360 Advice Needed - Autocross / Street Engine Build

[nm9stheham]

Is cutting the pistons a possibility? How much needed, is there enough meat?

If the engine is together, that would be a pain. .005" removes about a 1 cc. So getting 5 cc's out would require a .025" cut. It is an option I would certainly consider..... but would need measuring the domes as noted.

Oil pan would be the milodon. It's a tight fit. What Kmember are you running? But hard to put on a fit with motor in car. Protects motor investment. Also not cheap.

If the OP if gonna pull some cornering G's, THIS is good advice. IMHO, the OP should spend some time reading up on pan baffles, one way doors, etc.

I'm late to this show, and I think autoXcuda's input is better than what mine would be anyway. But, I can comment on this cam if it's still a consideration. I run that lunati 60404 in my 340, which is a .060" over '68 340. Compression is 9.8:1 with the KB 243's .018" over the deck. Heads are iron 308's, chambers are 65cc's, 2.02/1.60 valves, stage II ported and flowing 264 cfm @ .500". I run it with a eddy air gap, holley ultra 750 double pumper, doug's headers, and currently have it in front of an 833 with a 3.09 first gear, 26" tall tires and 3.55's.

Idle for the street is getting a little borderline, it only pulls about 11-12" of vacuum at idle, which is around 750 rpm. I had to play with my timing to run California 91 octane, I'm at 22* initial but I run heavy springs in my distributor and my total is limited to 32* all in mechanical. Advertised power range is 2200-6400, and that's the truth. It does not like to pull below 2200. And really it's not happy until its at 3k if you're going to stomp on it. Past 3,500 it will push you back in the seats hard, and it goes from 3,500 to 6k in a heartbeat.

Overall, it's a big cam for the street. For the daily driving I do it can be a bit of a pain. On the track you'd want to keep it at 3k or higher, stall is supposed to be 2800 or more. The 3.55's are smaller than what the cam wants, my plan is 4.30's and a T56 to keep the top end speeds, but still have 2 gear with the revs up for autoX. Here's the idle

***Edit***
Here's the compression and DCR info for it, as I said I've had to pull timing to manage this for 91 octane
View attachment 1715100326

Nice comprehensive post, blu. FWIW, the lower 500 RPM performance on this cam's advertised RPM range is not too surprising.... I find that most cam mfr's including Lunati and Comp, push the lower RPM limits down too far, so they look better on paper. Crane's RPM range numbers to be more conservative and more reliable.

That 91 octane sure is more of a problem than I expected. OP, what is the source of 94 octane out there?

I think at 5500 rpm up sustained you are going to get some loss of lift and/or valve float. The weak link to RPM is usually valveteain before bottom end.

And that may point to a milder ramp cam. Or the solid lifters; they will avoid the pump-up problem but then there may be increased lifter weight added to the valvetrain weight.

 

[Kicker92]

I haven't measured the actual volume of the heads, they are still shipping and are en-route for Tuesday.

A little background, I had the original 318, then built a 360 for it about 18 years ago. Balanced the bottom end, with the KB107's, flat decked the block and put J-heads with 2.02's on top. 340 Intake, 625 carb, etc, all the usual stuff.
It was parked a long time, and just got it back from storage this summer. Well, drove a few times, and tons of white smoke out the back. Cracked in the #4 cylinder wall.

In the meantime, I've been autoxing with a focus SVT, then the GTI, and really enjoy that more than straight line. Descided to tear downs the resto build, and modernize it a bunch. Wiring/charging upgrades, manual 16:1 box, stiffer bars, and plan on 13" discs. I want this to keep up with some of the modern cars if possible.

 

[nm9stheham]

Have you measured the volume of the chambers on the new Edelbrock heads yourself? Sometimes they can vary from advertised spec.

FWIW, my son found his to be within 1 cc of advertised all around. I think a lot of fellows get more volume than in reality when they seal up the chamber being measured with a bead of RTV. A .010" thick bead will add around 2 cc's to the measurements or open chamber heads and a bit less for closed chamber heads.

 

[autoxcuda]

Your pistons are setup for stock heads.

Have you consider just keeping and running them?

