Found a pleasant surprise. Need help from pros and experienced folks to make next decisions.

[TX73SE]

Good afternoon all,

I finally got some free time (and money!) to tinker on this project, now that I sold my last project.
Once I’d bought the car, and did some further research I knew the heads on the engine weren’t original to the car(906 heads on a 73 charger 400 2bbl).
This afternoon I got inspired to pull the head and find out what I was working with before I starting making parts decisions.... and purchases.
A little back story, The guy I bought it from had purchased the car from a friend who’s uncle owned it and supposedly the engine was rebuilt and never run/ finished up due to health issue, guy died, car sat for 30 years. I don’t typically take 2nd hand information much to heart with used cars.
But Since the engine block matched the vin of the car I knew it was original, and given everything wasn’t buttoned up and bolted in, it was plausible.

I opened it up today and was pleasantly surprised to find clean bores and new .030 over pistons.

I can tell they’re flat tops, but would greatly appreciate insight on how to determine an approximate compression ratio so a can make other decisions.
From removal I can tell the heads were redone as well and never run.

I’d like to determine:

1. was the block decked so the compression would be higher?
2. Were the heads shaved?
3. Sell these and get some aluminum heads? (but then what’s the expected compression ratio?)

input from experienced members is greatly appreciated. I just want a cruiser, and budget is very much a factor for me.
I’ve looked at both the summit k6401 cam kit and the Hughes whiplash cams. Obviously compression ratio is a big factor in the whiplash cams but I thought it was a bone stock 400 with low 1973 compression 7.5-8.5 and crappy smog heads.

With this new info I’m trying to adjust and make a better decision since I don’t need to pull the short block.


Thanks in advance for any and all thoughts.

Daniel

 

[1 Wild R/T]

Do you have a set of feeler gauges? If so bring a piston to top dead center & measure to see what your deck height is....

If that first picture has the piston as high as it'll go I'd be putting different pistons in it... The bores are fresh a quick hone & new pistons.. You could reuse the bearings, if your totally on a budget you could reuse the rings...

If the piston comes up the bore further you might be okay... Measure it & we can tell you....

You should CC the heads too... Very important if you really want to know & it can be done cheaply...

 

[Don Frelier]

The rust inside worries me.

 

[1 Wild R/T]

The rust inside worries me.

Yeah, another reason the short block should come apart... I've seen worse & the engine still ran & made decent power but I personally wouldn't want to take a chance...

Most of that should clean up pretty easy...

 

[33 IMP]

I agree with 1 Wild R/T. Those look like cast rebuilder pistons, and they look "down in the hole" a bunch at tdc. Chances are good that the compression is no better, and possibly worse, than stock. Measure like Wild shows, if there is .100 or more, likely 7 3/4-8 1/4 to 1.
The trouble with 400s, is there are lots of great pistons for stroker 400s, stock stroke not so much. You might have to live with what you have.
Once you have a deck height, you can get an idea (without precise measurements, it wont be precise) of what your c.r. will be, using c.r. calculators on the net. Without a measurement of the heads, figure around 90 cc's.

 

[1 Wild R/T]

I agree with 1 Wild R/T. Those look like cast rebuilder pistons, and they look "down in the hole" a bunch at tdc. Chances are good that the compression is no better, and possibly worse, than stock. Measure like Wild shows, if there is .100 or more, likely 7 3/4-8 1/4 to 1.
The trouble with 400s, is there are lots of great pistons for stroker 400s, stock stroke not so much. You might have to live with what you have.
Once you have a deck height, you can get an idea (without precise measurements, it wont be precise) of what your c.r. will be, using c.r. calculators on the net. Without a measurement of the heads, figure around 90 cc's.

KB 240 is 1.908 which should be about .025 in the hole with 5cc valve notches... Not Ideal but off the shelf & a reasonable C/H...

 

[1 Wild R/T]

Using 89cc for the chamber volume, & standard stroke/rod length/bore/shim head gasket etc...
The KB gives you 8.7, the typical rebuilder piston gives you 7.6...

Start reducing chamber volume & you can actually get somewhere... take .040 off the heads, use the KB & a shim gasket & you get 9.4.... Not bad.....

 

[Challenger340]

When Calculating.... measure how far down the hole the Pistons are at TDC.... then use around 2.4 CC's for each .010" down added to the clrc volume when doing a CR calc.
They look like very low compression rebuilder Pistons from here ? Aluminum Heads may NOT be a real good idea on those ?

 

[Challenger340]

KB 240 is 1.908 which should be about .025 in the hole with 5cc valve notches... Not Ideal but off the shelf & a reasonable C/H...

This is good advice, especially if considering the addition of Aluminum Heads ?

 

[TX73SE]

I appreciate it guys... there is no rust in the bores. Just some dust, I cleaned it up looks like good cross hatching still. I rubbed oil on the piston tops and the bores to be safe until I figure out next steps.
What would you think about using as is with the 906 heads and the Hughes whiplash cam that’s specifically made for lower compression engines?
http://www.hughesengines.com/Index/...V2hpcGxhc2ggTXVzY2xlIENhciBjYW1z&partid=30173



thanks again for the input. It’s greatly appreciated. I will say if I have to tear it down and replace pistons, any funds for aluminum heads is probably out the window As I’d need a machine shop to help me with the reassembly. My prayer when I saw this was they’d work well with the edelbrock 74cc aluminum heads. Or roll with the 906s and the whiplash cam to better compensate.

These were just my thoughts based on reading the forums regarding lower compression. The two cams I’ve considered would be the whiplash cam or the summit k6401.

