I'm looking at cams now -- for street performance. ('89 w M6/3.33).

My goals in a cam include max gain in low-mid performance. (or at least not losing any low end ). I really don't want to lose the use of 6th gear on the highway (1,400 rpm at 70 mpg with my 3.33 rear end). Keeping the car capable of good mileage on the highway seems prudent in this day/age. And, keeping decent idle/off-idle performance should work in conjunction with that goal.

I've read enough stories about people who've swapped rear-ends that I'm not anxious to swap to taller gears. Too many have been disappointed with this move. Instead -- for a street car -- building a lower rpm car seems a better move (at least for me). I'm O.K. with a motor that should be shifted below 6k rpms during WOT).

After reading about cams, I realize that a faster-ramp cam is necessary to achieve high-lifts w/o extensive duration. I've read that cams are being made now that pick up the valve quickly and set it back down slower. They have steeper ramps.

It sounds like the idea is to get decent lift w/o the duration and overlap more ideal for high-rpm intakes (miniram). This results is better idle, off-idle and low-rpm performance. Yeah, I have a stick (where I could rev it a little), but I don't want to have a car that shakes and loses "street" refinement.

One suggestion was made by Comp Cams -- use their 260XFI cam. With only 202/210 duration, it achieves int/exh lifts of .56". Since those duration numbers are similar to stock duration, ramps have to be much steeper to get the valve further up/down.

Another statistic I read concerned the stress on push rods. They were described as needing to support the weight of the ENTIRE car! That's some serious stress! Obviously, steeper ramps adds to that stress. Throw in stouter springs and the "slamming" of valves and I really wonder.... (I'm not in a panic here, I just want to know the reality). What do steep ramps do for motor longevity?

I guess another question is about duration. At what duration #s does a motor transform from refined to beastly? I'm O.K. with -- and would even like -- a little lope at idle. But, it should pull smoothly and drive with street-car character. Should I try to find a cam with 210ish/218ish duration that gets .55ish lift?

Overall, I really want to hear about ramp incline, duration, power potential, mpg, longevity, etc... I'm as interested in how it works vs. how much it adds, when it comes to picking the "right" cam).

gp

 

Whats the cubic inch? intake? ,heads?,compression?

 

And, here I thought I'd typed TOOO much!

350 stock bottom end. Heads will either be ported 113's (maybe TPiS?)or AFR 180's milled to 58cc.

Intake either LT runner/base or stealth ram. (Since I want good low-end and idle, the former might be better). Remote chance of still picking miniram.

Head choice will come down to what I decide with cam/intake. (I know, that's backwards). Since my goals point to a cam that's "good" from 1200-5200 or 1500-5600, then ported heads might make the most sense. Saving the money on the "best" heads might make sense if the revs won't "ask" for massive flow.

I looked at a couple of UTube videos of the cc503 cam (suggested in a PM) and it sounded beastly with rough idle. Impressive for a racer but might not demonstrate enough "refinement" for passengers.

I also know you can change teeth to "tip a cam in" or let it run out more. But, I'm not sure if/how to allow for this. Or how much change you can get.

And, picking all the parts to go with the swap is fun. Wonder if everything has to go. (lifters, push rods, cam bearings, etc....)

gp

 

As we discussed before, you need to treat the heads/cam/intake as a system keeping in mind what you want. You specified a good idle, strong low-mid range torque, and good mileage. This dictates smaller runner heads for good flow velocity and a cam with relatively small amounts of overlap. The other thing you need to decide is if you may want to build a stronger engine in the future. This might dictate that you buy a head with more flow capability than you need for this build so that you could reuse the heads.

IMHO, your stated goal of strong off-idle and mid range performance would favor the choice of a TPI style intake over the others. You want to pick the heads and intake such that they complement each other. You will want the heads to have very good low and mid lift flow numbers to work best with this type of intake. Huge maximum flow numbers aren't needed here because a LT runner intake can't flow enough to take advantage of it, but my previous comments to you about future plans applies here. You mentioned AFR 180 heads. They are incredible heads, but TBH you really don't need all the flow they offer for this mild combination. Even a heavily modified TPI style intake can't flow enough air to take full advantage of them. That said, I believe they would work great with this type of combo and still offer enough flow capacity if you wanted to build a much wilder motor in the future. I would look at all the various head offerings in the 170-180cc range and pick the head that offers the most flow at or below .400" lift. Bigger is not always better, and that is especially true for mild motors. I think a set of ported stock heads would work great with this type of mild setup. They sure worked well for me even with a stock cam and no headers.

