High Compression 390

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stumblinhorse

stumblinhorse

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I am putting the parts together for my 390. I didn't want to hijack another thread so starting a new one.

I am putting together a street 390 using the Scat Cranks kit. It uses +4.7CC pistons with a 6.123 rod length and 1.465 Comp Height. So with .01 in the hole with Edelbrock AL (60779) 63cc heads and the edelbrock .050 head gasket, SCR would be 10.9 or so...

I am looking for opinions on if there needs to be anything special for an engine like this? I was thinking of using the Voodoo FT 262 or 268 cam with the motor.

One tidbit of info is that the engine will mostly be at between 6000-7000 ft above sea level. This motor will go into a 69 d100 truck with a 4sp 3.55 8 3/4 open rear end.
 
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I might be wrong but those cams seem to small for that CR especially for a truck.
 
Is this car 4 speed or truck 4 speed?
agree about short cam with that much compression although lunati is good choice
by FT are you thinking soild or hyd?
what's the usage- towing or ???
 
Np435 4 speed. Hydraulic FT. Used for fun, no towing or work.

268 cam seemed pretty big to me
  • Advertised Duration (Int/Exh): 268/276
  • Duration @ .050 (Int/Exh): 226/234
  • Gross Valve Lift (Int/Exh): .494/.513
  • LSA/ICL: 110/106
 
IMO, jump another 10*’s of duration. The big cubes eat some cam duration and with the huge amount of extra arm you have, torque production will not be an issue.
Also, more valve lift! With that listed valve lift, you could run prepped stock heads. Use the available superior flowing ports of the Edelbrock heads to your advantage. Otherwise, what the heck did you get them for?!?!

Last thing, why the .050 thick head gasket? Use a thinner one (.039) to get a good quench area and a minor bump in the ratio. Is a 93 octane available by you?
 
rumblefish360 said:
Last thing, why the .050 thick head gasket? Use a thinner one (.039) to get a good quench area and a minor bump in the ratio. Is a 93 octane available by you?
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The Edelbrock heads says they need the Edelbrock head gasket and it is .050. 93 octane is not available here, 91 is it.

With the smaller cam voodoo I get pretty good lift without a rough idle and keep pretty good street manners. At least that is the hope.
 
stumblinhorse said:
The Edelbrock heads says they need the Edelbrock head gasket and it is .050. 93 octane is not available here, 91 is it.

With the smaller cam voodoo I get pretty good lift without a rough idle and keep pretty good street manners. At least that is the hope.
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The problem with a small cam and high CR is you'll probably have too much dynamic CR for pump gas. Obviously your not looking for every last bit of power drop the cr if you haven't already built the engine.
 
Wallace calculator points to you being fine if you close the int valve around 46 abdc@.050 and @6500 ft elvation. 177 psi 9.81 dynamic.

Focus on the psi part, this is elevation.
 
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stumblinhorse said:
The Edelbrock heads says they need the Edelbrock head gasket and it is .050. 93 octane is not available here, 91 is it.

With the smaller cam voodoo I get pretty good lift without a rough idle and keep pretty good street manners. At least that is the hope.
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OK, as you see fit. Have fun.

(Spelling)
 
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Should I go away from the fast ramps of the voodoos? Is there another cam line that might be better?

The 276 voodoo closes at 43*. Specs are:
  • Advertised Duration (Int/Exh): 276/284
  • Duration @ .050 (Int/Exh): 234/242
  • Gross Valve Lift (Int/Exh): .513/.533
  • LSA/ICL: 110/106
 
I must be just a dumb old man . What is a 390? I know 360, 383 and the stroked versions. Is this a gen3 version?
 
Why would you go away from a fast ramp cam?
This is what you want. The quicker the valve opens and closes the better and quicker the air and fuel charge rushes in helping to create power.

Look at the heads flow specs. Add 1.6 rockers to change the intake lift from .513 to .547 & the exhaust from .533 to .568. More lift the merry.

I personally like the cam. The wording of “Is there a better cam” is often asked and it comes down to one of two things. Personal taste/reaction (the way it acts in a running driving engine) of the cam being used and/or what the dyno says works best for what it is your doing.

As I said before but also I failed to mention that the cubes are big via the stroker crank which eats duration up a little bit but also, a manual transmission can always step up in cam size by one step.

The above cam IMO is what I would do for “A fun truck.” What intake & carb are to be used?
 
The intake I already have is a Weiand Stealth, that I will probably open up the ports a little. The Carb I have is a Edelbrock 600 that I will try and go up to 750 if I can't get it right. I have found that stepping down a size at this altitude makes tuning a little easier.

My plan for rockers is to break it in with the stockers, then get 1.6 rollers and new PRs after about 500 miles. So I will plan on the 276 cam instead of the 268.

What I have been on the fence and getting help from @nm9stheham is the 11:1. Don't want the engine to be a PIA. But since I am doing the rebuild I figured I have 3 choices. In the kit in pistons are +4.7 or +23 or go custom, around +15, for extra money($100). But then I see, @AJ/FormS people are running 11:1 at much lower elevations. I haven't ordered the stroker kit or cam yet. I only want to do that once...
 
stumblinhorse said:
The intake I already have is a Weiand Stealth, that I will probably open up the ports a little. The Carb I have is a Edelbrock 600 that I will try and go up to 750 if I can't get it right. I have found that stepping down a size at this altitude makes tuning a little easier.

My plan for rockers is to break it in with the stockers, then get 1.6 rollers and new PRs after about 500 miles. So I will plan on the 276 cam instead of the 268.

