Should i even bother with with getting a higher compression ratio?

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DumpsterFire

DumpsterFire

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Have a 360/5.9 magnum I've torn down for pretty much just a street car dart. I was going to leave it mostly stock and dress it up like an LA. It's honestly probably more than enough engine for the car but the urge to do something is pretty strong. The 9 to 1 compression feels low but if I get it to somthing like 10 to 10.5 with new pistons am I really wasting my time? I'm trying to see what a smart route to slightly higher comparison and a slightly more aggressive cam would be. Want to pretend I didn't just slap an old truck motor in even if that would be the reasonable thing to do
 
How do you know if 9:1 feels low? Have you driven it?
 
DumpsterFire said:
Have a 360/5.9 magnum I've torn down for pretty much just a street car dart. I was going to leave it mostly stock and dress it up like an LA. It's honestly probably more than enough engine for the car but the urge to do something is pretty strong. The 9 to 1 compression feels low but if I get it to somthing like 10 to 10.5 with new pistons am I really wasting my time? I'm trying to see what a smart route to slightly higher comparison and a slightly more aggressive cam would be. Want to pretend I didn't just slap an old truck motor in even if that would be the reasonable thing to do
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You run the cr that matches your cam, sounds like your running the stock cam so stock cr is fine.
 
The compression and a bit larger camshaft will make
a significant difference in power.
 
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I got the 380 HP crate comes with a pretty healthy cam and 9:1 CR works fine. But with this cam I could run more CR for more power.
 
depends on intended use. i did a low buck sock 74 360 for my dart. has a small mp cam and is plenty for me. i do have a low gearset 904, good converter and 3.23 gears. runs on 87 octane and cruises great. plenty of power for me.
 
abodyjoe said:
depends on intended use. i did a low buck sock 74 360 for my dart. has a small mp cam and is plenty for me. i do have a low gearset 904, good converter and 3.23 gears. runs on 87 octane and cruises great. plenty of power for me.
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It's going to have 3.73 gearing. I'm think I can get away with that being that it's through a 5 speed
 
If I'm being honest I don't need anything just trying to price out what getting it somewhere around 10.5 and a new cam would be and what would be good stuff to pick
 
DumpsterFire said:
If I'm being honest I don't need anything just trying to price out what getting it somewhere around 10.5 and a new cam would be and what would be good stuff to pick
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Why this fixation on 10.5:1 ? Last thing you want is a pinging mess of an engine. You would need a fairly large cam with 10.5:1, You can run a fairly decent size cam with 9-9.5:1 CR, just don't run more cr for the hell of it. 10.5:1 over 9:1 is only about a 5% power gain so about 15-20 HP.
 
DumpsterFire said:
Have a 360/5.9 magnum I've torn down for pretty much just a street car dart. I was going to leave it mostly stock and dress it up like an LA. It's honestly probably more than enough engine for the car but the urge to do something is pretty strong. The 9 to 1 compression feels low but if I get it to somthing like 10 to 10.5 with new pistons am I really wasting my time? I'm trying to see what a smart route to slightly higher comparison and a slightly more aggressive cam would be. Want to pretend I didn't just slap an old truck motor in even if that would be the reasonable thing to do
Click to expand...
Time to figure out the entire build plan and budget.

If you do not intend to have any work done on the cylinder heads and do not intend to replace the cylinder heads I would not personally bother with the cost of new pistons and rings and cost to balance that rotating assembly. I would definitely check rod and main bearings. If it is coming apart further for inspection replace the camshaft bearings too. Then just install the Hughes Engines valve spring complete kit and camshaft snout extension, and then get your original camshaft reground and run the original lifters. You will have to measure to see if new pushrods will be required after the camshaft regrind.

If replacing he cylinder heads anyways, I would then go with more compression and camshaft but then the cost really starts going up.
 
Bobzilla said:
Time to figure out the entire build plan and budget.

If you do not intend to have any work done on the cylinder heads and do not intend to replace the cylinder heads I would not personally bother with the cost of new pistons and rings and cost to balance that rotating assembly. I would definitely check rod and main bearings. If it is coming apart further for inspection replace the camshaft bearings too. Then just install the Hughes Engines valve spring complete kit and camshaft snout extension, and then get your original camshaft reground and run the original lifters. You will have to measure to see if new pushrods will be required after the camshaft regrind.

If replacing he cylinder heads anyways, I would then go with more compression and camshaft but then the cost really starts going up.
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I've already completely torn it down. Really just trying to figure out how into the weeds I should go
 
Bobzilla said:
Time to figure out the entire build plan and budget.