I've CC'd edelbrock small chamber advertised at "63 CC". They are 65 cc. That seems consistent with what other get.

The edelbrock 65cc seems to consistently come in at 67cc.

 

[Kicker92]

So, current status:

- Engine and tranny are out of the car.
- Rear end will get opened up to get discs and can change gearing if needed at that point
- Torque converters are sitting on the floor, so easy choice.

Engine:
- New short block is with my machinist, he has decked to +0.005" (his recomendation with a 0.039" gasket) and align honed, bored +0.030", etc.
So the short block is done, just being assembled. (would prefer not to change this, but will if needed)
- Camshaft I have from previous build is the Comp 275DEH, not installed
- Heads are on order, Edelbrock #60775. These are setup for a roller cam, but I have good aftermarket dual springs, retainers, etc from the J-heads.
- Roller rockers are on the way, Mancini aluminum ones (thanks to FABO)
- AirGap intake is not ordered yet, but seems like the logical choice.

So overall, a pretty easy stage to make some changes, especially with the oiling system.
I'll do some searching and reading about that one.

I have a burret, and will cc the heads once they arrive next week. I will be doing any head work, and enjoy that part.

Camshaft is an easy one to change, and not very expensive. I would rather swap that than find another new set of rockers.

 

[autoxcuda]

Save your money on rear disks and do the pan upgrade. Drum are fine for autocross. And even ok for occasional and beginning track use. Red brick valiant had rear drums for a long time.

You can buy a used Edelbrock RPM intake and put that money toward a good double pump carb.

 

[nm9stheham]

I've CC'd edelbrock small chamber advertised at "63 CC". They are 65 cc. That seems consistent with what other get.

FWIW, my son got 63.4 to 64.5 cc. Once we discounted the thickness of the RTV bead, that made them come on on the mfr target.

 

[72bluNblu]

Thanks to all you guys for jumping in to help, this is exactly why I'm asking the questions at this stage.
It's seems that I have some mis-matches in this setup, if I understand correctly:

1.) DCR is generally too high for 91 pump gas: Baseline @ 8.8:1 , goal would be to reach under 8.2:1
Possible solutions with current bottom end:
- Increase cc's of cylinder heads (I think some CNC prepped edelbrock heads are 68cc's, drops DCR to 8.3:1)
- Increase head gasket thickness (0.054" gasket would drop it to 8.4:1, but quench height would become 0.049")
- Increase cam duration from 275 to 284 (only lowers to 8.7:1)
or a combination of the above???

2.) Gear ratio / high stall converter:
- Seems like 3.55 gears with a 2500 stall would be an ideal compromise here.
- Alternative might be to keep the 3.91's, but put in the stock 11" converter.
A bit slower off the line, but the gearing puts me at about 5600rpm at 110 mph, and backroad cruise of 2000rpm at 40mph

3.) Manifolds:
- I'd like to look of it being mostly factory, and the lack of headaches that seem to come with headers.
- That said, if this thing is going to die off after 4500-5000 rpm, or have heat issues from choking that off, I may need to change.
- Headers would need to be shorty style, any suggestions who makes a good pair for the a-bodies?

4.) Oiling issues?
- I have a windage tray, and a high volume pump.
- Other than that, the oiling system is stock and I haven't considered it much.
What did you end up doing to keep it picking up oil at the track?


Thanks,

Ryan

If the OP if gonna pull some cornering G's, THIS is good advice. IMHO, the OP should spend some time reading up on pan baffles, one way doors, etc.

Nice comprehensive post, blu. FWIW, the lower 500 RPM performance on this cam's advertised RPM range is not too surprising.... I find that most cam mfr's including Lunati and Comp, push the lower RPM limits down too far, so they look better on paper. Crane's RPM range numbers to be more conservative and more reliable.

That 91 octane sure is more of a problem than I expected. OP, what is the source of 94 octane out there?

And that may point to a milder ramp cam. Or the solid lifters; they will avoid the pump-up problem but then there may be increased lifter weight added to the valvetrain weight.

