Hey everyone, I have posted here before regarding various 340 combos. I have learned a lot about the ideal setup I would like to build for my car, but other car/life projects have gotten in the way and I am looking for something to make my 70 challenger a little more competitive with the friends modern muscle cars at the track for the time being.

I am on a VERY tight budget, and plan on building something much better in the very distant future, but I figured if I could use what i've got to make a bit more power then I could have a little more fun with the car.

What I have now- 340 bored .030 over. Steel crank from a 69 340, Eagle H beam rods, Speed Pro flat top pistons, J heads with a tiny bit of port work, .480/.480 230/230 cam, street avenger 670 carb. I'll be installing 4:10's in the rear by the end of the summer. Unsure of the exact compression, but I am fairly sure it is probably (much) lower than 10:1

My plan- I have a Victor Jr. (maybe a Victor, forget which) stored in my garage that a friend gave me. My plan was to find some ported Eddy heads and a 750cfm double pumper for sale on the boards, spec out a bigger cam and put it all together with the Victor intake to make more power on a tight budget. I also have a full aeromotive A1000 fuel system (overkill, but should work) lying around with braided lines and all for a 19 foot long car, so I can install all of that and put a 100 shot plate system on it if I feel like pushing my luck.

Is it even worth doing all of this with the flat top pistons though? I believe the Eddy heads will bump me up a tiny bit from the J heads due to their chamber size, and if I can find a milled set then even better. What do you guys think? How much power can be made with the flat tops? If I can find the heads and carb for the prices I have seen them going for, I think I can cover this whole build for less than $1000 after selling my old parts if I don't have to touch the bottom end.

What is the part number of the eddy heads? You could get them in open chamber or the closed.

If they are open, with the FT piston you have, you can easily run 10.5:1 (measured) compression with that cam. BUT BUT BUT, to get that compression ratio out of those pistons (again..ASSuming open chambers) the piston MUST come out of the deck at least .017 PLUS the amount of the difference between the head gasket you are using and the .021-.024 head gasket Chrylser used from the factory. So, lets say you have an .039 thick gasket. .039 minus .024 is .015, PLUS the .017 the piston SHOULD be out of the deck and you get a piston that is .032 ABOVE THE DECK.

You can mill on the heads but the 340 should have a positive deck height when using OC heads. I have run them as high as .054 out, but it's hard to find a guy who will do it.

If you get the compression up, and if you have a Victor of Vjr and a 4.10, you are way too small on camshft. For a small amount, you can have a custom ground cam. While the cam you have is not bad, you are wasting HP IF you do all the other mods you have said you would do.

In no particular order:

Cam Motion
Bullet
Racer Brown
Mike Jones

There are others who do custom cams that are rather inexpensive. I personally Like Jim at Racer Brown. Far too many people think that RB has old grinds that are out dated and it's not true. Jim is 100% old school. No web site, don't do credit cards and has a list of lobes a mile ling. If you call him and give him the straight poop you will get a great cam for your application. The other 3 I mentioned do the same as well.


BTW, the above compression numbers are general numbers and you should CC the chambers and calculate final number. The numbers I gave would be for a 72 cc chamber and I would rahter mill .040 off the deck than .060 off the heads.

Stay away from the openchamber Edelbrock heads if at all possible,they are a real stupid deadend. most of the time the popup pistons are not that far above the deck anyway and much better to adjust with gaskets if you are stuck with the pistons.

I'm playing with a set of the open chamber heads Edelbrock heads on my Duster right now only because I got them for a "real good" deal. I ported them and went a 9.74 and 9.73@135 mph first day out.

How are the open chamber eddy's a dead end?

It's damn hard to get a piston out of the deck with a head gasket.

Thanks everyone! I haven't purchased the heads yet, I was hoping to eventually find a deal here for some used ones with port work. I am in no rush ( I actually don't have the cash yet anyway) .

I WOULD like to bump the cam up, I really don't mind going big on the cam as I'd like to get the most power possible out of the combo and really make use of the Eddy heads. I am just worried about running a bigger cam with the flat top pistons, not having enough compression and all.

As far as piston to deck clearance, that is something I am unsure of right now. I didn't build the motor, but when the time comes to do this project I'll be able to find out when I take it apart. I'd venture to guess it is stock deck height right now with off the shelf speed pro pistons or MAYBE zero decked. I don't think anything more was done, it was just a basic rebuild. I am really not looking to take apart the bottom end for this build and have machine work done, but if it would be of some big benefit while running these pistons I may consider having the block decked. It would certainly be cheaper than buying new pistons/having it rebalanced.


