Small block question

[273]

What should a decent built 318 built to a 390 stroker make for hp? I know there are a million variables but average. Performance heads and I believe a 750 or 850 Holly double pumper….. It will go on a dyno but not now. I bought it built so I’m curious, it revs fast and sounds awesome! Any thoughts would be appreciated, thanks

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IT's probably making at least 1.2 lbs-ft per cid and peak hp around 5500 rpm


441 hp @ 5500 rpm
468 lbs-ft @ 4000 rpm

Would be my guesstimation

Cid x lbs-ft per cid = peak torque

390 x 1.2 = 468 lbs-ft

Peak torque x 90% = torque at hp peak

468 x 90% = 421 lbs-ft

421 x 5500 / 5252 = 441 hp

 

[Phreakish]

Great catch on the kickdown!
Repair/fix that before you drive it anywhere!
@CUDACOX has a 318/390, in his 68 cuda, he may chime in.

When I bought my dart, the kick down had been disconnected. Car had about 15 miles on it since the owner had swapped the carb and it was already too late. Trans failed after I hooked it up and had out about 60 miles on it (freeway). Clutches welded to a couple friction and I could no longer reverse, LOL.

It may already be too late for @bamech68. I'd be planning to at least put new clutches in it if the plan is to stick with the auto. Hopefully maybe it might be OK, I just wouldn't bank on it.

 

[66fyssh]

Let me add this also. For safety sake, it's best to have two throttle springs. The part stores sell them as a set with one spring fitting inside the other. If the one spring breaks, then your throttle will go wide open. If you have two, you're covered.

You must post up some pictures of the truck. Mopar or not, it sounds cool.

 

[bamech68]

Let me add this also. For safety sake, it's best to have two throttle springs. The part stores sell them as a set with one spring fitting inside the other. If the one spring breaks, then your throttle will go wide open. If you have two, you're covered.

You must post up some pictures of the truck. Mopar or not, it sounds cool.

 

[bamech68]

Disregard the first few, not sure how they made it in…….

 

[bamech68]

Cool little truck

 

[66fyssh]

Love the truck!!!

My wife wants me to build her the same gen 3100. She even found one but it got away before I could ask about it. Not sure if it was even for sale. Wife loves the grill on these.

 

[harrisonm]

xe268 isnt making 450

You are probably right. I was basing that on the fact that my mildly modified 340 with an Air Gap, 750 CFM carb, XE 268 cam and headers is at 370 HP. That is about 1.09 HP/CI. So with the OPs better heads and more cubes, I guessed 450. More cam might be a better choice, and the 268 might not make 450, but I bet it would not be Too much under that.

You guys kill me on these horsepower guesses. There isn’t enough info on this to even post up a guess. Lots of wishful thinking

You are absolutely right. I think that is why most of us are adding that caveat.

 

[harrisonm]

I’m asking for advice and anything you guys are willing to share, I will take and leave nothing. I’ll look into the linkage, thank you for offering your advice! The trans is the only thing not worked so I’m expecting it won’t last. What would you recommend?

The throttle linkage suggestion is actually a great thing to follow up on. I have seen a BUNCH of instances where people were wondering why they were not getting the performance they expected. Well, then the carb doesn't open up all the way.......
Also, I really appreciate your great attitude. Sometimes people ask questions and get irritated when members point out other things. You will get along great on this site.

 

[harrisonm]

Hey, @AJ/FormS, what do you mean by your comments on the fuel line? I looked at the pictures and could not figure out what you were talking about.
Thanks.

 

[AJ/FormS]

The fuel line seems to be going towards or across the fan, and the fan is a flexfan with no shroud.
Plus, at the track, yur only allowed so many inches of rubber line , which is all used up by the various jumpers.

 

[bamech68]

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The fuel line seems to be going towards or across the fan, and the fan is a flexfan with no shroud.
Plus, at the track, yur only allowed so many inches of rubber line , which is all used up by the various jumpers.

The fan is electric in front of the radiator

 

[bamech68]

The fan is electric in front of the radiator

That is an older picture …

 

[bamech68]

The throttle linkage suggestion is actually a great thing to follow up on. I have seen a BUNCH of instances where people were wondering why they were not getting the performance they expected. Well, then the carb doesn't open up all the way.......
Also, I really appreciate your great attitude. Sometimes people ask questions and get irritated when members point out other things. You will get along great on this site.

Thanks, I know what I don’t know and appreciate all the input!

 

[SpeedThrills]

That looks like a 600 cfm vacuum secondary. At least it looks like the one I had in the 70's. Could be a different ball game now.

In your first post, you mention that it has a 750 or 850 double pumper. From the "agree" clicks I got on this post, I guess I'm right.
Look for the list number on the air horn. If you're not familiar, google: "holley list number location".
With 390 cubes, it'll like a 750 a lot more.

 

[TT5.9mag]

The list number on the front of choke horn on the carburetor will tell you exactly what carb you have. Regardless of what it is, (it’s not a double pumper, or an 850, or 750) you’ll need the Holley bracket for correct mopar throttle pressure activation.

Info here.
How to set up a Holley 4 bbl for a Mopar

 

[bamech68]

I’ll check that out, thanks

 

[bamech68]

The list number on the front of choke horn on the carburetor will tell you exactly what carb you have. Regardless of what it is, (it’s not a double pumper, or an 850, or 750) you’ll need the Holley bracket for correct mopar throttle pressure activation.

Info here.
How to set up a Holley 4 bbl for a Mopar

I just ordered that bracket, thanks!

 

[bamech68]

What would be a good transmission for this combo? Again 8-3/4 rear, not sure what gears…

 

[66fyssh]

904 transmission will hold up just fine.

 

[bamech68]

I just ordered that bracket, thanks!

Just found the receipt, 600 cfm, you were absolutely correct!

 

[bamech68]

Cam and heads

 

[pittsburghracer]

Boy Edelbrock heads aren’t cheap horsepower anymore are they.

 

[crackedback]

that cam with a good tune will make 425-435 pretty easy

 

[Dale Davies]

What should a decent built 318 built to a 390 stroker make for hp? I know there are a million variables but average. Performance heads and I believe a 750 or 850 Holly double pumper….. It will go on a dyno but not now. I bought it built so I’m curious, it revs fast and sounds awesome! Any thoughts would be appreciated, thanks

View attachment 1716035294

View attachment 1716035295

With that manifold, I would be looking at a carb with annular boosters in the primaries. I hear the 950 works well. It is a hybrid carb and they put annular boosters in.