If you do not intend to have any work done on the cylinder heads and do not intend to replace the cylinder heads I would not personally bother with the cost of new pistons and rings and cost to balance that rotating assembly. I would definitely check rod and main bearings. If it is coming apart further for inspection replace the camshaft bearings too. Then just install the Hughes Engines valve spring complete kit and camshaft snout extension, and then get your original camshaft reground and run the original lifters. You will have to measure to see if new pushrods will be required after the camshaft regrind.

If replacing he cylinder heads anyways, I would then go with more compression and camshaft but then the cost really starts going up.
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I kind of have the same plan. Is it necessary to upgrade springs with a mild cam upgrade? Rookie questions but what would be the maximum cam lift?? using stock springs in a 5.9 magnum?
 
The Magnum engines already have decent compression. You're wasting your money on more pistons, but go right ahead.
 
sam69sat said:
I kind of have the same plan. Is it necessary to upgrade springs with a mild cam upgrade? Rookie questions but what would be the maximum cam lift?? using stock springs in a 5.9 magnum?
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Stock valve springs are pretty weak. An upgraded cam on the stock springs will be ok at lower RPM but will get into valve float easily. Not really worth it.
Max lift on the Magnum with stock pistons usually comes down to the clearance between the retainer and guide, or more realistically the retainer and the seal. Somewhere around .540" lift the Hughes spring usually clears, but each one is a little different.
 
sam69sat said:
I kind of have the same plan. Is it necessary to upgrade springs with a mild cam upgrade? Rookie questions but what would be the maximum cam lift?? using stock springs in a 5.9 magnum?
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Around 500 is the max. Stock springs are really soft. Like soft enough to be able to compress with your hand.

The hughes kit (which I have on my motor) gets you more clearance and stiffer springs that are well suited to a mild to moderate cam.
 
DumpsterFire said:
Have a 360/5.9 magnum I've torn down for pretty much just a street car dart. I was going to leave it mostly stock and dress it up like an LA. It's honestly probably more than enough engine for the car but the urge to do something is pretty strong. The 9 to 1 compression feels low but if I get it to somthing like 10 to 10.5 with new pistons am I really wasting my time? I'm trying to see what a smart route to slightly higher comparison and a slightly more aggressive cam would be. Want to pretend I didn't just slap an old truck motor in even if that would be the reasonable thing to do
Click to expand...

here is my mild 360 build. very mild 360 build. . its a LA motor that i'm lucky if it has anything over 8:1 compression.. i doubt you'll need anything more then what you already have but i guess its all subjective. my motor has plenty of power, runs on 87 octane, doesn't run hot and cruises awesome.. just had it on a 5000 mile road trip.
 
The stock Magnum ratio of 9:0-1 is a very good ratio for a street driver. Adding a cam of a reasonable street performer size will still allow the use of 87 octane really easy.

I have found my 2000 - 5.9 runs best of 89 or 93 with an aggressive distributor timing and a bunch of initial @ 20*’s. At this point, it doesn’t like the 87 octane. But runs fantastic with the aggressive timing on at least 89 octane.

The 5.9 has a 750 carb on top of a Edelbrock RPM and Super Comp 1-3/4 headers, it’s in a ‘79 Magnum with a 2500 stall and 3.55’s on 245/60/15’s. The car has been lightened up a bit and weighs in around 3200lbs.

These engines as described above just need a camshaft and valve springs to be an enjoyable hot rod. A better cylinder head is a great addition.
 
Oh! Crap.. sorry….

While more compression would add power, IMO, it’s not an effective venue to pursue. Depending! A street cruiser and a mild cam, say, 230*’s @.050 or less isn’t going to see big power gains that would (In My Opinion!) justify its cost.

If your looking to mow down some good strip times and use a larger cam, gears, single leg plane intake, then replacement pistons would be a good idea. I’d go right to 11-1 with aluminum heads well ported stock it with a big bump stick.

10-1, (camshaft sizing has a play in this,) with iron heads is about requiring 93 octane.
 
The roller camshaft below - as an example - is a decent area of duration to use on a street car with a minimum of 3.55.
It’ll make power in between 2000 & 5500 with stock heads.
A better higher flowing head will push up the rpm ceiling.

IMG_0668.jpeg
 
Build as high a compression ratio you can for the level of tuning you are capable of.
 
press the easy button:
>leave stock with a clean up hone, + rings and bearings
>oregon #2204 grind*
>hughes spring kit
>hong kong phooey air-gap
>650~750 carb
>re-curve distributor (this is key)

gobs of torque down town, tons of mid and enough top end to chooch. will run on 87, has great street manners, easy collection of parts that are all reasonably priced. no bag o' tricks necessary for assembly.

wanna get nimbly bimbly? home port the heads and add some roller rockers for splash more HP

headers aren't 100% necessary but will absolutely help all across the range.

*or something that's 480-ish & 215/220 on about a 110-- the split pattern favoring the exhaust is key
 
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