FireDemonSiC

Been trying to decide what route to go as far as camshaft slection. want to get as much of a diversified response as possible. Here's the skinny on the engine. It's a 3.766" bore by 3.75" stroke (Yes it is a 305 stroker and I would appreciate it if we could all stay on topic. Obviously if I've come this far I have my reasons for doing this build which do not include ignorance or stupidity). The heads this motor is using are the Trickflow 175cc aluminums for small bore motors. I just ordered them yesterday. Using a steel shim gasket I should be able to get just shy of 10.5:1 static compression depending on the deck clearance.

Full ROLLER valvetrain with comp cams beehives. Intake is a TPI (It is very important to mention that the runner length has been modified. We are NOT dealing with stock runner length. See attached photos) with siamesed SLP runners and the plenum fully ported and matched. Base is a stock GM base that has been ported to match the diameter and efficiency of the SLP runners. Exhaust is getting switched up. Will be longtubes with a 3.5" straightpipe. The car is pushing a 150 shot of nitrous which I am trying to factor into cam decision to an extent. Wet kit with a throttlebody plate.

Transmission is a built full manual 700R4 with a 3000 stall 9.5" street edge converter. 3.73 richmond gears out back. Vehicle is equipped with an EBL flash system, so tuning will not be an issue.

As for my goals with the engine and the car, its primary focus where it will spend at least 80% of its time will be on the street. It needs to have a good enough torque curve to keep me smiling from light to light and while zipping around town, but I also don't want to be left wondering what could have been when I let 'er rip on a 2 lane country road or for the days I do take it to the track. With that being said, I've been researching and discussing cam options with a few reputable people. I've come down to a few choices:

268XFI - While this is a no brainer cam for my setup, I'm concerned it might not take full advantage of my engine's top end breathing room.

280XFI - The exact opposite of what I listed above. While I know this cam will realize the full potential of my setup HP wise, I am concerned that a 280 will be "overcamming" and kill the torque curve, in the end to the point where it will be a very poor trade-off for the little extra bit up top.

Custom Grind 274XFI - My reasoning for considering this was obviously something in the middle of my dilemma. That little extra bit of duration I'm looking for without going too big. The trade-off for the small amount of mid-range I'll lose over the 268 might be made up for with the increased duration on the exhaust side making better use of N2O vs the 268. Still enough torque down low and under the curve to keep me happy especially considering stroker motors can make more efficient use of higher durations without sacrificing too much.

Lingenfelter L210035087 - Just for flavor, I'll go ahead and throw this one in the mix. Yeah, I know there's nothing outrageously special about the lingenfelter cams, but it looks like this one has a bit more duration on the intake side (Not enough that it will really matter) at 219/.050" vs 218/.050" for the 268XFI. It loses a fair bit of duration on the exhaust side (219 vs 224) which will hurt nitrous performance in particular, but I figured I could somewhat make that up with 1.6 rockers on the exhaust side. The reason I chose to list this cam is if I am reading the valve timing events correctly, the intake valve timing on the lingenfelter cam closes much sooner than the 268XFI (41.5* vs 63*) which will really put a bump in the dynamic compression. Now again, that's if I'm reading it correctly. Because the comp cams spec sheet says "CLOSES" while the lingenfelter sheet says "CLOSING" Does that mean oranges to oranges, or is the degree comp cams lists with the valve fully closed while the lingenfelter one is as the valve just begins to close? Here is the spec sheet for the lingenfelter and 268XFI cams:

https://www.lingenfelter.com/sites/l...ard%20v1.4.pdf

http://www.compcams.com/Company/CC/c...?csid=208&sb=0


So, what does everyone think? The block is going to the machine shop next week so I do have a bit of time to weigh my options and come to a decision, but I'd like to consider as many things as possible. Ideas? Thoughts?

