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Stroker question

Coronet R/T 68

Coronet R/T 68

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This question pertains more to the pistons that come with the stroker kits. The two kits I'm looking at are,
CNC motorsports
Mahle pistons with a -4cc dish that comes out to 10.7:1 with 84cc edelbrock rpm heads.
Hughes
Icon pistons with a -26.7cc dish that comes out to 10.3:1 with 75cc edelbrock rpm heads.
Both are 4.25 stroke with 7.1 rods.
My question is which is better? Small combustion chamber with bigger dish or big combustion chamber with smaller valve reliefs? I'm looking to stroke my 440 to 505 for pro touring purposes. I'm planning to put a lot of miles on it and hardly any track time, not looking to go over 5500-6000 rpm. I'm building the motor more for the torque for cruising more than anything else. Plan on using a edelbrock performer rpm intake and holley super sniper 1250 efi if it matters.
 
I think a lot depends on the cam you choose. But, I would lean towards the lower compression for cruising.
Mike
 
The cam options are staggering. I'm leaning towards a howards 723515-12. Intake duration of 278, exhaust 272. Lift of .500 with a centerline of 108 and 112 separation. It's a mild cam that works between 1600 and 5600. I thought the higher compression was more efficient?
 
Mahle pistons are a lot better than ICON pistons so if was a choice I'd go that way.

You don't want the Sniper 1250 for a street car, did you mean the Sniper 650?
 
Coronet R/T 68 said:
The cam options are staggering. I'm leaning towards a howards 723515-12. Intake duration of 278, exhaust 272. Lift of .500 with a centerline of 108 and 112 separation. It's a mild cam that works between 1600 and 5600. I thought the higher compression was more efficient?
Click to expand...

That cam is way too small for a 505" engine. Only 219/225 duration @ 0.050"
The mild 505 in my Convertible is the Comp XR286HR-10 (236/242 @ 0.050" duration) and it seems pretty mild in the engine with 10.3:1 compression (-17cc ICON pistons and 84cc Heads.)

For pistons I like the Mahle with the 1.5mm x 1.5mm x 3mm ring pack, but the 10.7:1 compression would work better with a larger cam or higher octane fuel.
I would polish the cylinder head chamber and de-shroud the valves a bit which would add a few CCs the the head volume and run the Comp XR292HR-10 cam (242/248 @ 0.050" duration) with the Mahle flat top pistons.

I needed to edit this. Although I like the idea of the Mahle pistons and larger cam, the high compression ratio and higher performance cam may not be what the OP wants. With a mild street car, really no reason to push high compression if running unknown quality of pump gas.

I like the extra features of the Super Sniper, I think Andy might be looking at the injector sizes/pulse width timing, and saying the regular Sniper would have better control of the injector pulse widths at the lower RPMs a street engine would be running at?
 
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451Mopar said:
That cam is way too small for a 505" engine. Only 219/225 duration @ 0.050"
The mild 505 in my Convertible is the Comp XR286HR-10 (236/242 @ 0.050" duration) and it seems pretty mild in the engine with 10.3:1 compression (-17cc ICON pistons and 84cc Heads.)
Click to expand...

I know strokers tend to eat duration but I'm not sure how much. In the interest of searching for torque and mpg I thought I would go on the the conservative side, maybe I'm way to conservative..
I never even considered deshrouding the valves and polishing the chambers.
I like the extra features of the super sniper as well which is why I opted for it. It doesn't seem to be doing great on my mild worn out 440 that's probably only pushing 275hp at this point.
 
For comparison, the 505 in the convertible with the XR286HR cam. The '69 Coronet Convertible is way over 4,000 pounds, using a 3.54:1 Dana 60, and 5-speed OD Manual transmission with 0.69:1 OD (Legend 700 trans), At 1,500 RPM in OD = 50 MPH. No problem driving around at 1,500 RPM, plenty of torque. I have RPM limiter set at 6,000 RPM and the engine revs there pretty quick. I think it is a nice driveable mild combination. I know the "small" cam I have is giving up performance at the track, but the car is for street and highway driving not drag racing.
On the Super Sniper i would use a fuel pressure sensor and connect to the analog input to log fuel pressures. Something like this:
https://www.amazon.com/dp/B00NIK98O...qP&pd_rd_r=52SP7HB2T0RCJF1C9AZE&pd_rd_w=fLVfi
 
Thats exactly what I'm looking for, a street car not a strip car.
Im fairly new to the efi and I'm out of my realm of knowledge on the fuel pressure sensor, what would that do for the efi unit?
 
Coronet R/T 68 said:
Thats exactly what I'm looking for, a street car not a strip car.
Im fairly new to the efi and I'm out of my realm of knowledge on the fuel pressure sensor, what would that do for the efi unit?
Click to expand...

Logging the fuel pressure will let you know if the fuel system is maintaining correct pressures for the EFI.

