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1 28th October 00:43
cory dunkle
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Posts: 1
Default '68 302 compression ratio...

I swapped some '65 289 closed chamber heads (not hi-po, have round pushrod
holes and setup for rail rockers) casting number C5AE onto my '68 302, which
originally had the lower compression open chamber 302 heads. I didn't
realize this engine had the low compression heads on it. How much will my
compression ratio increase with the new heads? Do you think I'll need to run
93 octane (ran 89 with the old heads)? I noticed on the 302 the pistons come
flush with the deck where IIRC on my 289 there were slightly in the hole.
Guess that's from the slightly longer stroke.

Anyway, the old heads looked pretty beat, particularly on the cylinder with
low compression. Before I took the heads off I did the dollar bill to the
exhaust test and it flapped back and forth with the pulses of the engine and
then was ****ed in. I was told that meant leaky exhaust valves. I didn't get
everything back together tonight, I stopped when it started getting dark and
the skeeters were getting bad. Gotta finish mounting my accessories and then
I'll do a compression test to be sure all is well.

I'm expecting a decent increase in power between the closed chamber heads,
new aluminum intake, and Holley carb (585 CFM I believe). Man was that
aluminum intake a back saver after putting the heads on... Anyway, I was
just wondering how much the closed chamber heads will affect compression

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2 28th October 00:44
whole lotta tom
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Posts: 1
Default '68 302 compression ratio...

The 1968 302 2V was rated by Ford as having 9.5:1 CR. Using the earlier
heads will raise that up to around 10.6:1. It's gonna want premium gas.



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3 28th October 01:57
cory dunkle
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Posts: 1
Default '68 302 compression ratio...

Thanks. I got it all together and of course it isn't working right (I either
have the worst luck or am just plain stupid). First I had the distributor
off one tooth. Then I had big vacuum leaks in a couple spots, fixed after a
quick run to the parts store to get the _right_ gaskets (oops). Now the car
idles fairly well, and sounds pretty good, but smokes. It's alright at idle
and lighter throttle but if I step on it it will blow smoke out of the oil
filler hole. My first thought was blow-by, but the car never did this before
the head and intake swap. It's got 97,000 miles and I can still see parts of
the cross hatch pattern of all the cylinders.

It was blowing _lots_ of smoke out the oil fill cap when I had the wrong
spacer gasket on there. Fixing the vacuum leaks I could find greatly reduced
that. So maybe I've still got some vacuum leaks? Perhaps the intake manifold
is leaking somewhere? Any suggestions?

I took it for a couple quick spin around the block yesterday when I was
testing and trying to get rid of the smoking, and it seemed to ping pretty
easily before I retarded the timing. The timing is a hefty bit more retarded
than it was with the old heads. It doesn't diesel though. I can probably
keep running 89, but I think for the upgrade to be worth it 93 will be in

Well if it's not one thing it's always another. I think Today I'll re-torque
the heads and intake to be sure they are all on there good and then spray
around the carb and vacuum connections for leaks. If you've got any other
ideas they are quite welcome.

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4 28th October 02:00
whole lotta tom
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Posts: 1
Default '68 302 compression ratio...

Yeah, a vacuum leak between the intake and head, for example, would increase
oil consumption and cause smoke from the exhaust, not the crankcase. Now, a
full point of compression added with fresh heads can cause an increase in
blow-by past old rings for sure. Also, the compression you are running is
quite high for stock iron head and todays gas. Baby it a while, but I'd be
looking to get back to the larger chamber heads for the long run.



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5 28th October 02:01
cory dunkle
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Posts: 1
Default '68 302 compression ratio...

Well I spent some time with it yesterday and minimized the blowing of oil a
good bit. I went for a couple quick drives around the block and got the
timing retarded to a bit before it would ping (it wasn't taking much advance
with 89 octane gas that's in it). It seemed to be running pretty good, and
sounded good so I decided to go for a spin across town and take a faster
road back. Drove great through town, nice and peppy performance. A couple
times I really stomped on it and there was a bit of smoke from under the
hood, but not tons. I was running with just a ghetto rigged open element
cleaner I had around, not the stock that had the connection from the oil
fill cap, so I figured that would help with the smoke.

