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I might be getting a balanced 390 with alum scj, or cj heads from a friend (if he decides to sell). The whole story is the engine was built by a frend of this friend (an engine builder, not a backyard shade tree) and he was going to put this in a sleeper project. The frend of the friend decided to go with a 460 instead so he sold the 390 to my friend. He needed an engine for his pickup, so the friend of the friend detuned the engine becasue it was going in a work horse pickup (and would be way to much for the truck the way it was). Before they detuned it, it was in the 5-600hp range, and is currently in the 300 something range.
I think the shortblock was left alone, but don't know. I wanted to 'retune' the engine, but was wondering if it could be put back up to its former glory by a cam swap (it was changed for mild manners and low end trq), headers, single plane intake, and a big carb?
I am a little shaky on what they do to 'detune' and engine so if you could point me to a source or something, that would be awesome.


thanks!

 

Red so many of your phrases have no meaning.

You need to state the specks before & after to allow someone else to understand tuning and de-tuning.

If I may,




John

 

Sadly I don't know. I was asking a general question and was hoping for a general answer. e.g. would you have to change the comp ratio to lose 300 hp? or would that be simply from a cam/carb swap?

 

How about you talk to the guy who ''Detuned'' it to find out exactly what was done?

OJ

 

that is part of the plan, but wanted to find out what I could beforehand. The builder is a very busy guy and tough to get ahold of, so it might take me a month to find out this stuff. So I was hoping to at least some imput on pumping it back up.

 

Let's try a different approach,

1- Ask the seller what is he offering you exactly?

2- What is the asking price?

3- Will you be getting a running or ready to run engine?




John

 

In some cases, they "detune" an engine just by changing the cam timing. However, you mention a different cam being installed to do the "detune".

The problem is the compression. If the engine was in the 500-600HP range, I bet it had high compression and a big cam.

Without lowering the compression (pistons), or at the very least using thicker head gaskets, a smaller cam or changing the cam timing, it sounds to me like this engine will have some "issues" in terms of pinging easily.

You really need to find out what pistons were used, which heads (Edel, I'm assuming, because you say aluminum), and which cam, and what was done with the cam timing.

 

Yeah i like to find out how you build a 600hp FE..and detune it to make 300hp...and have it still idle or even run...Maybe they pilled 3 plug wires off ?? and I dont care for the friend of a friens aunts borthers nephew built it idea without being able to talk to the man in person.. Sounds like a bunch of BS to me..nd price alone will tell you if it was ever a 600hp motor.. Is he asking $12K to $15K for the motor ?

 

I agree with Russ. Get hold of the guy who built the engine and ask him what was done to it.

Swapping out cams makes sense to change a 1/4 mile race engine into a RV/ truck load hauler. And if that's so, it probably all that was done to it.

Now if you can't find anything out, (and I'd be suspicious if you can't), you can tell some things from looking at it. Aluminum heads will stand out. Remove a valve cover and check the valvetrain set-up. I doubt a 500-600 Hp engine will have stock rockers, rocker shaft supports, etc. Check the intake? Is an aluminum 4-barrel one? Basically, look for signs of aftermarket parts as best you can. For example, if it's a cast iron 4-barrel, it's probably original and I doubt it was ever a 500-600 Hp engine.

Not many people want to change a race engine like this, but if I was going to do it, all I'd change is the cam. Basically, it's consideration of cost and effort.

All in all, if the price is really good, and it runs, go buy it. You might be dissapointed, but perhaps still have a decent engine.

 

thanks for the tips.
I have been talking to my friend about this motor for over a year and just recently asked him how much he wanted for it (the whole truck actually, it's in a clapped out 69 f250 that he had plans for). He had a single plane (I think streetmaster) intake on it but swaped on a duel plane alum to get better low end and a lil better gas mi.
What he told me (before I asked to buy it off him) was that he asked his friend (who was a pro engine builder at the time) to build him a good 390 for his truck (300-350 hp ect ect) and the friend told him that it would be $12-1800 to build it like that from scrach, but he had a hot rod 390 that he would detune and sell to him for $300 (the shortblock, he paid another $600 for the alum heads). So my friend decided to go with that instead.
so, hopefully... it is only a cam swap away from being a beast again. I'll definitly get ahold of the builder if I go for it, but wanted to make sure that a comp change was not a reg thing for 'detuning' and that a good cam and big carb would add 300 hp back to a motor.

 

Good luck with this, but you may note the price range Russ mentioned, and that may not be far off for a 500-600 Hp engine. I doubt $1200 to $1800 would get you in that Hp ballpark even if the labour was free.

It's also doubtful someone would merely change cams (and maybe intake)and drop the price to $300. The cost of the new cam alone, plus lifters and gaskets might be be about $300.

I'm very trusting, but in this case, something smells fishy.

 

I know they were good friends for about 25 years, so he may have done the cam change ect for the cost of the parts. but, I dunno.
The 600 hp was while it was in a hot rod, my friend wanted more than stock (thus the 300-325 hp build he was planning on) but no where near the 600, so the friend gave him a deal and sold him the detuned engine.

just to clear up something, $1800 Should be enough for a slightly more than stock rebuild, right?

Anyway, I really appeciate your input, it helps a lot.

 

To get 600hp out of a 390 it would NEED nearly fully ported aluminum heads, complete roller cam/valvetrain, high rise aluminum intake, etc. Then a bottom end that wil hold it. Probably 13:1 compression or more. Like Russ said, major dollars. I'm putting a 390 together now with fully ported alum heads, port matched high rise intake, roller cam, etc. and it's only going to be about 525-550 max. Takes a lot more than a cam swap to lose 300 hp.

What I'm building is a 6500rpm motor. If I built it to run 8000+ it might make 650hp.

 

For $1800 you might get an improvement over stock if all you did was new rings, bearings, valve job, gaskets and a different cam and lifters. And that's doing everything yourself, including honing...only the valve job farmed out...but that's not going to bring in huge HP gains over stock, or if it did, the engine wouldn't hold together long.

But yet, it might be a noticeable imporvement over stock, yet not a totally rebuilt engine.

My suggestion would be that if you can get it at a decent price (under $1000 "IF" it has the aluminum heads), then buy it, tear it down, see what you've got and start sorting out what you want to do and what you can afford. Talk to your local machine shop, and come back here and ask specific questions on various parts as you discover them if you like.

And be prepared to find major problems, like a cracked block or head. May not be likely, but it's when you're on a budget that you are usually tempted by a pig in a poke.

 

Ok, that sounds like a good plan. Will do.