hi guys, so my 340 has L2316 (TRW ?) pistons, I haven't measured how much out of block they go yet . I would like to use the small chamber edelbrock 60779 heads with fel pro 8553pt head gasket. question is how to check and see if this combo will work. is it just a simple piston to valve clearance measurement , or might the piston actually hit the head itself. thanks
340 edelbrock build
- Thread starter abodee
- Start date
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nm9stheham
Well-Known Member
As above....you're working in territory where in the final build, it boils down to the exact parts. With everything to stock specs and height, those pistons will stick around .018" out of the deck, but it can vary from cylinder to cylinder due to deck slopes. (Sloping top to bottom or front to rear....) Then throw in some rod length variations and the amount the piston sticks up out of the deck varies even more.
If it all lined up like stock numbers and you put in .060" thick Cometic head gaskets, you'd end up around 10.1 Static CR. This is high enough to start asking on how you intend to use this car/engine and what cam you have or plan to use....??
With the Felpro 8553PT's you could easily end up with the piston tops as little as .030" from the bottom of the heads, or even less if you had a long rod or 2 in there. That is darned tight and gives little safety margin before real problems, especially if the bores and pistons are worn and the pistons rock much in the bores. (We don't know your engine's history...)
The piston-to-valve clearance is a separate issue from compression ratio and piston-to-head clearance. The valve eyebrows are decent on those but it really boils down to the cam. So again, what are you thinking for cam?
If it all lined up like stock numbers and you put in .060" thick Cometic head gaskets, you'd end up around 10.1 Static CR. This is high enough to start asking on how you intend to use this car/engine and what cam you have or plan to use....??
With the Felpro 8553PT's you could easily end up with the piston tops as little as .030" from the bottom of the heads, or even less if you had a long rod or 2 in there. That is darned tight and gives little safety margin before real problems, especially if the bores and pistons are worn and the pistons rock much in the bores. (We don't know your engine's history...)
The piston-to-valve clearance is a separate issue from compression ratio and piston-to-head clearance. The valve eyebrows are decent on those but it really boils down to the cam. So again, what are you thinking for cam?
nm9stheham
Well-Known Member
BTW, the way to do this is get a dial indicator setup and carefully measure the height of each piston versus the surrounding deck area. Measure both top and bottom at each pistons and rock each pistons for max height out of the bore; the Edelbrocks have quench areas at both top and bottom of the cylinders and so you need to check both top and bottom piston-to-head clearance.
thank you so much for the replies , it is a lot more clear now. I plan on running the edelbrock rpm cam #7177. I know now that there are much better cams available, but I have it so I will probably use it . Also sounds like I need to buy the thicker head gasket.
nm9stheham
Well-Known Member
OK.....yes the 8553PT gaskets would be a sure worry.
That's not a super high lift cam by any stretch of the imagination, so the piston-to-valve clearance will very likely be fine. Still, you want to check it because the duration is so long.
Man that is a reeeeeally slow ramp cam. And the duration is very darned long, with an inteakce closing angle at 81 degrees ABDC. Good thing that you are jacking up the compression ratio....with a 308 advertised duration DCR is gonna drop to under 7:1. So the low RPM range is gonna be kinda weak, and cranking compression will be less than a stock 340 (!)
What is the use for this car? Straight drag race? Circle track racer? That duration is not normal for a torquey streeter. That thing will wind out good (if you have headers and a good intake), but it'll be be weak below 2800-3000 RPM.
BTW, .060" thick Cometic head gaskets are gonna be pricey..... just trying to soften the sticker shock! But they can be reused.
That's not a super high lift cam by any stretch of the imagination, so the piston-to-valve clearance will very likely be fine. Still, you want to check it because the duration is so long.
Man that is a reeeeeally slow ramp cam. And the duration is very darned long, with an inteakce closing angle at 81 degrees ABDC. Good thing that you are jacking up the compression ratio....with a 308 advertised duration DCR is gonna drop to under 7:1. So the low RPM range is gonna be kinda weak, and cranking compression will be less than a stock 340 (!)
What is the use for this car? Straight drag race? Circle track racer? That duration is not normal for a torquey streeter. That thing will wind out good (if you have headers and a good intake), but it'll be be weak below 2800-3000 RPM.
BTW, .060" thick Cometic head gaskets are gonna be pricey..... just trying to soften the sticker shock! But they can be reused.
I noticed the price of those head gaskets, thats why I wanted to run the felpro. engine has rpm air gap intake and tti headers. I also have a comp magnum 280H cam I could use. while smaller than the edelbrock, would it have an advantage over the edelbrock cam ? the car is just a street car that I want to haul ***.
nm9stheham
Well-Known Member
Dang, I know I would put the 280H cam in without thinking twice for street use, especially with the Edlebrock AL heads. Now, your DCR is up at 7.9 and the low RPM torque will jump right on up. And with the intake and headers that you have, the thing will keep pulling well on past 6000 RPM. A head gasket of around .060" will give you a decent quench gap which will help combat detonation along with the AL heads.