Yeah I was a little surprised about the 91 octane too. I have iron heads so that’s part of it, plus the open chambers, over the deck pistons etc don’t help with my quench. And the 3.55 gears don’t help either, recommended gears are 3.73 for that cam but I think even that may be optimistic, I think 3.91’s are more realistic. Heck even the manual transmission, I had to go to a double pumper with mechanical secondaries because everything is instant, I couldn’t bring in enough fuel fast enough with vacuum secondaries. And I run an A/F gauge for tuning, so I’m not guessing based on plugs.

The fast ramps on the Lunati I think are a little deceiving. I’m no engine guru though, seems like the DCR still only gives you a snapshot and the window is really small because of the fast ramps. Cranking pressure on my 340 is 175-180 psi.

For oiling I agree with autoxcuda, the milodon road race pan probably the best pan you’ll get off the shelf anyway. I run it, it has all the tricks with baffles and trap doors. I use it with a stock windage tray and a hv oil pump.

I have mixed feelings about the TTI shorties. I may have had expectations that were too high, but I switched back to my Doug’s D453’s a little more than half way through the install off the TTI’s. Ground clearance improvement was less than I expected, clearance issues were worse (no better than the Doug’s, just different). I have a write up in my build thread My "new" '74 Duster- or why I need a project like a hole in the head

 

[nm9stheham]

The fast ramps on the Lunati I think are a little deceiving. I’m no engine guru though, seems like the DCR still only gives you a snapshot and the window is really small because of the fast ramps. Cranking pressure on my 340 is 175-180 psi.

That cranking pressure is abnormally high for your levels of SCR and cam and the DCR that results (7.7 using the advertised duration numbers). I get the same SCR number that you posted with a .028" thick head gasket. But that cranking pressure would be for about an 8.5-8.7 DCR.... gauge problem perhaps?

If it is really that high, then I can only think the cam is about a tooth advanced....naw.... I would not expect that.....but +15 degrees on the cam makes the cranking pressures come to that range... or being 1000' below sea level!

 

[72bluNblu]

That cranking pressure is abnormally high for your levels of SCR and cam and the DCR that results (7.7 using the advertised duration numbers). I get the same SCR number that you posted with a .028" thick head gasket. But that cranking pressure would be for about an 8.5-8.7 DCR.... gauge problem perhaps?

If it is really that high, then I can only think the cam is about a tooth advanced....naw.... I would not expect that.....but +15 degrees on the cam makes the cranking pressures come to that range... or being 1000' below sea level!

Yeah I don't know how you get a different SCR. I can understand the DCR a little because of how the intake closing is calculated, different calculators use different figures. I was using the UEM calculators ABDC @ .050" +15*, which may give the DCR a little high with the fast ramps. If you use advertised duration and do the intake duration (276) divided by 2, add the lobe separation (110), subtract the ground in advance (4) and subtract 180 you get 64 for the ABDC and get a DCR of 7.845.

But all the numbers are right here for the SCR. I contacted KB directly to work out the numbers for the pistons because of the over the deck pistons and valve reliefs, that's where the 7.3 for the piston head volume and 0 for the deck clearance numbers come in, and it doesn't matter what calculator you use if you plug in those numbers you get 9.8 for the SCR.

The cranking pressure is about 10 to 15 psi higher than what most of the calculators say, but that's a crapshoot anyway. Cranking speed changes the cranking pressure, temperature, ring sealing, humidity, gauge, etc. Too many variables. To be within 10-15 psi of the calculation is no big deal, no reason to suspect anything at all beyond standard variation. You're getting too wrapped up in the calculators, cranking pressure as measured isn't a perfect indicator of SCR or DCR, there's too many variables at play.

 

[nm9stheham]

OK, actually I did get your SCR.....?? And nearly the same DCR, with an ICA of 65.5; pretty close agreement. I have gotten consistently good agreement with computations and measurements of cranking pressures, so that took me by surprise. But field measurement variations are there for sure, as you say. (And I don't think for a moment that the cam is 15 degrees out!)

 

[72bluNblu]

OK, actually I did get your SCR.....?? And nearly the same DCR, with an ICA of 65.5; pretty close agreement. I have gotten consistently good agreement with computations and measurements of cranking pressures, so that took me by surprise. But field measurement variations are there for sure, as you say. (And I don't think for a moment that the cam is 15 degrees out!)

