i ordered some stuff for my 390. wanted to know if anyone had any experience with a setup similar or a desktop dyno. bought a set of dougs 664r fenderwell headers, edelbrock performer rpm intake, and a compa cam 33-238-4. pulls 1300 through 5500. just curious what to expect from this combo. was thinking bout going a little bigger in cam to one that pulls 1500 through 5800. not sure though. going to be running a holley 750 on it.

thanks

 

You guys related?

https://www.ford-trucks.com/forums/7...-my-build.html

Check the Hot Rod link, they use aftermarket heads. Check last post, he is running a 390 with this cam gives other info on his build.

Compression?

 

huh, didnt see that link, i definately searched, but only through about 8 pages. thanks for the link, so, with this cam, will i be able to run regular or will i be running premium? looks like regular, but could you clarify?

 

RE: 87 octane, don't know. The fellow with CR in the 10s has to run premium.

I think if you have CR in the 9.5-9.7 range, you will still get the best results in this engine with timing out to 12 degrees and premium fuel.

Others who have actually done more than drive and reassemble stock 390s and read a lot on this site may chime in.

Note my previous disclaimer in the form of stating my estimate was a WAG.

 

my engine is a stock truck motor. 8.6 cr

 

I don't think you'll be happy with that cam at 8.6-1 cr. The compression ratio figures greatly into the the hp/torque curves. For best performance you have to match the cam to the static cr of the engine and shoot for as high static cr as possible without detonation (pinging). It's kind of like this....you can run higher static cr if you have more cam as the cam will lower the dynamic cr. At any rate, for the 33-238-4 somewhere around 9.5 - 1 or a little higher is about right. If you're over 10 to 1 then it's probably gonna ping unless you run premium...don't ask me how I know...LOL. Other things do factor in this. Read some of the threads about quench. In general, for best quench on a typical FE head you want a zero deck....meaning the pistons come right to the top of the deck. One way to cheaply raise the CR on a truck (low compression) 390 is to use 360 pistons in it. The 360 pistons have a different pin location plus they a true flattop with just the valve relief cutouts. I used these in my build and have been very happy. They will put the piston top within about .010 of the deck...not bad...and if your inclined then you can deck the block to finish that. There are also a few head gasket options that you can use to fine tune your cr...everything from a steel shim....thinnest at about .018 compressed....to a thick composite that is around .43 compressed....don't quote me on those #'s....memory isn't what it used to be lol. At any rate, you can check out the different head gaskets and you'll discover what I'm talking about. Also, get all the specs on your engine and use one of the online compression ratio calculators. It will help you design your build. Shoot for 9.5 to 9.7 CR and I think you'll be very happy. My build is pretty much what you're talking about. In my gallery you can find a lot of engine buildup pictures...some of them will show you some of the things I've talked about.

Good Luck!

Tracy

 

all i did was call comp cams and told them what i had and thats what they recommended. they recommended actually going to a bigger cam, one that pulls starting at 1800. they said this cam will have no problems with the low compression ratio. i would hope that they have people there recommending cams who know what theyre talking about in making the recommendations.

 

No PROBLEMS with that cam and low compression, but what I think Falconstng is saying is that YOU won't be happy as you'll be wondering why you don't have more power to show for your efforts. The low CR results in lower power.

Make sense?

 

What Tracy is saying, the cam will work with the combo ! But, to get all you can out of the cam and the best results from your motor you need Compression ! and some head work wouldnt hurt either..

And with the cam companies know day..they just want to sell the cam..Hell there not driving your rig....They could careless.... Tracy was just suggesting you compliment your cam with some other work, So when you lite it off the first time...You know something is under the hood...other than a low Comp motor that goes bumpity bump at idle but runs like a turd...But alot of guys want that..Because they want to sound cool even tho the rigs wont get out of there own way....JMO

RJ

 

so what you just go get stock 360 pistons and it will jump up your CR? hmm i may have to do that. what will that bump it up to?Mitch

 

390 pistons are available in several CR, depending on your heads. Bigger chambers = lower cr with a given piston.

I don't think 360 pistons will work at all.

Lots of info here, but what you really need is the combustion chamber volume in cc's. This is a known item as there aren't that many 390 heads, perhaps those better informed can tell you. If you carve into the chamber to unshroud valves or smooth it out, that will effect it.

United Engine and Machine Co.

 

Actually 360 pistons do work. In a 360 the rods are different length and the standard flattop 360 piston makes for a low compression engine. The 360 and 390 are the same bore though. The same piston that makes low compression in a 360 will work nicely when used with a 390 crank and rods. The piston pin height is different and because they are flattop with just the valve relief then your piston top will end up pretty near the deck height....giving you somewhere around 9.5 - 1 up to maybe 10 - 1....all depending on your head cc's, where the piston top actually ends up, and the head gasket that you use. I learned this trick on this forum a few years back. Back then you could get stock cast 360 pistons at a really good price. I believe that there has been some change in the parts and that the cheaper ones are no longer available. Take a look at my gallery and you'll see .060 over 360 flattops used in my 390. I used D2 heads that were ported, polished, surfaced, and I started out using the Mr. Gasket Steel shim head gasket (minimal gasket thickness for higher compression). Unfortunately for my engine, I pushed the compression ratio too far with the cam I used and I got stuck having to run premium fuel. Not that I mind too much as I built it for play and I don't use it as an everyday driver. At any rate, there are a lot of piston options out there and a lot of different costs. Back when I built my engine I used the 360 pistons because they were the cheapest way to get to the compression ratio I wanted. If money is not an object or you're targeting higher rpms....spraying it....or just want to be able to abuse it more then there are better pistons to use.

Good Luck!

Tracy

 

Mark me a failing grade at reading your prior post. Thanks for the update.
I'll be quiet now.