nm9stheham
Well-Known Member
As a point of reference, the shallow flat area in the heads is around .090" deep on stock castings. With that step being about .030" high, that seems right for the KB243's, but I don't have any to doublecheck for you.
Cam advice for more torque from 340
- Thread starter WSUTARD
- Start date
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WSUTARD
Well-Known Member
My engine is on a stand right now. If I rotate it over will there be a way for me to see the bottom of the piston? If so I can give it a go since the oil pan is off. I would still need to remove the lifters before turning it over then the metal shield on the bottom.
nm9stheham
Well-Known Member
Yep you can see right up to the piston bottoms. Good call to remove the lifters! Or just look up underneath with a flashlight....
IMPORTANT!!! Keep track of the lifters and EXACTLY where they go. Once they are run any little bit with the cam, they 'wear in' with the individual cam lobes, and cannot ever be switched from lobe to lobe. If you swap lifter positions by mistake, it will destroy the cam lobes.
I knocked over a box of used lifters the other day where they were kept in order just a coupla weeks ago and some got jumbled... they all went right into the trash can.
IMPORTANT!!! Keep track of the lifters and EXACTLY where they go. Once they are run any little bit with the cam, they 'wear in' with the individual cam lobes, and cannot ever be switched from lobe to lobe. If you swap lifter positions by mistake, it will destroy the cam lobes.
I knocked over a box of used lifters the other day where they were kept in order just a coupla weeks ago and some got jumbled... they all went right into the trash can.
WSUTARD
Well-Known Member
So based on your statement, if I change out my cam I need to change the lifters also?
yellow rose
Overnight Sensation
yellow rose
Overnight Sensation
WSUTARD
Well-Known Member
Message received.
WSUTARD
Well-Known Member
I just poked my eyes around and I can't see any markings on the bottom side of the pistons. I advanced the crank and couldn't see any marks.
It looks like KBs are marked on the side, according to this KB243 pic.
yellow rose
Overnight Sensation
Wasn't yelling. Just didn't want to se a thread stared in a few months about a flat cam and everyone howling about how you should have went with a hydraulic roller.
WSUTARD
Well-Known Member
I just spoke to the machine shop my heads are at. They said that the heads have been milled prior but not a substantial amount and advised against milling them any further since they are a really nice set of X heads and I ran the risk of having the piston hit the head since we dont know all the specs.
At this point I think I am going to take the timing gears off and see if I can confirm the cam to be what it was advertised as then make a determination from there.
At this point I think I am going to take the timing gears off and see if I can confirm the cam to be what it was advertised as then make a determination from there.
nm9stheham
Well-Known Member
Roger on the new lifters.... absolutely with a new cam.
Has the shop actually seen these pistons? I cannot see these heads and pistons getting ANYWHERE close. You have open chamber heads and the piston top surface is about .020" above the deck and if you used the 1008 head gasket, then that puts the piston top about .020" BELOW the top gasket surface. Then you have all that open chamber depth. It won't be close, unless the heads have been shaved .060" or .070" .
Having said that, then all you need to do is have the head shaved flat to get the head gaskets to seal up. And since you had a bit of coolant leakage, if the shops says the head are true (flat), then the deck probably needs checking for warpage.
And if you can get the depth of that open flat area of the head measured, that would be helpful. CC'ing a few head chambers would be even better. Boy are you gonna learn a lot!
Has the shop actually seen these pistons? I cannot see these heads and pistons getting ANYWHERE close. You have open chamber heads and the piston top surface is about .020" above the deck and if you used the 1008 head gasket, then that puts the piston top about .020" BELOW the top gasket surface. Then you have all that open chamber depth. It won't be close, unless the heads have been shaved .060" or .070" .
Having said that, then all you need to do is have the head shaved flat to get the head gaskets to seal up. And since you had a bit of coolant leakage, if the shops says the head are true (flat), then the deck probably needs checking for warpage.
And if you can get the depth of that open flat area of the head measured, that would be helpful. CC'ing a few head chambers would be even better. Boy are you gonna learn a lot!
nm9stheham
Well-Known Member
Well, they were only /6 lifters after all...