I dunno. I mean, my gauge might be a little out. I've used it awhile and the readings it gives have always "made sense", but that's not to say it couldn't be off a bit. Less than 10 psi I would think, otherwise the readings its given me on other engines wouldn't make sense. But if it's close to 10 psi the numbers on this start making more sense don't they?

And yeah, 175 psi is a little high. But then again if the cranking pressure was much lower, or if the DCR was less than 8 I probably wouldn't have to pull a few degrees of timing either. So I just look at it go, yeah well, it makes sense I have to pull a few degrees of timing and push the timing curve back a little because the cranking pressure is 175, and that's a little higher than expected/calculated. But it fits with what I'm seeing during tuning, so, maybe the calculations were a bit off.

I should probably stop de-railing this poor guys thread. Moral is, for 91 octane my combination is a little borderline with open chamber iron heads, and that Lunati cam is a little big for street use and 3.55's.

 

[Kicker92]

No worries, it's nice to hear a comparison to a pretty similar setup / usage, still on-topic...

I've been trying to wrap my head around cam timing, but struggling a bit here.
It seems like the key event for DCR is the intake closing ABDC. That changes the dynamic stroke length and this the amount of compression.

As far as DCR is concerned, the longer duration cam just delays that event in the cycle?

I could achieve a very similar effect by installiing this cam at 110° ICL, instead of the as-ground 106° ICL
That drops the DCR by nearly 0.3 points. (8.52 from 8.79)

What I can't picture though, is how that changes powerband, peak RPM, and what happens on the exhaust cycle and overlap.
Anyone know some good links to clearly / simply explain Cam timing and it's effects?


Thanks!

 

[rumblefish360]

I wish that was easy to explain in such a simple manor. But I don’t think it is, or really, I can’t. Hummmm

Changing the timing events, regarding or advancing changes when the valves open and close. Since only a few degrees is done, the position relative to the piston allows more or less air and fuel in given where the piston is during these events.

Remember, there is a 2:1 ratio on the crank to cam gear. So a few degrees on the cam is a lot on the crank and where the piston is positioned in the cylinder to allow the air and fuel to come in.

 

[nm9stheham]

Yes you can. It does like you say (makes the intake closing later), and changing the installed cam timing is a common way to do this. It is not uncommon for cams get advanced to make up for lower compression engines; you're going in the opposite direction. And that is one reason why the big drag engines are running 12-13:1 SCR or more....huge cams, and no DCR at all if the SCR is not driven way up.

The common changes are:
More advanced = lower RPM torque and quicker drop off in high RPM HP
More retarded = the opposite
Google for 'cam timing effects' and you will find all sorts of info. QUANTIFYING those changes versus so many degrees of cam change is the trick.

BTW, it is common these days for cams like these to come with some ground-in advance. Perhaps this is to make the bigger cams work better for low end torque loss with longer duration cams, but it is very common.

RF360 suggested a longer duration cam for this very reason: to lower DCR. But that comes with longer overlap and the detrimental effects on low RPM operations, economy, etc. Another way to approach this is to go with a wider LSA. If you kept the same ICL, with a 112 LSA the intake closing will be 2 degrees later; with a 114 LSA, the intake closing will be 4 degrees later. Then you can lower DCR without the long overlaps. If you browse the cam catalogs, you will see that torque-oriented cam are on 112 and 114 LSA's.

And that has been done before. I know few people on this site old enough to remember this, but after gas doubled in price after the Arab oil embargo in '73, a series of cams came out to do just this: ground on 114 LSA's with a long advertised duration for a later intake closing to keep DCR under control on hi comp engines, but got much better mileage using very slow ramps to a narrow .050" lift duration. Crane sold them as 'HE' series cams (hydraulic economy).

You are going down the same road I went down 40+ years ago: the pistons wanted were 11.2 SCR, too high for pump gas. (They had 'quench domes', used to achieve quench in open chambers.) So I ended up with grinding out 6-7 cc's per chamber and used a wide LSA HE cam... and which lowered DCR to around 8.3-8.4. There were no Excel spreadsheets or internet, and so I did not understand DCR at the time LOL... there was just the concept of 'effective' CR. Ended up with 10.2 SCR on iron heads so still had to be careful on timing, but it ran 93 with no issues ever and pulled hard from 2500 to 6500, on a stock TC. It could have had stepped up HP with a bit longer .050" duration cam on the same LSA and advertised duration, but this was an 'all-around' car so it was good for my use.

