Joe,
This is how my buddy Dave gets away with 15:1 SCR on his street-class big block engine. The cam has like 790 degrees of duration (not a typo) and it overlaps so bad that most of the compression bleeds back off at lower rpms. 12:1 is about the highest I'd go on a pump gas motor though

 

Joe,

I ran the 1010s on the car for over 3 years and probably 8-10,000miles. I used them for the same reason you did to maximize CR and achieve a ideal quench area. But then they just let go. The problem first showed up a surging idle. Drove me nuts for a year thinking it was something I needed to modify in the tune. Then I started to notice some smoke from the exhaust even when it was warm. But coolant temps would be fine. I finally found what it was by accident as I was looking for an oil leak. I must have found it at the right time because there was no sign of oil in the crankcase. I pulled the oil pan down just to make sure once I did see a milky foam under the oil filler cap. I went looking for answers from TFS and AFR, they both told me to use the 1003. TFS said that's what they used with their heads whenever they build a motor and have done so with no issues.
Once I went with the 1003, I probably drove the car another 3 years and maybe 10-12k miles. I sold the car to someone nearby and he's still driving it. In fact, he went to the track last fall and ran a 13.5+ @ 104.5

 

How about .790 lift ?? There is only 360* in one crank revolution.

 

No, no... This is one of those "new type" cams that hangs the valve open constantly. Basically no point when the valve is closed, so no static or dynamic compression.

 

That will save on head gaskets for sure!!

 

Haven't you heard of "infinite overlap" cams?

 

Damn, I must be way behind on the technology. Next thing ya know, they will have computers that can control the engine systems.

Chuck, sorry I did not mean to jack the thread. Just having some fun. Leaving now.

 

As long as you guys are enjoying yourselves.

 

Hey don't worry. It's an interference engine so the piston will close that valve automagically.

 

Here's what happened....My short block builder screwed up the compression ratio on my engine. Instead of the 11:1 reported to me, it actually was 12.2:1. I don't know if that compression ratio is too high for Felpro 1010 or 1003 composite type gaskets but my builder seems to think so and is suggesting we go with thicker gaskets.

They threw a couple options my way.....

.080 gasket which would yield a 10.97:1 compression ratio

or

.093 gasket which which would yield a 10.6 compression ratio.

Of course the first thing that pops into mind is my quench area. As it sits right now my quench is .052.

Here are some other specs. with the 1010 gaskets(assumong .038)

Head cc 53
Piston dome -55
Block deck .014 (difference between top of piston and top of block)
cc total 2.93
Swept volume 785.653

alot of these terms are foreign to me and I can use some guidance from you guys. .052 sounds like I do not want to go with a thicker gasket. Therefore some bowl work on the heads sounds like a possible option.

Any thoughts?

Thanks,

Chuck

 

Is that 0.052" using the presumed numbers that the C/R was initially
based on, or the corrected numbers?

Before I knew better, I used thicker gaskets to compensate for declining
octane levels. Looking back, it was a cost-effective but counter-productive
fix for me.

Much has been written about quench distance/squish area.

.

 

The .052 is what it was with the 1010 gaskets(.038-.039)

 

I personally would focus my efforts on opening up the combustion chamber.

 

Another possibility might be to use a valve relief cutter to create or
enlarge pockets in the piston tops.

So much painstaking effort goes into shaping the chamber that it seems
a shame to start over. If there is sufficient material in the piston, then
while it is still a job that deserves care & precision, fly-cutting reliefs
in the tops is something could be jigged up for repeatability and the
end result would have less potential impact on flow. Strikes me that
costs would be lower for whomever winds up footing the bill, too.

Objections? Caveats?

.

 

Chuck, glad to hear you are getting answers.
One thought on fly cutting the pistons is, this will change piston weight. Enough to require a re balance ?? Other than that its a good option.

 

Fly-cutting might change piston weight enough to make re-balancing
advisable.

But my vote is that balancing appears to be $100-$200 (at retail)
proposition, these days. It is a fairly straight forward process. By
comparison, reworking the chambers to an acceptable volume and flow
performance is a more-painstaking operation and it is possible to spend
more money for this.

What about cutting and not rebalancing?

When the piston weight is reduced, my vote is that this has the same
effect as increasing the calculated weight of the reciprocating
components - a technique used for overbalancing. In other words,
if an engine was balanced to 50% and then the pistons were cut
by some amount, the net result is that the engine would then be
overbalanced.

