360 w/8.4:1=?power

[360moparjunkie]

First of I am not an engine builder (just building our engine) and appreciate all the help of you members out there.

I have confirmed true static compression @ 8.4
I would like to operate up to the 5800 rpm area give or take.
Heads are 72 J heads w/ comb. chambers cc'd @ 66
I have not chosen a specific cam/lifter/spring assy yet.
What power range can we realistically expect run up to knowing that we have the static limitation of 8.4? When do the numbers become just a fairy tale with a normally asp. engine....260,280,300,320,340?...........?

Still looking for an budget street strip combo that produces the most power for the least $$$$.

Thanks again. :read2:

 

[BrianT]

I'm no expert, but I'll chime in while we wait on one. If you build the bottom end solid, and pick the right cam and intake, I would think that 300 hp would be easily obtainable. Put a 150 shot on it, and go have some fun!!

 

[ramcharger]

low compression equals low power and poor idle with any performance cam. This compression ratio will severly limit your cam choice, although it should run on kerosene, lol. Your rpm limit with a cam that will be tolerable on the street will be about 4800-5000 rpm. I think you'll be lucky to break 220 hp.

 

[360moparjunkie]

If we are to change from flat tops to raised how many or how large of dome in cc's are we looking for?

We still want to run pump fuel.

BTW, our head chamber cc was 66

Thanks

 

[goldduster318]

http://www.moparmusclemagazine.com/techarticles/mopp_0105_dyno_test_360_smog_motor/index.html

You'll be fine. I have a similar combo using magnum heads and an edelbrock air gap. I would be lucky to have more than 8.4:1 compression and my car runs like stink. Just keep the cam small and you'll likely need to use a bit more initial timing.

 

[ramcharger]

http://www.moparmusclemagazine.com/techarticles/mopp_0105_dyno_test_360_smog_motor/index.html

You'll be fine. I have a similar combo using magnum heads and an edelbrock air gap. I would be lucky to have more than 8.4:1 compression and my car runs like stink. Just keep the cam small and you'll likely need to use a bit more initial timing.

Magnum heads have about 14cc smaller combustion chambers...... You sure you're lucky to have 8.4:1?

 

[360moparjunkie]

Just for the record, when buying pistons go with a reputable company.
I purchased my pistons through magazine mail order years ago (forgot the brand) these flat tops were advertized @ 9.8 to 1.
My true static comp. is 8.4.
Head chambered cc @ 66.
If the heads would have cc'd @ 70-72cc's the compression would have been that much worse!!!!!!!!!!!!!!!!

Assuming these are just crappy pistons and not a tall block issue.

GD318, thanks for the moral boost!

 

[goldduster318]

It has federal mogul 8:1 pistons at +.040 bore, and stock deck height. I doubt that's giving me much for compression.

 

[360moparjunkie]

Not feeling lucky just yet. (that doesn't happen until the tires just boil!)

What is the standard cc chamber size of the magnum heads?

Maybe magnums would solve the comp. issue.

Still looking for more answers.

THANK YOU

 

[ramcharger]

Just for the record, when buying pistons go with a reputable company.
I purchased my pistons through magazine mail order years ago (forgot the brand) these flat tops were advertized @ 9.8 to 1.
My true static comp. is 8.4.
Head chambered cc @ 66.
If the heads would have cc'd @ 70-72cc's the compression would have been that much worse!!!!!!!!!!!!!!!!

Assuming these are just crappy pistons and not a tall block issue.

GD318, thanks for the moral boost!

It's not unusual for pistons in a stock, unmachined block to sit .025 or more below deck. This is why you should do a mock up of your rotating assembly so you know how much to have the block decked. A good machinist will also have the tools to make these measurements from bore centerline to deck and you can give him the rod length and piston height.

 

[ramcharger]

Not feeling lucky just yet. (that doesn't happen until the tires just boil!)

What is the standard cc chamber size of the magnum heads?

