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Author Topic: What's my compression ratio  (Read 2980 times)

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What's my compression ratio
« Reply #60 on: February 11, 2010, 09:12:47 AM »

Quote from: POLARACO
I sure hope Leaburn is wrong about the amount they took off those heads.  383's aren't that forgiving in that department.
Yeah, pretty sure they didn't take off a quarter of an inch... CBarge2010-02-11 17:58:59
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Steve

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What's my compression ratio
« Reply #61 on: February 11, 2010, 09:39:44 AM »

Sheeesh
 
I never even looked at that.  You're right
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Leaburn Patey

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What's my compression ratio
« Reply #62 on: February 11, 2010, 01:09:15 PM »

Steve,you really did not think I said 1/4 inch??
Hope not.Sheesh.
Like I said,I am not 100% sure and have no numbers in front of me.
 
Ed,thanks for your reply.
It reassures me that Bullet is doing it right.They are professionals with a high profile and good reputation around here.
Rob did telling me the cc's  gave a clue to how much they planed the heads.Thanks.
 
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What's my compression ratio
« Reply #63 on: February 11, 2010, 02:18:17 PM »

Yeah, I would say they just cleaned them up, which is proper. You got the formula to calculate, just need to figure the depth of the piston at top dead center, put a flat edge across the top of the cylinder and feel gage the depth for the most accurate compression, and the thickness of the head gasket itself, but I would say real close to just above 9-9.5:1 which is good enough.
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Leaburn Patey

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What's my compression ratio
« Reply #64 on: February 12, 2010, 11:50:17 AM »

Spoke to Rob today.
Compression will be at 9.0:1
The pistons are here-flat tops that have no valve reliefs.
However,they sit lower in the hole.
So,good news that is reassuring.
I decided also to get them to do up the shortblock.
That way all the critical tolerances will be checked,and less work for me.
I can put the heads on after i work them up.
 
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What's my compression ratio
« Reply #65 on: February 12, 2010, 02:00:33 PM »

Sounds good!
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Steve

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What's my compression ratio
« Reply #66 on: February 12, 2010, 04:22:41 PM »

Good! 

Now I don't have to do it.  
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Leaburn Patey

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What's my compression ratio
« Reply #67 on: February 14, 2010, 11:02:26 AM »

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What's my compression ratio
« Reply #68 on: February 14, 2010, 02:55:55 PM »

I prefer adjustable rockers, removes the chance the lifters are going to pump up and allow the valves from sitting with enough pressure on the seats to prevent valves from burning. it also allows you to get a set of anti-pump-up lifters, which help prevent valve float, and you can set the valves to zero lash (another anti-valve burning technique), where you simply rotate the engine until one valve is open on a cylinder and that automatically puts the other valve closed, adjust it to the point of zero pressure or movement without any preset pressure and tighten it down. When you get the first one done, rotate the engine so that valve is now open and do the next valve until all 16 are done. If the valve does something like float and touch a piston, which is rare, but if it does, the lifter has an extra .150 it is able to bleed down to prevent the valve from bending, and the anti-pump-up itself is a performance bleed to prevent them from floating above the notorious 5300-5500rpm of stock Mopar lifters and non-adjustable rocker engines. Just don't let anyone talk you into Rhoades lifters, they sound like they are loose all the time, and you don't need them, they are really for high rpm racing (street use allows them to bleed extra at lower rpm to give better vacuum by reducing your cam duration. Good idea, just noisy, been around since mid 1970s).
 
Pushrods are cupped end with ball tip for the lifter, and other than the hassle of determining the special length for fixed rockers, I don't think the cost is that much more than simple stock pushrods (maybe a buck or so more per).
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Leaburn Patey

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What's my compression ratio
« Reply #69 on: February 14, 2010, 03:35:52 PM »

So,are the Comp's good choice???
They describe that conventional ball end-type pushrods can be used.And are adjustable.
 Or do you recommend a different name??
So,are the hydraulic lifters that came with my Comp 268H (CL-21 215-4) cam no longer any good for my application?
Remember it is not a race motor with highway gears.
My open valve spring pressure will only be 305 or so.
Just need reassurance I get the right parts.
I would rather use the stock set up,but I was told I need custom length pushrods.
Plus some aftermarket set ups require machining of the bosses,and factory valve covers cannot be used.
I want to use factory valve covers.
Much rather spend the money on the right parts now rather fix it twice later.
CBarge2010-02-14 20:44:03
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What's my compression ratio
« Reply #70 on: February 14, 2010, 04:00:51 PM »

These rockers are really nice and I would use them myself, so good choice.

You can still use the stock rockers if you like (save a bunch of bucks there, reimburse me 25percent, ), and the lifters are fine with the cam, but here is what you need to do. Find out how much was removed from the block deck and how much was removed from the heads. If this amount is between .015-.020, everything stock will work without an issue, the lifters themselves should be the same height from the base to the plunger, it's the way they make aftermarket cams to fit stock engines. If this amount shaved off the head/block is greater, there are shims that can be added under the rocker shafts themselves to return to factory height (let's say .030 was shaved off the heads/block, the shim is .030 to return geometry back to factory), I think Mopar Performance carries them, they are just curved thicknesses of metal to add as a shim and there is nothing wrong with using them to regain geometry, otherwise make some yourself, it is a recognized correction in the Mopar manuals. The only real thing you have to worry about is the one rocker pedistal that has the oiling hole coming through it, make sure the hole in the shim allows the oiling of the rocker shaft and all is good to go stock. dana442010-02-14 21:03:38
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Steve

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What's my compression ratio
« Reply #71 on: February 14, 2010, 04:35:16 PM »

Lemme ask you a dumb question.
 
Hypethically. . . .
 
There's at least .020 of slop in a relaxed rocker on a 383.  Wouldn't it lift the valve sooner and hold it open a bit longer?  Not to mention more lift.  Assuming ot was all stock hardware. . .
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Leaburn Patey

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What's my compression ratio
« Reply #72 on: February 14, 2010, 06:30:19 PM »

So,shimming the stock set up is a good economical suggestion that will work if everything measures up OK..
The heads were 88cc.
They cc'd to 87.8
So,is there a way to calculate how much they shaved to get to the 87.8 cc??
I know for a fact the block deck was shaved ten thou.
 
My understanding is I should be OK without having to buy special pushrods or rocker kits.
The rocker arm kit will cost almost if not more than the pistons.
I did find some cheap alloy kits but they would be overkill for my application.
Another question..
How about 1.6 ratio??
Any improvement or gains in it for my application??
CBarge2010-02-14 23:37:44
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Leaburn Patey

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« Reply #73 on: February 14, 2010, 07:48:58 PM »

Found this PRW stainless steel set in a 1.6 for less money than the Comp kit..
http://www.prwonlinestore.com/stainlesssteelrockerarmkit1.aspx
CBarge2010-02-15 00:49:30
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What's my compression ratio
« Reply #74 on: February 14, 2010, 08:20:18 PM »

That .020 slop is from the lifters bleeding down over time, all hydraulic lifters do this with our engines (it's why they rattle for a second or two after startup sometimes, not to worry).
 
Like I said, I like adjustable rockers, aluminum, stainless, some are cheaper than others, they are all good compared to non-adjustable ones. As far as the 1.6s go, now you are talking about clearance issues depending on the cam you have, but in looking at the lift, you calculate to under .500 easy, so no problem at all. If you want to save the money given the small cut off the head and block, save the money, like you said, it isn't a race engine, flot away.
 
dana442010-02-15 01:25:23
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