compression ratio question

[oldschool]

i'm rebuilding one of my 500" motors.it specs:

4.375
4.150
indy 295 cnc sr,s
indys dualplane or mopars 337 manifold
solid roller 272/276 @.050 .661/.661 or 276/283 @.050 .737/.672
1.6 rocker arms
1000 cfm 4150
2" step tti headers
my question is what power/torque difference would i see going from 12.7 cr to 13.5 cr? its at 12.7 now would it be worth milling my heads for more compression? i run sunoco 110 and it is in a street car.also what about the differnt cams? i have both. i have been using the smaller one and it does real well one the street.it,s a four speed car with a 3.54 dana.
either way i will be dynoing both cams and different manifolds,i will post the results...are you out there ron?need some input...

[firefighter3931]

With the 3.54 gears and 28in tall tires i would be more inclined to use the smaller cam with a tighter LSA. The 276/283 grind looks like the stick that's in your 580in build with the 112 lsa...is that correct Brian ?

As for the increase in compression ; the higher the static compression the less the return on investment. Lower compression builds show better increases when upping the CR. I would hazard to guess that you might see 3-4% increase in peak power going from 12.7 > 13.5 

Looking forward to the 337 manifold test. It would be interesting to see them back to back on the same dyno without any other changes. 




Ron

[Challenger340]

What Pistons are you using OS ?
Domes ?
How Big ?

Reason I ask, from my experience anyways,
is that the 4.375" Bore Diameter, is very limited in Power Increases, shown by Milling C.R. increases, if you've already fallen into the "Old" .055" Quench "trap", depending upon Dome Piston used, when Fuel Octane Requirement has been met.
You're using 110 Sunoco right ?

Long story short, IMO,
depending upon Dome, you may not gain hardly anything, more just move "events" around.

[oldschool]

With the 3.54 gears and 28in tall tires i would be more inclined to use the smaller cam with a tighter LSA. The 276/283 grind looks like the stick that's in your 580in build with the 112 lsa...is that correct Brian ?

As for the increase in compression ; the higher the static compression the less the return on investment. Lower compression builds show better increases when upping the CR. I would hazard to guess that you might see 3-4% increase in peak power going from 12.7 > 13.5 

Looking forward to the 337 manifold test. It would be interesting to see them back to back on the same dyno without any other changes. 

Ron

hey ron. yes the cam is the first small one i used in my 580.it seemed to small so i went to the bigger one that i dynoed with.this motor had 13.2-1 cr before.the new pistons only give 12.77-1.i would only have to mill my heads .030" to get 13.5-1.i already have to run race gas so i'm not trying to get away from that.just wondering what would be lost going down about half a point.it would seem to get as much as the gas would support,within reason.my other motors are 13 plus cr,so i dont mind the gas .i buy it by the drum .
also got my 337 manifolds.i port matched one for the 580 and installed it.it works awesome! i would guess it picked up at least 40-50 horsepower over the dualplane with an increase in torque also.i cut the little 1/8" step off the carb flange and use a 1/2" birchwood spacer from aed.i also use a k/n drop flow control air cleaner.everthing fits perferct under the hood . it is in a 70 charger.
im going to chassis dyno soon.i will test the 337,440-3,440-2d and will post.this car has been a blast.the power just never stops  .
im going to dyno the 337,440-3,440-2d on this 500" build also.i bet the 337 will be very close to the 440-3,but be able to fit under the hood.i will give up a little power to keep the factory hood on are beautyful cars

[oldschool]

What Pistons are you using OS ?
Domes ?
How Big ?

Reason I ask, from my experience anyways,
is that the 4.375" Bore Diameter, is very limited in Power Increases, shown by Milling C.R. increases, if you've already fallen into the "Old" .055" Quench "trap", depending upon Dome Piston used, when Fuel Octane Requirement has been met.
You're using 110 Sunoco right ?

Long story short, IMO,
depending upon Dome, you may not gain hardly anything, more just move "events" around.

the pistons are flat top,with 6cc valve pockets.they sit .005" in the hole.head gasket is a 1009 .039".the head cc now is 70cc.i would only need to mill .030" to make the heads 65cc.that should get me about 13.5cr.
i do use sunoco 110,i even use it in my 580 with 14.16cr.my other 500" motors are 13-1.i just dont want to loose to much power.i have to use race gas anyway.this motor before was 13.2.what do you think the loss would be going down 1/2 point?it would seem to run as much as the gas will support 

[firefighter3931]

With the 3.54 gears and 28in tall tires i would be more inclined to use the smaller cam with a tighter LSA. The 276/283 grind looks like the stick that's in your 580in build with the 112 lsa...is that correct Brian ?