NOW you need to think about the rockers and such to make sure the valve train stays under control. I suspect that will be the limiting factor at high RPM with what you have.
Make sure your ignition timing tuning is not too far advanced at the low RPM's. No need to run 20+ degrees of initial timing with this setup.
And this torquey combo will launch well with a lower RPM torque converter. Otherwise, you're wasting some of that good low RPM torque range that you just achieved. Better fuel mileage....if you care.
Once you get is all working, your last biggest worry with the 280H and these heads and pistons will be destroying tires LOL
NOW you need to think about the rockers and such to make sure the valve train stays under control. I suspect that will be the limiting factor at high RPM with what you have.
Make sure your ignition timing tuning is not too far advanced at the low RPM's. No need to run 20+ degrees of initial timing with this setup.
And this torquey combo will launch well with a lower RPM torque converter. Otherwise, you're wasting some of that good low RPM torque range that you just achieved. Better fuel mileage....if you care.
Once you get is all working, your last biggest worry with the 280H and these heads and pistons will be destroying tires LOL
wow ,that edelbrock cam must really suck. I bought it when I seen the edelbrock package made 417 horsepower (I got sucked in). I guess I have to go with the comp 280. its a 4 speed so I don't have to worry about torque converter. as far as rockers go , still thinking about Hughes and comp and even stock adjustable 273.
Once you know how much the piston is positive, then get a custom cometic gasket for clearance. Pricey? Yes. Worth it? Every red cent!
nm9stheham
Well-Known Member
The 308 doesn't suck in some applications... it's just not made for low RPM operation, like you are going to encounter over and over on the street. I had a similar 300+ degree duration cam in a 4 banger rally engine...... it was dead below 3800 RPM but it would wind out past 7500 RPM all day long. That 'dead below 3800 RPM' was not the best for the racing venue I was in with a poor ratio 4 speed, and that was a good lesson about not going too aggressive on cams.
At least the slow ramps on the Edelbrock cam are easy on the valvetrain. The Magnum ramps are not the fastest but considerably faster than the Edelbrock. The stock springs on the Edlebrock heads are a bit softer than the 901 springs recommended for the 280H cam (327 lb/inch versus 387 lb/inch), but I am not sure that will make enough difference in the RPM at which valve float occurs for concern in this combination. Using lighter aluminum rockers like the Hughes rockers would help reduce any chance of valve float with the softer Edelbrock springs. There was a recent thread in this forum about stronger springs for use on Edelbrock heads.
The Hughes rockers seem to get good recommendations. I can't comment on the the others. But at least you are going in the right direction. I can't comment on the use of stock stamped rockers here; the lift is not awfully high so they might work out if you get short on cash.
comp 901 springs are going to need alot of shims to get to the 1.80 install height on a eddy head...at least .150 ...with coil bind at 1.100 ...not much lift above .500...eddy springs good to .570...Based on the numbers from Summit racing ....I would use the stock eddy springs.
Installed Height (in):1.650 in.
Seat Pressure at Installed Height (lbs):101 lbs.
Open Height (in):1.250 in.
Coil Bind Height (in):1.100 in.
Open Pressure (lbs):242 lbs.
Spring Rate (lbs/in):353 lbs./in.
Eddy spring
stalled Height (in):1.800 in.
Coil Bind Height (in):1.130 in.
Seat Pressure at Installed Height (lbs):120 lbs.
Open Pressure (lbs):310 lbs.
Installed Height (in):1.650 in.
Seat Pressure at Installed Height (lbs):101 lbs.
Open Height (in):1.250 in.
Coil Bind Height (in):1.100 in.
Open Pressure (lbs):242 lbs.
Spring Rate (lbs/in):353 lbs./in.
Eddy spring
stalled Height (in):1.800 in.
Coil Bind Height (in):1.130 in.
Seat Pressure at Installed Height (lbs):120 lbs.
Open Pressure (lbs):310 lbs.
nm9stheham
Well-Known Member
I would too.... it is just that some folks have gotten wrapped around the axle here over 10-15% differences in spring rates... so I wanted to get out all the rate data.
superbeesrt8
Well-Known Member
I just did a 360 with the Keith black positive deck piston with the closed chamber heads I used mr gasket 028 head shim cost 18 dollars and felpro 1008 all clearance worked out fine motor is a 360 engle 245-245 560-560 motor runs great does not overheat no oil leaks
ok , I have the mls cometic head gasket. my question now is, what is the best way to prep the surface of the block without tearing it down and taking it to a machine shop. the internet has me scared that they won't seal if I don't have it smooth enough. thoughts, questions comments or concerns ? thanks you .
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