Holy cow! Called Summit this morning and they assured me that they could get me a rotating assembly with 12cc pistons for $549 from Eagle. They just called back and quoted me over $1000!
Well back to square one on this. The pistons by themselves for 12ccs are $300. Then get them mounted on my rods and get the whole works balanced another $250. That's $550ish. About what the rotating assembly with 7cc pistons cost.
I did however have another though. What if I bought a stroker crank 3.75" throw and combined it with my stock pistons and rods?
With these heads and cam and 17cc pistons that would give me 9.94 SCR and 8.32 DCR at sea level and 7.72 DCR at 3000 ft. This just may be the answer. Of course block would have to be clearenced and not sure about the cam clearence. How could I check that without mocking up the block? Or is a small circle cam always required?
Nothing like trying to engineer something from back seat huh?

 

i think we agree. once the throttle is opened enough to make the same HP the cyl pressure is the same(as long as rpm and cruise load remain the same)
In any case, too much timing causing pinging, is easier to control, than self-ignition from too much cyl pressure. Self-ignition is ignition without a spark and is the dreaded "death rattle" of excessive compression.

 

Increase stroke, decrease compression height of piston, stock pistons don't work. With the right combo you can run standard base circle cam. I have one in my 383.

 

i'd just keep the stock pistons, rods, crank, and drive off with a mild cam. it's near 9:1 right? That's just enough for a fun ride.

 

REELAV8R

My specs. May be helpful.

'76 L-48, 4-Speed, 3.36
383 with Eagle 3.75 crank & 5.7 SIR rods
Speed-Pro Hyper 12cc dish pistons
Centerforce II clutch
'0' deck block
Internally balanced
Comp Cams XE274 cam & Roller Tip Rockers w/Crane Posi-Locks
Accel distributor
Trick Flow 23 degree heads
Edelbrock Performer RPM Intake
Correct Stock Q-Jet with professional rebuild
Dynomax Jet Coated Headers & Chambered Exhaust
Big Block Radiator Core w/Permacool Fan
Hurst Competition/Plus shifter

Heads are 64cc. Quench is 0.041. Static CR is 10.21, Dynamic CR is 8.25.

Timing is 35* all in @2600 rpm + 15* vacuum advance using an AR15 can. Per Lars, max adv should be @2" Hg less than maximum vacuum @ idle.

Intake closing is 64*ABDC.

Car has been running for at least 4 years in this configuration, using BP 89 octane pump gas, without any problems.

 

Comes internally balanced.
http://www.cnc-motorsports.com/eagle...1-pistons.html

 

Lets just say that you grind the cam and finish it. Then the last thing the machinest does is index up the cam and dril and tap the cam gear holes.

The Lunati guy set the intake at 5.5 BTDC The Crane cam guy drills it 4 degrees retarded at 1.5 BTDC So all 4 cam events are 4 degrees later.

 

I'm surprised to hear you say this matt. It would be SCR 9.21:1 figuring 17cc piston and 1 cc crevice. The DCR drops off radically as altitude goes up though. I may end up doing just that. Have to see.

Yes this helps Glen. What altitude do you run at?

So no different than me retarding the timing. Just runs the exhaust valve closer to the piston if I remember right. That being the smaller valve would make it less likely to be a problem as far as it being closer retarded as opposed to timed in straight up.

If I decrease compression height I loose the quench. You think stock pistons are still too high CR?
What actually interferes with the cam base circle that can be changed to not interfere with it?

 

Glen242 I just ran your numbers through this calculator
http://www.wallaceracing.com/dynamic-cr.php
and this is how it breaks down;

SCR-10.21
Effective stroke-2.95"
DCR-8.03 (This is at the Moon township alt of 1100 ft)
Dynamic cranking pressure-159.75 psi
VP index 144

Then I ran mine with the 7cc pistons for my set up and this is what I got;

SCR 10.38
Effective stroke-2.83
DCR-8.03 (at 3000 ft my min altitude of operation)
Dynamic Cranking Pressure-159.75
VP index 136

Two things jump out at me. First the DCRs are identical, and second so are the DCPs (dynamic cranking pressures).
The VP index on yours is higher indicating better torque down low as would be expected.
My effective stroke is shorter so the pressure rise in the cylinder would be on a steeper gradient but still achieve the same DCP when all done.
So these two engine would be very similar as far as detonation is concerned. Mine is roller cammed so this could make a difference, but you are running an XE cam and this is supposed to provide rapid opening rates on the valve and probably better filling vs a normal ramp flat tappet cam. Almost all of the Trick flow heads have a better flow rate than the Dart SHPs I'm using. All together your cylinder filling should be nearly the same or maybe better than mine would be.
Biggest difference is the transmissions and final drive ratio's.
Still, you run yours on 89 without problems? That makes me believe that the 7cc pistons would work just fine in my combo with 91 octane.

