need help with supping up a 250 for an offroad and highway

[Anonymous]

if I put a 170 head on a 250 will my compression increase?

I also have heard that puting the 6' rods out of a ford 2.5L 4 cylinder will help too.

I will probably use an isky cam that runs 1000- 3800 rpm

will i want to advance the timing to make this work?

I think that i will use the webbers of the old 911 porche6 cyl
these are 3 barrels so it would be an individual runner system one barrel per cylinder with 2 carbs so it should be easy to tune.

I want to use this in a 1968 Intranational Scout with a T18 or 19 tranny (not sure which), 33' tires, and 3.50 gears because I want to cruise on the highway at 75 mph.

 

[Anonymous]

The head swap should bump the comp. up, I have'nt heard of the rod swap though, as far as the WEBER carb set up, how are you planning on mounting them?, it sounds like a good set up if you fab'd you own intake.
By doing a little bit of home porting to the exhaust , a header with free flowing pipes, maybe a mild cam yor 250 should have plenty of tourge to turn those tires. Good luck.

 

[MustangSix]

The 170 head will bump compression, but you will probably lose power thru the little valves, ports, and plenum, esp on a 250.

The longer 2.5 HSC rods (not the 2.3 OHC) will bring the pistons back up to the deck and will give you a very high compression ratio with the stock head. You will probably need to do some relief work on the chambers to get the CR down to a reasonable level. No more than 9.5:1 is about what you should shoot for with most cams on pump gas, but around 9:1 would be better.

Intere$ting carb choice.

 

[Anonymous]

the stock manafold has six ends that run to each cylinder. cut them off and weld each to steel tubing. 6'feet of tubing, six manafolds 1' long each, then bend them at the appropiate angle mabe 90 degrees since they are down draft. tthen get the ends that fit the 3 barrels and weld them on and mount the carbs. I will probably need to cut the hood to fit the tall manafold and carbs.

THis will eiither be a scout or a broncoII, the bronco 2 only weighs 2500 lbs and the sscout weighs 3800, so I think that the bronco 2 is the better choice. I can move the radiater up aginst the grill and I can grind the 2.5" grill down to 1 cm and tuck the radiater between the core support and the grill.

I can take off the front end and put on a dana 30 and put on leaf springs on the front and bigger leafs on the back all of of an old f-250 and put on 4 long shocks , pitman drop arm, power stearing , front disc breaks, no abs for me I think, regear the front and rear to 3.50, put on some 33" bf goodwrinch,

rollbar metal dash 4 way horness, T18 ot 19 and that is it, this thing is gonna be a beast with 18 miles to the gallon around town I hope.

 

[Hot 6t Falcon]

Hunter,

The long connecting rods will give you approx a 9.9 compression with the stock 250 head.

Try the numbers at
http://falconperformance.sundog.net/compcalculator.asp

Number Of Cylinders 5
Bore Diameter [inches] 3.68
Stroke Length [inches] 3.91
Combustion Chamber Volume [cubic centimeters] 62
Head Gasket Compressed Thickness [inches] .035
Head Gasket Bore Diameter [inches] 3.81
Piston To Deck Clearance [inches] .005 ??????????
Select Piston Type Flat Top Dished Domed DISHED
Dish/Valve Relief/Dome Volume [positive cubic centimeters] 7

The KICKER IN THESE NUMBERS IS THE Piston to Deck Clearance at .oo5 intstead of the stock .115 The stock 115 equals a compression of 8.1. The .005 equals a compression of 9.9.

If you added a 170 head (50 cc) to the stock connecting rod 250 your compression would jump to 9.2

Learn how to play with the Compression Calulator by using the 250's numbers above (except put .115 in the piston to Deck clearance slot for the stock rating.

Good Luck

 

[Anonymous]

If I use the 6" rods 170 head that will give me a high cmpression. 'Now will it help to get a cam that is longer duturation on the exaust,?

I like the isky cam 1000-3800rpm will this cam have a long enough duteration on the exaust, what should I look for on the cam specs?

now if I advance the ignition will I still be able to run on premium?
will octain buster help?

will headers improve volumetric effiency? what is the volumetric effincy on a 250?

where is a good torque calculater?

 

[MustangSix]

I think your plans have some hurdles to overcome.

If you use the 6" rods and a 170 head, you will have an engine that will not run on anything but race fuel. Use one or the other, but not both. Higher CR is not always better. The low speed cams that you are looking at are designed to build cylnder pressure. Again, not good with extremely high CR.

I think you underestimate the amount of effort it would take to build and install those flanges. They will require a great deal of fabrication to install. Welding cast iron is not easy and difficult to achieve consistency.

In addition, those carbs are too small for a 250. They were originally fitted to a 2 liter (122 cube) six. You will run out of breath at a very low rpm. (Have you actually priced 40IDA-3's? : )

The stock 250 is a torque monster. It pulls max torque at 1600 rpm. With some simple porting, the addition of a holley or autolite 2bbl, headers, and a modest cam, you can easily and economically meet your cruise requirements on pump gas.

 

[SONNY]

here in australia a company called ACL make a piston and ring combo to suit 200ci rods for the 250ci motor,this strokes the 250ci engine and they instantly rev to 6,500.the 250ci inline six has been the biggest selling engine in australia,and there has been alot of mods to these here

 

[MustangSix]

Sonny, that's a good workable solution for an Oz 250 engine, but not for the US 250. The problem here is that the US engine was designed with as much as .140" of deck, i.e., the piston does not come all the way to the top of the bore.

The objective is to change the deck to something closer to get better quench, but doing that increases the CR. As David calculated, you could end up with close to 10:1 if you retain the stock head. If you use a smaller chamber head from an early 170, you would end up at nearly 12:1 CR. Those kind of increases won't get you any big increase in power, but will still require VERY high octane fuel, less than optimal timing, water/alcohol injection, or some other not-too-user-friendly approach.

 

[SONNY]

ok don't know much about your engines,i just thought they'd be the same.you guys need a container full of 250 2v heads sent over there.lol

 

[MustangSix]

you guys need a container full of 250 2v heads sent over there.lol

you got that right!