Maybe magnums would solve the comp. issue.

Still looking for more answers.

THANK YOU

Magnum heads are around 56cc. As you already found out, that can vary from head to head though... If you combine these heads with a thin cometic gasket, you should easily be able to 9:1.

It has federal mogul 8:1 pistons at +.040 bore, and stock deck height. I doubt that's giving me much for compression.

You've got a point there. Depending on the gasket you're probably in the mid 8's for CR.

With 65cc heads and a .040 Cometic gasket and KB flat tops on a block that I had decked .022 (pistons .005 below deck) my measured comp ratio is 10.23:1. Just food for thought.

I can run much higher CR here in the rare air than someone at at or near sea level with a tiny cam (213/218 @ .050 dur on a 112 LCA).

 

[360moparjunkie]

Block is mocked.

.1092" below deck @ tdc.

Another member suggested just buying taller pistons as the cost effective solution towards more comp.

220hp max is not what I was shooting for. (if I wanted that I'd build a ford or chevy. LOL)

After all, I have this thing already apart. Let's make a liitle power. Huh?

 

[ramcharger]

Block is mocked.

.1092" below deck @ tdc.

Holy Somolians! Those pistons suck, lol! The KB hypers are cheap compared to heads, so I'd go that route.

Another member suggested just buying taller pistons as the cost effective solution towards more comp.

He was right.

220hp max is not what I was shooting for. (if I wanted that I'd build a ford or chevy. LOL)

LMAO :cheers: More could made but forget about streetability with that CR. What's your intended use for this build?

After all, I have this thing already apart. Let's make a liitle power. Huh?

Agreed 100%!! 8)

 

[360moparjunkie]

My intended build is a street strip runner.

Weekends only. I have two other factory dodges that are very reliable.....this on does not need to be. I rather go a little faster w/ this one if you know what I mean.

Feet above sea level here is no more than 80'
We have dense air....and now cool, moist, dense air. A correct engine runs good here this time of year.

 

[needsaresto]

Agreed 100%!! 8)

I agree Ramcharger,those pistons are probably lower than a stock one.

Change the pistons. KB107 is the 360 piston. Those should get you 9.5:1 even with 360 heads.

 

[ramcharger]

My intended build is a street strip runner.

Weekends only. I have two other factory dodges that are very reliable.....this on does not need to be. I rather go a little faster w/ this one if you know what I mean.

Feet above sea level here is no more than 80'
We have dense air....and now cool, moist, dense air. A correct engine runs good here this time of year.

You lucky dog you! A 20% loss of power on a naturally aspirated engine is a given at this altitude. The NHRA figures a .7 second loss.

I agree Ramcharger,those pistons are probably lower than a stock one.

Change the pistons. KB107 is the 360 piston. Those should get you 9.5:1 even with 360 heads.

That's what I'm using with the above mentioned build but with the block decked. Great choice needsaresto and 9.5:1 sounds about right.
Moparjunkie, run these pistons and but be sure to mock and measure like you've already done.

Add a Lunati 60403 cam, get the correct valve springs for your app and make sure your heads are done right and you should see high 300's easy. You'll a need a 2500 rpm stall with this cam. You'll also want to run at least a 750 Holley and a single plane will bump the top end up but a Eddie RPM would be the way to go. Don't forget to get a good name brand distributor with an adjustable mechanical advance.

 

[bongy337]

My intended build is a street strip runner.

Weekends only. I have two other factory dodges that are very reliable.....this on does not need to be. I rather go a little faster w/ this one if you know what I mean.

Feet above sea level here is no more than 80'
We have dense air....and now cool, moist, dense air. A correct engine runs good here this time of year.

Take a look at this article. Too much information can be rather confusing. I thinks this piece will answer your concerns. Good luck !

http://compcams.com/Community/Articles/Details.asp?ID=-409383413

 

[360moparjunkie]

I'll be looking into these parts.
Thanks a million!

