skinny z

Since the fuel pump lobe went flat on my XR276HR (and I don't like the electric pump that I've installed to keep the show on the road), I'm in the market for new cam.
I intend to keep my Vortecs, with have been upgraded with Bee Hive springs, screw in studs and guide plates (and have lift clearence beyond .550"). I also run Pro Magnum 1.6 rockers. The current valve job on them duplicates the OEM spec which I understand is pretty good.
That said, while I'm reasonably happy with the performance (12.7 @ 108 and 1.7 60' w/ 3750 lb race weight) and mileage (22+ mpg hiway) perhaps a cam change will bring the package up to another level.
So, the question I'm asking is: who has done what with stock (or near stock) Vortecs and what are the results?
I understand the 062 castings (three points on the head face) are flow limited at lifts beyond .490" or so on the intake. It was posted here that flow actually DECREASES beyond that and doesn't recover. Take that bit of info as you will.
Is there something to be gained by choosing a lobe that has a max .490" lift while maintaining a duration that will produce power in the rpm range targeted (SCR to follow suit as needed). I've been searching the Comp Cams master lobe index.
I'm looking at that style of intake lobe combined with as big an exhaust lobe that's practical. Tighten up the LCA to 108 with the typical 4 degrees of advance built in.
Suggestions? Experience?

86LG4Bird

iTrader: (1)

Go MORE than that lift since you have the heads upgraded to handle it. You want as much TIME as possible at that lift, so that means peak is going to be significantly higher. And no, you WON'T lose significant flow at peak lift to offset what you've gained.
Forget about going with "as big an exhaust lobe that's practical". Stay within about 6 degrees of your intake duration and about the same lift. On a NA setup with the Vortecs, that's about as good as you can do.

skinny z

Interesting.
Reading the flow numbers shows that flow decreases with lift past .500".
I've also read that the flow doesn't recover as you decend past that mark (and I know the Internet is often full of crap). Understanding the conventional thinking about lift and the fact that higher lifts give you more time at a targeted value, I've done precisely that with my XR276HR and 1.6 ratio rockers. That is, if .500" is ideal then go to .540" which gives more time at the .500" mark.
But...
There are few out there that have made great power with lower lifts and I question why they do it (using lower lift values that is). There's a verified 358 making 480 hp at 5900. Lift is .485" on a solid flat tappet cam. No duration specs are listed but with peak power at 5900, it's a safe bet that advertised intake duration is in the 280+ range.
Not sure what to think. I have the oppotunity (need actually) to replace my cam this off season and I'd like to make a move that will a) Make me faster and b) not kill the excellent driver I have now. (Still pretty quick at 108 AND 20+ mpg carbed).
Thanks for the input.

86LG4Bird

iTrader: (1)

An engine does not behave like a flow bench. There's no fixed pressure drop across the head port/valve during the intake stroke. It's a very dynamic situation, a lot more action going on than the head sees on a flow bench.
I know you can make big power numbers with low lift and high duration, as in lift-limited "stock" racing classes. But those engines are far from what you would want in a street motor. With roller cams especially, for every example you can find of a low lift combo, it would be a better street/strip motor by bumping the lift up and taming the duration, or even bumping the lift with the same duration. Flat tappets are more limited as to how much lift can be achieved for a given duration without unduly abusing the valvetrain, so I can understand the example you quoted.

skinny z

Based on that, and the conventional thinking I had mentioned earlier as well as advice of other known engine builders, you can't get enough lift into an under valved engine such as a SBC. (Undervalved as in sq.in. of intake valve area vs cubic inches to fill).
I suppose then that the notion of the Vortec achieving poorer flow with increased lift based .490" or so is more a matter of flow bench results? One would still be better off putting in as much lift as possible while targeting a specific duration value.
It's tough to use a computer model to try and identify any real anomoly with the Vortecs. I don't have enough data available to build a useful example. That said perhaps I'll continue on with my existing cam profile, maybe tweaking the LSA or maybe even adding MORE lift. I like the overlap values where they are (LSA notwithstanding) as it's resulted in some decent hiway mileage although a lot of that I can attribute to carb that's tuned to within an inch of it's life at cruise rpm.
I've got an entire off season to contemplate my choices.

