Hi,

About two years ago I rebuilt my 225/6.  The beast was

over 350k and starting to use 1qt every 750 miles and

a little more than 'sipping' cooling fluid.

I used a set of FedMog slugs rated at 8.2, flat tops.

Engine originally rated at 8.4, also having flat top

slugs.)

I shaved .010 off the head and drilled .030 over.  I left

the heads alone other than to do a VERY minor cleaning of

the seats ... I doubt I did any damage to volume.

(Original bore/stroke was 3.40/4.12 ... unknown head cc.)

Fluxed, peaned, stressed, everything came out OK.

BEFORE I did this work, I threw in an 8 1/4" 2.45 rear end

as the old one I had (7 1/4" 3.53), tweaked the shafts

pretty badly, messing up the rear end in general.  With the

stock 1976 build-up and the tall gears and nearly 320k on

the engine, I made Las Vegas and back to Reno at roughly

32mpg.  After this build, I dropped to just about 18mpg.

(Power seems not to have changed in feeling, between the

before/after, except when I hit the secondaries to jump.)

I am looking to do a different cam as the one I got from

Sealed Power (CS380) has too much of an overlap, somewhat

low numbers at the .050, and seems to be a bit lamer overall

to the stocker.  To do the study, I was told I needed a good

CR #, minimum 9.4 to high 10.5.

Short of pulling the full engine apart and doing quash,

deck, gasket and head, and other measurements to see what

I have, I was wondering if one can estimate PSI to CR?  One

person said that at roughly 4500feet (above sea), a 115psi

is minimum and a 135-140psi is reasonable to preferrable.

But that does not tell me the CR.

The rest I did (of significance) to the rebuild was this:

(of course, since it has been two years ago I do not have

the Summit Racing receipts to say ALL parts received in the

stock-rebuild 225/6 kit from FedMog and Summit Racing cannot

look back 2 1/2 years when I bought the kit ... FedMog

cannot help w/o knowing the part #s):

Clifford Performance intake (medium length as I have power

    breaks so no hyperpak) - water heated

Clifford Performance exhaust (2 1/4"

Eddy 500cfm, jetted down several times over the period,

    and re-needled (to try to save some gas)

New timing chain and gears

MSD 45kv spark coil

Champion platinum split plugs

MP electronic ignition (electronic original so no mods)

    and the 'orange' box

22" 3 tube thick radiator & 7-blade fan

18,000gvw style tranny cooler

I rebuilt the 904 with stock 904 rebuild kit, no change on

the stock torque converter.

If I need to, I MAY put new plugs in as well, but I am not

looking to push the engine TOO harsh as I do want to keep

it a daily driver and still use REGULAR.  HP to maybe

160 would be fine by me.  (Originally rated 'federal' at

100.  (CA was only 85.))

Any help would be appreciated,

Thanks!

Gregg

1976 Plymouth Volare 2-door 'special'  

Greg,

   First of all, this is a neat project. You can get a lot of power from a slant 6. I've even seen a guy pull consistant mid 12 second 1/4 miles in a slant 6 powered Valiant at Englishtown Raceway.

There are some things that really stick out here. First, your compression ratio should be around 9.0-9.5 to run more efficiently, especially with that cam. The lower the CR, the more inefficient the engine. To figure out what your CR is there is a formula where you plug in your bore, stroke, and chamber CCs, and it puts you in the ball park (I can't seem to find it right now, but if I come across it I'll let you know). 9.0-9.5 will work good with today's fuel. To bring the CR up you can use a thin head gasket or mill the head or both. You need to figure out your chamber size and get a book on hopping up the 6 cyl. engine. And while the head is off, get a good 3 angle valve job done, that is almost a must.

Next is that rear. Unless all you do is highway driving (and even then that's pushing it), those gears are waaaayyy to much. A good all around street gear is somewhere around a 3.23 to 1, good acceleration and good gas mileage. Your engine is working too hard with those gears.

And last, I would recommend a set of tube headers, either duals with 3 cylinders feeding each one or 6 int 1, I'm not sure which is better, the book should be able to tell you.

I hope this is a help. If I think of anything else, I'll get back to you. Good luck on your project!

................Robert  

Hi,

I guess what I was more looking to, was this:

Say, that at the stock 8.4 that is claimed by the

factory when they built the engine, that the COMPRESSION

would be measured at 100psi.  (How true, I do not know,

but I am using it only as an example.)

If the engine was boosted to 9.0, the compression would

be, say, 115psi.  If to 9.5 it may be as high as 134psi.

Etc.

That the engine had been around for roughly 3 decades,

I would wonder if anyone that had worked on them over

the years would be able to say that a PSI of say, 140,

may convert to a 9.? to 10.? ratio, just from experience

of working and testing engines.

Thanks again,

Gregg  

Greg,

   The psi theroy sounds like it would work and there might be someone that might be able to get close using that process, but I think the reason they don't use it is because of so many variables, such as leak down and blow-by of the cylinder rings and/or walls, valve condition and the different cam profiles and timing (when the valve opens and closes in relation to the piston's position in the compression cycle).

You see, if I remember right, The intake valve is held open after the piston has reached BDC (bottom dead center) and as it starts to come up into the compression stroke and then closes after a number of degrees of crankshaft rotation after BDC. At low RPM (like when you're trying to take a compression test) the air/fuel mix is partially  blown back up through the intake valve. At high RPM (like when it is runnig) the air/fuel mix is still filling the cylinder from the momentum of it being just pulled into the cylinder, so the valve "blow-by" is overcome. So different cams will effect it differently.

And if I was you, I'd go with the dual exhaust with 3 cylinders into each one. There is simply nothing that sounds like a split-manifold in-line 6 cylinder. It IS awsome sounding!!

I hope this was of some help to you. Let me know. Good Luck!

..................Robert  

Greg,

   Here's that compression calculator I told you about:

   

     http://www.torinocobra.com/Randys_tools.htm

Good luck!

............Robert  

cylinder plus chamber volume divided by chamber volume should give compression ratio  

cylinder volume divided by compression ratio -1.0 equals chamber volume