Anyway, I got on the faster road and accelerated to 55, the car felt fast
and smooth. I was surprised how much power it had compared to it's old
anemic self. A few seconds later it went kaput. The engine started surging a
little, I pulled off to a side street and it stalled when I started turning.
I looked it over and saw the point gap looked too small and the rotor was
dirty. I re-gapped the points and cleaned up the rotor. I looked for vacuum
leaks and plugged up a questionable line. Started it and it ran a little
better but did the same thing, rough running, misfiring and wouldn't idle.
So, I must have broke something, and it's not the distributor. I have
excessively low compression on one cylinder, and slightly low on a couple.
That's all definitely worn rings as the heads have only a couple thousand
miles on them at most. I have a feeling that when I put these higher
compression heads on the engine I cured one problem but made another one
worse. I didn't realize the car had open chamber heads, after all, my '67
289 had closed chamber heads and ran on 87 octane, this had open chamber and
ran 89. I don't think it's that bad cylinder or any of the low ones that's
making it run so bad and miss like that though. It's definitely missing on
more than one cylinder, so there's something else wrong with it too. Maybe
I'll investigate that a bit. I almost wonder if the 89 octane is part of the
problem, but then if it was it wouldn't have ran so good with no pinging or
anything and then died. I'd imagine there would have been audible death

I think at this point I have no logical option except to either rebuild the
bottom end or buy a short block. So I think I'll be shopping around for a
good engine shop (anyone know one in South Jersey?). The thing that really
peeves me about this, even more than this happening at the least practical
time (financially, that is) is that in all likelihood if my uncle had just
taken good care of the car when he drove it for 6 years this would likely
not have happened. He ran 87 octane in it so you could hear it knocking and
pinging constantly, and it dieseled whenever he turned it off. Whenever I
saw the car it barely had any oil in it, and it ran like crap. He would
always make fun of me and tell me he didn't need to go fast and the car ran
just fine, that I was just obsessed with speed. Fact of the matter is that
the car was destroying itself, and being quick is a characteristic of a
healthy engine. Apparently he didn't want to stop fast either because it had
no front brakes and the back brakes leaked. I won't even go into any more
detail about his abusing that car, but his saving a couple bucks a week on
gas is now costing me at least $1000. I doubt he even saved half that on
gas. To top it off he just gave away his shitty assed Mitsubishi that he
knew I wanted. I mean really, what ever happened to family? So now, one week
before school starts back up I have no working car and it's gonna cost me a
hefty bit of money to fix. Perfect timing, eh?

Sorry, just venting my frustrations. At least on the positive side I'll have
a virtually brand new engine after this is all said and done. I guess when
you figure that the car was free it's not so bad. It's just a bad time,
especially after I spent so much time and money fixing the rest of the car
which my uncle neglected. Oh well, I guess shit happens.

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6 28th October 06:18
jason james
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Posts: 1
Default '68 302 compression ratio...

Cory, believe me if the motor is pouring smoke out of the bonnet under
acceleration,...the thing is knackered. That blow-by is made up of exhaust
gases and unburnt fuel-air. The exhaust part heats up the piston as it blows
past and eventually the piston collapses (not literally, but shrinks due to
overheating losing any gas-seal left).

You need to at least re-ring it and possibly replace pistons if they mic-up
undersize due wear-punsment.

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7 28th October 06:18
cory dunkle
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Posts: 1
Default '68 302 compression ratio...

I'm thinking a short block is probably my best option right now. I'm not
going to screw around with re-ringing, as that is just asking for trouble,
in my opinion. This engine was abused to no end for 6 years by my uncle, so
if I'm going through the trouble to re-ring it I may as well take the whole
thing out and do it properly, with machine work where needed. I don't really
have the time to do it myself at the moment, so a short block is my best
option. It's just a matter of getting the old engine out and the new one
in... I suppose I can probably rent an engine lift for the day from

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8 28th October 06:19
jason james
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Posts: 1
Default '68 302 compression ratio...

Depends on your money situation.Older tech low reving motors will get by
with a re-ring and rod bearings as long as the pistons have not suffered due
excessive breathing (bby). If good V8s are cheap then that is a better way
though as long as they are water-tight and have decent oil-pressure.
Floor hoists on wheels are good to use. They give greater manouvrability
when juggling the donk out.

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