24 replies to this topic

[lakeside]

the same

[TerrA LX]

All 253's are standard (read small) valve heads, some 308 and worked 308 heads have large valves where the inlet head actually sits over the bore on a 253, problems are valve shrouding and on high lift applications the valve can actually hit the block.
otherwise they are same same.

[Struggler]

Sorry James, VN heads can be successfully fitted to 253's (ask Herne !!).

You would need well over 0.500" lift before the valves even looked close to hitting the block, even then you could relieve the block in the valve area, just like any Clevo or BBC.

[TerrA LX]

Before you even get to 500th lift you still have the disadvantage of the bore cutting into the cone that is formed behind the head of the inlet valve, something relieving the top of the bore for valve clearence will not rectify, you need a minium of a 4" bore for the large valve set up to function correctly.
I am not saying the set up wont work because even a side valve ford works.

[mr5000]

ive been working away at my heads at the moment on the 253 port polish and match ported with the intake the exhuast was already spot on getting the valves and guides re done ill let you now how it goes once in

[Struggler]

Before you even get to 500th lift you still have the disadvantage of the bore cutting into the cone that is formed behind the head of the inlet valve, something relieving the top of the bore for valve clearence will not rectify, you need a minium of a 4" bore for the large valve set up to function correctly.

The difference in flow from a 3.625 bore to a 4.000 is not as great as you might think. I am not saying there isn't a difference, but in the real world it hardly matters.

You are assuming that air and fuel flows over the valve in a conical pattern. One day if your've got nothing better to do get a garden vac. and silicon it to the head face as if the barrel of the vacuum was the bore of the engine. Turn on the vac, crack a valve open at about 0.250" and spray some paint at the intake port. The resultant spray pattern will show you exactly where air and fuel flows through the port and out past the valve. All is not as it seems.

A 4V Clevo intake hangs well over a 4" bore (a lot further than a 1.94 on a 3.625 bore), yet they still work well.

Saying that you need a 4" bore for a 1.94" valve to work properly....... I guess we will have to disagree. The difference in flow would be in the order of 2.5 to 3%.

Fit your big valve heads to your 253 and rev it up. They need the airspeed.

JMHO

[Struggler]

I must apologize to ALX76 if you think I am having a go at you. I'm not.

[TerrA LX]

No need to apologize, this is an open public forum there is no personal attack here just differences of opinion.
I never said it wont work, just not as good. i just cant understand when for 50 (or more) extra cubes adds up to 50 or more horsepower.

[Struggler]

i just cant understand when for 50 (or more) extra cubes adds up to 50 or more horsepower.

It doesn't.

Generally peak power is close to the same, torque however is a different story. The smaller engine will also need more rpm to make the power, but it will make it. The larger engine, having more torque, will also move a vehicle quicker. Herne's 253 with the VN heads made 100kw at the tyres, this is exactly the same as a standard VN/VP. The only difference is the cubic inches. The 304 however does peak a lot earlier.

[TerrA LX]

bout the same horsepower you would get from standard valve heads with a 465 holley.
I see where you are going tho, with the right heads/cam you could get 600Hp from a 253 at 12 000rpm.

[Uncle Chop Chop]

I found this thread by doing a Google search, so I thought I'd ask a couple of questions.

Sorry James, VN heads can be successfully fitted to 253's (ask Herne !!).

You would need well over 0.500" lift before the valves even looked close to hitting the block, even then you could relieve the block in the valve area, just like any Clevo or BBC.

Firstly I will assume that is lift at the valve, not the cam? And if the bore is taken out to the figures quoted in the following thread:

http://www.gmh-toran...troker-options/

Then that would give more scope for more lift?

Stock 253 bore is 3.625"
Stock 305 SBC bore is 3.736"
030 over 305 bore is 3.766"

To get the right deck height with a 253 mini stroker you need to use the 305 piston which neccesitates the 0.110" to 0.140" overbore. Like I have said before, the 253 has really thick cylinder walls and can easily accomodate this sort of overbore.

FWIW a standard 305 SBC has a stroke of 3.48" so using a 355 crank in a 253 with the 305 pistons will net 305 cibic inches, a 030" overbore will lift it to 308 CI. The 305 pistons will need to have the tops trimmed down to remain level with the deck with this much stroke.

Hope this helps.

But if I go the above route with the 3.48" crank and zero deck height, would the problem then be piston to valve clearance?

PLEASE NOTE!

The maximum intended revs will be 6000 - 6500, so maybe a bigger cam won't be needed? Fuel will be 98 octane.

[Struggler]

Way to go thread miner !!!

 

Yes, that is lift at the valve.

 

I have never run into piston to valve clearance issues with a 253/308 and have run in excess of 0.600" lift.

 

The stroke will not affect the PTV clearance (in this case).

 

I just measured a stock 253/308 head. The valve sits 0.400" below the deck face. Add a head gasket and deck clearance and there is heaps of room. I have had a head on a 253 block and looked up from the crank side, the stock valves clear the bore. You may have to relieve the deck on the intake side a little if you use a 1.94" valve. It won't be much. With the 305 bore it will probably clear. Worth checking during assembly though !

 

Seriously, if your spending this much on a 253 then the extra $300 odd to upgrade to a 4" bore block (304/308) is really well spent.

 

Hope this helps.

[Uncle Chop Chop]

Thread miner? My grand kids simply taught me how to use Google. You mentioned using a 1.94" valve. I intend on using the stock sized valves, so it looks like everything will clear OK. And as for using a 308, I have a spare Trimatic 308 block a couple of feet away from the telly. But it's an all matching numbers car, so the 253 has to stay.

[UCgazman]

You can also get bellhousings that are turbo pattern - trimatic, I think Dellow make them....

[Mort]

CRS have bell housings as well and it wasn't cheap, i think it was about $500 for the bell housing alone

 

Quag, i rang an engineering shop in Mackay, they hadn't done one before but would have a go at it, they were going to charge me around $400 to do the job, thank frOck i found a complete tri-matic engine.

Edited by Mort, 06 June 2013 - 10:15 PM.

[EunUCh]

This post might be a bit of useless information but I think its worth a mention.

The 253 in my opinion is a humble,honest little engine,although they often get ditched for something bigger,bit like starfires.

The one my Mrs had in Her little sunbird had big valves fitted and a very small cam with a  Roty. carb.

My stock other than 40th overbore in my LH with a Strommy would leave Hers for dead,with an auto.

Thats not the only case,a neighbour of mine has the same set up as my Mrs had in His tonner,same deal, my stocker

would leave the thing for dead,and the tonner would only just pull away from my starfired UC,I drove all cars so am not dreaming about the performance.

Point being,the 253 does not seem to like the big cam/valve combo.so leave the valve size well alone,stick with stock valves or if you have the time and money fit slightley smaller valves.

Another point worth considering if anyone is playing with the 253 is the head gaskets.The 253 head gasket is not or shouldnt be the same as the 308 despite what they tell you on the packet or at the parts shop.

Obviously the 253 has a smaller bore than 308 so a correct size head gasket is a must,if you can find the metal ones fitted on some of

the early 253's they can be used with some of the good sealants these days,they were prone to leak,but I doubt very much if you will find a set.

ACL make a head gasket for the 253. http://www.aclperfor...siteGaskets.htm

 

 

 

 

 

 

 

 

[rexy]

yep but last heard these where around the 300 mark...drilling was less than a hunge...

Done by a reputable business will be a lot more.
Harrop will do it well in Melbourne. $370 eighteen months ago.