86LG4Bird

iTrader: (1)

1. Most importantly, Forget completely about the nitrous when picking the cam. Seriously. Optimize the cam for NA operation, and you will make more total hp when the 150 shot is added. "Nitrous" cams are not for little shots like this. Any cam similar to those you list have more than enough early exhaust opening and exhaust duration to evacuate the spent gases with the 150 shot.


2. With only a 3000 stall, I'd be thinking ~268 to 274 duration cams. However, I wouldn't run either of those particular cams you list. I assume you're thinking the 113 LSA because of the nitrous? .....see #1
Think NA power, which in your case means maximum TOTAL power.


334 ci is not a lot of cubes, and for street driving I'd want to maximize torque just after that 3000 stall point, which is probably going to call for something like a XR 270 or XR 276 cam with 110 LSA and 4 deg advance (106 ICL). I prefer the XE lobes over the XFI for valvetrain durability above 6500 rpm on a street car that will see significant miles. If you plan to shift lower than that, then the XFI lobes on a similar LSA would work out great. Also, consider a custom cam from Lloyd Elliott www.elliottsportworks.com I'm pretty sure that would net you a few extra ponies over any cam you or I could spec out from the Comp lobe catalog.

FireDemonSiC

I totally agree with your suggestions. I'm just trying to pick an approach that gives a piece of the pie to everybody, hence the idea of the 274XFI grind.

I plan on revving the engine to 6500rpm max, maybe a few hundred lower than that.

FireDemonSiC

Looking at the XR276. I actually had considered this grind as well but was leaning more on the XFI line due to the higher lift numbers. I COULD throw some 1.6 rocker arms on with the XR276. That would bump total valve lift up to .536/.544. I would think that should be ample lift for my combination and intended use. I honestly do like the idea of a 110* LSA better due to the characteristic choppy idle sound. Like I said, tuning isn't an issue

TxTtopZ

Yeah, looks like youre right on track with what were doing... I've dealt with Lloyd (Elliots port works) and that dude wont steer you wrong. Im not a fan of N20 but that doesnt mean I disagree with using it on your set up. A small 305 stroker can def. use it.

So for the rest of the combination what are you using? 5.565" rods or the 5.700"?
What pistons? Who's crank?

83 Crossfire TA

iTrader: (2)

while a bigger shot will gain more from an N2O specific cam, N2O specific will typically just mean a little more exhaust duration and LSA. it will cost you maybe <5hp/lb-ft NA and gain you more like 20 each on a 150 shot...

I know what I would do if he plans on staying with the spray. OTOH if it was just something that I screwed around with occasionally....

More than the xfi 268 intake lobe will likely move him out of the power band that the intake and heads will be happy with, and will put his torque peak over 4K with the small cubes shitty breathing and 3K converter won't be a recipe for fun.

I do agree with the tighter LSA if he was staying strictly NA, and then something like the XFI 260 ground on a 110 LSA would be really interesting. it would keep the power band down to where the intake and converter would be happy and give monster torque in the mid range. I'd be that combination would have a lot of people wondering if he had a big block, or at least a big cube small block under the hood, even though it would give up maybe 6-10hp at the top end.

an XR 269 (no real 270) will have THE SAME intake .050 duration as the XFI268, and the 276 will only have 4 more degrees, so in the end they will be very similar cams with a slightly rougher idle. Um, what's the advantage? A little bit easier on the valve train?

He already said he won't go over 6500rpm and he doesn't have the parts to support over 6000rpm... there is 0 reason not go go with a more agressive lobe like an XFI lobe here, except that he has a history of having valve train(spring) problems.

No, don't... I've haven't seen him come up with anything at all interesting (though everyone does bow at his feet...). I've put in for a suggestion a few times and 2x I got cam specs within a degree of the sort of generic cam that was in the car at the time and had significant gains by picking lobes that I did what I wanted on my own. One time to the tune of 8hp at the same rpm, and 34lb-ft at 300rpm lower (making for a much more usable power band) and a second time with a gain of .38s in the 1/4, with no other changes.

