Compression question

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Thank you all. I have it back in the garage and I'm not 100% sure which direction I'm going to go. I have the intake off, I'm at the point were I believe we are pulling the engine and heading in one of the following directions. I've seen re manufactured long blocks for around $1500-$2000. Or have this engine rebuilt or rebuild it ourselves but as you all can see that may be out of my scope of work. Or buy a Magnum out of a later vehicle as suggested. I have some questions about that particular option:

Do they use the same motor mounts, water pump, exhaust manifolds?

We have an Edelbrock Ld4B intake, will that bolt up to a later 5.2 heads?

Again, I can't thank you all enough! This has been a struggle and it's nice having a place to go for friendly advice and help.
 
stixx said:
OP wrote this above... Shouldn't a compression test be done at WOT (as Dana67 did)?
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When looking for percentage differences as in to find bad valves, rings and such, it does not matter. If you're looking for total cylinder pressure, sure, block the throttle open. But for diagnostic purposes, you can do it either way.
 
RustyRatRod said:
When looking for percentage differences as in to find bad valves, rings and such, it does not matter. If you're looking for total cylinder pressure, sure, block the throttle open. But for diagnostic purposes, you can do it either way.
Click to expand...
After reading all your compression tests I decided to test mine as I have just put a larger cam in my 410 stroker. Hughs roller hydr 234 in 238 ex on a 110 lobe separation. # 1 was 195 # 5 was 193 and #7 was 195. I stopped at this time as I thought these were good numbers for this cam.
 
AJ/FormS said:
The numbers are all so low Ima thinking the cylinders and rings were super dry. No matter, the heads need work for sure, and the rings smell like toast.
Could it be made to run? sure but at what sacrifice?
I'm with Rusty/post6

Grab a Magnum somewhere; she's a 9.5 engine with pretty good heads.
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I have some questions about the Magnum option:

Do they use the same motor mounts, water pump, exhaust manifolds?

We have an Edelbrock Ld4B intake, will that bolt up to a later 5.2 heads?
 
Calipag said:
I have some questions about the Magnum option:

Do they use the same motor mounts, water pump, exhaust manifolds?

We have an Edelbrock Ld4B intake, will that bolt up to a later 5.2 heads?
Click to expand...
The Magnum IIRC has dual mounts; both LA and truck. The truck mount sometimes has to be worked over to fit certain headers or exhaust manifolds.
The front of the engine, if from a truck, has a reverse rotation pump. If you get rid of the serpentine system, you can use all the LA stuff.
The mechanical fuel pump only works on the early non-injected Magnums due to different cams in the EFI models.
Magnums are balanced different from the LAs so the balancer and the flywheel have to stay with each respective engine.
Not all log-manifolds will work in cars, Trebleg has the scoop on those.

Magnums are a good choice. They have an advertised Scr of 9.5 and, together with their better heads, are quite a bit more powerful than LAs.
 
Well, it looks like we will have the 318 rebuilt. I don't have the space or ability to do it our selves. This is a going to be a driver but I was going to put the 340 cam in it. We are running the LD4B intake with a 600 edelbrock. They are going to rebuild my heads. I've read a ton of threads and I think this what we are going to do. Unless, there is something I should be doing while at the machine shop?

Thank you all
 
Calipag said:
Well, it looks like we will have the 318 rebuilt. I don't have the space or ability to do it our selves. This is a going to be a driver but I was going to put the 340 cam in it. We are running the LD4B intake with a 600 edelbrock. They are going to rebuild my heads. I've read a ton of threads and I think this what we are going to do. Unless, there is something I should be doing while at the machine shop?

Thank you all
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In my experience, for a streeter, with street gears and stock stall, both times; the factory340 cam into the stock-compression LA318, was a mistake. The bottom end goes soft and the power doesn't start 'til 4000. With 2.94s this is is ~42mph. The 268/276/110 aftermarket cam can be a good choice...... if Hi-Compression is achieved. However, for a DD I personally wouldn't recommend it, the fuel mileage is atrocious no matter what rear gears you run.
The factory 340 cam in a LA318 will need a hi-stall Convertor no matter what, and 3.23s minimum with an automatic.
The aftermarket 268cam will want about 9.8Scr. The factory Chrysler cam will want a bit more.

The reason for the compression difference is that the Chrysler cam is advertised at .008 lift whereas some/most aftermarkets are at .006. This means the Chrysler cam is actually bigger than 268 comparatively speaking, from intake valve closed seat to seat, which bleeds cylinder pressure back into the intake. Because of this, with a stock 1800TC, the bottom is soft, cuz it is stuck below 2200 until ~23mph with 2.94s; ~25mph with 2.76s..... and a DD spends a lot of time down there.
After about ~2000 this reversion begins to go away,and by 2200 power production can begin. The power starts at ~4000/42mph with 2.94s, and peaks around 5500/58mph; both in first gear.
Is that what you are after?

The stock LA318 compression ratio, if you value take-off power, limits you to a pretty small cam window. And the higher your operating elevation, the smaller the window.
 
AJ/FormS said:
In my experience, for a streeter, with street gears and stock stall, both times; the factory340 cam into the stock-compression LA318, was a mistake. The bottom end goes soft and the power doesn't start 'til 4000. With 2.94s this is is ~42mph. The 268/276/110 aftermarket cam can be a good choice...... if Hi-Compression is achieved. However, for a DD I personally wouldn't recommend it, the fuel mileage is atrocious no matter what rear gears you run.
The factory 340 cam in a LA318 will need a hi-stall Convertor no matter what, and 3.23s minimum with an automatic.
The aftermarket 268cam will want about 9.8Scr. The factory Chrysler cam will want a bit more.

The reason for the compression difference is that the Chrysler cam is advertised at .008 lift whereas some/most aftermarkets are at .006. This means the Chrysler cam is actually bigger than 268 comparatively speaking, from intake valve closed seat to seat, which bleeds cylinder pressure back into the intake. Because of this, with a stock 1800TC, the bottom is soft, cuz it is stuck below 2200 until ~23mph with 2.94s; ~25mph with 2.76s..... and a DD spends a lot of time down there.
After about ~2000 this reversion begins to go away,and by 2200 power production can begin. The power starts at ~4000/42mph with 2.94s, and peaks around 5500/58mph; both in first gear.
Is that what you are after?

The stock LA318 compression ratio, if you value take-off power, limits you to a pretty small cam window. And the higher your operating elevation, the smaller the window.
Click to expand...

Thank you for that info. I believe we will stick with just a stock build as we are not changing anything else (drastically) at this time. I still have my first car and have changed many things over the years. This is my sons first car and will have the opportunity to change and modify things as the years go along. We bought it 6 months ago and he hasn't had a chance to enjoy it. We will get the engine freshened up and get it back on the road for him to enjoy. That's one of the great parts of this hobby, if you don't like something you can always change it.

Thank you again for all of your help and knowledge
 
If you have to bore it, you might as well bump the compression up; Pistons cost about the same.
If you have to replace the cam... you might as well bring it into the new century; cam kits all cost about the same.
Good luck with whatever path you choose.
I might as well tell you that an LA318 with a small 4bbl,a free-flowing dual exhaust, and a 2400 TC(2800 better), with any 3 series rear gear (the bigger the better), in any A-body..... is a lotta fun, even a stock-rebuild low-compression one; (again, more pressure is better).
I would choose compression over the 4bbl, and hi-stall over gears; if I had to.
You will need a SureGrip.
 
Found the reason for the dead hole but no apparent reason for my #6 cylinder having such low compression. It's heading to the machine shop tomorrow.

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