902 Heads - tell me all you know!

[ViperMan]

Hey guys,

I've been responding to the guy who posted an RV motor up for sale a few weeks ago - we've worked out the negotiations and such and I'm pretty much planning my trip down to get it.

He called me back with casting numbers from the heads - it's a '74 Block, and the heads read "3769902"

I'm not too sure what to make of that information, so maybe you guys can help me out.  He went on to explain that these are 902 heads, and that they had better flow than the 906's (which I actually confirmed through some good ol' searching on the boards here.)

What I would like to know is some precursory information for the rebuilder - what am I in store for as far as rebuilding this?  I want to try to bypass any emissions components that I can, and really get a good understanding of what I still need to do to these to get some power.  Now, I DO plan on replacing springs and valves and rockers, and of course some good porting and polishing, smoothing the deck surface if needed - what else is there?  Do I still need to replace the valve seats?  I think that was already done with these, right?  I should be able to run unleaded with no problem, right?

What else?  Share with me all you know!  Thanks!

Jeff

[Chryco Psycho]

basically the same as the 906 , Yes you need hardened seats installed on the exhuast side , you can go up to the 1.81 dia exhaust valve while doing this

[ViperMan]

I guess then enlargening the exhaust valve is recommended?  Not the intake side?

What does the "flame hardened" valve seats on these heads "mean?"  I fell under the impression that I would not need to modify the valve seats for these heads.

But okay - what else should/would/could I want/need to do?

Jeff

[Chryco Psycho]

enlarge the intake valve If you are stroking the engineto 500+ " , on a 440 the gain is minimal
 I always install hard seats , the flame hardening is not very deep & if it starts to break through you may have to pull the heads to redo it , jsut do ti while it is off
 I always port the heads , install springs & retainers to match your cam choice , by the time you pat to rebuild & prot the heads you will have $800 - $1000 spent , you may want to look at the 440 source heads

[ViperMan]

Well, I mean, what do you recommend?

440 Source - I just looked at their site - definitely looks like a great value and a great product.  But it's aluminum, so I'm always going to run the risk of gasket leakage (I've been told that for the best reliability and least leakage issues, stick with iron heads) BUT, they're also not going to have the emissions components to worry about...  And of course I don't have to worry about engine shops and the like.  However, with new heads, I have to spend a lump sum at once - with rebuilding heads, I can do "a little here, a little there" and spend the same amount of a controlled period of time.  There's also the fact that I can have a "rare" set of heads on my engine, plus the ability to say "I built those" as doing springs and rockers and valves by hand really isn't that tough...

I guess the only question is, by going with 440 source heads, will I be getting a whole helluva lot more power then by rebuilding the 902's?  I know there's significant weight savings, but what about power?

Hope I'm not askin' too much.  I appreciate your imput, CP.

Jeff

[Moparal]

What you going to do to the short block? It probably has the big rods and external balancing. Lower compression to. If your making a 500 HPand under engine the steel heads will do good, but like Neil said , you will have to put money into them to make them good as new. But your theory about a little here a little there would do it. Hardend seats and 181 exhaust would work well for you. As I recall open chamber heads flow about 10% more on the intake side then the exhaust. around 10 bucks a seat here to buy and install the seats. Then you need the guide work done.  Never sink a valve into the seat. This lowers the compression and puts the valve tips higher up , so machine shop guys end up cutting the top of your vavles, and it opens other doors of issues you don't need or want.  Get a set of 300 buck I beam rods, forged crank .010 in the hole pistons with valve reliefs fly cut in them, balance it, deck the block true, Only take enough metal off the heads to get them flat, throw in a cam that meets your dailey requiremants for gear size,vaccum, rpm, and intake, go have fun.  Lots of other details between the lines of what I just typed, but this will add to more questions and suggestions to be answered by the Guru king of mopar on this site. Neil the frozen canook Chryco psycho macanical wonder of the northern continent

[ViperMan]

I'm kinda agreeing with Al - I think I'll stick with the 902's I'm getting...

Now explain just a few lingo items to me - "never sink a valve into the seat" - what does that mean?  Cutting the top of my valves?  .010 in the hole pistons?  Valve reliefs being cut - isn't that the same as domed pisons?  I was aiming for those (just did some browsing on 440 Source) - I'll probably call them to get their advice on exactly what to go with - I'm interested in keeping weight low on the pisons and rods - I was going to get their tapered I beam setup.

Just explain to me some of your other terms up there so I can understand ya better.  Thanks for the input.

Jeff

[Moparal]

Lots and lots and lots of half hearted machine shops will sink your valves into the seats instead of installing new seats. This This in itself lowers the comp ratio, causes valve burning quicker and also makes the valve taller at the top where your rockers go. So they cut the top of the valve stems to get them all the same height. Which changes flow patterns and causes pre mature stem failure since the harness is cut off.   .010 in the hole is about where you want your pistons to be when at tdc. It really helps the performance issues Neil will tell you about, and with a thick .042 hd gasket or better it helps with clearance issues . 

How much you pay for this block and heads?

