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Mr Polson

Building a Clevo

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Righto everyone, I'm slowly beginning to gather bits and pieces for my Clevo build, and need some advice. 

 

Firstly, its a 302 from a very early XB. It will be staying 302 unless someone has a cheap set of '51 crank and rods/pistons all in standard size and requiring no work. Its not bored, and doesn't need it (not out of round or anything), so it'll be staying as it is. I am on a budget for this.

 

Heads are 2V closed chamber, and haven't had any work done to them from what I can tell.

 

Now, my aim is for it to be more powerful than stock (obviously), but I still want it to be easily streetable, and daily driven if the need was to arise.

 

Will be replacing just about everything as I do this build.

 

So far, I'm looking at getting single groove valves/collets, good pushrods, roller rockers, new lifters, new cam (hydraulic), new ignition system (something decent but not a really expensive system), a carb of some sort, an aftermarket intake manifold, and it will have headers of some sort, and anything else I haven't mentioned that needs replacing.

 

So, what I need is advice on if I should do any work to the heads, what to look for in a cam (I don't really understand how to decipher all the lift, duration, etc, like I know what it means but not how it affects the motor), good brands (dont worry, I know NOT to use procomp), and any other advice that is needed for building a good decent Clevo!

 

If I've left out any info that you need to offer decent advice, ask and I shall provide!!

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as good as a tidy 302 can be you have to turn them past 7000 to have any kind of grunt and there dogs down low like that

 

as much as you want to use what you have to save money get a 351 crank and rods, for the extra $$$ you will have 50 cubes of extra power before you even add intake, single groove valves, so on to suport more power skimp these bits as there easy to add later for little cost

 

ive been in real basic 351s that pull like trains and are nothing engines ive not yet been in a 302 that have impressed me and ive been in a few

spend on the bottom then do the top when the money comes, it will be fine with a cast intake stock dissy and multi grooves for the (get it going buildup) then upgrade as the money tree recovers

 

remember V8s need to go like a V8s not a stock ba falcon

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Yeah sounds like you wanna make the top end and cam decent but for what? A stock 302 bottom end. No point putting roller rockers on that. If i was you i would pull back on single groove valves, r/rockers etc and spend more on the bottom. A good 351 bottom with some comp and a mild cam with std heads cleaned up will give you a much better result and as dave said then later on you can build on the top end.

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I agree with the fellas above, the only thing I would go with is the single groove valves for security, using your closed chamber heads and a 51 bottom you can afford to go a bit bigger with the cam also which will be bring a bigger smile to your face.

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The issue is finding a 51 crank and rods that are standard size and in good nick, might be easy up on the mainland but its a bit harder down here.

 

I want to build the whole motor before it goes in, no rush to do anything, once its in the car I want it staying in and staying together.

 

I need a manifold and dizzy because I don't have either, I'm NOT going to go and buy stock parts and then replace them later.

 

I'm not stressed about making large amounts of power, its mainly going to be a weekend cruiser, not a drag racer.

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If you're replacing the pistons, get the ACL ones with higher gudgeon pins to suit 302 rods. That way all you need is a crank. In the scheme of things, a crank grind doesn't break the bank. However, if you stay with a 302, I reckon you'll be reasonably satisfied with 300 hp, or 1hp per cube. That's a nice street motor that will fire up and purr every time.

 

They were (optimistically) rated at 240 stock, so an increase over this needs a decent, split-pattern cam and nice exhausts. Intake could be something like an Edelbrock air gap. They're pretty popular for an upgrade over the stock 2-barrel, but less of a jump from the later 4-barrel 2V, which are actually pretty good.

 

I'd go for a Holley 600 vac sec-type carby, but here's an idea: why not the Holley 570 truck avenger? They come with annular boosters which are good for filling in the hole down low where a big cam would give grief. Annulars are better at atomising the fuel, especially at lower speeds so the torque is stronger but the tradeoff is top end, thus why they're not rated at 600 but 570 cfm due to the (slightly) more restrictive boosters. It would make next to no difference on a 302, this would be my choice of carby. Or a remanufactured Rochester.