As for the increase in compression ; the higher the static compression the less the return on investment. Lower compression builds show better increases when upping the CR. I would hazard to guess that you might see 3-4% increase in peak power going from 12.7 > 13.5 

Looking forward to the 337 manifold test. It would be interesting to see them back to back on the same dyno without any other changes. 


Ron

hey ron. yes the cam is the first small one i used in my 580.it seemed to small so i went to the bigger one that i dynoed with.this motor had 13.2-1 cr before.the new pistons only give 12.77-1.i would only have to mill my heads .030" to get 13.5-1.i already have to run race gas so i'm not trying to get away from that.just wondering what would be lost going down about half a point.it would seem to get as much as the gas would support,within reason.my other motors are 13 plus cr,so i dont mind the gas .i buy it by the drum .
also got my 337 manifolds.i port matched one for the 580 and installed it.it works awesome! i would guess it picked up at least 40-50 horsepower over the dualplane with an increase in torque also.i cut the little 1/8" step off the carb flange and use a 1/2" birchwood spacer from aed.i also use a k/n drop flow control air cleaner.everthing fits perferct under the hood . it is in a 70 charger.
im going to chassis dyno soon.i will test the 337,440-3,440-2d and will post.this car has been a blast.the power just never stops  .
im going to dyno the 337,440-3,440-2d on this 500" build also.i bet the 337 will be very close to the 440-3,but be able to fit under the hood.i will give up a little power to keep the factory hood on are beautyful cars

Brian, thanks for the feedback on the 337 manifold....looking forward to your chassis dyno numbers. Sounds like the 337 is the hot ticket for hood clearance on a big cube build. I will have mine on the dyno later this fall. 


As for the cam swap ; one thing to consider is the piston to valve clearance...are you sure you have enough with the "larger" camshaft ?  The wider lobed profile with increased duration would benefit from an increase in static compression....assuming you have the P/V clearance to make it work. 



Ron


Ps. I'll be interested in Bob's thoughts on this topic....he's built some wicked big cube bracket motors of this size and has a lot more experience in this type of build. 

[oldschool]

im going to dyno both cams and the different manifolds.the bigger one might be to big for the cubes,and stay streetable anyway. im going to test it because i have it laying around.it seemed to small for the 580 but you know how a big motor eats up a cam.i will mainly be looking at the torque and where it makes power. i think i will go with the higher cr,just because i know it works well.this motor was about 15 years old.it was just wore out.

i should be chassis dynoing next week,and dynoing the 500" in about 3-4 weeks. i will post all the pertinent info.

[Challenger340]

Hi Brian,
I'm a little "confused" here, too many Engines, so I'm staying with the original question, 500" CR increase/same Cam.

If you are using a Flat Top Piston at 12.7, and contemplating a move to 13.2 by milling, IMO, that'll be an a good thing, should be broader with slightly earlier/higher peak Tq#'s.
Dunno 'bout the hp "up top", same-same maybe ?
It May like a little less Total Timing as well, because of the added initial heat.
also,

IMO, I don't think the Bigger Cam swap will make much difference "apples to apples" in the 500". You may gain somewhere, only to lose elsewhere for "streetability", if ya know what I mean ?

Manifolds;
Sorry, I know nothing about the 337 for comparisons. Just being honest here.

Most of the Dyno'ing I've been doing, has followed paths of trying different changes on exisiting builds, or new builds that test "theories". Best way to "test", is to leave EVERYTHING same-same, except for the "one" change, then "see" the difference.
or,
Find out what it did NOT like, then "reverse" to see what ot DOES like ?

Brian,
I'm gonna take some stuff to "pm" if you don't mind ?

Ron,
Can I "CC" you as well ?

Bob out.
 

[Rob R]

I'd say 10-12 ft lbs

[oldschool]

UPDATE:
i went with the higher compression.
i stayed with the smaller roller cam.
instead,i ordered a new set of 1.7 rocker arms from t&d. i hope this build responds to the higher ratio arms like the 580 did.they really woke that motor up! i guess i need to get ready for some clearance grinding for the pushrods,and some frequent valvespring changing.....