K.O. SWINGER
Meeting in the alley since 1976
you are getting great advice BUT with those pistons and heads and that cam if it is even close to those specs 165 psi cranking compression is all you will get max. that setup will scream but it needs 391 ish gears, power sweet spot will be 4000 to 6600 and yes there are much better cams for bottom end power.advance the cam 4 deg it will help
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WSUTARD
Well-Known Member
Here were my compression numbers back in August. I didn't do #5 or #7 due to the header.
Driver
1 141
2 135
Pass
1 140
2 140
3 135
4 132
Driver
1 141
2 135
Pass
1 140
2 140
3 135
4 132
WSUTARD
Well-Known Member
And I'm at 500 ft elevation.
yellow rose
Overnight Sensation
That's lucky to be 9:1 compression. If you heads have had a clean up cut on them, your Pistons will need to be .050 out of the deck to get 10.5:1 or close to it.
WSUTARD
Well-Known Member
What is chasing 1 point going to net me?
Also, wouldn't mulling the head down just decrease the volume of the heads and negatively effect the amount of flow?
Also, wouldn't mulling the head down just decrease the volume of the heads and negatively effect the amount of flow?
yellow rose
Overnight Sensation
One point at that CR is about 40 HP, depending on the combo.
And I would mill the block and not the head...don't want to start the dreaded crevice volume thread again.
WSUTARD
Well-Known Member
40hp! Wow. Well, I can tell you now that the block isn't going to be milled. I'm not taking the bottom end out of it. That is just way beyond my threshold of competence right now. We are even off the scale for me talking about this.
WSUTARD
Well-Known Member
Just to make sure, will I be able to see the cam specs without pulling the cam out if I pull the timing gear off?
yellow rose
Overnight Sensation
Maybe. If you pull the gear and remove the retainer you might be able to see the numbers.
roccodart440
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Those numbers look pretty low to me.
I'd be looking into a new cam to get those CC numbers up since milling the heads is out of the question.
Crane 690141 & 690221 come to mind.
nm9stheham
Well-Known Member
Yes, that is in the neighborhood of the high 8's or low 9's for SCR. Which is what this has been about, and the DCR is likely where this has been point all along: it's in the high 6 to low 7 range. We have a 340 with a true 10.0:1 SCR that shows 159 psi average at 2400' of elevation. DCR is in the low 8's; it spins the rear tires in an early A body with half throttle, 3.55. rear gear, and a 600 or 675 carb: torque out the wazoo.
What you have in this case it a pretty common situation: moderate SCR at best and a low DCR due to a large-ish cam. The result is well known: poor low end poop, but it winds out at the high RPM's great. Where you say that you want to go is known territory too: raise the SCR to get the wider torque band extend to the low RPM's and make sure you keep the cam small enough to not kill it down low. With something like the 268 sized cams, you get into that sweet spot. You can do other combo's but this one is like falling off a log to get to work decently.
40 HP? Don't get caught up in HP here; that is NOT what you are after based on what you want to do the get the low RPM performance up; you are after torque. Getting the SCR with a thinner head gasket and some milling will really pay off here. THEN you keep up the DCR with the smaller cam. It is gonna make a world of difference.
What you have in this case it a pretty common situation: moderate SCR at best and a low DCR due to a large-ish cam. The result is well known: poor low end poop, but it winds out at the high RPM's great. Where you say that you want to go is known territory too: raise the SCR to get the wider torque band extend to the low RPM's and make sure you keep the cam small enough to not kill it down low. With something like the 268 sized cams, you get into that sweet spot. You can do other combo's but this one is like falling off a log to get to work decently.
40 HP? Don't get caught up in HP here; that is NOT what you are after based on what you want to do the get the low RPM performance up; you are after torque. Getting the SCR with a thinner head gasket and some milling will really pay off here. THEN you keep up the DCR with the smaller cam. It is gonna make a world of difference.
joec
Well-Known Member
guys lets be real, you cant tell anything by cranking comp.It could be 12-1 with a big enough cam and crank 130.With his posted cam his cranking comp could be correct.
WSUTARD
Well-Known Member
Ok. I'm going to order the XE268 or 262 today, the kit with lifters.
Milling might be out of the question. I will speak with my machinist again.
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