InfernalVortex

iTrader: (4)

Dude if it were me and I was building a street car, I'd run an LT4 Hotcam on there and use regular 1.5 ratio rockers instead of 1.6. It iwll put your valve lifts right at .500 if I recall correctly, and the duration will still be aroudn 218/228. Hotcam vortec setups are damn quick, do a search to get an idea.

Im going to assume you're equipped for roller cams giving the XR276 cam you had.

Going beyond that stall point for lift in the Vortec ports wont mean you have a net loss in power, but it will mean your return on your investment so to speak starts decreasing rapidly. You want to maximise your duration and minimize lift - look into the Comp Cams 4x4 cams. That's precisely what they're for - more duration and lower lift, without getting into the crazy lift-rule type cams which from what I understand are brutal on the valvetrain.

Roller:
http://www.summitracing.com/parts/CCA-08-414-8/

Flat tappet:
http://www.summitracing.com/parts/CCA-12-243-3/

You can afford to go bigger than those, but I'd suggest beyond that you go check out the comp lobe catalog and just look through. The roller lobe section is pretty short and you should be able to pare it down pretty quickly to stuff in the neighborhood that you want to run.

skinny z

Given the direction of this thread, why would I step BACK in camshaft profile by going to an LT4? Less duration and the ramp profile is getting pretty old compared to the latest XFI or even the XE designs. I can see an increase in DCR with the shorter duration but the 112 LSA isn't really suitable. I'm even considering tightening up the LSA to 108 from the current 110.
You do raise an interesting point with the low lift/high duration cams being tough on valvetrains. That's the kind of info I was looking. I've already busted a rocker stud (at cruise rpm) and I figure the 1.6 ratio rocker arent' helping any.
As for the Comp catalog, I've been living in it for the last couple of days. I've picked a few lobe profiles from the master lobe index trying to keep the lift in or around .500" and the duration similar to what I have now. I've found profiles in the XFI line that have very fast ramp rates. The duration at .050" is the same as my current XR276HR however the advertised duration is a few degrees less. That would be interesting. What I'd like to do is build the cam with this custom profile and see how it stacks up against my current piece with respect to overlap and "area under the curve" so to speak.
Where does leave me with the Vortec flow curve? It seems there are two thoughts here at the same time. Keep the duration up and the lift modest (as in the 4 x 4 cam profiles) and the other notion of putting as much lift in as possible to keep the "sweet spot" open as longer.
As for the LT4 cams being quick, I'd bet I have them covered if you compare apples to apples.
Keep the ideas coming. I'm all ears.

InfernalVortex

iTrader: (4)

Ive seen combos where those hotcams do some amazing thigns with vortec heads.

I didnt notice til I was halfway through writing my post that you actually did list what your old cam was... I just didnt read it as thoroughly as I should have, hence my hotcam suggestion. But they are common and cheapish, so that has its own advantages. But I didnt realize at the time it was smaller than what you had.

As far as worrying about the valve train, I'd bet as long as you dont run those lift-rule cams you'll be fine. Some of those solid roller lobes are pretty intense, too, but you're running a hydraulic setup, so those are irrelevant.

I'd be very curious to hear how a lower lift high duration roller setup like the 4x4 cams would compare to a more modest duration high lift setup in some vortecs. I would assume that with the drop off in flow past .500 or so lift on Vortecs that a low lift, long duration cam might spend more time in the ideal lift ranges than a high lift setup, but who knows, maybe that's not the case - even if that is the case it may not necessarily be a better performer.

skinny z

No worries about firing off a reply and then catching the rest of the thread. I do it all the time!
As for your curiousity, that's my intent exactly. Can a cam be spec'd that has 224/230 at .050" duration range but keep the lift below .500"? I've found lobe profiles that are pretty close .At the present time, I'm at .530/.540 with 1.6 rr. Maybe too much intake for the Vortecs but the exhaust needs all the help it can get.
I've even started a new thread asking for Vortec combinations and some 1/4 mile data.