Ramcharger, take a look at the PM I've sent to you.

MoparJunkie

 

[74scamp360]

this is my problem as well, i've bought a 360 for my scamp and i'm not 100% sure on the year but it's into the later 70's so i can't imagine it's making much more compression then 360moparjunkies is making. I don't really want to have to pull the motor completly apart but..., good luck on your build 360moparjunkie

 

[rumblefish360]

I agree Ramcharger,those pistons are probably lower than a stock one.

Change the pistons. KB107 is the 360 piston. Those should get you 9.5:1 even with 360 heads.

The KB107's are speced at 9.8-1 with a .039 gasket and 72 cc heads. With a .054 gasket it'll drop to apprx. 9.5-1.
With Edelbrock heads it's approx. 10.5 (.039 gaskets)
With Magnum 56ccc chambers, it's 11.80. With a .054 gasket, it comes to 11.33.

bongy337 points to a good write up, one I was thinking off. That low compresion mill makes decent power with a small cam. However, if you figure in a comprsion pont being about 3% more power and a zero deck slug with great quench, it'll (power) rise quite well.

Making some power with a low compresion engine is possible, but, it'll lack a snappyness and run not as well as it could. The feeling between the two would be a muddy feeling and a snappy throttle.

As mentioned above, cam lightly or kill it all togther.

 

[360moparjunkie]

bongy337...Great article. I've seen this one before and loved it.

These guys are pros IMO. Would any of you critique their choice of camshaft....or for this article was it SPOT ON.

I would be willing to just follow this build to a tee; however, I cannot put faith in the results being the same unless I knew what their actual static compression was on the test motor used in the article. Mine possibly being lower could cause my build to flounder.

Rumble, Awsome figures there.
If I were to use those pistons and came up with lower figures than yours.
This would point directly to my deck being taller than average for whatever reason. (and not the pistons)

If I knew the center line of crank to deck meas.
or
knew the center of piston pin to top of piston

This could also help prove the reason for such crappy quench on my motor
(.1092")


Thanks from "not so sunny" Modesto, California

 

[7172 duster]

350 hp easy to make.

 

[goldduster318]

I agree with 7172 Duster. As with the article I showed from Mopar Muscle...330-350hp is easy to make...even with the low compression. Mine probably makes between 350 and 370 with the magnum heads. That 225 max hp thing is just plain wrong. I drive a 3500 lb, 225hp 5-speed manual truck with 3.42 gears every day...and the duster is frighteningly faster with a 4-speed and 3.23's. My truck easily runs a 15.7 1/4 mile at 92 mph and a crap 60'. If my Duster couldn't go under 14.00 with traction, I'd be shocked.

Compression ratio isn't everything. In fact, the 360 magnum truck engines were around 8.5:1 compression as they had dished pistons. They made 245hp and 340 lb-ft of torque with that restrictive beer barrel intake.

 

[lead69]

Ive built quite a few low compression engines-the run what ya brung deal-and they can run hard.The last 360 I built had a quench of about .085 and a true compression of 8.71 and made incredible power.I used .028 head gaskets and some 75 318 heads with stock vlaves and some port work but you could easily mill stck 360 heads down and have about the same flow as my ported 318 heads.I used a gasket matched performer with a 600 holley, cheap headers and a comp xe 274,also you want alot of initial timing and a quick mechanical advance.The cam ran great with that compression,had about 10in of vaccum at idle and remember the old addage,the poorer flowing the heads the bigger the cam.Now of course there are pratical limits to this and you need a mild stall and gears but dont be afraid of a cam with 230 @ .050 of intake duration or less,but with 8.5 or lower I would probaly run the comp xe 268 or silmilar.This went into a 70 dart I put together with a 904,mild 2k stall and 3.23s and was a solid low 13 car,it would have ran 12.80-90s with gears and was a blast on the street,heres a couple pics of it finished.

 

[74scamp360]

that's a cool car lead69