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Clevo open chamber heads...

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G'day members. Today I got some 2nd hand open chamber heads from a 351. They've been cleaned, sand blasted and crack tested. I know that this is a bit of a 'vague' question, but what should I think about doing to them. I would like a 'moderate' upgrade. Port and Polish? Bigger valves

 

I have been collecting parts for many years. I've got a Holley 750 vac sec carby, tri-y extractors, twin 2.5" exhaust system, but the rest of the engine is undecided. I want a 351 as a minimum, possibly a stroker kit. I am wanting to make 400hp at the flywheel.

 

I know that the cam will also be an issue, but what is the best option for the heads?

 

PS- it's an XC ute, I have a 5 speed manual, and i'm tossing up between keeping the 2.92 diff, or get a 3.5 or somewhere in between.

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The reason that I got the open chambers over the closed chamber is that I was specifically told by some of you guys on the other forum that the open chambers are more suitable for me.

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G'day members. Today I got some 2nd hand open chamber heads from a 351. They've been cleaned, sand blasted and crack tested. I know that this is a bit of a 'vague' question, but what should I think about doing to them. I would like a 'moderate' upgrade. Port and Polish? Bigger valves

 

I have been collecting parts for many years. I've got a Holley 750 vac sec carby, tri-y extractors, twin 2.5" exhaust system, but the rest of the engine is undecided. I want a 351 as a minimum, possibly a stroker kit. I am wanting to make 400hp at the flywheel.

 

I know that the cam will also be an issue, but what is the best option for the heads?

 

PS- it's an XC ute, I have a 5 speed manual, and i'm tossing up between keeping the 2.92 diff, or get a 3.5 or somewhere in between.

im no guru on clevelands but if you only looking for 400hp fly, just use the standard 351 crank and rod combo, just get the refinished and arp bolts fitted to the rods, they do rev! as long as you have everything balanced.

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I just had my open chamber heads done up. I had them surfaced, oversized valves, valve seats relined, mild port and polish, fitted with Manley valves, crane seals, crane springs and crane retainers. I am going to run crane silver series roller rockers, pushrods and guideplates and a crane something or rather cam with and edlebrock performer manifold witha 600vac holley. If this helps you!

 

headsncam8.jpg

 

Cam specs if you are interested.

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I just had my open chamber heads done up. I had them surfaced, oversized valves, valve seats relined, mild port and polish, fitted with Manley valves, crane seals, crane springs and crane retainers. I am going to run crane silver series roller rockers, pushrods and guideplates and a crane something or rather cam with and edlebrock performer manifold witha 600vac holley. If this helps you!

 

headsncam8.jpg

 

Cam specs if you are interested.

only a small cam hendrixhc? what power you aiming for anyway? should make for an awesome cruiser!

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only a small cam hendrixhc? what power you aiming for anyway? should make for an awesome cruiser!

 

No real figure on mine Bud. Long as the bastard starts, runs and beats Hyundias off the line ill be happy!

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im no guru on clevelands but if you only looking for 400hp fly, just use the standard 351 crank and rod combo, just get the refinished and arp bolts fitted to the rods, they do rev! as long as you have everything balanced.

 

Ive gone for 30thou os SRP pistons and balanced bottom end with all ARP fasteners. I have steered away from anything with PRO or COMP in the title!  ;)

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With the standard crank and rod combo. What sort of power figures can I look at before things start to break?

alright to give you an idea as to what they can handle

dad spins his stock crank rod setup to 7500rpm, flat top pistons, runs 850quick flow carby, custom solid cam with 650lift, alloy chi 2v heads, high rise chi manifold, and thats at about 550hp at the flywheel.

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STD crank and rods, good for 7000rpm. A workmate builds 351s for his ski/race boat and uses 4MA cranks and reckons they're good for 7500. You won't need to spin it anywhere near that hard to meet your target. 400 hp is easy for clevo bottom end, just make sure it's all balanced.

 

Open chamber heads aren't as efficient as closed, and need a few more degrees of timing. They also need a split pattern cam with more exhaust duration to scavenge the larger chamber. Std comp is 9.2:1 from memory. Give them a skim down 20-30 thou, (any more might affect your pushrod length), and that will take the compression up maybe half a point.

 

I didn't catch whether you've got 2Vs or 4Vs, but I assume they're 2Vs. In that case, they respond well to cleaning up around the bowl and short turn, and maybe take a bit out of the roof at the mouth, both inlet and exhaust.

 

Don't go for too much of a cam. Torque is what V8s are all about, and a grumpy, peaky engine will give you the shits in no time.

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Nothing wrong with closed chambers I've run the on my 351 in my customline for over 3 years, i used to have open chambers on it with same short motor, it was no where near as responsive or torquey as the closed chambers

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LoL. It's obvious that I don't know much about V8's, as others had said that open chambers were better for my needs. Oh well, if the open chambers are "nowhere near as responsive or torquey as the closed chambers", I guess that's ok, because my daily driver is a non-turbo 2H diesel HJ60 Landcruiser, which does the 1/4 mile 41 seconds. 

