68 truck 318 cam. How big can i go?

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bw68d100318

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68 d100 318 np435 4 speed with like a 7:1 granny, 3.73, 29" tires, manual brakes/steering. I understand compression is about/under 8:1. Ported/polished 302's with big valves, rpm intake or a single plane, 600-750 eddy card (I want to try a Holley, but I have the eddys). Headers to 3" duals, h-pipe, dumped in front of the axle.
I want the biggest cam I can run for an rpm limit of 6500-7k. Not much strip time, but I drive 95% of the time at 65-75 highway, but I like to tear around. No towing. I'd like to see 450hp, and a power and of 4000-7000. I've read IQ52'S posts on low compression builds, so the compression doesn't bother me. I may throw a turbo on it in the future, and am also wondering if the cam should be changed at that time. I'm guessing something in the 275-285 range with high 500's lift. I've no experience with big cams and small blocks regarding driveability.
 
Also curious if I should try to get a cam with less overlap, like 114 degrees to not bleed off whatever compression I have at low rpms.
 
Take a look at the Comp DEH 265. That should work really good.
 
That cam Rusty recommend is bang on for your combo.

But for some reason you want more than your engine can deliver. Yes you can do a lot more with low cr than most people think but not a 450 hp 7000rpm stock short block 318 screamer.
 
I appreciate the feedback. I didn't think I was being too unrealistic. I have a hot rod build with a low compression 318 that hit 400hp with un-ported heads. They did mill the heads to raise the compression.
 
bw68d100318 said:
I appreciate the feedback. I didn't think I was being too unrealistic. I have a hot rod build with a low compression 318 that hit 400hp with un-ported heads. They did mill the heads to raise the compression.
Click to expand...

On whose dyno? That was one happy piece of equipment.
 
Stock comp. on a 68 318 should be 9.2:1. Correct me if I'm wrong.
 
bw68d100318 said:
It's my understanding the truck engines were lower compression.
Click to expand...

No, they are a better engine, most had forged cranks and good internals.
Probably the best 318 I ever had was in a rusted 69 D-100.
I added a old 340 manifold with a AFB, and a set of headers.
It had a flat bed with 3.91 sure grip, it would fry the tires forever.

You are bringing back memories, I traded a 4 door dart and $50 for the old truck.
Driving it home, it started raining hard, I ended up soaking wet clear to my crotch, the floor board were super rusty with big holes.

Patched the old girl up, drove it for 2 more years until it was really unsafe to drive.
Put the motor in my first duster, ran it for years.
After building a hotter motor for the duster sold it to a guy because it was a matching year motor for a boat he was restoring.

You could not blow it up, I think the stock cam must kept the redline down where it did not come apart.
 
That's not a low cr build they squeeze 10:1 out of it.
If you use that as the basis for your build, you'll need more cam, cr and head flow to gain 50 more horsepower.

Those 400hp 318 recipes that float around would be good for a light deep geared A body but wouldn't be very fun in a heavy under geared truck.
 
273 said:
That's not a low cr build they squeeze 10:1 out of it.
If you use that as the basis for your build, you'll need more cam, cr and head flow to gain 50 more horsepower.

Those 400hp 318 recipes that float around would be good for a light deep geared A body but wouldn't be very fun in a heavy under geared truck.
Click to expand...

I bet a 68 truck weighs about the same as a A-body.
The trucks have pretty steep gears, most are 3.91 from the factory.
They make for cheap fun rides.

Here is a pic of my old 71 that I totaled, it was a daily driver reliable old truck, not the rusty one I talked about earlier.

truck52006.jpg
 
I don't mind bumping the compression by milling the heads, but I'm wondering if a bigger cam than they used would be hard to deal with on the street. I think I can get the heads to flow at least as well as they did. My truck is pretty light and has 3.73 gears, and getting going with a stupid big cam shouldn't be too bad with a 7:1 first gear.
I drive about 30,000-40,000 miles a year in my '68 or my '70 powerwagon with a 383. Both are rock solid reliable and I've rebuilt/replaced most of the running gear and most of the engine systems. I'm getting a game plan together for the '68, which will be my hot rod.
 
sireland67 said:
I bet a 68 truck weighs about the same as a A-body.
The trucks have pretty steep gears, most are 3.91 from the factory.
They make for cheap fun rides.

Here is a pic of my old 71 that I totaled, it was a daily driver reliable old truck, not the rusty one I talked about earlier.

truck52006.jpg
Click to expand...

That's a sweet color,and a nice looking rig. I'll post pictures of my jalopies tomorrow.
 
bw68d100318 said:
I don't mind bumping the compression by milling the heads,
Click to expand...


If you mill so much off the heads, then you have to get the intake milled to compensate for proper fit. Then you have to keep those heads and intake together and can't interchange them on other engines.

Just something to keep in mind.... #-o
 
krazykuda said:
If you mill so much off the heads, then you have to get the intake milled to compensate for proper fit. Then you have to keep those heads and intake together and can't interchange them on other engines.

Just something to keep in mind.... #-o
Click to expand...

I think I'll just have the intake side of the heads milled so any 318 intake will work. Seems more logical than milling the intake.
 
Here is the skinny on milling to increase compression. The compression on these engines is lower than what they are rated for. By a good bit. Chances are your 318 will blueprint down in the high 7s. Probably 7.8 or so. Sad but true.