86LG4Bird

iTrader: (1)

There's some confusing information in this thread. Infernal, maybe you've found some exceptions, but 4x4 cams are typically high lift/aggressive ramps with low to modest duration. They're really meant for trucks that dont' get revved over 5000, and are VERY hard on a valvetrain if you rev it like I think skinnyz wants to do in a street/strip car application.
The LT4 Hotcam is an old style lazy lobe design, has a lot of overlap (seat to seat timing) that its .050 values don't indicate; it is VERY easy on valvetrains. Stepping back to 1.5 rockers on that cam would make no sense. It's a decent cam, but as you said, he already has more cam than that.
skinny, with the duration numbers you're considering, you're beyond the range where you need to worry too much about exhaust flow through those Vortec ports for NA use. If you find a cam with numbers you otherwise like, don't hesitate to use 1.6 rockers on the intake and 1.5 on exhaust to keep exhaust lift within your springs' capability. I picked up some low end torque and 1/4 mile performance changing from 1.6 to 1.5 exhaust rockers on my 228/234, .610/.610 cam in my LT1.
I'm assuming your present cam is the CC503 (XE lobes, 224/230 dur @ .050, .536/.544 w 1.6's)? If so, you are FAR from getting the potential out of it in a 3650 lb car. Changing cams is not your road to better performance at this point. .......However, if you must, then I'd just contact www.advancedinduction.com for a custom cam. They have some grinds specifically designed to make great power with good street manners with stock LT1 heads, which have virtually identical ports to stock Vortecs.

86LG4Bird

iTrader: (1)

Which Beehive springs do you have? If 915's, then I'd be hesitant to run any more cam than you already have. It already has rpm capability at the limit of what the 915's can control while accomodating that lift. If 918's, then you have some headroom.

InfernalVortex

iTrader: (4)

That definitely explains why the 4x4 flat tappet cams have so much more lift than the roller 4x4 cams.

skinny z

[QUOTE=86LG4Bird;5053457..... rev it like I think skinnyz wants to do in a street/strip car application.....
The LT4 Hotcam is an old style lazy lobe design, .....
I'm assuming your present cam is the CC503 (XE lobes, 224/230 dur @ .050, .536/.544 w 1.6's)? If so, you are FAR from getting the potential out of it in a 3650 lb car. Changing cams is not your road to better performance at this point. ......[/QUOTE]

I keep the redline at 6000. That's about the limit of my cast crank (ARP rod bolts and hypereutectic pistons).
Agreed on the old LT4.
I know there's alot more in the car without a cam change. It's the need to replace the cam because of a flat fuel pump eccentric that has me thinking about possible cam upgrades.

I have the 918s. I've also had the guide bosses cut down for positive style seals so there's more clearence than I'd ever use.

Looking through one of Vizards Vortec flow charts, it doesn't illustrate that the flow decreases with lift past .500. It does show a flat line above this level however.
He's also spec'd a cam very similar to what I currently have. Interestingly, it's a single pattern cam whereas I thought Vortecs liked more exhaust duration. I'm not sure how the EQ head differs from the OEM Vortec in terms of performance potential.

http://www.popularhotrodding.com/eng...k/viewall.html

86LG4Bird

iTrader: (1)

Did you resize the rods when you rebuilt it with the ARP bolts? If so, I'd say that 6000 imposed rpm limit is more conservative than you need to be, and you could utilize more of your cam's potential by shifting about 6500. If you didn't resize, then I agree 6000 is prudent. What type of rods do you have?
I shift my rebuilt stock bottom (cast crank, resized LT1 rods w ARP bolts, hyper pistons) at 7100. I have about 200 passes on it over the past 2 years.
I mentioned Advanced Induction earlier. Another advantage of going with their cams is that they're billet core, and much higher quality than Comp. You won't have to worry about wiping out a lobe again. The minor price difference is well worth it.

