408 SB with 318 Heads?

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360duster

360duster

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Hi Guys,

im in the process of building a 408 for my valiant. Due to the lack of money i have to do it step by step. I don´t have cylinder heads now, dream about using the RHS X-heads in the future. With a bunch of other parts i got a set of rebuilt 318 Heads and wonder how they would work on the 408. What do you think about, is this idea totally BS or will they work to 4500 rpm for example? Just want to check if i can use them to get the car on the street with V8 (sorry to the slant 6 lovers, it´s a great engine but i need more power.....:-D), later i will swap for sure to another head with better breathing capabilities.

Please let me know what you think about, thanks!

regards Michael
 
It will probably run like a 318. Heads are where the power is and they are a really bad place to not spend money. I would build the engine the other way around. Start with an old 318, put on a good top end (RHS and maybe an RPM intake), then when you have the money you can build a 408 bottom end.
 
I think those 318 heads you have will choke the crap utta the engine but, if it gets you rolling down the road, use what ya got. And if you got 318 heads ready to bolt on, OK! Don't purchase 318 heads though. Your better off leaving it on the stand if you need to purchase heads.
 
Thank you guys for your opinions! I know that it´s not the way to make power, but as rumble and Babyblue said i can get it on the street - and that´s what i want the most. Saving for a good set of heads would make me wait another year, with the heads i already have i can get it on the street next year.....and get the better heads later.

@rumblefish360: i needed a trans for the SB swap and got a good deal for a complete engine / trans etc. out of a running car (guy swapped to BB). These heads were recently rebuilt. If i had to buy only the 318 heads then i would leave them.

@Babyblue66: for this combo i thought about sth. like a comp XE262H or XE268H.

Again, thanks for your thoughts and opinions! maybe i win the lottery....:-D

regards Michael
 
You are wasting money putting it together like that. The cams are TINY. like regardless of heads they will disappoint you. With the heads you propose to use, it will idle like a pro. It will not do much past 4K if that high. I will run, but not make any power. I'd leave it on the stand before you toss good money into such a futile effort. Sorry, but you're building a 4" stroke industrial engine. Not even a passenger car engine.
 
Agree with what has already been said,too little cam not enough head..don't waste your time..
 
I feel constipated just thinking about it! Maybe put the entire 318 in there for a while, if you have one.
 
It is doable but... one more thing that has not been talked about is compression. If you put the small chamber 318 head on there compression might be throught the roof on that 408 engine. It really is dependant on how you are building the engine, but at somewhere near 0 deck you would be looking at 12 to 1 compression. So you would have an engine that wouldn't run on pump gas and runs out of steam @ 4000 RPMs. It would be a torque monster though, and might have something like 300 Hp @3850 RPMs hahaha

So I vote run the 318 for now, get used to the baby V8 then swap the monster in there.
 
Ok guys, now i got some good facts, im convinced to do it not - i imagine the industrial 4" engine like moper said and now i forget this idea. Thanks at all for your help!

regards Michael
 
that industrial motor reminds me of my brothers john deere model d!! 501 cid 6.75 bore x 7 inch stroke!! only they run outta steam at a blistering 900 rpm! :cheers:
 
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