CAM ???

[Anonymous]

I have a 1970 Ford Maverick with 250 cid.
Engine is ready to rebuilt.

For mild performance increases Ford Falcon Performance Handbook know as stock cam can be adequate.
For the rebuilt, I must change my present stock cam.

Here's the big question, I puts new stock 250 cam or ISKY 256 (or others) ???

Characteristics :
9.2:1 CR
Stock 1 bbl Carter rbs
1980 head with 3 angle valve job + exhaust port divider
C4 automatic
3.00 gears


thanks,

 

[Mustang Boy]

check out www.classicinlines.com they have like 10 different cams to pick from any where from mild to wild and most of them would work good with ur build up and may i also say u might wanna put a small 2brl carb on with an adapter plate

 

[Gene Fiore]

Be aware on a Maverick with a 250 there is not enough hood clearance to put a 2 bbl carb using an adapter. You would have to cut a hole in the hood for it to fit.

 

[CZLN6]

Howdy Back Wally & All:

Between the two, I'd go with the Isky 256. Even though they have similar durations specs, the Isky will have much fatter lobes for a much better .050" lift duration. Which mean, even though the opening to closing duration is about the same, the Isky will open faster then a stocker. But-

Given your specs the Isky will be a little tamer than you need in a 250. it's specs are-
Isky 256- at .450/.450" and @ .050" - 202/202 duration.

Here's two others to consider-
The Comp 260 at .440" lift and @ .050" -212/212 duration.

FSPP- ARC-268/274 with .455/.480" lift and .050" - 208/218 durations.

All will give your engine good vacuum and a good idle. In any case, your engine will be begging for more carburetion and a header exhaust.

Adios, David

 

[wsa111]

Wally, if you want to add a little extra go with Mike's http://www.classicinlines.com/proddetai ... 2DHSP%2D12

This camshaft will require valve springs with at least 80# on the seat.
But the rate of lift is a lot faster than the comp 260 & I have no experience with the isky.
Your 250 will absorb the extra duration with the 264 camshaft.
David's recommendations are right on if you want to stay with stock valve spring pressure, but if you want to go the extra $$ for valve springs & especially 1.6 rocker arms then go with Classic Inclines more agressive profiles. William

 

[AzCoupe]

Here's what I came up with, based on the following specs. Assuming they are correct, and you are using a Felpro gasket.

Bore = 3.68
Stroke = 3.91
Gasket bore = 3.81
G thickness = .055
Deck clearance = .012
Dish volumn = -7cc
Chamber size = 62cc
Static C/R = 9.3 (my cam utility program shows it to be 9.28)

Basically, you want to pick a cam that allows the proper rpm range (depending on the type of driving you do), with the intake valve closing between 55-64 degrees abc. With the above specs, this will keep the dynamic C/R in the ideal range of 7.5 to 8.0 for best performance on regular pump gas. A cam in the 260 range, with a 110-109 lobe center, would be fine. The FSP 264-110 closes at 62*abc. The Comp 260 closes at 60* abc. The ARC 268-274-110 that David recomended, would also be an excellent choice for the above setup. A cam with a 108 lobe center, would be ideal with a manual tranny.

 

[xctasy]

Don't deck the US 250 block lots. The bolt holes and mating faces are formed by Ford with a gentle as cast taper, and cracks can propogate from the stud holes when the block is decked. The block has only about 350 thou of deck thickness, and every bit of that supports the water gallery and engine rigidity.


The stock 250 has a 103-110 thou short fall from the piston to the top of the block, and this is very bad for detonation and performance.

Best option is to just grab 81-82 255 V8 or 1986 to 1993 2.5 HSC I4 Ford Taurus/Mercury Tracer pistons. MustangSix did this on his 66 Mustang

These slugs are 85 thou taller than the stock 200 or 250 pistons, and have a flat top.


With the stock 5.88" long rods, and these pistons gets close to a zero deck engine. It's not perfect, but close.


Option two is to order some 6.06" Aussie conrods (found on every 98 to 06 Falcon 4.0, and easily got from wreckers), and mate them to stock aftermarket 6.5 cc Ford Mustang 200 pistons. The engine will then be close to zero deck.