What I have been on the fence and getting help from @nm9stheham is the 11:1. Don't want the engine to be a PIA. But since I am doing the rebuild I figured I have 3 choices. In the kit in pistons are +4.7 or +23 or go custom, around +15, for extra money($100). But then I see, @AJ/FormS people are running 11:1 at much lower elevations. I haven't ordered the stroker kit or cam yet. I only want to do that once...
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You can only run so much dynamic/cylinder pressure on 91octane before you have issues. Closing earlier than 46@.050 will put you on the edge ... and you dont seem a very capable tuner if you're here asking US for cam advice, bub, so I'd really think hard and try to understand what and why is being said.

I wouldn't use less than 278 duration or I'd drop the compression down for a smaller cam.
Are you building around a compression ratio?
Are you handcuffed to it?
 
MOPAROFFICIAL said:
You can only run so much dynamic/cylinder pressure on 91octane before you have issues. Closing earlier than 46@.050 will put you on the edge ... and you dont seem a very capable tuner if you're here asking US for cam advice, bub, so I'd really think hard and try to understand what and why is being said.

I wouldn't use less than 278 duration or I'd drop the compression down for a smaller cam.
Are you building around a compression ratio?
Are you handcuffed to it?
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Wow, thanks... I guess I am asking for opinions from people that might have more experience in this than I do. Not sure what a forum is for if not that. After I do this I will be glad share my experience with people. But at this point I have never built a 390 stroker 11:1 motor.

For the CR, there are not a lot of choices out there for pistons. So right off the bat I was thinking that 11:1 was too high for what I was building. But it is right on the cusp of ok at 7000 ft of elevation with AL Heads. I can build a 9.6 CR motor with cast iron heads and call it good, but wasn't sure I was selling the motor short at that point.
 
If you can afford it go hydraulic roller . I myself am done with trying to break in flat tappet fast ramp cams.
 
stumblinhorse said:
The intake I already have is a Weiand Stealth, that I will probably open up the ports a little. The Carb I have is a Edelbrock 600 that I will try and go up to 750 if I can't get it right. I have found that stepping down a size at this altitude makes tuning a little easier.

My plan for rockers is to break it in with the stockers, then get 1.6 rollers and new PRs after about 500 miles. So I will plan on the 276 cam instead of the 268.

What I have been on the fence and getting help from @nm9stheham is the 11:1. Don't want the engine to be a PIA. But since I am doing the rebuild I figured I have 3 choices. In the kit in pistons are +4.7 or +23 or go custom, around +15, for extra money($100). But then I see, @AJ/FormS people are running 11:1 at much lower elevations. I haven't ordered the stroker kit or cam yet. I only want to do that once...
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Whatever you do...don't DONT do this rediculous idea of breaking you engine in with stock rockers and then doing a change. Bad idea.

Get the rockers you want to run, the call B3 racing engines and have Mike get your geometry correct. And no, I don't care what name is on the rockers, they won't have the correct geometry. Once you get that sorted out, then start the engine. Why do all the monkey motion work that you want to do I have no idea.


Second things first. Why are you looking online to buy a cam. It's 2018. Pick up a phone and CALL someone who actually grinds cams and ask them. You have a unique situation. Why buy a cam that isn't specific for your application.

You can call:
Racer Brown
Cam Motion
Bullet
Mike Jones
Erson
Isky
And many others.
The top two provide me with 99% of the cams I use.

You'll be much happier if you call all of them, figure out which guy yet get on with best and buy a cam from him. I prefer to talk to the guy grinding the cam. If you call Racer Brown, call AFTER 5pm ET and he will answer the phone.
 
mbaird said:
If you can afford it go hydraulic roller . I myself am done with trying to break in flat tappet fast ramp cams.
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That is how I got to this! I started with a simple rebuild, then started looking for a 360 block, couldn't find one then decided instead of 360 I will stoke a 318 for a few dollars more! Now look at me, for another $$$ I could do a roller 11:1 390 that will put out 400HP.
 
stumblinhorse said:
@yellow rose thanks for that advice. I will do that definitely. I was worried that I don't know enough to have a good conversation with a grinder. But I call them.
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Trust me when I say a good cam grinder will make you feel way more comfortable about getting a cam than what you are trying to do by yourself. All the names I posted want to make sure you get exactly what you need. Their reputation rides on it.
 
I think your heading in the right direction for sure.
I wouldn’t run 11-1 at your elevation and the lack of 93 adds to the issue.

While I think the catalog cam is a good pick, calling a cam grinder is also fine. I just have noticed that if you call 9 cam grinders you’ll get 9 different cams. I am not trying to put a cloud over a custom grinder. Tell them everything about the engine and the drive train in the vehicle your using and you will get what you need and a what should be a better product than guessing at this.

Yellowrose is pointing the way well for you.

AJ is able to do what he does with the help of good math and years of experience from himself and what history has taught us all. Otherwise, pushing the envelope can be dangerous and disastrous costing more money and less than what was hoped for power.

Being that I live on an island, I can get away with a bit more (murderous builds) than you can. Some crap I have bolted together and run would just simply be ether junk or undriveable 5K feet up.

Go for the intake porting and bigger carb if possible. Stick with the .050 head gasket.
Your gonna like that mill when your done. Again, I think your heading is good.
 
That damn rabbit hole gets you every time !
The last motor I built I decided to keep my budget down and went with a hydraulic flat tappet.
After 1 wiped lobe and 3 sets of clicking lifters I am now assembling a new roller motor for that car. An extra 300 bucks seems cheap in retrospect .....
 
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