skinny z

Yes, the rods were resized.
Rods are OEM. Either "X" or "Pink".
I actually shift at 6500 on the 1-2 shift so as to drop more into the meat of the torque curve. The 700R4 has a large spread between 1st and 2nd gear (as I'm sure you know).
I know I COULD move my redline up however I like to be on the safe side.
I'll check out the Advanced Induction web site. I have lots of time to gather information and put together a plan. I've been considerjng a little port work on the Vortecs (seeing as the guides are smoked and have to go in the shop for service anyway) and that may lead me into a different direction regarding cam spec.

skinny z

Reading through several old threads here and it would appear that the faster Vortec cars (besides being lighter by about 600 lbs) run a little more duration and about the same lift as my XR276HR w/ 1.6 rr. Some with LSA's of 110, others at 108.
Seems the lift bugaboo of diminishing flow past .490" is largely ignored.
450 hp is around the resulting hp judging by trap speeds. Calculator theory says I'm in the 420 range, (hard to believe though even with a trap speed of 108 in a 3700lbs chassis).
Looks like there isn't much room to move up in performance (cam wise) unless I make the step to more of a drag oriented car as opposed to an all around vehicle. Bigger cams generally equal less drivability although I can't say if a XR282 or 288 (to 5800-6000 rpm respectively) is going to kill my mileage. I enjoy 22+ mpg on the hiway.

InfernalVortex

iTrader: (4)

So from your research the XR276 is one of the better cams for vortec heads?

I've gotten quite bored with my little baby XE262 (218/224) cam... wou ld love to move up to something quicker... and I just couldnt find the big thread taht had Vortec build ET's and part numbers. I know my car has more in it.

skinny z

My guidelines:
Used as a daily driver (when the weather's nice)
Weekend drag racer with slicks. 3500 stall. 700R4 with 3.73 rear gear. 3750 lbs.
Decent mileage as I'm often on cruises of a couple thousand miles or more.
Performance and drivability to match about what I have now. A little quicker is the objective.
Optimize the characteristics of the Vortec head.
This is what I've found:
David Vizard spec'd cam for "Sledgehammer". 224 @ .050", .352" lobe lift , 108 LSA.
Cam Quest program:
High Performance Street, Choppy To Mild-Rough Idle, 280 HR or XR276HR.
Drag - Excellent Bottom-End Torque, Choppy Idle, XR270HR, 268XFI HR, XR276HR.
Drag - Street Machines, Rough Idle, Lower Stall Converters Ok, 286HR, XR282HR.
The quick Vortec cars in this forum have cams that are consistently larger than these previous specs. Solid rollers seem to be the hot ticket if you really want to be fast. Not too friendly for a cross country cruiser though.

It would seem that lift values over .500" and seat duration of 224 or slightly more is the suggested route. LSA's of 108 are spec'd by Vizard for any 350 he builds (or so it seems). That's not EFI friendly however I run a carb so I'm considering 108.
What I have to do is check the current profile I'm using now and see how it stacks up with a tighter LSA. A small increase in overlap isn't bound to impact the drivability too much.
I'm just about at the limit of my static compression ratio except for using a steel shim head gasket or having some machine work done. A cam with more duration will require a bump in my SCR to keep the compression pressure up. I like a DCR of at least 8:1 and my cranking pressure around 200 psi via a compression test.
Still more research to do.