FireDemonSiC

This is kit I've had waiting patiently for over a year now.

http://www.summitracing.com/parts/es...3053/overview/

FireDemonSiC

Great points. Now to make things more interest, let's throw a cc305 into the mix and how it compares to the generally settled upon 268XFI:

268XFI - 218 / 224 duration @ .050" (268 / 276 Adv.)
.535 / .531 lift (Using my existing 1.5 roller rockers)
113* LSA / 109* ICL
Intake valve closes 63* ABDC (Dynamic compression ratio of 8.5:1 assuming a static compression of 10.45)


CC305 - 220 / 230 duration @ .050" (276 / 290 Adv.) <----- There's our extra bit of intake duration and exhaust duration for N2O
.547 / .544 lift (By upgrading to 1.6 roller rockers)
114* LSA / 110* ICL (Did I mention that I love a choppier idle ? )
Intake valve closes 40* ABDC (Dynamic compression ratio of 9.66:1 assuming a static compression of 10.45; dangerous?)


How do the two compare?

TxTtopZ

Doesn't say rod size or piston compression height? Im not a fan of Eagle but that's another story. 260XFI looks like it might have too early intake closing event and create too much DCR.

86LG4Bird

iTrader: (1)

CC305........absolutely not. That would be far worse than any other cam mentioned in this thread. It's a proven dog. Long ago, several people used that one in 350's and have moved on. And it's not hard to see why; the old Magnum lobes have less area under the lift curve than the XE, XFI and other better lobes. Long slow ramps that bleed off cylinder pressure at low and mid rpm's (Your IVC event for this cam above is way off; I guarantee it will give a lower DCR than the other cams).
I'll repeat: for this engine, disregard the "little" 150 shot when choosing your cam. You need to optimize the NA powerband characteristics to make it a fun snappy car to drive around; adding exhaust duration and earlier opening is just going to compromise the low and mid range torque. The comment made above about possibly costing ~5 hp NA and giving ~20 on the jug is simply not true here. Your total hp with your engine will be better by just picking the correct NA cam.


83 Crossfire, I agree with all of your other comments about staying smaller with the cam duration in light of the 3000 converter. If he were shooting to optimize ET's with slicks, I'd tell him the same thing (it's what I would do personally ). I just got the impression that he's more interested in street performance with normal street tires where that hard hit would be wasted. Also keep in mind that Edge is one of the "looser" brands when it comes to actual stall versus rated, so his will behave more like a 3200 Yank or Vigilante.

FireDemonSiC

Car is running DRs with full suspension (Lower control arms, subframe connectors, PHB and torque arm to name just a few components).

I'm thinking it might just be within my best interest to either stick with a 268XFI or contact comp for a custom grind with just a bit more duration than that. Definitely not a 280 though.

Also, you are correct about the DCR. For whatever reason I found last night that comp lists the valve timing on the cc305 at .006" which is why the intake closing ABDC number was 40. Strange...

FireDemonSiC

After reviewing data and hearing everyone's responses, I think the two choices I've come down to are either a 268XFI with 1.5 rockers or XR276 with 1.6 rockers. XR276 obviously gives a bit more duration however with a stroker motor that might not be sacrificing too much streetability and also leaves some headroom for if I were to swap to a shorter runner intake later down the road. However, the 268XFI will better maximize my current setup and not leave me disappointed with the powerband which in itslef might be what persuades me to swap intake setups. Although more finnicky to tune, I'm not afraid of the 110* LSA either and it will have a much more appealing idle sound to it than the 113* LSA of the 268. DCR of either cam should be about spot on. Definitely not a 280 though.

Man, this is a tough call...

