trying to get some info on some magnum heads for a small block, a member here said you could possibly help thanks

Lots of peopole here could help, Patrick is a good one.

Can I ask, What are your questions?

wanting to know about the 340 magnum heads, i have a short block 340 and was intrested in were i could find some and also the specs on them

340s did not come with magnum heads, only 318s and 360s cam with them. They came out in 1992-2002, 340s were made from 68-73.

Specs for them I can think of off the top of my head are 65cc chambers flow about 215cfm OOTB can flow about 270 full ported and 2.02 valves. They come from the factory with 1.94 IN and 1.65 EX valves and full ported with them can flow 260. Valve lengths are about 4.9 inches. Valve stems are 8mm instead of the 340s .375 stem diameter, this helps flow and reduces valve weight. They do not have the heat crossover passages. They use a 10 bolt valve cover but the old 5 bolt covers have holes in the sam places and some guys say they use them with no problems. Advertised Rocker ratios are 1.6 on the magnum and 1.5 on the 340. In actuallity most 340 rockers are more like 1.45 and magnum rockers closer to 1.65 so with the same cam you get more lift .

They will swap from the later motors to the 340s and are a very good swap. To do the swap you will need new pistons if it is a 68-71 340 72-73 340 pistons are fine. (a note on the early pistons, if you have some really thick head gaskets you might not have to swap pistons, it depends on the exact deck height of your block and how thick of gaskets you get) You will need lifters with pushrod oiling holes, 99% have them but check to make sure yours do, it is a small hole in the bottom of were the pushrod goes in the lifter. You will need different pushrods because the length is different and they need to be hollow so oil can flow through them. You will need magnum style rockers and bolts. The intake will need to be swaped OR drill and tap the 340 style intake bolt holes into the magnum heads.


If you need specific specs I have several books I can look in here at my house.

Hopefully Patrick will chime in soon, where is he

Patrick were are you ??

you're getting everyone but patrick & I was the "member" that suggested you page him! I sure hope when he does arrive that he has some good info to share. He will.

Why don't you send him a PM?

i dont know his actual member name, but someone told me he probably would answer out here. Here is a question, can i bolt these magnum heads to my 73 340 , just have to change the push rods ? what about the lifters for a stock 340 cam 429/443 ? Is this an easy modify, thanks for your input

The heads will bolt on,but use different head bolts. As long as the pistons haven't been replaced with a dome piston they will work,but check your piston to deck clearance to confirm this.Lifters need to oil thru the pushrods,most MP lifters won't do this. Look at them,do they have a hole in the pushrod cup? Most companys carry a lifter that will work,so thats not a problem. You won't be able to use the LA pushrods,but they are easy to replace.You will need to redrill the heads to use an LA intake or you'll be limited with intake choices. I like to tap the oil passages on the decks surface to shut of the oil to the LA valvetrain but others have had no problem allowing the magnum heads lack of this passage block the oil passage. What have I forgotten?

thanks for the input, in regards to redrilling the heads , how far off are the holes to the intake ? is it easier to drill the intake manifold? the pistons in the block are the correct piston for stock for the 73 340, so i dont think i would have clearance problems. How much compression should i expect thanks

I redrilled the heads,there was at one time a jig built to help,but it's not a must have to do this. Modifying the intake doesn't look too appealing althought it can be done.Compression will increase about 1/2 point.

Here is some good "Patrick" info to tide you over until he shows up!!!

https://board.moparts.org/ubbthreads/show...e=0#Post3134434


But wait, there's more

http://www.moparts.org/Tech/Archive/smallblock/7.html

Mags work great on a street/strip car and make more power in stock form than any other iron (non-W-2) head. They made 380 horse on the crate 360's and I think 435 on the crate 402's...... I am on my second set of mag heads that I ported myself and I like em alot. They are not the choice for all out power but the relatively small intake runners give you nice throttle response and the small chambers get your compression ratio up nicely which is just what you need for a hot street car...... TBF

TBF could you give me guesstimate with your experience on this on how many CC's I could add by trimming the eyebrow & unshrouding the valves(& anything else) in the chamber shown? I have magnums in a project coming together & my CR is too high & I don't want to ch my pistons. thank you for your time Bro. PS Patrick is deceased.

so are any cast of the magnums more desireable then another ? Is it true the ones before 98 arent as good as the newer , i think i read they went till 2002

Dead & gone. I'm not exactly sure what happened.

uh, no, I'm still here. been a busy weekend


are the pistons above or below deck? if above deck, you'll need to measure how much, and look for a head gasket that is .040 thicker than that measurement (say, if they're .018" above deck, you'll want to look for head gaskets that are ~.060 thick).


baby's crying, I'll write mroe later....

Whew! Glad your alive Patrick!


would be hard to remove more than 2 or 3 CC without ruining the chamber. You could mabey put in tuliped valves 2.02 diameter and run a deshroud cut out to the edge of the bore. You could probably take another cc out by removeing the second quench pad but I hate removing quench area, it helps resist detonation.