Small block 400

[HotRodPC]

Not all early 70's heads had hardened seats. I had a set of heads that were damaged as a result of unleaded fuel and IIRC, they were 73 Julian Dated heads.

 

[Green79Scottsdale]

Also, the chamber size (around 64 cc) is too small for a 400.

Why do you say it is too small?

Assuming a "stock" 8.5:1 CR, going from the stock 76cc to a 64cc will raise your compression about a full point, to around 9.4:1, on a 400. I see nothing wrong with that. Still fully compatible with pump gas and all the benefits that come with better compression.

 

[MadOgre]

Not all early 70's heads had hardened seats. I had a set of heads that were damaged as a result of unleaded fuel and IIRC, they were 73 Julian Dated heads.

Apparently they started installing hardened seats in 71' and still had non hardened seats up to 73' But anything 74' and up should have hardened seats from the factory.

 

[MadOgre]

Why do you say it is too small?

Assuming a "stock" 8.5:1 CR, going from the stock 76cc to a 64cc will raise your compression about a full point, to around 9.4:1, on a 400. I see nothing wrong with that. Still fully compatible with pump gas and all the benefits that come with better compression.

And depending on the cam you might even want to go a little higher to get your dynamic compression up to 9.2/3 or at the very least you dynamic compression will be lower than 9.4 which will work fine on pump gas.

 

[MikeB]

Why do you say it is too small?

Assuming a "stock" 8.5:1 CR, going from the stock 76cc to a 64cc will raise your compression about a full point, to around 9.4:1, on a 400. I see nothing wrong with that. Still fully compatible with pump gas and all the benefits that come with better compression.

I just did the math, and you're right! Guess I had my "zero deck" hat on.

However, pistons with big dishes (22cc-24cc) will need to be used to attain 9.4:1 or less, especially with iron heads.

 

[MikeB]

And depending on the cam you might even want to go a little higher to get your dynamic compression up to 9.2/3 or at the very least you dynamic compression will be lower than 9.4 which will work fine on pump gas.

Check those DCR numbers and you'll find 7.5 to 8.5 is the ideal range for a pump gas street engine. 9.2 to 9.4 would be detonation city.

 

[Green79Scottsdale]

I just did the math, and you're right! Guess I had my "zero deck" hat on.

However, pistons with big dishes (22cc-24cc) will need to be used to attain 9.4:1 or less, especially with iron heads.

You are right as well. With the calculator I used, I used a zero deck and 22cc dished pistons to achieve the "factory rated" ratio. A guy at work had a 400 with the pistons as much as .055 in the hole!! I think that figured to about 7:1! Talk about ****** compression!

 

[MadOgre]

Check those DCR numbers and you'll find 7.5 to 8.5 is the ideal range for a pump gas street engine. 9.2 to 9.4 would be detonation city.

Not quite. lol

A 9.4:1 SCR engine is probably gonna work out to be about 8.3-8.6:1 DCR Which falls with in your requirements for 8.5:1 DCR to run cruddy 87 octane fuel. Which is what I have already said, in the post that you are referring to.

So my point is valid if you quit nit picking everything I say to death, and actually listen to what's being said !!! Talk about OCD

 

[bucket]

Not all early 70's heads had hardened seats. I had a set of heads that were damaged as a result of unleaded fuel and IIRC, they were 73 Julian Dated heads.

My '70 350 still is running the original heads, and I don't run any kind of lead additive either. A couple older fellas have told me it's not needed because the original seats are now work hardened. Think I'll be fine?

 

[MikeB]

Not quite. lol

A 9.4:1 SCR engine is probably gonna work out to be about 8.3-8.6:1 DCR Which falls with in your requirements for 8.5:1 DCR to run cruddy 87 octane fuel. Which is what I have already said, in the post that you are referring to.

So my point is valid if you quit nit picking everything I say to death, and actually listen to what's being said !!! Talk about OCD

I did listen. Here's what you said: "And depending on the cam you might even want to go a little higher to get your dynamic compression up to 9.2/3 or at the very least you dynamic compression will be lower than 9.4 which will work fine on pump gas."

Why the name calling? I'll admit when I'm wrong or make a mistake, as you can see in a post above.

 

[MadOgre]

Yes I said "the DCR will be below 9.4" which is in reality gonna be 8.3-8.6 DCR. Am I wrong? Is that not gonna work on 87 octane? Is his motor going to magically increase in DCR and blow up? because I didn't word myself correctly? Are 64cc heads to small because of how I posted my comment? Are they gonna cause pre detonation?

Would it be wrong to raise it a little with a cam and run better fuel? Which if you read carefully, I did not say that you should choose a cam to raise the DCR to run pump gas !!!

I did how ever state that if the SCR is 9.4 your DCR will work fine with pump gas!

If anyone has cause for complaint against me it would be @firebane because I implied that he was talking about 70s heads when he was probably talking about 60s heads in which case he is somewhat correct. And I am an ass for taking to many pain meds and misinterpreting what he said. I admit that.

So maybe you have only done the same in which case I should just take it in stride?

 

[firebane]

LOL woah woah woah.. What is going on people. Time to take a chill pill and all relax lol.

Yes I was referring to 60s heads simply because that is the era that the double humps (camel humps) were mostly found Which the OP or someone in this thread talked about.

We are all a wealth of information and a bunch of crochety old men at times...

 

[Don5]

Moving forward I still think the 400 is a great engine.

 

[HotRodPC]

Hmmm, kinda looks like I need to pull this thread over. Has everyone healed from their butt hurt now? Quit being Mad Ogre or I'll send you to your room. Getting into Dynamic and Static compression ratio's is complicated and not everyone is going to grasp the theory right off the first time so it might have to be explained a bit more in detail. For example, I've not seen it mentioned how the cam affects the ratio in relation to being able to run pump gas. Hence, valve overlap and leaking compression... So maybe another pain pill to chill you out a bit more might work better. A bit more patience in your explanation. And then adding OPINIONS in the mix where there isn't a Right or Wrong answer, where as you're obviously old school and there is new school technology that some of the younger guys are more updated about. Though, theory never changes in old vs new school, but there is newer technology available. But OK then. Everybody is good right??? Moving on to more productive posts now I hope.

 

[MadOgre]

Im good lol