I'm trying to get my engine pieced together. So far I've got this:

454 .30 over
Stock crank and rods
ARP Rod bolts
Forged pistons (thats all I've decided for now)
Comp Cams 294S Solid lifter
Stock 781 heads ported and 2.19/1.88 valves
Torker II Intake
Carb etc etc

My problem seems to be that I want at least 9.5:1 comp, even 10:1. As far as I know those heads have a 118cc combustion chamber. I'd need to reduce that to 100cc to even get 9.5:1. I've been told that milling heads is a bad idea because it can weaken them, and it causes problems with the intake not matching up. I don't think I could get a piston domed enough without bashing the valves to non-existence.

Other than getting new closed-chamber heads, do I have any options?

 

You can run closed chamber pistons with open chamber heads to increase the compression ratio; but not the other way 'round.

Decking open chamber heads enough to reduce the chamber volume from 118/119 (standard volume) down to 100 ccs calls for a lot of metal to be removed and I wouldn't do it.

As a rule of thumb, that much of a cut will increase your compression ratio by about half a point. For some reason, my Dyno 2000 program won't allow a 118 or 119 cc head volume to calculate CR, so I'll have to resort to the long, mathematical, Texas Instruments way.

I ran closed chamber pistons (+.060) with open chamber heads on the street for years in a 468 BB and had no problem whatsoever. TRW and others make a set of forged pistons for this application which have a "half dome". I've got a set hanging on the wall in my storage house and I can get the # off them if you need it.

I just did the calculations assuming a 9cc head gasket volume, zero deck and not factoring in valve reliefs or dead space. With flat top pistons and a 118 cc combustion chamber, I came up with just under 8.5CR. Reducing the combustion chamber volume to 110 raised the CR to about 9.6.

I don't recall how many cc's are displaced by closed chamber pistons with short domes, but that info should be available in some of the catalogs, like Performance Automotive Warehouse (PAW), or the piston manufacturer's website.

Once you can determine how many ccs are involved with the closed piston dome, you'll be able to calculate and get a fairly accurate CR, even without factoring in valve reliefs and the dead space between the top ring and the piston deck.

Jake





[Modified by JAKE, 2:15 PM 11/26/2001]

 

Use the TRW L2399-F pistons and have the block decked to 0 height .That with a 0.38-0.42 Fel Pro head gasket and the fact that certainly the heads have been milled a little will get you right at 9.3 compression ratio.With that little cam you don't want any more compression than that.It is important to 0 deck that block.It will take off about 0.008 using that piston.A word of caution to those that choose to use a closed chambered piston in an open chamber head! Check for clearance!
edited to ask if you have already purchased the cam? If not,post your trans ,gears ect and we can come up with a killer combination!


[Modified by mountainmotor, 7:32 PM 11/25/2001]

 

Excellent advice on checking clearance. Anytime you make mods of this nature all the clearances should be checked; it's just the best way to build an engine.

Not only can you determine piston to head clearance, but you can determine how much camshaft lift you can run. Then the pistons can be flycut if needed to allow a really high lift cam before everything is balanced.

Be sure to have a spark plug (of the type you'll be running) screwed in to detect any interference problem. My set of closed chamber pistons bolted in without any mods to the pistons for the .600 roller cam I was running, but you've gotta check.

Jake

 

I haven't purchased anything (but the block and heads) yet, so let's build a motor. I have a Super T-10 trans with a 3:36 rear. I wanted to shoot for about 550 HP. What do you mean by little cam? I thought it was a pretty agressive cam? What about the TRW-2465, they're a step up from the 2399 it seems, and quite a bit more dome.

Enlighten me :)


[Modified by ddn, 4:48 PM 11/26/2001]

 

I don,t type well so bear with me!
Headers will be a must at this power level.
The floor of a Torker II is too flat for optimum performance.See if you can pick up an old Torker"the one that the carb sits side ways on".It will need stagger jetted but I can help with that.You can always epoxy the floor of the Torker II to pick it up some.When port matching either of the two,leave the floors alone!But you are stuck with one of the two because of hood clearance.
An old boat motor of mine that ran two hard seasons is now in a 66 Vette with an additional 25k on it.I used the 2465F pistons in it along with the 781 heads.That is a good choice pump gas compression if you deck it .015 and use a FelPro .038-.042 gasket to get right at 10.1 compression.The intake valve pockets will need to be deepened .100 and radial clearance an additional 0.040 with those pistons. I would use the Isky part # 396257 cam.The grind is the Z-57 solid.It is a boat cam but not the one used in the above motor.
300 254 590
310 264 590
LSA 110
RPM range 25-6500
put the intake in on a 104 centerline
The lobe design of this cam is not quite as agressive as some but it will last a long time if broken in properly.You won't be down but a few HP compared to a more agressive profile and longetivitey is very desirable.I usually run a single pattern cam with oval port heads but the optimum tail pipe lenght of 18 inches for max extraction of the exhaust is not available with the C3. Flat cam lobes are costly to more than just the cam and lifters.Use solid lifters with the piddle valve.