 

Ignition, well the stock Bosch electronic is pretty reliable, MSD in recent years seems to have some bad reports of reliability. I like the old oil-filled coils. The newer resin type ones seem to just fail with no warning.

 

2V clevo heads flow better than any factory Windsor head ever built. That said, they often need work on the short-turn radius (these are nasty and sharp) and the bowl needs blending to unshroud the valve a bit. The guide bosses can do with some streamlining and the roof of the mouth can take off 2-3 mm to about 2 inches into the port, then match the manifold face to it. That's about it, this will gain the most for your port work, any more and you're spending hours chasing the last 10 hp. Get some back-cut valves, maybe 3-angle cuts but only on the inlet. Exhaust needs nice wide single cut seats to conduct heat out of the valve.

 

Hope this helps.

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Thanks Gerg, that info should help regardless of whether I stay 302 or go 351 :)

 

No matter which one I go I'm still going to have to choose a cam (yes I know the choice will depend on cubes), the problem I face is I don't understand all the different specs of a cam and how they work together.

I know the basics, like lift is how high it lifts the lifter/pushrod thus opening the valve further, and duration is how long it's open/lifting whatever, and overlap is to do with how long both valves are open.

 

But can someone explain how exactly it all works together and what to look for/how to decide on a cam?

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When looking at the specs, ignore the advertised duration (the longer one) as this is not indicative of the true characteristics of the cam. Instead, look at the duration at 0.050" valve lift, that is when all the slack/flex in the valvetrain is taken up and when flow actually starts to happen. So if advertised duration is around say 280deg, then duration at 0.050" might be about 210deg. Lobe separation can indicate how much overlap the cam has but not always. It also depends on the shape of the lobe. Nevertheless, it's a general indication of how much overlap there might be.

 

With a given duration, if you have say a 108 deg LSA, then it will have more overlap than 110 or definitely 112. The narrower you go in LSA, the more scavenging effect at higher rpm but at the cost of low-rpm torque due to exhaust gas actually bouncing back into the cylinder, and will give a rougher idle. Scavenging needs a good exhaust to work, so running stock manifolds and single 2-1/4 with a wild cam is a silly move.

 

If you go wider in LSA, it will tame the idle somewhat and be more torquey but will start to run out of puff sooner. Go too wide and you'll drop volumetric efficiency because the inlet is open for too long and mixture will be pushed back out of the cylinder before it closes again.

 

Playing with cam timing alters the engine speed at which the cam works best. Advancing brings the rpm band down, retarding brings it up higher. A barely tolerable cam in a 351 might be too hairy for a 302, general rule is that things happen 500rpm later in a 302, so torque and power need more revs to start happening. You could advance the cam a little to compensate for the smaller engine but I'd just go one step down in cam size and install as instructed.

 

One thing about Clevos is that they like more exhaust duration, due to the fact that while the exhaust flows quite well, it's quite a lot less than the inlet. It's less than the accepted formula of 70% (or thereabouts), so to compensate, they make cams over a certain size with what they call a "split" duration, where the exhaust is held open a bit longer than the inlet to allow more complete scavenging.

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Forgot to reply to this!!

 

Thanks for the detailed posts gerg, think I'm starting to understand it now!

 

All you earlier posters will be happy to know I've found a set of 351 crank and rods... Just have to actually buy them (have some other things to come first).

 

So, anything I should do to the bottom end once I get it? Will it be right to just use crank rods and pistons as they are, or is there stuff I should do to them?

 

What sort of CR will I have with 351 crank/rods and 2V closed chamber heads? 

 

According to uniquecarsandparts.com.au a 351 XB (its an XB motor) put out 260bhp... I reckon I'd be more than happy with anywhere between 300-400hp. 

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So, anything I should do to the bottom end once I get it? Will it be right to just use crank rods and pistons as they are, or is there stuff I should do to them?

 

 

 

According to uniquecarsandparts.com.au a 351 XB (its an XB motor) put out 260bhp... I reckon I'd be more than happy with anywhere between 300-400hp. 

 

 

Just get it checked for square and straightness, by your engine dude. Not too hard to get 351 HP from a 351 C, and at this level, you wont need to epoxy the block or 4 bolt the mains, save that for a drag engine. 351's are are good solid engine, from a truck. Good low down torque, nice all round engine for cruising.