IMO, you need to pick the heads first. Again, pick the heads to maximize flow at low to mid lifts so that you get good responsiveness and efficiency in normal street driving. This will also define your compression ratio, which you need to know before you pick a cam. Plan on running head gaskets in the .040" range to pick up as much compression as you can.

The intake choice comes next because it will determine the basic torque characteristics and power band of the motor.

I would choose the cam last. To truly optimize the cam, you need to look at a number of factors such as head flow characteristics (lift at max flow plus the ratio of exhaust to intake flow), your planned usage, and Dynamic Compression Ratio (the "true" compression ratio that takes cam timing into account). For your stated goals, I would look at cams in the 212-218 intake duration and 225ish exhaust duration with lobe separation angles of no less than 112 degrees. The lift numbers need to be determined based on the max flow lift number for the heads you choose. These cams will all be very streetable and make great low and midrange power. The larger cams in the range will have a little lope at idle.

 

Pick the cam for the desired operating range, end of story. Faster ramps are better as you have more usable lift. Make sure your compression is within the right range after your cam pick. if the DCR is too high you're in trouble.

The 503 is a medium cam. I've been using it (or the SLP version, and now the crane version) of it for about 10 years now in various engines and I think its a perfect 'middle of the road cam'. Its probably a bit out of your powerband, as you suggested a 5200-5600 peak. The 503 is almost out of the fight around 5800, and is in full float by around 6200.

Again, check your DCR on paper with any combo you consider. It sounds like you want a slightly upgraded stock setup?

-- Joe

 

I've talked to a few people who seem to insist that a miniram (or stealth) provides ample low-end with AFR180s. But I can easily see the power advantage of the LT TPI setups in the "TPI Shootout" performed by CompCams (performed on a 383 motor). There is nearly 50hp under the curve from 2500-4500 rpm (vs short-runner intakes).


This will be the only build. No future plans. I've seen LT runner setups listed at 260 flow. AFR's 180cc say 270cfm @ .5 lift. Is that much flow really "wasted" if the cam is designed for 1200-5400 rpms? Local full porting looks to run about $800 w stock valves or $1,100 to upgrade to 2.02/1.6". AFR's are $400 more than that.

The local porting shops says they should be able to hit 250cfm, maybe 20cfm more with larger valves. This is AFR territory but they don't have past specimens as proof. (Though they can flow for $80/set).

I went down and saw their work today. It looks very thorough... runners, chambers, bowls, transitions, everthing.

AFRs??

Would ported 113's have better off-idle/low-end/street performance than AFR 180cc due to the smaller intake runner?

I checked into extra milling and looked at gains on the CamQuest calculator. I'm hearing the milling isn't worth the extra hassle. The same porter also said that the china rails should be milled to match head milling. "Big pain, little gain" was their quote. CamQuest shows only modest gains it I change from 8.5 to 9.5 compression. (as a test).

CompCams recommended the 210/218 cam with .525 lift @ 1.5 rockers. This sounds about right, but I assume the steep is much more severe than stock (since the duration is nearly the same).

This thread was primarily to investigate longevity issues. How much will the "ramp up" shorten life-span (if any)?

Will a 218/225 cam be "easier" on the parts assuming same lift? (The ramps would lessen somewhat.)

CamQuest says this work is leaning on the 400hp barrier. The right cam gets 430+hp with a miniram (closest I can find to stealth). With this much power, should I stop being concerned about low-end losses for 6th gear highway use? And, off-idle performance?

Can AFR 180's with a stealth/mini and .55-.6 cam make enough power to pull down low? Or is the goal of good low-end and the use of a miniram mutually exclusive?

Can you get a higher duration cam, a miniram, and mechanically advance the can one/two teeth (to pick up low-end response)?

I'm fully understand the point of matching parts, but don't know how much cake I can get and eat it too...

Another local porting shop -- that's run by an experienced 60-yr-old pro-stock racer and owner of a '90 vette says the miniram is best. Hands down, no question. He says he started with a ported large-tube setup, then swapped to a stealth, then finally a mini. In reality he says the mini out-performs above 5,500 rpms. But he still says it's an awesome street intake and would NEVER go bad.

He pretty much thinks I'm an idiot for even considering the LT Intake -- even though you and I know dynos don't lie.

Not sure how "talented" he really is but he's gone so far as to cut the tops out of his 113 heads to alter their design. Say he got them to flow over 270 cfm. But, it was WAAAAY TOO MUCH WORK.

He -- like another forum member -- likes the option of GM Fastburn Vortecs for the non-porting option. And, he says he trained the new cylinder head porter that I went to visit today. Of course, he thinks he can do better. He's the master to grasshopper.