 

TOOL
fender lip timing tape.
Today i made a 22" long tool to adjust the timing quickly without a timing light.
3/8" aluminum tubing, one end squeezed in a vice to fit across the top of the dist cap, other end squeezed flat to make a pointer. On the fender where the hood comes down i put a homemade timing tape. 3/4" of movement is ~8 degrees. marked every 3/16" so in between marks is 1 degree. The first thing i noticed is the cap has ~3 degrees of slop in it. so it has to turned one way to take out the slop.

 

I use a timing light.

 

OK mako what is your plan for a tank of bad gas?
Pull over, and, do you carry the timing light in the car?
.....and hook it up
how long will this take?
But, i realize all your engines run on low octane, right? so you don't ever get bad gas, right?
So, this tool is only for adverturous guys that want to run high CR. And don't have an under dash timing control. NOT ME, NOT YOU.
Just a easy tool to make

 

I have a digital timing retard control for the nitrous. Knocks 4 degrees out when it engages. I also have it on a toggle that can bypass the NO2 for engagement. Never needed it for bad gas. Never got bad gas and mine runs on 93 only. Usually fill at BP.

 

Just made 1 for my 61. Twice the dist moved and it was hard cranking. Also this would be handy anytime dist is out for a cam swap, etc.
So now i can spot check it real fast, without a timing light.
What i like is:
1. no need to run engine or crank it.
2. can easily make a 1 degree change, and get it right the first time.
3. no wires to hook up, no need to watch out for the fan belt.
4. no need to clean off timing marks and chalk groove. no eye strain. no blinking bulb to match up in motion. no wasting gas, and no fumes in my garage.
.
Reports say up to 30% of hi-test is really regular. If u never got bad gas, it is likely runs fine on regular.
Mako, isn't your car all apart for a long time?

 

Car has been torn down, rebuilt, driven, torn down, rebuilt, driven, now frame off, as I should have the first time.

 

If you buy stoker rods that claim to clearenced for the cam, then are they clearenced for the cam and the block both?
As far as balance goes. Externally balanced crank is cheaper. I have the flex plate and harmonic balancer already for an internally balanced crank can they be used for an externally balanced rotating assembly?
Are there any known issues with a 377 stroker vs the 383 stroker?

Tossing around the idea of just stroking this with stock bore. Then when that wears out or if I want to revert back for some reason will still have bore metal to work with.
I can buy the individual items, Crank, Rods, and pistons and use the bearings and rings I already have and have it all balanced, for less than buying the assembly.

 

No, the cam hits on the rod big end cap near the rod beam. the amount of block clearancing is directly related to how big the rod bolt head is. Like your ARP 12 point rod bolts need lots of clearancing

No, external is just what it says. The damperalong with the crank and flex plate is weighted and drilled to work as a matched balanced set


No, You can juggle the bore and stroke to aquire some CI number. 350 based 377 is a 4.00X 3.750 400 based block is a 4.125 X 3.480 It is more rare to make a smaller motor by destroking.

 

I'm looking at these rods here. Would they work? In the notes it says clearance for stroker applications.
http://www.summitracing.com/parts/sc...make/chevrolet

Press fit or floating pins does it matter other than the free floating I could replace down the road if need be?

What I meant to say is can they be adapted to be used for external balance ie weight added or removed?

 

Rods clearanced for stroker is talking about cam clearance on the big end rod beam

Floating pins are for another rotational point and you are not binding or deforming the roundness of a forged piston. as to changing them.... If you have a pin go bad, you have alot more problems than just the pin. I have some broken valve forged pistons and you can't get the floating pin out.


Exteranly balanced dampers are made differently. They have a weighted side. Internally balanced are neutral.

You could weld on weight to the flex plate.

IMO - Don't build a externaly balanced motor.

 

Anyone know where the Eagle company is located ???