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Just get it checked for square and straightness, by your engine dude. Not too hard to get 351 HP from a 351 C, and at this level, you wont need to epoxy the block or 4 bolt the mains, save that for a drag engine. 351's are are good solid engine, from a truck. Good low down torque, nice all round engine for cruising.

get it built well and balanced and you can see it to 7500rpm even with 11.5:1 Comp

Go Flat tops, decent solid cam, 2v closed chambers worked, weiand accelarator with 750 Holley. Good for just over 200rwkw.

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get it built well and balanced and you can see it to 7500rpm even with 11.5:1 Comp

Go Flat tops, decent solid cam, 2v closed chambers worked, weiand accelarator with 750 Holley. Good for just over 200rwkw.

 

 

Flat tops and closed chamber heads might be a bit too much compression........ Unless you get the heads releived a touch

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Flat tops and closed chamber heads might be a bit too much compression........ Unless you get the heads releived a touch

yeah just get heads releived bring comp around 11.3-11.5:1

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Why solid cam? I was planning on staying hydraulic. I'm not overly worried about high it can rev (my xflow has only gone higher than 4k once haha). More after a cruiser that can beat most cars off the line.

 

11 won't be too high will it? I'd like to run it on 95 rather than 98, not due to cost but availability in some places of Tassie.

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Why solid cam? I was planning on staying hydraulic. I'm not overly worried about high it can rev (my xflow has only gone higher than 4k once haha). More after a cruiser that can beat most cars off the line.

 

11 won't be too high will it? I'd like to run it on 95 rather than 98, not due to cost but availability in some places of Tassie.

That comp would be definitely on 98! if not over 100.

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Dish tops and closed chambers are perfect for street driving, and hydraulic cams a perfectly fine on the street there's no need to build a monster, particularly if you've never driven with that kind of power before, a good tourquey can is a comp cams 268h, designed for a clevie in a motor home. I run one in the 351 my customline it pushed my 2100kg barge to a 13.5 down the 1/4 and it's a real basic engine, stock crank, rods, pistons, UN ported 2v closed chamber heads, bolt on roller rockers a torque power dual plane air gap intake, stock manifolds and a twin two inch exhaust with a 600cfm edelbrock Corby. It made 260HP at 5300rpm at the rear wheels but it made 400ftlb at 2000rpm, I use it for towing, go for a cruise with a bunch of mates and it will rip a skid at the drop of a hat that's all you really need in your Ute with a good 4-500kg advantage overt car would be plenty of fun, you don't need to go crazy you just need to build a nice combo

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That does sound like a pretty good combo Thom, and that's a nice amount of torque!

 

As I said in my first post I'd like it to be able to be driven daily if the need arises, and I do live in the city so it has to be decent to drive at low speeds/city/peak hour. (Not that Tassies peak hour compares to the mainlands).

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yea well the gtho is a pig so i reccommend not going with phase two specs haha fuck it loves a belting though, but if you wanna go slow up to a set of lights.. it doesnt like cruising, not at all.. so i with my limited knowledge know that my xw ute gets 200hp at the treads its a completely stock 351 with a 750 double pumper.. stock manifolds.. big exhaust :D and it feels like a rocket and would light up the wheels at the drop of a hat. so if you go cam, high flow everything up bit.. should pull like a train :) oh and sound fucking beautiful.

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By my calculations if you used flat top pistons in a 351 with closed chamber heads comp ratio would be around 13?

 

not sure though... same method got a result of 11 for a 351 with open chamber heads...

 

Nah not after a purpose built racer, just a tough cruiser that can still pull off the line.

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Not that it removes much, but have you compensated for the valve reliefs, and how far down the bore a piston is at tdc, plus head gasket thickness when compressed?

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Heres my zj after i built the 351 for it

351 with 302 heads. 10.5 compression with dished pistons and Big mutha thumper cam from comp cams.

Bit of other gear in it too lol

 

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That would be my other choice for A cam is a thumpr (no spelling mistake) they sound wicked but in reality they are very driveable, make good torque too

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