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alright to give you an idea as to what they can handle

dad spins his stock crank rod setup to 7500rpm, flat top pistons, runs 850quick flow carby, custom solid cam with 650lift, alloy chi 2v heads, high rise chi manifold, and thats at about 550hp at the flywheel.

Thanks for that info, I strongly doubt that i'll ever break those figures, even if I want to.

 

Judging by your responses, I get the impression that I have to match the cylinder heads with a particular camshaft- eg I cant just modify the heads and then decide which cam im using?

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In my opinion you need to decide a compression ratio first which determines open or closed chamber heads, low to mid 9's with open and low to mid10's with closed, low comp means you will need a cam with less duration, higher comp can have more.

Then modify heads and get flow figures, this determines the lift of the cam, there is no point having 600+ tho of lift if the heads don't flow past 500tho lift. So you match the cam lift to the heads.

So really you decide comp first, then modify heads then decide the cam.

This is just a basic basic approach, as the rest of the combo has to be well put together and tuned properly.

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The closed chamber heads will give you increased compression over the open chamber ones. Get them re-surfaced, triple angle valve job, port match them to a "good" gasket , (ie Felpro, not the cheap chinese stuff), polishing is wasted time unless you want mega horsepower. Get the heads cc'ed, and work out your compression ratio. Trouble free motoring..... :)

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Thanks for that info, I strongly doubt that i'll ever break those figures, even if I want to.

 

Judging by your responses, I get the impression that I have to match the cylinder heads with a particular camshaft- eg I cant just modify the heads and then decide which cam im using?

u gotta match the cam to what revs u wanna pull what comp ratio ya got etc etc then ya match ya torque conv. and diff gears and wam bam u got ya self a package

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OK! So the closed chamber heads have more compression. You said that I need to decide the compression ratio that I want before I do anthing else. You also suggested that the comp ratio for 351 with open chambers is around 9.2:1 as standard. Correct me if im wrong, but alot of you guys with these big power engines are on between 10-12:1 compression. What can you do with say 11:1 compression ratio that you cant do with 9:1? What's the difference? How do I decide what compression ratio is right for me? Remember I said that I want 400hp at the flywheel with a MINIMUM 351 (i'm leaning towards a decent stroker kit like 393 or 408- though not procrap or anything like that).

 

I also have a set of 6.125" rods from a 302. Can I up my compression with these rods and some specific pistons? Thanks for your input so far guys.

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A 351 is as big as you can go with 302 rods. No pistons exist for 6.125 rods on strokers. In fact, the more you stroke it, the shorter the rod has to be.

 

More compression is more efficiency. It enables more energy to be released from combustion. Squeezing the mixture into a smaller space makes it burn faster and more completely. It's basically free horsepower, up to a point. Go too big and you'll have detonation problems. Iron-headed street engines might be ok up to maybe 11:1, depending on the cam you're running.

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Stroker kits are great value these days.

The difference between the compressions is dynamic compression, which is the comp when the engine is running and what's left after cam overlap, overlap bleeds off comp, bigger cams have more duration and overlap, so if you start putting a big cam in a lower comp motor it becomes sluggish and dosen't perform in the bottom end, it will allow the engine to rev harder but won't be any good to drive. If you start with a higher comp you can use the advantages of a bigger cam without going too low in dynamic comp. hope that makes sense

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OK, thanks for the advice guys. I'm sort of starting to understand where you're coming from (a bit :wacko: ). What compression do I need to aim for if I am going to run the engine on regular unleaded, or is my understanding heading in the wrong direction, lol?

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OK, thanks for the advice guys. I'm sort of starting to understand where you're coming from (a bit :wacko: ). What compression do I need to aim for if I am going to run the engine on regular unleaded, or is my understanding heading in the wrong direction, lol?

definitely wont run regular on comp around 11.2:1, that needs ultimate with possbily octane boooster, or it will ping

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I just got myself a 4ma crank, and another virgin block yesterday (so it's not going to be a stroker anymore). I've already got the 302 rods, now the 351 crank, open chamber heads, holley 750 vac carby, tri-y extractors, twin 2.5" exhaust Tremec V8 T5 gearbox. I'd like to do some minor upgrades to my heads, add something like an edelbrock performer intake, suitable pistons, maybe 3.23 or 3.45 diff and a mild/moderate cam.

 

I was speaking to an engine builder about what you guys have said about finding the right compression ratio as I still cant completely understand. He said that I've "got to know what I want to do with the engine". I say that I want a street/cruising engine that I can run on regular or 95 unleaded, that sounds really nasty, but is not a pig to drive.

 

What am I going to get if I put this engine together with the stuff I have (adding all the components I need)?

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