Expectations from build

[acelondon]

Hey everyone!

I'm restoring my 74 Charger right now, and have it torn completely apart. While i slowly work on the rustbucket, i'm working on the engine on the side, and have some questions only experience can answer. My planned combo is as follows:

Stock 318 from the car
High compression pistons. How high can i go? 10-10.5:1?
360 heads that have been lightly worked, but not shaved. Hence the pistons.
340 resto cam from Comp Cams.
Custom Megasquirt EFI

If all looks good inside this pig, i'll stick to stock bore and stroke, just to save money. Will likely get everything balanced/new rods so i can get more RPM. It's not a racecar. Most of my funding is getting poured into a TKO600 tranny kit.


So, main questions:

Can i go 10:1 comfortably? Any idea how to figure out which pistons will do this with open chamber 360 heads? I've had very little luck researching it.

How much performance can i expect from this combo? I need to size the throttle body and injectors to the expected possible horsepower of the metal under them. I don't want to just buy all parts for 500hp, and then barely use half of it. This would kill drivability, just like overcarbbing.

It seems like no one cares about the 318, but there has to be someone out there that enjoys theirs!

Thanks in advance, everyone.

[Dino]

I remember reading an article on souped up 318s and the numbers were impressive to say the least!  It's been a long time so I can't remember where it was, maybe a search will lead you to it.  I like the idea of having a reliable 318 with some pep.   

[acelondon]

Motor trend a few years ago got 400hp all day out of a 318. But they did a lot of expensive machine work that i'm not sure is really needed. Porting stock/police heads vs. just using 360 heads, basically.

[acelondon]

So, i guess no one has ever done a dyno pull of a 318 with 360 heads and a 340 cam? I guess i'll be the first next year when this rust bucket is done. Then i'll post more sheets when the turbo is installed.

[c00nhunterjoe]

Stock 318 with your advertised 10:1, 360 heads, 340 cam- i estimate 240 flywheel hp.

[acelondon]

Thanks! I've been asking this question for about 6 years, finally got an answer!

Now i find it even more hilarious that Allparts.com has an excerpt from a guy saying that he drag raced seriously with this setup!

[c00nhunterjoe]

You dont have to be the fastest in brackets, just consistent....

[acelondon]

Very true!

[chargd72]

Hey everyone!

I'm restoring my 74 Charger right now, and have it torn completely apart. While i slowly work on the rustbucket, i'm working on the engine on the side, and have some questions only experience can answer. My planned combo is as follows:

Stock 318 from the car
High compression pistons. How high can i go? 10-10.5:1?
360 heads that have been lightly worked, but not shaved. Hence the pistons.
340 resto cam from Comp Cams.
Custom Megasquirt EFI

So, i guess no one has ever done a dyno pull of a 318 with 360 heads and a 340 cam? I guess i'll be the first next year when this rust bucket is done. Then i'll post more sheets when the turbo is installed.

This concerns me.  If you even have a 5% chance of adding forced induction down the road, you need to modify your build plan.  Believe me, I know.  Building up a 318 is all I wanted just a few years ago.  I spent the money on it and now I can't wait to get it out.

[acelondon]

I would change the pistons at the point. I know that much. I just wondered how this old engine would not make 400hp all day. Do 360 heads flow that badly? if i can get it to pull at 6500rpm, that's 400hp.

[Kern Dog]

The 360 heads will drop the Compression ratio in a 318 by at least 1/2 a point. The 318 from 1967 to around 1972 was an 8.8 to one engine. From 1973 to around 1985, the 318 was closer to 8.0 to one.  If you are set on running those 360 heads, you will certainly want to change pistons. For this, you will need to bore the engine to do it right. You are spending time and money to do an engine rebuild. I'm sure you want it to be reliable, powerful and not be an oil burner, right?
One of the reasons that 318s were such a reliable engine was that they were fairly low compression engines with heads that didn't flow well along with camshafts that were real small. The engine was designed for durability. It was also designed so it wouldn't hurt itself. If your engine starts to lose power at 4500 rpms, the usual response is to upshift. Most 318s had HP peaks in the 4400-4600 rpms. You are not going to hurt them shifting at such a low rpm.
Spend the time to rebuild a 318 for more power and you are sure to be running it well past 5000 rpms, even close to or beyond 6000. This is where things start to break if proper machine work and parts selection is not chosen. The cylinders of many Mopar engines are often still reasonably straight even after 100,000 miles of use IF the car was well maintained. I had a '79 360 from a Cordoba in a junkyard. The car must have been poorly neglected because while the engine was standard bore, it took almost .025 before the bores were clean from scuffs and scratches. This meant I was obligated to take it to .030. In some cases you can simply "hone" the cylinders and put the stock pistons back in with NEW rings. Using new higher compression pistons on a standard bore block? That is where this gets a bit fuzzy.
If the new pistons fit the bores with the adequate amount of clearance, this might work. I've never done it though. If I wasn't boring the block, I reused stock pistons. If I wanted higher compression, I'd use new pistons and have the block bored to match the size of the new pistons.  I see that you want a higher compression ratio, this makes sense for power and economy. I'd let the machinist check the block and report back. The bore taper will probably make the decision for you: Too much taper means you need to bore the engine to make the cylinders correct again.
In short, boring and honing is only one expense of the entire build, but it gives you a fresh start on an old block. It is the most reliable foundation to build from.

[c00nhunterjoe]

I would change the pistons at the point. I know that much. I just wondered how this old engine would not make 400hp all day. Do 360 heads flow that badly? if i can get it to pull at 6500rpm, that's 400hp.

If you think revving the engine to 6500 means it will make 400 hp, then we need to go back to the drawing boards. If this were true, then i suspect my 383 makes 600 hp since it pulls hard to 8.

[BSB67]

If you think revving the engine to 6500 means it will make 400 hp, then we need to go back to the drawing boards.

I've read this post a couple of time, and I'm just not getting it.  Maybe he thinks its the rods 

He will need to make 1.25 hp/cu.in to get to 400 hp. Doable, but not with that parts list and plan.

Spend a few hundred bucks and get a 360, put a nice cam, headers, heads, w/ a decent compression ratio, and 1 to 1.1 hp/cu.in is easy

[acelondon]

My 400hp number is an estimate based on rpm, displacement and rpm.

http://www.bgsoflex.com/roughhp.html
This tool is accurate enough to get an idea, and it holds true for the factory horsepower for all 4 cars I own, and the LS builds my friends and I have done. I know it's not perfect. If the 340 cam and 360 heads can keep the air moving at 6500rpm, it better beat 300hp at least.

It doesn't factor in things like valve shading, I know. But that's why it's called an estimator.

I guess I'll listen to everyone and stuff the 318 in the shed and put a LS in it. 450hp from a 6.0 is child's play.

Thanks everyone for your help!