NufNuffZ28

iTrader: (10)

Man, I typed a huge thing and it all got deleted


Basics of it were

1) get rid of NOS plate. NX nozzle at same jetting picked us up .4/10 on a stock car

2) XR276 sounds good. You need more exhaust bigger for the nitrous

3)No matter what, your TPI will only turn 6000(and still making more power).

4) 300 stall is fine, but for MORE track use bump it up slightly

Orr89RocZ

iTrader: (20)

268 on a 110 would be fun.

FireDemonSiC

Single most important consideration to remember: This is primarily a street car (Not a DD but would have no problem reclaiming that role if the situation ever called for it) that will see occasional track time.

As far as the 110* LSA on a 268XFI, I was considering that, but want to leave myself a bit more open in terms of future possibilities without sacrificing a boatload of my current setup's torque within the street range.

Like I said, this is a tough call. Maybe I should just say hell with it and install VTEC?

NufNuffZ28

iTrader: (10)

3000 stall will be fine.......

Just switch your nitrous setup!

FireDemonSiC

I was referring to cam selection with that last post. I drove the 9.5" on the street for a few days after I installed it to get a feel for it and loved it. Just could tell it was starving for a better power band than my boat anchor flat tappet had to offer.

As for the nitrous swap out, FIRST I have to get it running right before even considering any changes. Ask me what happens when the valves float at 4500rpm while on the juice from **** poor springs...

FireDemonSiC

Let me stir the pot again here. What about an XR270?

It's honestly not that far off from the 268XFI. Same duration numbers (With the exception of 2+* on the adv intake duration) and I could achieve .528 / .536 lift numbers with 1.6 rockers (Since TPI and street car, I am thinking that going too big on the lift numbers in conjunction with a higher duration is going to kill midrange torque). It does have a tighter LSA and ICL at 110 / 106 vs 113 / 109 for the 268XFI. Valve timing is also slightly earlier. DCR would be approximately 8.5:1

86LG4Bird

iTrader: (1)

Yes. See post #2
In light of the extra information that's come out in this thread, I'm even more in favor of it.


BTW....higher lift won't "kill midrange torque". It won't hurt it at all.

TxTtopZ

268 on a 110 would have some serious TQ. Can you say wheel spin in 3rd?

InfernalVortex

iTrader: (4)

If you're worried about teh LSA and ICL, that's what the cc-502 cam is for. It's the same as the Cc503-xr276 relationship. So you can go that route. Just depends on how much lift you want. The CC-502's grind numbers is 269-HR-12 so that may be what 86lg4bird was talking about earlier? It certainly matches up with what he's saying as far as I can tell.

FireDemonSiC

I'm thinking of contacting comp and having a custom grind done. Something with an XFI lobe so I can get the higher lift numbers without having to go 1.6 on the rocker arms and give up valvetrain geometry stability. A bit more duration. I'm thinking something like .222 / .228 @ .050" which would be about a 272XFI and with 110* LSA.

83 Crossfire TA

iTrader: (2)

Untouched internally LT1 (T56 and >4000lb car on 17" nittos), 220/230/112 gmpp cam, 11's NA and 10's on a 150 shot... It was my DD... do you think I cammed that for NA or N2O, and would I feel _any_ difference if put a shorter exhaust lobe in it?

His car is lighter, smaller cubes, with not as efficient a head (that flows maybe slightly more with that small bore) and the intake flows less, the converter is much tighter than my >5K clutch engagement... he has similar constraints WRT to what he wants it to do... the more modern XFI lobes will let him do more with less duration, the smaller displacement and limited top end (I was shifting at over 6500) also will want less duration...

We won't get into my current 305 build...

Orr89RocZ

iTrader: (20)

I'm all for it. Longer stroke is gonna eat up some cam. You'll be fine with something like that and you really dont need to worry about float until 5600 ish rpm with those xfi lobes and a spring that doesnt have atleast 130-140 lbs seat pressure and 350+ open for double springs. My friend ran the 280xfi on 120 lb seat 320 open single springs and float occured at 5700.
With your beehives it should go to 6000 just fine

FireDemonSiC

For sanity's sake, I think I've decided to go with a 268XFI but I am strongly leaning on having it ground with a 110* LSA. The one drawback is comp is asking $411 for JUST the cam -____-

Orr89RocZ

iTrader: (20)

Wow is it on billet core?