 

[CZLN6]

Howdy All:

Mike- check the deck height in your computational inputs. I think you meant .120" on a typical '70 250?

Wally- your are asking about an appropriate cam for your combo, and we got off on how you got to your stated CR of 9.2:1. can you fill us in? Did you mill the head? How much? Did you deck the top of the block? How much? What pistons and rods are you using?

It is clear all here agree on more cam than the Isky 256 offers. Let us know what your decide.

Adios, David

 

[AzCoupe]

Thanks for the corrections guys. I removed that part, just incase someone didn't continue reading. I didn't realize that about the 250 blocks so its nice to know. I meant deck clearance, rather than deck height (my error) and used that because I didn't know the specifics. It is also recommended, as per the Falcon Handbook (page 15). I was tring to figure out how he got to 9.2, but should have asked first rather than making a general assumption. My bad.

 

[Anonymous]

Bore = 3.68
Stroke = 3.91
Gasket bore = 3.83 (overbore .020)
Gasket thickness
compressed = 0.05 (felpro)
Deck height = .085 (0.125 block decking .04)
Chamber size = 52 cc (head milling .06)
Dish Volume = 6.5 cc
Static C/R = 9.2:1
Stock rods and stock cast dished pistons (Sealed Power 9.2 c/r ;dish 6.5)

At the beginning, my first choice was flattop Tempo 2.3 HSC I4 pistons because requires less decking and milling, but according to Performance Handbook , dished pistons seems helping to control combustion and in minimizing pre-ignition.
I did not only know that 250 block with lot of decking as prone to cracking

With flat top I have just only mill the head .06
Or
Mill the head .04 + Decking the block .025

??? : : :
Thanks Wally,

 

[CZLN6]

Howdy back Wally and All:

Wally- I hope we didn't scare you off with too much information.

Our concern with a 250 engine is that it is difficult to attain a true 9 plus to 1 compression ratio without some major machining and/or parts swapping. The problem is the huge deck height of about .125" or more. Deck height is measured from the top of the piston to the top of the block. Add to that the compressed thickness of an aftermarket composite head gasket of .050" and the total Deck clearance goes to a whopping .175". Not what you want for efficient combustion.

A tighter deck clearance of about .040" creates quench, when the piston comes up and squeezes unburnt air/fuel mixture out of the non-chamber part of the head and the top of the piston and into the combustion chamber. This high speed turbulence makes for a more efficient burn- increasing engine efficiency and reducing the likelyhood of knock.

Given the choices of parts available for a 250 getting to a .040" deck clearance is very difficult to obtain.

Xctasy suggested way to reduce deck height in a 250. But, since your engine is already built, you're not likely to redo it. The good news is that any cam that increases duration will also reduce cylinder pressures- reducing the tendency for knock. The longer exhaust duration of the FSPP ARC-268/274 will also help to evacuate the exhaust.

But, having a true 9:1 static compression ratio will be needed with this cam to help offset the loss of power in the lower rpm range.

Again, I hope we haven't overwhelmed you with details. Give us some feed back.

Adios, David

 

[Anonymous]

This lot of informations is very appreciated

My block is disassembly, I'm ready to milling and decking.
The characteristics that I have write in the previous message is my goal.

My head is a 1980 head (E0...) that I measured to 64 cc.
My 250 block that I measured to .125 deck height.

: But in this case, flattop or 6.5 dished pistons is suggested for my goal ??? :

Sorry for my english, I just started to learn english recently, I'm from Montréal, Canada.

Thanks, Wally

 

[AzCoupe]

I'm confused on the chamber size. In one place you say 52cc, then in another 64cc.

Chamber size = 52 cc (head milling .06)

My head is a 1980 head (E0...) that I measured to 64 cc.

Don't worry about your English, your doing great. Better than some Americans do, especially for just learning.

 

[JackFish]

Don't worry about your English, your doing great. Better than some Americans do, especially for just learning.

That should be "you're doing great", as the contraction of "you are"...
... just helping out with the English...

 

[Anonymous]

At present, my head measure 64 cc. and my deck height .125.
I envisage to reach 9.2:1 C/R (with Felpro gasket and .02 overbore)

If(I think) I use dished pistons (6.5 cc), I should make milling the head .04 (to obtain 52 cc), and decking the block .06. (to obtain .085 deck height).

