250-2v build - what do I need?

michael_cini

michael_cini

Well-known member
Hi everyone,

I will be taking my 250-2v head to the machine shop soon. So, before I do I need to gather everything I will need. It will be going on my 75 US 250 engine which I want to be a daily driver. I want more power but I want the engine to be easily maintained. I am planning on using a Holley 350 carb and leaving the bottom end stock for now (perhaps in the future I will add a new cam, let's see how it performs first). What all do I need. I know I need head gasket, intake gasket, head bolts, valves.

Does everyone suggest that I use the oversized valves?
Do I need to get new rockers or will the originals suffice?

What am I forgetting? Thanks for your help.

Michael
 
hey
you realy need to put a new cam in it and it wont lose its drivability down low (stock log cams really crap)
stock rocker gear will work
if machine shop wants to put new valves in it then id go o/s if not just use those ones.
thats about it.
 
RickWrench is building up one right now; hopefully he'll chime in for you. He keeps great on-line records so you can just follow along.
 
In my experience a 350 is OK but the 500 two barrel will definately perform baetter provided you keep to cams with less than 215 degrees at 0.050 lift. The heads can use a littl exhaust port help, the inlet is fine.
A solid lifter cam grind will rev better if you can go the adjustable rocker route, which i think for you guys is a bit of an issue.
The stock intake is fine, but try to get a smooth adapter to the holley two barrel carb.
Headers and divided centre exhaust is good, and run an exhaust with about 2.25 diameter.
A7M
 
thanks for the tips aussie7mains. i will start off with the 350 holley and see how she runs. if needed i will go to the 500 later. but it sure seems like alot of CFM's! i almost forgot about the center divider, i have to get me one of those. i was planning on using the holley carb adapter that mike sells. is it not smoothed well?

aussie7mains":1d8pe19t said:
In my experience a 350 is OK but the 500 two barrel will definately perform baetter provided you keep to cams with less than 215 degrees at 0.050 lift. The heads can use a littl exhaust port help, the inlet is fine.
A solid lifter cam grind will rev better if you can go the adjustable rocker route, which i think for you guys is a bit of an issue.
The stock intake is fine, but try to get a smooth adapter to the holley two barrel carb.
Headers and divided centre exhaust is good, and run an exhaust with about 2.25 diameter.
A7M
Click to expand...
 
the center divider is a myth. I wouldn't bother. So many have complained about it rattling once installed and no one can actually say for sure it helps. I don't believe it's worth the gamble to gain, if anything at all.
 
yeah, i don't know. there does not seem to be any concrete conclusion on this one. and there have been quite a few people with problems, but i also think that many of them installed theirs in a quick way with the head still on the engine. but, i could be wrong.

LaGrasta":2dgyoqgq said:
the center divider is a myth. I wouldn't bother. So many have complained about it rattling once installed and no one can actually say for sure it helps. I don't believe it's worth the gamble to gain, if anything at all.
Click to expand...
 
If you must use it, don't bash it to fit like that other 2V head someone cracked...
 
the divided whould be a must to me after seeing a long and 2v head.
unless you could get extractors that where made to take the hole port then it whould be arguable.
but seperate ports has been the go for a long time now.
 
I had bronze spacers made to replace the springs on the Rocker Shaft.
Apparently that stops problems with the rocker arms walking around...
 
interesting idea. did the machinist do this for you?

ZC-Cruiser":2xajhf5g said:
I had bronze spacers made to replace the springs on the Rocker Shaft.
Apparently that stops problems with the rocker arms walking around...
Click to expand...
 
that's the only comments you have adam? you usually have alot to say about everything...but it's usually a good thing!

addo":40i1qltd said:
If you must use it, don't bash it to fit like that other 2V head someone cracked...
Click to expand...
 
Well, you can probably guess which member I'm referring to. ;)

Beyond that I still personally like the small carbs on these. Carter or Stromberg - both will do fine; the Carter BBD off a slant 225 isn't a bad unit at all. The greatest inefficiency in these heads is exhaust restriction (easy to minimise with bigger valves), followed by oversized inlet runners (much harder to fix).

Pair it with a cam ground to match your flow specs - these are floating around the 'net - just allow a little extra flow over stock on the exhaust side if you increased the valve head diameter. Keep your RPM in a practical range when choosing a cam. People still seem to get this wrong!

They're no sacred cow; just a greatly improved product over the original. If you don't get it perfect first time, back up and try again. Only when people put too much emotion into the build (while lacking in hard data research) do they find this potential aspect daunting.
 
michael_cini":1pgbh31l said:
interesting idea. did the machinist do this for you?

ZC-Cruiser":1pgbh31l said:
I had bronze spacers made to replace the springs on the Rocker Shaft.
Apparently that stops problems with the rocker arms walking around...
Click to expand...
Click to expand...
Yep, assembled the head and then machined spacers to suit the gaps...
 
alright, thanks for the help so far. what do you guys suggest i shoot for as far as compression ratio and cam size? thanks.
 
Considering that cam will affect dynamic compression, work backwards.

Start with the intended wheel/tyre size, gear ratio and trans type (any rotational losses?) - then look at operational speeds. That'll give the RPM bandwidth. Remember to add a little "push" up top for overtaking!

From your fuel choice, operating specs and head flow, the cam will design itself. That will include static CR recommendations.

I know it's the least exciting way, but it will pay the best dividends.
 
hey adam,

thanks for the reply. but that was a bit over my head, i'm afraid. i have the answers to some of your questions though. perhaps you can enlighten me more.

tires/tyres - 185/65r15 tires (will go up to 195's with next tire change).
rear gears - 3.25
trans - C4
operational speeds - primarily city driving, but some highway too.
fuel choice - 91 octane.
operating specs - what else do you need to know?
head flow - damn i guess i have to look up the 250-2v specs. sorry.

addo":1oy92str said:
Considering that cam will affect dynamic compression, work backwards.

Start with the intended wheel/tyre size, gear ratio and trans type (any rotational losses?) - then look at operational speeds. That'll give the RPM bandwidth. Remember to add a little "push" up top for overtaking!

From your fuel choice, operating specs and head flow, the cam will design itself. That will include static CR recommendations.

I know it's the least exciting way, but it will pay the best dividends.
Click to expand...
 
With your present tyres:

10MPH is 1098 RPM (nominal; converter slip would take care of some)
60MPH is 2679 RPM, give or take
90MPH is 4018 RPM approximately

So you want to make power from 800 or so, up to 5500 RPM - that gives a nominal top speed of 120+ MPH, but drag and the rest make it very theoretical! Based on that data alone, a cam of around 440 thou lift and 280° stated duration (214°/0.050") would seem pretty close. The 2V flow specs will probably affect the intake lobe profile slightly.

You didn't say what profile would go with the larger 195 tyres planned, so I can't calculate for them.
 
thanks adam,

the larger tires would be 195/65r15's.

addo":107rjb7d said:
With your present tyres:

10MPH is 1098 RPM (nominal; converter slip would take care of some)
60MPH is 2679 RPM, give or take
90MPH is 4018 RPM approximately

So you want to make power from 800 or so, up to 5500 RPM - that gives a nominal top speed of 120+ MPH, but drag and the rest make it very theoretical! Based on that data alone, a cam of around 440 thou lift and 280° stated duration (214°/0.050") would seem pretty close. The 2V flow specs will probably affect the intake lobe profile slightly.

You didn't say what profile would go with the larger 195 tyres planned, so I can't calculate for them.
Click to expand...
 
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