[Chryco Psycho]

I would seriously look at a rotating Assy from 440 Source , it will work out to about the same cost or less than rebuilding you stock components anyway + you get 512 CI , I would recommend the 512 ci with 7.1" rods , 1/2 stroke crank @ 4.25" & a light weight piston to match the head , if you are using alum heads you can increase compression approx 1 point without detonation problems on pump gas , To Get Quench using your heads you will need a special quench dome / dished under the valves to control compression , with the Alum heads you will get a closed chamber head allowing for quench with a flat top piston , the 440 source head will work well with with a flat top piston & the stroker , the head may not yeild much in the way of power gains but combined with the extra CI it will make a Lot of power on pump gas
 Valve reliefs are the notches cut into the piston top to increase clearance between the piston & valves so high lift cams can be used without clearance problems

[moper]

What they said, with some minor alterations. On iron heads, I simply always install oversize new stainless valves for a few reasons. First, if you can feel or measure the difference in performance (as in loss from going bigger low dwon), your sharper than any dyno I've tested with. Second, using the larger diameter moves the new seat surface out like Al mentioned, and the four other angles being cut in fresh iron will increase power just thru doing the valve job right. You will need unleaded seats like CP said. All valve jobs in used heads result in the valse "being sunk" unless you specifically replace every seat. It's not a big deal, unless the shop doesnt worry about things like spring installed heights and rocker geometry...lol. You need to simply buy pistons with good valve releifs. Dont bother fly cutting anything, becuase to pay for cheaper pistons, then pay to have them cut, almost equals buying a little better piston that has the right releifs. "Going bigger" leads to some issues of it's own, and I dont agree that bigger is better for every user. AS far as 440Source's heads... Not a single set of them has been delivered. Simply assuming they are as advertized is plain stupid. Theres a alot more ways to mess up a head casting, plus all the machining, then there is to mess up a rod or crank... And the rods and sometimes cranks need work most of the time. Wait until some sets are shipped, and some good guys look them over before you spend dime one. I would not build for wuench with the 902s, but truthfully, I would try to convince you to run RPMs or the straight plug MP RPMs and build it modern. A simple 440, rebuilt with RPMs, some hypereutectic or Diamond forged pistons, a med sized hydaulic cam, and you'll have over 500hp on pump fuel for under $6500.

[ViperMan]

I don't want to buy a rotating assembly.  I want to build an engine.  Anyone can buy a rotating assembly - hell my DAD could buy a rotating assembly, and he sold his '72 340 'Cuda for a DOLLAR in 1998!  But he can't build an engine - I can, and I want to.

I guess when it really comes down to it, I'm going to take the heads to a local buddy who has a performance shop and bounce some ideas off of him, tell him what I want and have him do the machine work.  I'll also have him handle the machine work on the block, and that way we can determine our clearances, what we have, and what we need.

At least now I have a good understanding of what I need to consider and what I need to make sure gets taken care of (although this quench thing is somewhat new to me.)  I feel confident that I can decipher all of this information and build a good motor that'll fit my needs.

I need a smoke, now... 

Jeff

[Chryco Psycho]

buying the rotating assy does nothing to chnage building the engine , the only difference is less machine work you will have to pay for that you cannot do anyway
 I am just suggesting ideas to choose from

[Moparal]

   Spoken so true. And options are what he needs. Either rotating assembly has to be checked and assembled.

[ViperMan]

Doesn't a rotating assembly include the crank and such?  Or am I misfiguring something.

I do definitely need options.  I'm still thinking though that by piece-mealing this, I can pay for everything in "pieces" instead of having to afford a big lump-sum.  So far, besides the machining work (which I really don't know how much that will cost) the biggest ticket items are things like the crank and pistons at $500+ prices.

And for the deal I'm getting the engine for - I don't want to give the amount away just yet, but let's just say the crank will cost MUCH more.

Hey CP I definitely don't want you to think I'm arguing you or denying your advice.  I'll tell you that I'm still considering getting the 440 source heads as I could probably turn around and sell the 902's on ebay and get some money back for them, being that they're considered rare.  Though I do also agree that no one has actually SEEN these heads yet.  I'm just trying to figure out the difference between buying complete heads and building my own, and what I'm learning is that the difference in both price and performance is pretty minor.  That's why I'm thinking that my benefit is going to be with building my own heads so that I can space out the costs.

I really do appreciate input from all of you - I take all of it into consideration and believe me - you have my full attention when I read your responses.

Thanks again.

Jeff

[Moparal]

You can buy a rotating assembly 1 piece at a time you know. Crank,rods, pistons.

Like the engine I just built is a stock 68 forged crank, then I bought eagle rods, then I bought kb 237 pistons .030 , I assembled it. Then I took my 906 heads and opened up the throat under the valves, installed 214,181 valves 4 angle valve job, cut the guides for larger lift cams, had new guides and hardend exhaust seats installed. Shaved the heads  .006 to true them up, centerlined the cam, rebuilt the carbs and let it fly. Took 2 months that way, but I enjoyed it.

Here's an idea on how to center line your cam
but this is a little deeper than you will be doing