I would use Clay Smith Engineering Dual springs with the seat cups.These are a must especially on the exhaust spring seat.Set the springs at 135lb seat pressure.They will come down a little after run in.PC style valve seal will have to be used with these springs.

Use a Holley 4781 with 82 primary and 85 secondary jets for a start then come down as needed.Use 5.5 power valves in each end.
Whoever ports the heads should really work the exhaust roof and the short side radius of the intake.The Manley Proflow ehaust valve should be used for an additional gain.
A later style 4 core "HE" radiator will cool it with the correct fan
Passenger car rods with ARP bolts will be fine.
On that Big Block I highly recommend using +0.005 rings and filing them to fit.
Comp 1.7 Roller Tip Rockers are more than ample and so is a good set of stock length good 3/8 pushrods.
Be shure to have the machine shop pin fit the pistons for extra life and to free up a little power and have the block align honed.You are going to need a little extra rod size clearance but not much.Balance the rotating assembly.
There are other cams that came to mind but this one will get you where you want to be.Use this combo and scare the others off the road with the sound and have the power to back it up!
More power is available with a hood change!"intake"

[Modified by mountainmotor, 8:11 PM 11/26/2001]


[Modified by mountainmotor, 8:13 PM 11/26/2001]

 

mountainmotor,
THANK YOU SO MUCH! The information I get on this forum is incredible. I'd love to talk to you more about this, so let me break it down a bit.

I'll probably just go with a Torker II because it's easy and cheap to get, it also fits under the stock hood. I DEFINITELY plan to change to a L88 or other hood, but for now, money is limited, and $500 on a hood is $500 less on the engine itself.

What would the difference between the 294S and the Isky Z-57 be? I know it's not really a function of the cam, but aren't marine cams designed to rev slower but make lots of powa? Or is this way off? I do plan to run Hooker side pipes with 2" primaries.

Ok on the springs.

I will run a Holley temporarily, but I plan to switch to EFI. Maybe the Holley 950 MPFI, maybe a custom built system, that'll come with the big cowl induction hood probably.

Any reccomendations on someone to do the heads? I got a quote from Roger's Porting Service (specifically mentioned 781s by chance) and he wants over $1000 for all the work including valves. When I can get Edelbrock aluminum heads fully assembled for $1600, I won't be going THAT route. I'm sure a machine shop in my town or up in the cities can do good work on the block, the heads are another story. How about for balancing the rotating assembly (including flywheel).

What do you think this combo is good for? 550HP/600lbs/ft?

Thanks!! :chevy


[Modified by ddn, 9:19 PM 11/26/2001]


[Modified by ddn, 9:39 PM 11/26/2001]

 

I have used a 294 in a 327 Chevy.It needed more that is why I called it a small cam along with the fact that sometimes when putting a engine combo together overcamming a little is desirable to bleed off some of the low speed compression.
Typically a Jet Boat cam is nothing more than a oval track design.Usually a single pattern cam ground on a 108 LSA in an effort to get the max torque up in the 5k range with a duration of around 260@.050
This Z-57 is a higher revving V-Drive cam
Get this! A couple years back I built a guy a 10.5 Rectangular port 468 V-Drive motor and used the one step up"dual pattern" Isky that is 263 or so @ .050.and put a Team G 4500 intake on and he came after it ,put the motor in the boat with a 850 carb adaptedto it.I never saw the boat run but rumors were he was killing most the Lake Racers with it and the motor turned 6600 rpm.He got some water in the gas somehow and brought me the carb to go through .I looked at the list # and it was a 700cfm Holley double pumper!Moral of the story? I guess there is not one but I would have never purposely stuck that carb on a 468 inch motor.I suspect many street driven cars are over carbed.
About the heads.I think I know where there are some new 118 cc Rectangular Port heads less valves with bronze guides and hardened seats.These are take offs from crate motors.They are up North and shipping would be reasonable.The price would probably be about 600.00 for a pair.I will check for you if interested.

 

This might not be real useful as you want more HP, but my brother assembled a 461 with low compression TRW's. He struggled to get slightly over 9 to 1 with the small chamber oval port heads.

He wanted a 294 S, but decided to go with 282 S. Car made 325 HP at the wheels on a conservative dyno-a Z06 makes about this much on this dyno matter of fact. Car will run easy 13.50's with a near stock stall and 4400 pounds-69 Caprice. Motor peaks at 5200 with a very flat torque curve. I can post if you would like.

:)