Sorry, got off track... Anyone with that kind of experience telling me to get a grip and use a mini gets my attention. Until I get into a 400+ hp car with a mini, it's hard to know if he's "wrong". And, since I've driven LT1's with their similar intake -- which were very "streetable", I really have to wonder!

Too bad I only want to do this once!!!

gp

 

How do you figure dynamic compression? How could it be too high starting at 9.5 (or less) with the combo I describe? Are you asking me to worry about something that isn't an issue (for me)?

Yes, slighty upgraded to 350+hp. How "nasty" is the cc503 idle?

What "steepness" of cam ramp warrants bigger/better rods? When does it stress the motor more? Answer this and I'll do the DCR thing -- if you really think I need to.

gp

 

Here's another idea...

How about getting AFR 180s for $1400ish and install with 1.6 or 1.7 rockers. That still get's me north of 250cfm and I don't have to pull the cam!

Perfect match to the TPI. Can you say LT4 with better pickup?

 

Wow, you certinally ascribe allot to those heads..

Anyway, I think it's about $250 to have the AFRs cut down to 58CC, which you'll probably need to keep compression.

 

I'm not sure how to answer this.

Your static compression has a role in your overall dynamic compression, however the cam has more to do with it. a 9.5:1 motor with a penut cam will have more dynamic compression than a 9.5:1 motor with a larger cam.

For a beginner, this is a pretty good read:

http://www.empirenet.com/pkelley2/DynamicCR.html

You also really need to take quench into consideration, as well as chamber design.

Steady at 800rpm and 40kpa. I don't know how to explain things in degrees of nastyness, I just know numbers. A CC-306 for example oscillates between 850-950 rpm, at around 65-70kpa. A stock camshaft idles around 650rpm, steady in the mid 30s.

Steepness doesn't have much to do with rods. Run the springs the cam maker recommends, set up the way they recommend. The pushrods are either hardened for guideplates, or not for self aligning. I use Comp cams pushrods, hardened, for the correct length - they are $35 for a set, where as non hardened are about $20 a set. Once you mock up your long block, you'll need to check the pushrod length to make sure your rocker stays centered over the valve stem. Deckheight and head machining will play a dramatic role.

-- Joe

 

I use the DCR calculator that is referenced in the link. It is a very good tool for dialing in the combo.

 

For a 5,500 RPM 350 motor I would sell your heads and get the 180 AFR,s have them milled. Run a thin head gasket and try to get compression up close to 11 to 1. I would choose the 268XFI if piston to valve clearance allows, ground on a 111 Lobe sep angle . And a ported to hell and back long tube runner set up or the first intake set up with ported base.

 

Do you guys have the calculator downloaded? I read the link and understood the basics. It doesn't sound like I'd be too high -- as suggested. It sounds more like I could end up too low?

CompCams recommended a 260XFI cam (performance from 1200 to 5200 rpms). The online description says "used with 1.6 rr. So, I assume the figures are for that ratio.

Intake = 260 degrees seat to seat (210 @ .05) lift = .56
Exhaust = 270 degrees seat to set (218 @ .05) lift = .555

LSA = 113, ICL = 109

If you need it (or to make it easier)....

Bore = 4", Stroke = 3.484"

IVO IVC EVO EVC (seat to seat in degrees)
21,59,72,18

What's the DCR for this setup? How would it change with 1.5 rockers?
------------------------------------------------------------------
How does it change with the 268XFI recommended by Hoobly?

Intake = 268 degrees seat to seat (218 @ .05) lift = .570
Exhaust = 276 degrees seat to set (224 @ .05) lift = .565

LSA = 113, ICL = 109

IVO IVC EVO EVC (seat to seat in degrees)
25,63,75,21

The 268XFI is listed at 1800-5800rpms. How can I determine how well this would pull at 1,400rps on the highway? (assume LTRunner)
-------------------------------------------------------------------
Would it make sense to consider mechanically advancing/retarting either of these cams?

And, the $64,000 question... Is the guy at my head shop correct when he says I don't need to worry about piston-to-valve clearance for any cam with less than .600 lift?

That's a lot of questions.... I'll ask about "Quench" later.



gp

 

I can't remember the size of the stock L98 piston, I wanna say its around -13cc. So lets say -13cc, 58cc chambers, .044" quench (felpro 1010 gasket on a 9.005" deck, or a .020" shim on a 9.025" deck)

With a -13cc piston set up 'right' it comes out to 10:1 static which seems a little high, so lets plug in a -16cc piston and I get 9.71:1 static which seems about what is advertised for L98's.

