Choosing pistons and camshaft for 360 street build (economy + fun)

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VintageRocker

VintageRocker

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Hi everyone,
My Demon has a 360, I'm building a (casting #3418496, 1971–1974 block) for a street-driven setup, mostly city and occasional highway driving. I’m based at high altitude (~8,600 ft), so good throttle response and fuel efficiency are important — but I still want the car to be enjoyable and torque-rich.

Here's what I currently have or plan to use:

* Heads: 3418915-G (J-style), I guess 1.88 (stock no modified)
*Intake: Edelbrock Performer 2176 (Brand New)
*Carb: Edelbrock AVS2 1906 (Brand New)
*Ignition: MSD 6AL + Pro-Billet (Brand New)
*Exhaust: Dual 2.5" Thrush welded
*Transmission: A833 4-speed manual
*Rear end: I'm not sure but it must be stock

Use: 70% city, 30% highway, daily/street driving — not track

The block is already bored .030”, but it’s worn — so I’m deciding between going .040” or .060”, or sleeving it back to STD or .030 as well.

My question:
What piston and camshaft combo would you recommend for this build, prioritizing fuel efficiency, durability, and good torque below 4000 RPM, but still fun and responsive enough for spirited street driving?

I’m open to pistons like Speed Pro H116CP, and cams like Comp XE256H, XE262H — but would love your input based on your experience and compatibility concepts (I want to preserve my heads).

Thanks in advance!
 
For a 100% street engine, those are the wrong pistons, IMO. You're going to find it difficult to get compression under 10:1. I've used them before. It's gonna take a pretty lumpy cam to get cylinder pressure down to where spark knock will not be an issue on pump gas. What I would do is simply use stock replacement pistons and get compression right on top of 8.5:1. Good driveability, no chance for spark knock, run on 87 octane. There's just no down side as long as you cam it accordingly.
 
I think at 8600 ft you can build a fair bit of compression and be totally fine. Not more than 10:1 is probably fine on pump gas, but you may want to see if you can run more. I would go with a cam under 210 @0.05” intake duration.

Your atmospheric pressure, and therefore cylinder pressure, will be scaled by 0.73 relative to sea level.
 
I'm no expert on high-altitude builds, so take my advice for what it's worth. For city driving (70%) go with at minimum 3.55 gears with your 4-speed. IMO, your cam, intake and carb size are more in-line for a 318 build than a 360. with ~9-1 Compression, you should be looking at something equivalent to the Comp Cam XE268 (still mild), Performer RPM or Airgap intake and a 650-700 CFM carb. The J-Heads with 1.88/1.60 vlaves is all you need for the above combination. I would go get a Harbor Freight electric grinder and smooth out the ridges in the valve pocket area. Very simple to do and well worth the effort. You can go online and see all kinds of tutorials on this, you can do all 16 bowels in under an hour once the heads are disassembled. I typically take my heads to the machine shop, have them cleaned, magnafluxed and take them back home to do any porting and then take back for the machine work. You said "spirited driving" so I'm giving you a combination that will set you back in your seat and still be something you could jump in and drive across the country.
 
RustyRatRod said:
For a 100% street engine, those are the wrong pistons, IMO. You're going to find it difficult to get compression under 10:1. I've used them before. It's gonna take a pretty lumpy cam to get cylinder pressure down to where spark knock will not be an issue on pump gas. What I would do is simply use stock replacement pistons and get compression right on top of 8.5:1. Good driveability, no chance for spark knock, run on 87 octane. There's just no down side as long as you cam it accordingly.
Click to expand...
That is what I did mid 90s with a 340 street motor.
I had steel crank rotating assy. But used 72-73 style pistons.
A 268 cam. A/C blew cold, all the power stuff worked. Car ran strong on any gas available.
Street builds are about compromise
 
Wow thank you folks, a lot of great info in just a few minutes... I'll check everything with patience
 
RustyRatRod said:
For a 100% street engine, those are the wrong pistons, IMO. You're going to find it difficult to get compression under 10:1. I've used them before. It's gonna take a pretty lumpy cam to get cylinder pressure down to where spark knock will not be an issue on pump gas. What I would do is simply use stock replacement pistons and get compression right on top of 8.5:1. Good driveability, no chance for spark knock, run on 87 octane. There's just no down side as long as you can it accordingly.
Click to expand...

He’s already at almost 9000’. Add in a hot day and I’d think he’ll need a lot more than 8.5:1 piston to make the car get to the grocery store even…

For the OP, can you consult local engine builders and speed shops to see what their customers have had success with? High altitude like that kills power
 
VintageRocker said:
Hi everyone,
My Demon has a 360, I'm building a (casting #3418496, 1971–1974 block) for a street-driven setup, mostly city and occasional highway driving. I’m based at high altitude (~8,600 ft), so good throttle response and fuel efficiency are important — but I still want the car to be enjoyable and torque-rich.

Here's what I currently have or plan to use:

* Heads: 3418915-G (J-style), I guess 1.88 (stock no modified)
*Intake: Edelbrock Performer 2176 (Brand New)
*Carb: Edelbrock AVS2 1906 (Brand New)
*Ignition: MSD 6AL + Pro-Billet (Brand New)
*Exhaust: Dual 2.5" Thrush welded
*Transmission: A833 4-speed manual
*Rear end: I'm not sure but it must be stock

Use: 70% city, 30% highway, daily/street driving — not track

The block is already bored .030”, but it’s worn — so I’m deciding between going .040” or .060”, or sleeving it back to STD or .030 as well.

My question:
What piston and camshaft combo would you recommend for this build, prioritizing fuel efficiency, durability, and good torque below 4000 RPM, but still fun and responsive enough for spirited street driving?

I’m open to pistons like Speed Pro H116CP, and cams like Comp XE256H, XE262H — but would love your input based on your experience and compatibility concepts (I want to preserve my heads).

Thanks in advance!
Click to expand...
I Googled the altitude of Miami Florida and it should a altitude of 6.5 feet.
 
I don't think that the op can have that high of a altitude being that close to the ocean
 
Problem with cam recommendations your gonna hear everything from stock to fairly wild. It really depends on you, take the comp xe line you mentioned, you could make a case for any of them 250/256/262/268 on a daily driver, if you like to play it safe pick on the milder side if not larger. Something like the xe262h be a good compromise.
 
Doesn't elevation just bring performance of all engines down in power relative to one another ? I don't see the need to over worry about it.
 

I've sold several balanced rotating assemblies to guys here on FABO that live in the 6,000' plus elevation. At that altitude the thin air reduces the efficiency to pump air about 20-25%

If you intend to use an engine at 8,600' elevation you'll need at least 12 to 1 compression so you can squeeze that thin air into something usable if you want any power at all.

It's a different world at that elevation.

Tom
 
vntned said:
H116CP pistons will not get near 10:1 with unmilled open chamber heads. Use them.
Click to expand...
Yes. They can. I built a mild 360 with stock heads cleaned up with a .010" mill. Compression ended up a little over 10.5. They have a tall compression height and only two valve reliefs. They will get some compression.
 
Stock open chamber heads are in the 73cc range. Uncut, with a regular headgasket, the tend to measure in the 9.5:1 range. With the piston barely below deck, the valve reliefs in the piston and the large chamber, they don’t break 10:1 without milling, nailhead valves, thin headgaskets, etc.. Calculated compression vs actual tend to be very different.

And even if it does hit 10:1cr, there’s nothing wrong with that in a streetcar running good gas.
 
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