Now I am wondering about the open vs closed chamber. I figured I would have to go closed to get the compression up with the flat top pistons but it seems like the only way to get the CR up would be to run the open chambers and have the block milled down for a positive piston to deck clearance? I am assuming that the 9 something to 1 compression I currently have with flat top pistons and probably a zero deck height would be too low to be running a bigger cam.

Oh, and MadScientist, thanks for the cam tip. I will go to one of those vendors for the cam when I am ready!

How much power do you guys think can be made out of this thing while keeping the flat tops?

Madscientist needs to think outside the box.

Here's an example: The goal is to have 0.040" clearance between the piston top and the "squish" area of the closed chamber heads. If one adds all the numbers, it becomes obvious that with stock dimensions the high compression pistons end up sticking out of the block 0.018".

Now to get the desired clearance one needs a gasket with thickness 0.040" + 0.018" or 0.058". Send money to Cometic or scour the Fel-Pro catalogs, etc.

ANOTHER way to do it would be to mock up the block and measure how far the pistons actually stood out of the squared-off deck. The pistons would then be cut down the desired amount to get the surface of the "squish" area to zero deck. This would leave part of the piston still standing out of the deck.

The problem with buying the so-called "340 style" open chamber heads is that one is forever stuck with the squish area eliminated. Now if building a stroker engine, a custom piston shape is required to regain the mixture motion that the squish area would have supplied. On the other hand, the closed chamber head may require some material removal on the piston top to provide a desired compression ratio, but it is easier to remove material from a piston than to add it.

R.

Some of you guys are soooo closed minded and read to many books. I'm running flat-tops slightly below the deck, felpro gaskets, and an open chamber head.

Dog, you are making it way too complicated.

If the head is OC (and I have flowed both open and closed...it took many hours and lots of tests to get that stupid W-5 chamber in shape and I had to use an odd ball valve grind to make it right so just because it's closed chamber don't make it right)all you need to do is finalize CC size, meausre whay you have left of the open side (I try to keep it at .090 or so) and then add the gasket and do SIMPLE math. Lets see how it adds up:

Chamber depth (approximate..must be measured) .090
Gasket thickness (typical) .039
Equals .129
Minus deck clearance .040
Equals .089

That means to get .040 quench with these numbers the piston must be OUT OF THE DECK .089, and if you don't want the piston up that high, you can mill another .020 off the head and use a .027 gasket and you would be out less.

Obviously increasing the stroke changes things but the math is still the same. Those SP pistions you have are just like a factory 340 piston. Most 340's had an actual compression of about 9.8-9.8:1 from the factory.

And like someone else said, .040 quench is not that big of a deal when using Chrysler heads. For a production chevy, with a junk chamber and a bad spark plug location it's much more critical.

Just check where your pistons are in reality and then take it from there, i would still stay away from the openchamber heads its stupid to buy something that has no squish and will require a whole lot of milling to get that squish.
Measure where your pistons are and aslong as they are not to far out of the deck get a set of closed chamber heads and adjust the squish with the gasket.

I have a set of the openchamber heads and regret buying them would have been much better to change the shortblock to work with closed chamber heads.

I built several legal NHRA 1971 340 motors for stock years ago, circa 1992 to 1994, both of them made 430 HP at 5900 RPM with two different Isky legal "stocker" cams with round lobes on top, I tried one Lunati sharp nose cam, it made 10 HP less but made more HP from 5000 to 7000 on that average than either of the two otherIsky did I advanced and retarded all three cams to find what they wanted on the DTS engine dyno at Pettis Performance This was with all leagl NHRA parts, iron J and X heads, "100" iron intake, legal Thermoquad carb. and so on Gene Buhl used the same dyno and machine shop for his builds back then, he bought a set of "magic" cylinder heads for one of his motors, that one made 450 HP on the same dyno BTW, if you built those motor using NHRA "blueprint" specs and did the math those motors calculated out to have 11.56 to 1 true compression ratio, not 10.5 to 1 I built 9secondPhils 418 C.I. pump gas W2 headed 340 stroker motor, it made 525 HP with custom ground Comp solid lifter cam and a Holley 950 HP carb. on a Eddy W2 Victor intake His 1969 Baracuda fastback ran real low 11s on the motor and cracked the high nines with NOS IHTHs

Thanks everyone! I will definitely report back when I get around to tackling this project and find out where the pistons sit then work from there.

What do you guys think about carb after I do the top end/cam swap? I figured I'd go with a 750 demon as I have heard good things about them. I have a Holley Street Avenger on now which is too small and seems to be killing the top end. Would I benefit power wise with something like a 4150? I'm not really too concerned with street manners and gas mileage, as long as it CAN be driven on the street I am happy. Doesn't need to feel great, I just want to get all the power I can out of it on the track.