DCR with your XFI268 cam is 8.4:1. I used the .050" IVC + 15 method,
as the advertised valve events are at .004", not seat to seat.

An IRON headed engine on pump gas does well between 7.5-8.5. On an alum headed motor I shoot for 8.5-9, which seems to make the most power.

When building an engine, these are the types of calculations you need to do.

As far as piston to valve clearance, I always check it anyway, but unless you have a TON of both lift and duration, I've never seen a combo come even close.

-- Joe

 

The L98 uses 0.051" head gaskets stock. Since Gregg is not planning on touching the block, use 0.025 for the piston depth at TDC. I can't seem to locate the notes from when I cc'd my stock cylinders 12 years ago, but IIRC I got about 11-12 cc for the piston dish plus crevice volume.

After measuring all the volumes, I found that my (at the time) bone stock 9.5:1 89 L98 had an actual SCR of 8.88. I smoothed and polished the chambers, milled the heads 0.030, and switched to a 0.039 head gasket, which brought the actual SCR up to 9.99:1.

The DCR calculator is available through a link on the web page that Joe posted above. That is the DCR calculator that I use. I have tried several different ones but I liked this one best.

 

I don't know where/how to figure those #s out. I could guess from what's been said, but I'm not guessing if it's that important!

I saw the links for the pgm (w and w/o VB6). But I also saw the extent of info required. I don't have all the pieces. For experienced builders, I thought you'd have them handy.

You are correct about the stock block and it sounds like cam timing is the only real "variable".

I wanted to see at least one correct computation before I started calculating on my own. Based on the last post by anesthes, I still don't feel comfortable I understand what #'s I need and where to get them.

But, I did get the point about DCR. It was something I'd already read a little about in discussion of VE.

My perception was you could never exceed SCR with DCR because the cylinder will never completely fill. That's why I thought it could never be too high.

 

I assume the piston "dish" size + chamber size + gasket "volume" would equal the total chamber size. And, you need to know this for the DCR calc, right?

(gasket volume = pi*4*.051") ?

 

I built a motor a few months ago and used L98 replacement slugs from sealed power and could have sworn they were -13cc but I don't think 1-2cc is going to make a huge difference.

The only issue with a .025" gasket is, I couldn't find one that thin in a MLS with a firing ring. All I found was shim or copper. Shim is fine with iron heads, but when I use alum I like to run around a .039" MLS gasket with a firing ring. Like a felpro 1010 or 1003, so I always end up just bringing the deck down to around 9.005" assuming the piston height is 9". Some pistons setup higher, some lower, but I always try to keep the piston exactly .005" in the hole.


When I run the few numbers you provided I get 9.46:1 so I'm confused.
We have a .051" thick gasket, i'm assuming dead on 4.000" bore, piston is -12cc and .025" down in hole. 4" bore hole with 3.48" stroke, and 58cc heads (113 heads, right?) and I get 9.46:1 on my compression ratio calculator:

http://members.cisdi.com/~anesthes/comp.html

Even with 64cc heads I get 9:1.

Not questioning you, just wondering where all the extra volume is ??

I use that one or the KB one:

http://www.kb-silvolite.com/calc.php?action=comp

Either seem to work fine. I don't build motors much anymore, so I only get to use 'em once or twice a year

-- Joe

 

This is interesting info!

If I understand the link correctly, the dynamic compression should fall between 7.5 and 8.5. (And, the starting point (SCR) is 9.5 for my 1989.)

If by increasing the duration enough that filling gets too "efficient" (and DCR exceeds 8.5) I have a problem, right? And, if I understand the posts above, I could consider using 64cc chambers to lower this value.

Sounds like the "right" cam could point to the use of 64cc AFR's w/o milling.

Intuition says the 260XFI is so close to stock duration that there's no problem. But, the 268XFI has enough duration increase that the calculation should be made (especially if I were to consider mechanically advancing to recover low-end performance with it's 1800-5800 rpm range of use).

And, Todd, if you raised your compression over a point thru milling heads in conjunction with the stock cam, it still sounds like I won't have a problem with either of these cams! (The examples in the link had duration changes more significant with less than a 1 pt DCR change).

gp

 

Like I said, I did the calculations 12 years ago and this is from a middle aged memory, so apply the appropriate "calibration" factors.

I wish I could find my notes, but rest assured, I did measure piston to deck height at TDC, bore diameter, and chamber and piston dish volume. I do remember that the SCR was 8.88 because of the three eights. I did the calculation manually, so there's always the possibility I didn't do it right, but I remember that I checked the calculation several times.



Gregg:

I'll PM you later with DCR calculation results.