 

[1 Wild R/T]

Okay, the 75 cc heads would seem like a big help but you can't/shouldn't run a steel shim head gasket with an aluminum head so thats a 5cc add for the comp gasket.. so 80cc vs 88-90cc if the pistons are in the hole .120 like I suspect they are you'll be at 8.15... which is allot better than 7.6 but far from great...

Like I said earlier measure the depth to the pistons...

 

[TX73SE]

Okay, the 75 cc heads would seem like a big help but you can't/shouldn't run a steel shim head gasket with an aluminum head so thats a 5cc add for the comp gasket.. so 80cc vs 88-90cc if the pistons are in the hole .120 like I suspect they are you'll be at 8.15... which is allot better than 7.6 but far from great...

Like I said earlier measure the depth to the pistons...

Thanks for the info.

That's my plan tomorrow after work. I ran out of daylight and weekend today.

Would shaving the 906 heads some and possibly adding bigger valves be a compromise for performance? I measured them and they have new 2.08/1.74's

 

[1 Wild R/T]

Cut the heads .040 on the deck & .050 on the intake, use a shim type gasket, run your Whiplash cam & accept it for what it is, a compromise.... If it doesn't do what your hoping for save your $$ & build something when the time comes...

 

[69Bee]

Looking at the head pic, you NEED to replace the springs due to rust, so get the springs that match the cam.

 

[Challenger340]

View attachment 1099456 View attachment 1099457 I appreciate it guys... there is no rust in the bores. Just some dust, I cleaned it up looks like good cross hatching still. I rubbed oil on the piston tops and the bores to be safe until I figure out next steps.
What would you think about using as is with the 906 heads and the Hughes whiplash cam that’s specifically made for lower compression engines?
http://www.hughesengines.com/Index/...V2hpcGxhc2ggTXVzY2xlIENhciBjYW1z&partid=30173



thanks again for the input. It’s greatly appreciated. I will say if I have to tear it down and replace pistons, any funds for aluminum heads is probably out the window As I’d need a machine shop to help me with the reassembly. My prayer when I saw this was they’d work well with the edelbrock 74cc aluminum heads. Or roll with the 906s and the whiplash cam to better compensate.

These were just my thoughts based on reading the forums regarding lower compression. The two cams I’ve considered would be the whiplash cam or the summit k6401.

Seems like you already have a plan of action all figured out ?
So it doesn't really matter what anyone here says..... because the only really "relevant" advice would seem to be that which fits what you want to hear ?
That being....
I can buy Aluminum Heads and screw them on with a Whiplash cam and it will be fine.

Fill ur boots !

 

[Don Frelier]

Seems like you already have a plan of action all figured out ?
So it doesn't really matter what anyone here says..... because the only really "relevant" advice would seem to be that which fits what you want to hear ?
That being....
I can buy Aluminum Heads and screw them on with a Whiplash cam and it will be fine.

Fill ur boots !

That's a harsh assessment, seems to me he's still asking questions and trying to figure out a low budget solution.

Worth noting the Whiplash cam is likely tough on the valve train. Idle quality is poor and tough to tune but yes it will make some power.
Depends what you want and like.

 

[69sunfireGTX]

you can't/shouldn't run a steel shim head gasket with an aluminum head

And why is that? I have done this more times than I can count. Never had a problem yet.

 

[RemCharger]

I would rather put it "you can /but shouldn't "

And why is that? I have done this more times than I can count. Never had a problem yet.

 

[1 Wild R/T]

I would rather put it "you can /but shouldn't "

I can accept that...

As far as why not?

Because when the gasket is tougher than the head the embossed stampings on the gasket damage the head.... Aluminum heads expand & contract very different from an iron block, that movement causes the steel shim to etch the gasket surface of the aluminum heads....

Not a big deal till the head gasket fails... And you need to resurface the heads.... If your willing to step up to MLS gaskets than you can actually go thinner than .021... Thought that probably doesn't apply to Mopars... Cometic offers a lot of options for Chevies.. And at least a few for Mopars

From their website

Thickness: .018, .019, .020, .021, .022, .023, .024, .025, .027, .029, .030, .031, .032, .034, .035, .036, .038, .040, .042, .043, .044, .045, .046, .047, .049, .050, .051, .052, .053, .054, .055, .056, .057, .058, .060, .062, .064, .065, .066, .067, .068, .070, .071, .072, .073, .074, .075, .076, .077, .078, .080, .081, .082, .084, .086, .089, .092, .095, .098, .100, .102, .104, .120, .124, .140

 

[69Bee]

I can accept that...

As far as why not?

Because when the gasket is tougher than the head the embossed stampings on the gasket damage the head.... Aluminum heads expand & contract very different from an iron block, that movement causes the steel shim to etch the gasket surface of the aluminum heads....

Not a big deal till the head gasket fails... And you need to resurface the heads.... If your willing to step up to MLS gaskets than you can actually go thinner than .021... Thought that probably doesn't apply to Mopars... Cometic offers a lot of options for Chevies.. And at least a few for Mopars

From their website

Thickness: .018, .019, .020, .021, .022, .023, .024, .025, .027, .029, .030, .031, .032, .034, .035, .036, .038, .040, .042, .043, .044, .045, .046, .047, .049, .050, .051, .052, .053, .054, .055, .056, .057, .058, .060, .062, .064, .065, .066, .067, .068, .070, .071, .072, .073, .074, .075, .076, .077, .078, .080, .081, .082, .084, .086, .089, .092, .095, .098, .100, .102, .104, .120, .124, .140

Thanks, I think I need a new catalog. Mine is 2016 and only goes down to 0.027".