My Coronet with the 505 mentioned above has port EFI, but I recently put a FiTech TBI on my Charger and joined the FiTech user group on Facebook. I haven't had any real issues with the FiTech, but on the user group it seems one of the main problems is people not setting up the fuel system correctly and either loosing fuel pressure or not filtering the fuel correctly and clogging the injectors. They really should ship these with the correct post pump EFI filter, and pre-filter if using an in-line pump. The Fuel Control Center (surge tank) really seems to have created more problems that it solved.
I have mentioned before, that I got the FiTech a few years back before Holley had the Sniper system. I think the Sniper is a better unit, but I haven't used one yet.
 
I made sure the fuel system was up to par when I Installed it. I did however have a pressure regulator go bad already and had to replace it. If it happens again I'm going with a external regulator. I went back and forth between holley and fitech. Customer service or lack thereof for fitech pushed me in the holley direction and I purchased mine through efisystemspro.com and I dont have a single bad thing to say about Chris there, he has taken the time to help me figure out some of my gremlins. I think I might have jumped the gun though because I'm already looking at other efi units, might eventually go with a port injection also when it's all said and done.
 
I would think the bigger dish with smaller chamber would be better. I know 84 cc chambers with flat tops are a detonation machine with pump gas at 10:1
 
A lot of people today go the wrong direction, you want 300+* advertised duration / wide LSA for a big-cube street car with a mild converter. No reason to get concerned with static CR, very limited power loss (3% +/-) from even a single point. The higher the peak cylinder pressure is at lower RPM's, the greater chance of detonation. Take a look at some Dynamic Compression Ratio (DCR) calculators, I'm not saying this is the end-all-be-all for pump gas but they do have some relevance. David Vizard has a helpful chart I've attached. I went with 9.58:1 (static) for my 470 low-deck.
0311phr_compress_07_z.jpg
 
Wouldn't even make it out of the garage with 93-octane running 10.7:1 static with your first cam choice without detonation. Just my opinion, a lot of people get themselves in trouble being too conservative (believing that is the correct way to resolve detonation issues) with carbureted applications. We don't have knock-sensors in place or any safeguard that will automatically retard timing when the coolant reaches a specific temperature range. Always better to error on the side of caution and sacrifice a few horsepower for longevity.
 
Excellent mention of power gain/loss via compression point(s) on this. While a cam is designed to work within certain operating parameters and compression being a big one, your cam is small even for stock displacements. Keep the ratio on the lower side.

The larger the cam the more dynamic ratio it bleeds off. The large stroker can go up to a 230*@.050 and still drive the street nice and easy.
 
Sweet5ltr said:
I'm not saying this is the end-all-be-all for pump gas but they do have some relevance. David Vizard has a helpful chart I've attached. I went with 9.58:1 (static) for my 470 low-deck
Click to expand...
So in taking all of this useful information and figuring and doing some research, if I have a static compression of 10.3:1 and run the comp cam XR286HR-10(just for ease of figuring at this point because they list all of their specs) that will give me a dynamic compression of 8.6:1 this would be acceptable for pump gas? What are the pros and cons of low rpm, say 2000 for cruising or higher rpm, say max of 6000?
 
Dynamic compression is a minefield, I'd just ignore that concept until you get some more experience with specific combinations. If you're building a 505 with good heads and 10.3 compression then the 286HR cam should be a decent choice. It will have a little bit of lope at idle but not bad. Vacuum should be around 12 to 15 inches at 850 rpm idle speed. It should work okay with a Holley Sniper. If you order a custom cam you could ask them to grind the 286HR on 112 or 114 centers. That will give you a smoother idle which will work better with your Sniper kit.

Are you sure you have the 1250 Dominator flange Sniper? That is not the right choice for a street engine. The Sniper you would want would be the 650 which has a regular 4150 flange. If somehow you ended up with the Dominator flange Sniper then you should return it or sell it and buy the 650 Sniper. Here is a Sniper 650 on a Trick Flow intake on top of my 512 low deck.
DSC_2842 (Large).JPG
 
69 GTX said:
I would think the bigger dish with smaller chamber would be better..........
Click to expand...

Me too. No real personal experience directly on point to your question, but I just think the 75 cc chamber looks like a more modern, better design and that it would be more efficient.
 
andyf said:
Are you sure you have the 1250 Dominator flange Sniper? That is not the right choice for a street engine. The Sniper you would want would be the 650 which has a regular 4150 flange.
Click to expand...
The super sniper 1250 I have has the 4150 flange but it has 8 injectors instead of 4. Looks identical to yours, I've attached a pic. I have the dual sync distributor so I can use timing control, I'm not overly concerned with the lope or rough idle but I will have to look into that
There's no doubt I need more experience in building the stroker, I'm just trying to avoid dumping a lot of money into a motor and finding out I can't drive it till I go back and dump a lot more money into it.

20180707_182501.jpg
 
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