And I think all the comments from the other west coasters on 91 octane carry a lot of value; that really seems to be a different animal than 93 like back here in the east. Perhaps some of the Canadian 91 users will chime in.

 

[nm9stheham]

I dunno. I mean, my gauge might be a little out. I've used it awhile and the readings it gives have always "made sense", but that's not to say it couldn't be off a bit. Less than 10 psi I would think, otherwise the readings its given me on other engines wouldn't make sense. But if it's close to 10 psi the numbers on this start making more sense don't they?

And yeah, 175 psi is a little high. But then again if the cranking pressure was much lower, or if the DCR was less than 8 I probably wouldn't have to pull a few degrees of timing either. So I just look at it go, yeah well, it makes sense I have to pull a few degrees of timing and push the timing curve back a little because the cranking pressure is 175, and that's a little higher than expected/calculated. But it fits with what I'm seeing during tuning, so, maybe the calculations were a bit off.

I should probably stop de-railing this poor guys thread. Moral is, for 91 octane my combination is a little borderline with open chamber iron heads, and that Lunati cam is a little big for street use and 3.55's.

Tnx for the reply, blu. Sorry to go on....LOL I look at the DCR calculators as a good tool, but like any good tool, you have to use them, figure out their limits, and calibrate the results to the real world. When I run into something out of line, I try to figure out why. That darned 91 oxygenated fuel is the real problem!

 

[rumblefish360]

@nm9stheham
That’s correct & I figured it maybe the way to go. But, as we know about duration and the effect on rpm.... it may not be the way to go.

It can be a little difficult sometimes.

 

[72bluNblu]

I would just be careful with using the cam to adjust the DCR to try and squeak it in under detonation. The thing is that if the intended use for the car is street, road course, and autoX you don’t want a giant cam with a bunch of duration. It’s much more valuable to have torque in those engines, especially for street and autoX use. And if you want to keep the gearing reasonable to maintain a decent top speed for a road course without using an overdrive you won’t want a giant cam either. The Lunati I run is not a huge cam, but already I have to slip clutch and manage some footwork with 3.55’s and 26” tall tires, it wants lower gears.

Since the engine is still in the build stage, I would just set the SCR a little lower. Take a look at autoxcuda’s build. The simpler way to go about this is to give up a little horsepower. Which is honestly what I should have done, gone down one size on the cam, kept the gears and slid a fatter head gasket in while I was at it. I’d have lost some power, but I would have saved thousands over buying everything to do a T56 conversion. With a 360 and aluminum heads you should be able to make 400 hp in a very streetable engine, and that’s enough power to have fun with in your intended use. If you’re going to spend extra money, spend it on suspension and brakes. That will make your car faster than an extra 30hp.

I know if I was going to do it again I’d build a 450 hp stroker instead of trying to build a 425hp 340. Way easier to deal with. The stuff I did chasing the last 30 hp is what makes my car harder to deal with as a daily driver.

 

[Mattax]

I'll throw my .02 in on this, as the discussion has evolved.
Its possible to use the cam to get a higher CR engine run on pump gas. But, yea, I think that's something you want to work with a cam guy and engine builder with plenty of experience in doing.

But what I thought might offer is my experience has been similar to a few others - looking at squeezing more Hp is not neccessary. I too will be going to a smaller, more torquey, cam over my current and previous choice.

Also, I've learned that autocross is such a different game than track or 1/4 mile. You want excellent throttle response and torque at very low speeds. Like a road course, torque off the corner is the main goal. One issue on the road course with the torqueflite is that it does eat up some power. I think you'll still have plenty of fun.

My point with all this is look for a good torque curve - and maybe a little lower in the rpm range than you first mentioned. You may not care about vacuum, but it is important to have an engine that can spin up quick. Of course you can run a loose converter, but for doing all the different things mentioned (autocross, street, road course) it may not be the best way. That said, I ran a TurboAction medium stall with 3.23 gears and small tires (24" competion, 25" street) for years. It wasn't bad at all.

