Clevo open chamber heads...

[Thom 6,651]

I can run 91 in my 302 headed 351 runs better on 95 or 98 but will still run on low octave wohput pinging all i did was minor grinding on the combustion chambe to drop con to 11.5, the closed chamber combustion chamber burns unleaded better by design

[gerg 10,871]

• If you ever want to run it on 91, keep the compression below 10:1.

 

•Do all your porting before getting the heads done, and just tidy up the areas that need attention, don't go opening up the ports as they flow well at that size. Smooth out the short-turn radius and blend the valve pocket into the port, and you've just gained more than any further mods could do.

 

• split duration cam, 2000-5500 rpm, keep it below 0.500" lift if running stock rockers.

 

• 3-angle valve job, 2-angle seat cut

 

• 30% heavier valve springs

 

• If fitting new valves, go with single groove collets.

 

• don't do too much to the exhaust, maybe blend the valve pocket a bit, and take the lip off the short turn. Keep the single cut seat, same as the valve. Don't go stainless unless you're running hardened seats, your engine builder will tell you this anyway.

 

• Don't use a high volume oil pump unless it's a race motor running loose tolerances/cross-drilled crank/high constant rpm. The 302 I just built never goes lower than 2/3 on the oil gauge, even at idle when hot.

[xcsam 10]

You'll be fine with 302 rods and a 4MA crank, just use the special ACL pistons and you'll be laughing.

 

You mean pistons like this one or something different?

http://www.ebay.com.au/itm/ACL-Race-Series-Cast-Piston-Ring-Set-Ford-351-Cleveland-V8-8mkry9351-/360585485735?pt=AU_Car_Parts_Accessories&hash=item53f491dda7

[bear351c 10,270]

Those will be for standard 351 rods, if you use 302 rods the pistons have the gudgeon pin higher in the casting, so they dont hit the heads/valves.

[xcsam 10]

Does anybody know anyone in Melbourne, or in Victoria that is reasonably priced and can help me with my open chamber heads?

[xcsam 10]

I spoke to Dave at AFD the other day. He was very informative. He said that my 2v open chambers are fine, but I needed the AFD stage 3 port, which will potentially get me 400-450 flywheel hp, with the option of increasing those figures in the future if I wish to. I'm very happy with the price as well. Just one question  though, i'm planning to use an Edelbrock RPM air gap or similar type manifold. Is it worth the additional price to have the manifold ported to match the cylinder heads? What does porting the manifold achieve? I thought that they were pretty good to begin with...

[gerg 10,871]

If you open up the head ports at all, there will be less gain if the manifold doesn't match it. They can't make manifolds any bigger than stock because if they did and someone bolted one to standard port heads, there would be a lip that the air/fuel smacks into, and would be a nasty restriction.

 

Instead, they leave plenty of meat there for you to carve away to suit your own ports. The process is called "match-porting".

[xeeclipse 37]

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!

 

 

Cam specs if you are interested.

 

Dude you should be using closed chamber heads, this thing is gonna fuel up like no tomorrow. Once it's built can you please put the car in a confined space with Mcfly and run it for 10 minutes to teach him a lesson?......

[xeeclipse 37]

Just sat back down with a coffee and realised I mistook the advertised figures as the .050" specs..... :$

 

Apologies Mcfly, but in regards to comp that dude will definitely need rocket fuel

[mcfly94 169]

Just sat back down with a coffee and realised I mistook the advertised figures as the .050" specs..... :$

 

Apologies Mcfly, but in regards to comp that dude will definitely need rocket fuel

Mate if im wrong tell me? just don't dismiss what I say, how on earth is anyone supposed to learn anything if people are like that?

[Thom 6,651]

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

 

 

 

Jargon edit

Take it easy mate, he's just a young bloke trying to learn his stuff (which he's been pretty good at so far) just because he's not 100% right doesn't mean he deserves comments like that, especially when your not 100% correct either. cam timing, valve events, cylinder bleed off, static compression and combustion chamber design all factor into the equation for what octane requirements the engine will need, a closed chamber head with a dished piston will 9 times out of 10 be capable of running regular unleaded at compression ratios even as high as 12:1 wheras a open chamber head with a flat top piston is usually craving more octane some where between 9.7:1 and 10.5:1, and that's a pretty big generalization I just made but it's a rule of thumb quite a few engine builders I know stick to it as a rule of thumb for street engines

[gerg 10,871]

or you try run it on 91 with that comp like xeeclipse suggests

I can back that up to some degree. My mild 302 pings its tits off on E10 but loves 98. It's only a skimmed closed chamber so it would be 9.5:1 max. Backing off the timing enough to stop it rattling makes part-throttle too doughy, even with vac advance hooked up to manifold vac. MSD programmable for Christmas please?

 

The clincher is the cam; it's only a Crow 270/280 (or 206/214 @ 0.050") so at peak torque, at around 2500 rpm, it rattles something chronic. A bigger cam could help but iron heads are considered old fashioned for a reason.

[slydog 7,873]

Mate if im wrong tell me? just don't dismiss what I say, how on earth is anyone supposed to learn anything if people are like that?

 

Most of us try to help around here even you do McFly so keep your replies coming.Not everyone acts like he doe's and as shown he was wrong anyway but that type of comment or attitude is far from helpful or not needed here.We can all have different views but we can voice them like adults too.

[mcfly94 169]

Most of us try to help around here even you do McFly so keep your replies coming.Not everyone acts like he doe's and as shown he was wrong anyway but that type of comment or attitude is far from helpful or not needed here.We can all have different views but we can voice them like adults too.

yeah I know.

 

back on topic, how can we derive a rule of thumb for octanes relative to comp?

Some believe you can run comps of 10:1 and slightly higher on 91.

Yet dads zj in the shed will ping if he doesn't get his octane up to about 108 and that's about 11:2 comp.

 

So really it depends on the combo?

[Thom 6,651]

It really is combo dependent on comp vs octane needs

[mcfly94 169]

It really is combo dependent on comp vs octane needs

Thought as much, so once you have a combo? how do you know what octane you need? just up the octane till pinging stops? surely not?

[Thom 6,651]

Experience basically, it's a dark art and im still leaning it

[PRO250 1,506]

with the price of fuel id never have close chamber heads funny my ute has them and monsta comp and its not a happy camper at all on any form of pump gas

 

open chambers are the go on any basic street engine

 

open chamber heded clevo in action bout time i thru this up on this forum stock 351 bottom end unported cast heads, i dont think this engine was even ballanced LOL and it cracked on the road it would burn the tyres doing 100kmg and all you had to do was push the go pedal

 

ran 12.0 on the day well a few times and with no sorting and about 6km on the clock

 

 

[Clevo120Y 815]

It all depends on the chambers themselves and the material used, a more modern fast burn chamber will tolerate more comp on less octane and require less timing also, alloy heads can also tolerate generally more comp on less octane. As mentioned it is all about the entire combo, things like cam, intake and exhaust design and dynamic compression all play an important part.

[gerg 10,871]

Funny, many engineers will tell you that for the same comp ratio, closed chamber is more efficient and able to resist detonation than open chamber.

 

The difference is in the quench design, which keeps the mixture swirling and moving around the chamber instead of stagnating in one spot: bad for detonation.

 

Open chamber heads were a cheap and easy way of dropping compression in early unleaded engines. Going up in comp will either need shaving the head or lumpy top pistons (or both): neither are really ideal.

 

They're not the first choice but if you have to stick with them they'll do.

[bear351c 10,270]

I always run closed chamber heads on my 351, never had issues with PULP or LPG. Each to their own, I guess. So many variables.