If the change was small and consistent across all cylinders, it might be
possible to do skip rebalancing. But overbalance favours high speed
operation and if there is a downside, it will probably be apparent somewhere
at low speed operation (2-4K RPM). An issue for a street vehicle.

.

 

Not an easy solution regardless> How about the possibility of swapping pistons. After all is said and done, it may be cost effective. Especially if the replacement piston is slightly heavier. Builder can treak the pin weights, and grind the piston pads to avoid a rebalance, and the crank can stay in the block. Something to consider anyway.

 

Engine component balance is not really very critical. Balancing is something shops like to sell and claim all kinds of advantages for being within 2 grams and if you are going to do it then it should be close but I would not get all that nervous about it unless you were installing some new components that weighed quite a bit less. Overbalance is preferable to underbalance. Cutting valve reliefs in pistons would not affect weight enought to warrant the expense of balancing. I don't rebalance any of our stuff going to the track if it is within 5 grams underbalance or 10 over. Our tolerance is a range of 15 grams.

 

I've been curious about how much material might need to come off
each piston if someone chose to go that route.

The values chucks88 provided did not add up for me, especially the
-55 dome. So I worked back through the numbers to validate them
and I believe if he reviews the notes he received from the builder, he
will find that the builder's values should close to the following:

Bore: 4.03463
Stroke: 3.75
Gasket: 4.166 bore x 0.039 compressed
Head: 53cc
Dome: -5.5cc (not -55)
Deck Hgt: 0.014"
Deck Vol: 2.9331cc
Clr Vol: 70.13cc
Swept volume 785.653cc


** == Bore from Swept Vol ==================== **

(4.03463)2 * 12.8704 * 3.75 = 785.6529 (good enough)

** == Deck Vol ============================= **

(4.03463)2 x 12.8704 * 0.014 = 2.933cc

** == Gasket Vol =========================== **

(4.166)2 x 12.8704 x 0.039 = 8.712cc

** == Clearance Vol ======================== **

53 + 2.93 + (8.7 calc'd below) + 5.5 = 70.13cc

** == Compression Ratio ==================== **

(Swept Volume + Clearance Volume) / Clearance Volume

(785.653 + 70.13)/70.13 = 12.203:1 CR

If your target is an 11.0:1 CR, then my math suggests this could be
attained by increasing the piston dish volume by 8cc from -5.5cc to
-13.5cc. This would change the Clearance Volume from 70.13cc to
78.13cc, the revised Compression Ratio would be

(Swept Volume + Clearance Volume) / Clearance Volume

(785.653 + 78.13)/78.13 = 11.06:1 CR

Use the same approach to derive other CR's

Regarding fly-cutting and piston weight. Solid aluminum appears to
have a density of nearly 2.7 grams per cc at 20ºC. Using density,
removal of 8cc of material from the piston would seem to decrease
piston weight by 21.6 gm (8cc * 2.7gm/cc).

The calculation above is purely theoretical - you have to verify the
actual density of the piston material, then do your own figuring and
validation to ensure the desired results.

How does reducing piston weight by 21.6 gm affect engine balance?
I don't know but I worked through the following as an exercise.

Bob weight = Rotating Weight + (Reciprocating Weight x .50)

The piston is part of the reciprocating weight, therefore
my vote is that reducing piston wgt by 21.6 gm results in
an imbalance of 10.8 gm (21.6 x .50), relative to the bob weight.
Forces increase as the square of the change in velocity and there is
a formula to evaluate the effects of imbalance.
For 'W' I'll use 10.8 gm. For 'R', I'll use half the stroke and convert
to centimeters 4.7625 cm [(3.75/2) x 2.54]

If I've done my sums correctly, here is how an imbalance of 10.8 gm
(0.381 oz) at a radius of 4.7625 cm (1.875") affects forces at various
RPM
These numbers are per piston. I do not know whether the total
imbalance of the engine is cumulative. If it is, then it looks like total
forces from imbalance at 6000 would be 8 x 18.52 kg (40.74 lbs)
or 148.16 kg (326 lbs).

If I am in the ball park, then spending $100-200 to rebalance the
assembly looks like it would be a worthwhile expense.

Can someone confirm or dispute the reasoning, please.


.

 

My bad guys, .790 lift. I hope y'all had a good laugh at my expense...