InfernalVortex

iTrader: (4)

112 LSA isnt good enough for you?

http://www.compcams.com/Company/CC/c...csid=1106&sb=2

FireDemonSiC

Not enough lift.

FireDemonSiC

Honestly I have no idea. I wouldn't think it would be any different from a regular XFI core.

Orr89RocZ

iTrader: (20)

Just seems expensive. I thought comp charged the same price for custom catalog lobe cams if you chose the specs and shelf lobes.

And for these aggressive hyd rollers, demanding higher spring loads, a billet core is advised.

FireDemonSiC

I finally got ahold of someone who knew what they were talking about (The previous two times I called I think I got the same guy.

This tech said unless I specifically requested a billet core or that the custom changes were drastic enough to the point they didn't have an off the shelf core for it, the cost would be no different than a srandard off-the-shelf grind. Better bet I got his name and extension.

So now that we've established I can get a 110*LSA grind, only thing to make sure of now is that the lift and duration numbers of the 268XFI are best for my setup and its intended useage. I'm thinking yes, but still open to any further suggestions.

Orr89RocZ

iTrader: (20)

Thats more than enough lift for that motor.

FireDemonSiC

Definitely enough lift (It should be noted that I am using 1.5 rockers if XFI line so lift would be .535/.531 if 268). Moreso referring to duration. I'm thinking the existing numbers of the 268XFI fall right in between the sweet spot of not enough and too much. Also another thing to take into consideration, by changing the LSA to 110* we are increasing overlap.

Remember, this vehicle's primary usage is down backroads, stoplight to stoplight and cruising on an occasional trip.

Speak now or forever hold your piece.

Orr89RocZ

iTrader: (20)

Cam is good to 5800-6000 in that long stroke. Seems good enough for your useage. Could go inbetween 222/226 or similar to push abit more top end. Seems like a nice street cam. I like to go abit bigger on cams

FireDemonSiC

One thing to consider though is increasing the duration while also narrowing the LSA will also increase valve overlap. For this car's intended usage and given the fact it will predominantly be operated on the street, this might do more harm than good.

6000rpm seems like a number I'd be comfortable with. I want this little mouse to be reliable as much as feisty.

Orr89RocZ

iTrader: (20)

Thats not alot of overlap to begin with. I would not worry. Things dont start to get fun until 10-12 deg overlap at .050 on something like that lol

My street 383 was fine with 19.5 deg. Hell even my turbo car has 22

FireDemonSiC

What I am most concerned about is how going bigger will affect the torque peak at stall speed in the streetable range (3000 - 4000rpm) and even slightly below (Above 2500ish or even lower than that accounting for TCC lock-up, the latter being somewhat of a weak point but still a valid one none-the-less). I think it would be foolish to trade off 15+ ft/lbs for only 7~ PEAK horsepower. I am more-so concerned with the street curve, AVERAGE power and how happy I will be zipping around town than trying to impress people by playing a numbers game.

FireDemonSiC

Maybe a conservative change, say a 112 LSA with a 220/228 @ .050 would better suit my application?

Orr89RocZ

iTrader: (20)

Lol if you tell a difference in 10-15 lb ft you got one hell of a butt dyno. Depending on the converter you use, you will not notice a loss. Locked trq converter only happens in cruise mode. Your never gonna really accel hard in a locked converter. You really shouldnt anyway thats luggin a motor down

Your cam choices are good tho, 218-224 deg on the intake lobe, 4-6 deg split imo on a 110-112 will be fine in that motor. The long stroke is really going to eat up some cam and make the bottom end you need