As far as exhaust manifolds go, that's a toughie. Its not just about flow, there's also reversion at lower rpm - and that's worse with a high overlap cam. There's a couple of CompCams that may be of interest. 20-309-4 The other IIRC was the XE268. However, there's no point in trading ramp rate for reliability. My old 340 had the HE 280 cam in it and I think the XE 268 might be a bit better in torque in the low to mid (3000) rpm range. 340 exhaust manifolds is what I was using until a couple of years ago. Car ran best of 13.77 99.5mph

 

[nm9stheham]

Some pretty awesome comments in the 2 posts above, IMHO.

The thing about a wide and strong torque curve is so true in what the OP is doing. In rally, a 2500-6500 engine was better than a larger 3800-7600 RPM engine. The wider usable torque is everything, and even more torque on a dry paved surface. The CR helps in the torque department all over, as long as it stays away from detonation.

 

[autoxcuda]

I would just be careful with using the cam to adjust the DCR to try and squeak it in under detonation. The thing is that if the intended use for the car is street, road course, and autoX you don’t want a giant cam with a bunch of duration. It’s much more valuable to have torque in those engines, especially for street and autoX use. And if you want to keep the gearing reasonable to maintain a decent top speed for a road course without using an overdrive you won’t want a giant cam either. The Lunati I run is not a huge cam, but already I have to slip clutch and manage some footwork with 3.55’s and 26” tall tires, it wants lower gears.

Since the engine is still in the build stage, I would just set the SCR a little lower. Take a look at autoxcuda’s build. The simpler way to go about this is to give up a little horsepower. Which is honestly what I should have done, gone down one size on the cam, kept the gears and slid a fatter head gasket in while I was at it. I’d have lost some power, but I would have saved thousands over buying everything to do a T56 conversion. With a 360 and aluminum heads you should be able to make 400 hp in a very streetable engine, and that’s enough power to have fun with in your intended use. If you’re going to spend extra money, spend it on suspension and brakes. That will make your car faster than an extra 30hp.

I know if I was going to do it again I’d build a 450 hp stroker instead of trying to build a 425hp 340. Way easier to deal with. The stuff I did chasing the last 30 hp is what makes my car harder to deal with as a daily driver.

If anyone is curious, these are the specs on my motor. Very simple approach. single plane to sacrifice low rpm for upper rpm. Figured still more torque than my stiff tires and suspension could hook on the street anyways. Picked curved runner MP intake to maybe get little low rpm back and maybe tinge better driveabilty.

• SHORT BLOCK: ‘69 340 block, now .030 over. Scat cast crank kit from Brian @Indio Motor and Machine.
• BLOCK MODS: Oil passages smoothed and ported to reduce turbulence/cavitation and help flow. Valley smoothed and cleaned up to help oil drain-back. Water jackets/passages meticulously picked clean of rust and slag.
• OIL PUMP: Melling high volume. Passages smoothed and matched to rear main cap.
• HEADS: Edlebrock. Full Ported, int/exh carefully matched, combustion chambers matched to block,
• VALVE COVERS: Old Cal Custom finned ($40 swap meet) with steel core MP gaskets for good no leak and removable seal
• CAM: Comp 274S soild. .502/.511, 236/242 @.050
• ROCKERS: Comp Pro Magnum steel rollers.
• INTAKE: Mopar M1 Single plane, changed to squared carb flange, cleaned up plenum, port matched.
• CARB: Demon Silver Claw 750 cfm advertised.Firesleeve on pump to carb 3/8" fuel lines
• FUEL LINE: 3/8" sender and 3/8" body fuel line. Firesleeve near headers.
• IGNITION: MSD E-Curve distributor
• OIL PAN: Milodon Road Race/Pro Touring pan developed by Milodon from this project!
• Windage Tray: Milodon with Milodon main stud kit
• BOLTS AND STUDS: Milodon Heads, Mains, Oil Pan

COOLING SYSTEM:

•WATER PUMP: Milodon aluminum
•RADIATOR: Champion 4 core
•T-STAT: Milodon brass 160 degree
•FAN CLUTCH: Hayden #2765 (short 3 5/16" mounting)
•FAN : MP shortened
•FLUID: Distilled water, 2 bottles Justice Brothers Radiator Cooling System Protectant with water pump lubricant, 1 bottle Justice Brother Super Radiator Cooler​

EXHAUST

• HEADERS: TTI stepped. Port matched, ceramic coated outside, thremal barrier coating inside. Best quality.
• EXHAUST: TTI X-pipe with Super Turbos 2 1/2"

 

[Mattax]

Looking back at the starting post here, its still not clear to me how much of the engine has been committed to, but a fair amount has already been purchased.
To make some quick & dirty comparisons on a desktop dyno (Dynomation5), I put the 275 duel energy cam into a 340 (I know its a 360 but this is quicker) with generic 10:1 closed chamber high performance heads. (no experimenting with advancing or retarding the cams.)

FWIW, IF changing cams is on the table:
* The "Magnum Muscle" replacement cam will make more power than the Dual Energy from 1000 to 7000 rpm, except from 5500-6000 where they are the same.
* The XE 268 cam will make more torque and power than either of the other two until 4500 - 5000 rpm. From 5000 rpm up, the 275 Dual Energy cam makes more power than the XE 268.

Take this as trends rather than absolutes. You can always help the upper end in these programs by mild porting of the heads. In real life, that's probably true but you have to know what you're doing not to mess up the lower and mid range. Definately doable - if the heads aren't already on.
My understand of split duration is that it helps keep the power from falling off after peak - that can be useful for both autocross and track when you don't want to, or can't, shift up. The idea it helps when running a cast iron exhaust is one I held but from reading stuff posted by Mike Jones (Jones Cams) and some others, it may not be true.

Running all three cams with the most restrictive exhaust in the software shows pretty much the same pattern as with headers. The XE268's torque advantage becomes minimal compared to the "Magnum Muscle" which still has a noticible top end advantage.

Take this with a grain of salt. I know this program's output is shifted left from where I've seen in real life. In other words it peaks a 340's performance about 500 rpm early.

Finally. In my opinion, if you're running aluminum heads, its going to be hard to make it look like a stock engine. Take advantage of the class rules for the build. Decent headers will make big difference. If you beleive the simulator, you'll have more torque and power the entire rpm range with the Dual Energy 275 and small tube headers, than either of the other two cams using the best cast iron manifolds. Again, take with a grain of salt, but I think its worth consideration - there is more to be gained with headers than swapping cams.

The trick will be to get tuning, especially the timing to work with your combo and available fuel.

 

[Kicker92]

Cylinder heads just came in this morning!

I'll cc a chamber this weekend to figure out the starting point, but a couple of spots I notice to work on:

1.) Spark plug threads:
Deshroud and blend exposed threads for hot-spots.
Any idea if there's water behind here?

2.) Beside the valves:
Looks like there's some room to open up beside the valve to smooth the flow:

3.) Between seats:
Smooth and eliminate the rough edges for flow during overlap

 

[Kicker92]

Looking back at the starting post here, its still not clear to me how much of the engine has been committed to, but a fair amount has already been purchased.

Finally. In my opinion, if you're running aluminum heads, its going to be hard to make it look like a stock engine. Take advantage of the class rules for the build.

The cam I have was from the previous build. It's probably one of the least expensive items to change, and has not been installed in the new block yet either.

To clarify, this car will not be very competitive as it will probably and up in FSP or higher for SCCA events, possibly even SM.

My goal with this build is that anyone looking at the car, should have to look somewhat closely to realize that it couldn't have come from the factory that way.

Other than the smooth face of the cylinder heads, once painted, it should look just like this:

 

[Kicker92]

I've been running similar numbers in CamQuest, and it looks like in these flow rates, the manifolds are costing like 40-50 lb*ft across most the rpm range.

@ AutoXcuda, how do you have any ground clearance left with it low and the headers underneath? Even the TTI's look like they hang down low compared to the rest of the car.

Shortie headers with a factory looking heat shield may be my next best option.
Again, it doesn't need to be OEM mopar, but my goal is that is look like it "could" have come from a factory like that.

A bit of a different type sleeper build...