Compression

[Strokedcuda67]

this has been discussed in part in-several previous threads, but I have yet to see a clear answer by anyone as to combination of a scat 416 rotating assembly with Edelbrock RPM heads.

I have a 69 340 that I want to get a scat forged stroker kit and run with eddy heads, my dilima is which stroker kit. 48013 bi. Or 48015 bi. And also which performer heads to purchase 63 or 65 cc?

I would like to retain my 10.5 compression ratio or 11 to 1 given I will be switching to aluminum heads

Calculating I come up with
48013bi
4.070 bore
4 inch stroke
60779 heads 63 cc
.039 head gasket
11.87 comp ratio

Same scat roller assembly with 65cc heads is 11.44

Then with scat 48015 bi
Same specs except 20.50 piston dome volume
65cc heads=9.79
63cc heads 10.09

Can I run the 63 cc heads with 0 deck clearance.
Should I get the 63 or 65 cc heads
Should I get the scat kit with +5 pistons
Or the kit with + 20.5 pistons

And also can you tell with the scat rotating assembly what the deck clearance will be before installing it.

 

[scampy]

I would give scat a call,they can tell you deck height based on piston,they will also do a custom piston/pin height change for what ever you want or need for not much price difference.Our block was decked before so i needed a different pin height to keep compression in line with the flat tops,something else to keep in mind if you get any port work done on the heads the chamber will probably be bigger than the stock eddys.I worked with Jonathan Gonzalez there had a couple hiccups along the way but all worked out in the end

 

[Wyrmrider]

calculate your quench piston to the flat of the head aim for .030-.040

 

[stumblinhorse]

I have done a lot of research on this. the 65cc Edelbrock heads are open chamber. I am going to get the promaxx heads and have them enlarge the closed chamber to 66CC. I am going to use a 1008 .038 gasket and zero the deck. Compression on my 390 will be 11:1. But I live at elevation and that will be no issue for pump gas.

Couple things to consider on the scat kits is piston material. And decide what you a looking for. Their kits have 2618 pistons which are very rigid and loud and need more clearance. But they can be run hard at high compression and survive some detonation. The 4032 pistons are softer and quieter and will last longer but detonated they are going to fail. If you decide on 4032, you can get pretty much whatever compression you want made custom for a few dollars more.

But call scat and have them work up a couple options for you. They are good to talk to, and have lots of options that are not on any website or catalog.

 

[273]

I might be be wrong but if you got ask if if it's to much CR it probably is, same with cam.

 

[furrystump]

You want the closed chamber 779 head and the icon dished piston with the 20.+ cc dish. Zero deck taylor your head gasket to your target CR. Like one of these but in the right overbore
Parts and Accessories - +20.50cc Piston Head Volume (cc) - Scat-408
I have run the 779 heads with the 20.55 cc dished pistons with a .039 head gasket on pump gas forever. My pistons are .010 in the hole. I Changed pistons to the 5 cc flat tops and it is about 12.2 to 1 with a 63 cc head. It is not “easy” to get a streetable compression with a 4” stroke and a flat top piston. The dish piston gives you quench with the 779 head and the right gasket.

 

[furrystump]

With the 20.50 cc piston at zero deck with the 63cc head and a .027 cometic gasket your at 10.43 to 1 and you’ll have quench. That may be a little tight for piston to head clearance. But a .039 gasket gives you a little more room.

 

[stumblinhorse]

I am contrary to all the other advice. I am and would do the 5CC flat tops. If I was doing the 20CC dish, I would do the IMM/Indy irons and go 62CC and skip the AL head. Throw a felpro 1008...

Otherwise do the 5CC flat tops with a 65/66 Chamber AL head and have a very strong engine with a lot of cam options for top HP or low end torque.

 

[furrystump]

I am contrary to all the other advice. I am and would do the 5CC flat tops. If I was doing the 20CC dish, I would do the IMM/Indy irons and go 62CC and skip the AL head. Throw a felpro 1008...

Otherwise do the 5CC flat tops with a 65/66 Chamber AL head and have a very strong engine with a lot of cam options for top HP or low end torque.

with a .039 gasket thats 11.59 to 1. At 66 cc chamber

 

[Wyrmrider]

picky details furry stump
your suggestions are right on
the other must be retarded

 

[stumblinhorse]

I guess @Wyrmrider I will let you know how my 11+:1 compression turns out. Not sure why it needs to be retarded. 11.5:1 with al heads and a .04 quench with the right cam should run great on Ohio pump gas for the OP.

 

[Wyrmrider]

I hope so
I do not like to retard because of too much compression
however do not reduce quench to lower compression- is counterproductive
do a trial assembly and verify that .04
What pump gas can you get in Ohio
I would not try 11 here in California where I would use the dish piston combo with .030 quench

 

[nm9stheham]

I am contrary to all the other advice. I am and would do the 5CC flat tops. If I was doing the 20CC dish, I would do the IMM/Indy irons and go 62CC and skip the AL head. Throw a felpro 1008...

Otherwise do the 5CC flat tops with a 65/66 Chamber AL head and have a very strong engine with a lot of cam options for top HP or low end torque.

Yeah, but you are at 7000' elevation... you NEED to go small. For the altitude. That will not work at 1000' or lower altitude in southern OH for the OP.

 

[nm9stheham]

OP, I don't see any cam info. Or car/engine use. That is needed to complete the picture.

And also can you tell with the scat rotating assembly what the deck clearance will be before installing it.

You can get a good nominal number out of the info supplied. But you won't know exactly what you have 'til you put it together with your particular block. It is totally normal if one is going to adjust the deck heights and quench gaps accurately, to assemble and THEN figure out how much to mill off of the block. It is a necessary step for a high degree of accuracy.

 

[Strokedcuda67]

I appreciate all the help and advice. I decided to go with the dish piston set from scat and then see what my deck clearance will be. I can adjust the compression after I see where the numbers are when I get my rotating assembly. I am still open to cylinder head choice, and gasket thickness.

 

[nm9stheham]

Looking back at post #7, I am pretty much at the same point. Zero deck the 21 cc dished pistons and with a .039 gasket, you'll have decent quench. SCR will be around 10.2, with the Edelbrock 60779 heads with 63 cc chambers.

I personally would stick with a .035-.040" range for quench gap. The local circle track guys sneak it down close to .025" but that is as tight as they go, even with regular engine checks. For general street use over the long term, that is too tight, IMHO.

If you wanted to sneak up the SCR a bit, then deck the block another .004-.005", use the .039" head gasket, and you can fudge another tenth up on the SCR.

When you measure your piston-to-deck height, measure across the pins to the deck, and also at top and bottom. When measuring the top and bottom deck heights, rock the piston back and forth to get the range. No need to have rings in; just makes life hard. Measure deck height at least at all 4 corners. I do all of them and have seen an odd thing or 2. With your new rods and crank, piston heights above crank centerline 'ought' to be very consistent, but doing all holes will show up any oddities in the crank for example. All the data can also show slopes in the deck; sometimes I have to stare at the numbers a bit to see the 'trend'. I use just one piston and rod to take out any variations in rod length or piston CH in this phase of measurement.

This is just general info; whether that SCR is adequate or not, depends on the cam, for which info is still lacking, and the cam should be driven by use, which is also not known. The info offered is only as good as the info provided.

 

[Wyrmrider]

excellent tips nm9
if you have to cut the deck to much look at the .028 gaskets
the cam and DCR/ SCR go hand in glove
measure twice - cut once