If I use flattop Tempo 2.3 HSC I4 pistons :
I should make milling the head .06
Or
Milling the head .04 + Decking the block .025

: After the last discussion, I’m not sure if I must use dished pistons :

----------------------
Mike talk about The FSP 264-110 Cam ???
This is CSC-264-HSP-10 Cam :

Between :
The Comp 260 at .440" lift and @ .050" -212/212 duration.
and
FSPP- ARC-268/274 with .455/.480" lift and .050" - 208/218 durations.

There is difference in «driveability» for street use :

Thanks again,
Wally



[/quote]

 

[wsa111]

Wally, since you have a 250 engine a little extra duration will not hurt your idle quality.

If you want a smoother idle use the CSC-264-HSP-12, which has the 112 degree lobe center. But the CSC-264-HSP-110 will give you more power but the idle will be very slightly rougher.
As you can tell I am not at all impressed with the comp 260 cam. If you want to loose power use the 260, it just is too mild & is an outdated profile.
Anyone of Mike's 264's will do the job. I like the single pattern since you plan to stick with the single barrel carb & stock exhaust manifold.
I also recommend when degreeing in the cam, put the 112 lobe center @ 108 degrees which is 4 degrees advanced & put the 110 camshaft @ 106 intake center.
You will be very satisified with the outcome. William

 

[CZLN6]

Howdy wally:

I can't argue with William. I have a Comp 260 in my 250 and it is very mild. Definitely a step up from the stocker, but mild with my 4 spd SROD, Holley 500 cfm direct mounted and all the other stuff. It might be all right in your case with a one barrel and a C4 tranny. When I do my next engine it will be with an FSPP ARC-268/274 dual pattern cam. Mike waqsn't in business when I did mine.

IF you proceed with your plan to overbore .020", deck the block .040", mill the head to 52cc and use a stock type dished piston your CR will be 10.5:1!!! To high for your intended use.

Here's my suggestion.
Overbore .020", deck the block .040", use 255 V8 pistons which are .085" taller than 200/250 pistons. Mill the head only enough to gain a true, flat mating surface, staying as close to 62 cc chambers as possible, and mill a 7cc recess into the piston crowns mirroring the chambers. This combo will give you a zero deck height, and a CR of 9.7:1. The Felpro head gasket, at .050 compressed thickness still leaves a too fat quench height/deck clearance, but it will be way better then stock. Mikes FSPP CSC-264 will help to lower some of the cylinder pressure.

Note- the HSC 2.3 pistons have the same spec for pin height as the 200/250 dished piston the only difference is that they have a flat top.

What do you think?

Adios, David

 

[AzCoupe]

IF you proceed with your plan to overbore .020", deck the block .040", mill the head to 52cc and use a stock type dished piston your CR will be 10.5:1!!! To high for your intended use.

David,

I must be missing something? How did you come up with a 10.5:1 CR?

I used three different calculators and came up with approximately 9.3 on all three. Am I doing something wrong here?

This one is from the calculator on your website:
Number Of Cylinders: 6
Bore Diameter [inches]: 3.70 (3.68 + .020)
Stroke Length [inches]: 3.91
Combustion Chamber Volume [cubic centimeters]: 52cc
Head Gasket Compressed Thickness [inches]: .050
Head Gasket Bore Diameter [inches]: 3.81
Piston To Deck Clearance [inches]: .085 (.125-.040)
Select Piston Type/Size - Dished: 6.5cc
Results: 9.3:1

 

[73GreenMachine]

You guys are having trouble getting over 9.0:1 with a good piston\deck clearance? I just finished getting my 250 precrossflow motor built and ended up with about a 5 or less thou piston to deck clearance with 50 something(I think about 55-56) cc chambers(somewhere about 40 thou off the head at a guess) and ACL pistons. I think its code is 2508 with is 30 thou overbore and it has a 15.8cc dish. Using the calculator on the Falcon Six site, we came up with 9.7:1, which will hopefully work well on LPG, although I would think it would still be suitable for high octane petrol. Is the problem that you don't have this particular piston available?

 

[addo]

ACL set 6MKRY4105-030, maybe? What'd it cost you?