skinny z

Well it seems that when considering Vortec heads (in unported form) and my performance objectives (both in hp/torque and drivability/mileage) what I have (XR276HR) is about as good as anything out there.
I've researched tightening the LSA, shorten the duration to keep overlap under control and looked at potential lift targets considering the Vortecs limitations.
I've determined that there may be some measure of increased performance from a cam swap, particularly with something in the 108 LSA, 270 (adv), .550" lift range. Putting in LESS cam timing ups the compression pressure and makes a noticeable jump in low engine speed torque. Along the lines of 20-25 ft/lbs according to the simulation programs I've run. This doesn't do much for the overall peak power numbers though.
Solution: Step up to better heads. Keeping in mind the small intake port the engine prefers and the Vortec platform I've already established, the RHS Pro Torker Vortec fit the bill. The same simulation programs shows 30+ hp at the top end as well as the previously mentioned increase in torque realized from a cam swap.
The upside to me, performance notwithstanding, is that my current heads are in need of a valve job. That's about 75% of the cost of the RHS heads.
So for what it's worth, that's where my search for another cam has led.
Thanks for all the input to this point. It's always good to have a sounding board.
Looking for 2/10's off my previous best et.

InfernalVortex

iTrader: (4)

Im looking at this cam because it's a fair bit cheaper than Comp,a nd is VERY close to the XR276:

http://www.summitracing.com/parts/HRS-110245-10/

225/231 .501/.510 (summit's site is wrong), and 110 LSA

Would like to go a little bigger but you seem to imply there's not much to be had... but what about for something like this:

http://www.summitracing.com/parts/HRS-110325-08/

225/233 .525/.530 with a 108 LSA

The first has a 1600-5400 range, and the second a 2000-5400 range...

skinny z

The specs appear very close as you say however I can't speak for the actual profile. Is it an older grind perhaps predating the XE Comp series? Otherwise I would think that it will perform similarly to what I have now.
As for the 2nd selection, with a 108 LSA and the duration numbers, the overlap gets a little too much for what MY objectives are. The XR276 w/ 110 LSA has 59 degrees overlap. The Howards with 278/286 and 108LSA has 66. For me, that kills mileage and to a certain extent, the drivability.
Further up the page Howards has a 113215-08. 270/278 on a 108 LSA. Pair that with some 1.6 rockers and it's right on target for what I was experimenting with. In your case, with the T56, I been even more inclined to consider it. Tighter LSAs tend to tighten up the power band, and make the torque curve a little "peakier" (for lack of a better word). You can see that in the operating range specs. The manual shift allows you to stay in the selected rpm range.
Of course this is all dependent on your actual compression ratio. If you're running 11:1 or 8.5:1, the cam choices are entirely different.

skinny z

By way of comparison, your current XE262 has 46 degrees of overlap.

spurgeon76

It's an older grind but Chevy High Performance made over 400 hp with a Carb'd low compression Goodwrench 350. Comp Cams 268 Xtreme Energy camshaft (224/230 degrees at 0.050-inch tappet lift and 0.477-/0.480-inch valve lift with 110-degree lobe separation angle)

Read more: http://www.chevyhiperformance.com/te...#ixzz1l0BaexZm

DeltaElite121

108 LSA would probably be a good choice for using the vortecs since you're desiring a narrower powerband (compared to what it could be, potentially). You could probably go with a 106 if you wanted to depending on how you'de like to go about doing things (or how radical you'de like to get). I bought a cam from Crower that you might find interesting, but it's flat tappet. I'll see if I can dig up the cam card.

skinny z

Yes. The XE268 had been the mainstay of 350 engine builds for quite a while. Making 400+hp with it and decent heads seemed academic.
Like you mention though, it's an older grind and there are improvements to be had.

That would be interesting to see. I've been plugging specs into my simualtion program for about a month now and observing the trends. I haven't tried 106 LSA. That would make for a peaky engine but I imagine if you could stay in the powerband, you'd fly.

DeltaElite121

I know my cam from Crower is like .490/.490 with 1.5's ground on a 108; but the duration is higher. Off the top of my head it's like 238/242@50 IIRC.. a little out of your powerband, but I saw that they had some other ones like this cam in some regards that would work nicely with your application because they've got quite a few cams specific to certain uses in their catalog.