The reason is because Chrysler had terrible machining tolerances when it came to deck heights that were too tall and combustion chambers that were too large and pistons that sat way down in the hole at TDC.

Now, generally, it takes about .070" of an inch off a small block head to equal one compression ratio worth of change. That's a BIG cut. More than most machine shops can do in one pass.

Couple that with all the cuts they will have to take off the heads on the intake side and the labor will add up quickly. Milling heads is not a good way to increase compression. Can you do it? Yes. But plan on buying custom pushrods and possibly having rocker arm geometry woes as well. You could possibly even run into piston to valve clearance issues.

You have members giving you advice based on their DECADES of experience. I'd listen if I were you. We are trying to tell you the best way.

By running a thin head gasket and maybe taking .025 off the heads max, you can get to around 8.5:1 which is perfect for crappy pump gas on something you will drive everyday.

That cam I recommended will act like a Thumpr or Whiplash. It will sound bigger than it is because the DEH grinds have long exhaust duration and a big duration split just like the Thumpr and Whiplash......yet they will deliver more power down low, because that's what they are designed to do.

My advice is shoot for 8.5 compression. You might not be able to quite get there depending on how low the compression is now, but you can make a marked improvement and have a snappy street motor with smart parts choices.

Lastly, if you are just bound to have compression around 9:1 or greater, do it right and buy pistons. But you honestly don't need that on the street everyday to have fun.

You've been given good advice. You should use it.
 
RustyRatRod said:
The reason is because Chrysler had terrible machining tolerances when it came to deck heights that were too tall and combustion chambers that were too large and pistons that sat way down in the hole at TDC.
Click to expand...


We used to intentionally run the mini van heads on the fat side for the head faces. That way if we had to reuse/recycle a head and it got the block face scratched, we would do a clean up mill cut to get rid of any nicks and scratches that may have gotten on the heads. We ran them as a batch job when we got enough saved up....

Running on the fat side gave us the ability to recondition any heads that may have gotten some scars or scratches so we could reuse them. Otherwise, it would have cost alot of $$$ to have them scrapped....
 
krazykuda said:
We used to intentionally run the mini van heads on the fat side for the head faces. That way if we had to reuse/recycle a head and it got the block face scratched, we would do a clean up mill cut to get rid of any nicks and scratches that may have gotten on the heads. We ran them as a batch job when we got enough saved up....

Running on the fat side gave us the ability to recondition any heads that may have gotten some scars or scratches so we could reuse them. Otherwise, it would have cost alot of $$$ to have them scrapped....
Click to expand...

That makes a lot of sense for production. You cannot put it back once it's gone.
 
RustyRatRod said:
Here is the skinny on milling to increase compression. The compression on these engines is lower than what they are rated for. By a good bit. Chances are your 318 will blueprint down in the high 7s. Probably 7.8 or so. Sad but true.

The reason is because Chrysler had terrible machining tolerances when it came to deck heights that were too tall and combustion chambers that were too large and pistons that sat way down in the hole at TDC.

Now, generally, it takes about .070" of an inch off a small block head to equal one compression ratio worth of change. That's a BIG cut. More than most machine shops can do in one pass.

Couple that with all the cuts they will have to take off the heads on the intake side and the labor will add up quickly. Milling heads is not a good way to increase compression. Can you do it? Yes. But plan on buying custom pushrods and possibly having rocker arm geometry woes as well. You could possibly even run into piston to valve clearance issues.

You have members giving you advice based on their DECADES of experience. I'd listen if I were you. We are trying to tell you the best way.

By running a thin head gasket and maybe taking .025 off the heads max, you can get to around 8.5:1 which is perfect for crappy pump gas on something you will drive everyday.

That cam I recommended will act like a Thumpr or Whiplash. It will sound bigger than it is because the DEH grinds have long exhaust duration and a big duration split just like the Thumpr and Whiplash......yet they will deliver more power down low, because that's what they are designed to do.

My advice is shoot for 8.5 compression. You might not be able to quite get there depending on how low the compression is now, but you can make a marked improvement and have a snappy street motor with smart parts choices.

Lastly, if you are just bound to have compression around 9:1 or greater, do it right and buy pistons. But you honestly don't need that on the street everyday to have fun.

You've been given good advice. You should use it.
Click to expand...

I appreciate the advices. I'm not too concerned with the compression, it seems like the added cc's create a bigger cube engine at higher rpm's if you can get air\fuel flowing well at higher rpm's. Any thoughts on that?
 
Adding rpm is basically like adding cubes to your engine, everyone likes to talks that engine A is bigger than engine B (eg 318 vs 360) but that's only in a static condition but running your engine size dynamic.
eg (360 x 5500 rpm) ÷ 2 = 990,000 cubic inches
(318 × 6225 rpm) ÷ 2 = 990,000 cubic inches
( you can drop the (÷ 2) since no one cares about the exact size so if you want to ballpark what a 318 would have to turn compared to a similar built 360 just (360 x rpm) ÷ 318 = new rpm ) But at those rpm those to engines can both pull the same amount of fuel and air per minute having the capability to make same power.

But I think your talking about is that a low cr engine has a few more cc over a high cr engine at the same VE yes but the small gain wouldn't make up the power lost by inefficiency of the low cr for the gain in a few more cc.
 
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