for running nitrous. I have a book by David Vizard that actually reccomends these cams for running nitrous. What would you reccomend?

 

No, he does NOT recommend THAT particular cam.

There's A WHOLE LOT MORE to a cam than just the printed specs. The problem with that cam, like all of the rest of its 40-year-old brothers, is that the ramps are vvvveeeeeerrrrrrryyyyyyy lllllooooooooonnnnnnnnggggg and lazy. Not quick and snappy like modern cams. They're a relic from the days when there was no such thing as aftermarket heads, aftermarket valve springs, CNC casting, and so on. Totally obsolete.

Look at the Comp NX series of cams. The "numbers" might look similar; but they're COMPLETELY different.

A modern cam will give you considerably better performance for any given level of "big cam" penalty (poor idle, very bad gas mileage, soggy bottom end, impossible to drive when it's cold out, plug-fouling, etc.) that you're willing to tolerate; or conversely, less of that classic "big cam" misbehavior for any given level of performance. We humans have actually learned a thing or 2 about cams, as a species, in the decades since that old Stone Age thing was the hot ticket.

That "big cam" crap that you get out of those ancient Neanderthal junk cams, without gaining the benefit of actually having a "big cam", is why you'll hate it.

 

check your pm ,jimmy

 

I wan't saying that specific cam. I was just stating a point. I wouldn't use a summit cam. I was planning on getting one of comp cams nitrous cams. I had hoped that this cam would work out, since I was told it was a roller cam, but now it's not looking like a great choice.

This is the cam I was thinking of getting now
http://store.summitracing.com/partde...5&autoview=sku

with my 1.6 rockers the lift would be about .520/.534, so I would still need at least .540 lift. Suggestions?

 

Why?

What would you REALLY like your car to do?

Do you want a car that runs strong; or do you just want .540" of lift? What if you could make your car run better with LESS THAN .540" peak lift, than it would with MORE THAN .540" of peak lift? would you still want .540" of peak lift?

What do your heads do at that lift? Is there any ACTUAL BENEFIT in terms of flow, velocity, HP, or whatever else, that magically begins to occur at that point? Given that the bore shrouds the intake valve, do you know that the flow in your particular setup would even continue to GO UP if you got past .540", and not instead START GOING DOWN like it sometimes does, if you continued to increase the lift?

Do you realize that even with a cam that gives .540" of peak lift, that over 90% of the time that the valves are open, they'll be at less than .500" of lift; and 80% of the time, they'll be at less than .400" lift?

Do you want a roller, or not?

I'd think that there are alot more important things to think about, than .006" (less than the thickness of a sheet of copy paper) of PEAK lift, when designing a motor or picking a cam. But I'm an imbecile and a moron, so maybe I'm missing something?

 

With all due respect faulball67, it might be worth taking a minute or two to work out the entire combo, rather than getting focused on one part of the picture.

I've found that (despite his assertions to the contrary) sofakingdom is more often than not on the right track. When you're picking a cam for a street-driven car, the term "less is more" is absolutely vital to how satisfied you'll be with it.

The advice I generally give to people is to "Narrow it down to three cams, & then throw out the biggest one!" (I've used an over-cammed SBC as my daily driver for a while, it sucked until it warmed up & never came on until about 3500 RPMs, & then the heads stopped flowing at about 5100 - so I try to help others learn from my mistake.) Needless to say, with my current street/Bonneville salt car, I've taken several months to learn everything I can, & I'm STILL not convinced I've settled on the best cam yet...

I've taken a couple minutes to find a little bit of info that'll help you zoom in on the right cam for you - first, the flow numbers for your heads. This will be one of the biggest factors in figuring out which cams will function well in your car.

Next, here's a small brochure that specifically talks about picking a cam for a N2O'd small block. (Note that there's a line on p. 5 that reads "Ultra high lift cams are not needed to make power with nitrous".)

Finally, I don't have any real way of knowing what/how much knowledge you may have about cam specs/selection, so here's a pretty decent five-page article that may be worthwhile for you.

I hope this helps. And yes, you might be leaving anywhere from 8 to maybe even 20 peak horsepower on the table with the smaller cam - but you'll also have fewer concerns about valvespring life, piston-to-valve clearances, etc. and probably have a greater "average" power level with better driveability.

Good luck.

 

My basis for the cam is the rpm range at which it is rated compared to the rpm range I want run, to produce the best horsepower at the track, combined with other peoples real world experience with these heads, and computer generated dyno runs. I already have the stock head flow specs but thank you for actually being helpful. I really wish I knew my exact head flow specs. I would like to get them flow benched, but as I am not from around here, it is difficult.

I do know some about came selection. I know more about using nitrous and the increased exhaust flow I need in order to use the ntirous most effieciently. The reason for the cam is more in the duration than in the lift. I know I keep mentioning lift but it's not the goal. The lift is a result of the duration and LCA I'm looking for. The 1.6 rockers is the fact that I already have them for my current cam. I spent a pretty penny on them and they sure as hell aren't being resold after less than a 2000 miles of use. So please don't sit here and go "why do you want that much lift". I know what I want out of a cam. That's why I just started asking about lift.

 

Ok then, back to the original question... assuming you have a better cam choice in hand.

Have the heads machined for bigger springs and more clearance for larger cam lifts and be done with it. Its not going to be ideal but thats what you need to do if you're set on the cam, heads, and rockers.

 

What I've always done is whatever cam I think will give me what I want, go one step down. Hasnt failed yet.

 

Not dead set on using these heads. I'm trying to get a feel for what I'll need to (money wise) to do it versus going and buying a new set of heads that can take more lift and possibly flow much better. Looking like with machine work and parts I could probably sell the heads take the money combined with the money for machine work and new parts and just buy a set of brodix IK200's and get better numbers.

 

Oh yeah, no question about it. (I've read several times that by the time you figure all the $$$ needed to recondition & buy the parts for stock heads, you're already into the range where you could get decent aftermkt heads...)

In fact, what I am doing is "building my engine around the heads" so to speak - I've gone without coffee (& occasionally lunch), and saved my nickels for three years until I could afford to get the AFR heads that I was dead-set on. As you're no doubt aware, once you've got good heads, everything else becomes a lot easier...

I'm fairly sure that (if you decided to sell those alum. L98s) you could probably get most if not all of the cash needed to get a set of Vortecs or similar, maybe more...