cam help for a 250

[Anonymous]

where is a good torque calculater?
I see that the 170 had the torque curve at 2400 and the 200 at 2200 and the 250 at 1650 rpm.
does anybody make a cam that would put the peak torque at 2200 or 2400 and peak horse power at 3500?
can I have peak torque at 2400 or 2200 with out losing any of the low end of stock?

 

[xctasy]

Firstly, just get a cam with 195 to 205 duration at 50 thou, 264 to 270 degrees at fully open, and try to ensure the stock duration when both valves are open 30 thou is kept the same as the stock 252 degree factory Ford cam.


There is a lookup table I made some time back. It tells you how to predict hp using 9 inputs, and tells you where the power in torque is likely to come in. It notes these from histrical figures from most production engines from 1932 to 2003. I'll give you a low-end run down.

Normally, a stock low tech 60 to 80's OHV US engine will have max torque rpm and max power rpm, a factor of between 1.5 and 2 appart. When you cam it up, the algebraic difference between the torque peak and power peak gets narrower, sometimes less than a factor of 1.2 appart. In this situation, the engine looses a lot of the normal idle and low speed torque characteristics most of us hold dear.

In Oz, the X-flow 4.1/250 ran maximum power at 3600 rpm, maximum torque at 1800 rpm. The poorer breathing log head had similar torque and power peaks.

Heres the gossip on duration:-

1) If you are able to copy the stock cam overlap when both intake and exhast valves are at 30 thou lift, you will never reduce low end perfmance.


2) This holds true even if the duration of the cam at 50 thou lift(stock 195 degrees) or fully open(stock is252 degree duration) is increased. So if you new cam spec reads perhaps 205 at 50 thou and maybee 265 to 270 degrees at open, the cam won't loose low speed torque.

3) The 30 thou duration trick is something the 4 cylinder guys with automatics learned in the late 70's. Most after market cams these days have more intensity. They open with more severity. If you get a cam with the right lobe centre line and a soft intial ramp, it will give great low end torque without hurting the high end power.

4) If you use the 205 at 50 thou/270 degrees at open duration cam, with the stock valve openiong durationat 30 thou, you will find the following:-

the maximum torque is about the same from 500 to 1800 rpm, but that the torque peak will now be at 3000 rpm, with maximim power at 4200 rpm or so. Once you go above 270 degrees open duration , the low end torque performance gets stollen from the rich zone, and given to the poorer zone high up. By the time you have a 215 at 50 thou, 280 degree open duration cam, you've lost quite a lot of low end torque.

The great thing is that cams around the 270 degree range are plentiful, and the newer cams are optimised to take care of low end torque.


Lastly, the lobe centreline governs how the low end torque comes in, and changing the centreline from the stock 110 for a wider one (114, 116 or so) helps low end torque for the better in most instances. The penaltiy is less performance up high. Changeing the lobe centrline is expensive, but it is the key.

Hunter, the cam is the begining and end of happiness. Get it right for your application, and the whole world will smile, get it wrong, and you'll be madder than an Africanized Bee!

 

[wsa111]

Huntersbro, you need to specify what modifications you have done to your engine.
do you have the later cylinder head with larger valves from fspp, bowl modifications,what carburetion, exhaust headers?
if this is a stock 250 engine with no modifications, yes a slightly larger camshaft would be beneficitial.
however if you have a modified say an 80 head with fully ported cylinder head, with larger exhaust valve,at least a 350 cfm carb, with a decent header system with dual outlets, & a camshaft over 264 @.050. the centerline of the camshaft plays a big roll in your power range. a cam with a 112 centerline will have a smoother idle & less low end torque but more top end power than a 110 center line cam. however increase the duration, & you will pick up the top end power with the 110 cam or a 108 centerline. the 108 will have a very rough idle. you need a stick shift to deal with a camshaft of this type.
xtaxi is giving you good advise for a stock engine.
just remember with the 112 centerline cam, you are closing the intake valve later than a 110 camshaft, which will close the intake sooner,gives you more low end but a rougher idle because of the overlap.
camshaft selection if very critical if you are seeking the ultimate.
a camshaft is a compromise. good luck on your choice. :idea: william
the x-factor here is to advance the camshaft for more low end power or retard it for more top end power????? this applies to any camshaft you chose.

 

[Anonymous]

I have done nothing yet...

I am just trying to figure out how to do it before I start.

The vechile is a 1968 Scout 800 that weighs 2800 lbs.
It will get a 5 inch lift and 33" tires and a T18. This is going to be a weekend truck for the trail and highway.

I want to go carburated and headers and muffler, cam, longer rods longer rocker RATIO if neccicary


The 250 has 240 lbs of torque at 1600 rpm
I want 240 at 1600 and 270 + at 2400.

But I do not want to wind out the motor past 3500.
I want the peak horsepower at 3500.
I can be happy with only 130 horsepower.

as far as gear setting goes

I want to cruise on the highway 70 mph at 2200 rpm gear 4
that is 3500 70 mph in gear 3

I have heard that for example: if 2nd will wind out to 40 mph at peak power then in 3rd should be so that 40 would be right in the mid torque range
that 3rd gear should be

that is as far as I am along so far.

 

[wsa111]

Huntersbro, what you want is a stump puller cam.get a cam in the 195 degrees @ .050 in a 110 lobe center & advance the cam 2 degrees.
Give mike at fspp a shout, he can check with clay smith cams & see if they can grind a special camshaft near those specifications. :idea: william

 

[Anonymous]

can i have the torque and power peak at the same rpm?


is it possible to have 240lbs of torque at 1600 and 300lbs at 3000 rpm and max horse power peak at 3300 rpm?

I am not concerned about idle but I just want lots of mid range torque with low hp.
I want this to out run my Bronco2 2.9L automatic

 

[xctasy]

can i have the torque and power peak at the same rpm?


is it possible to have 240lbs of torque at 1600 and 300lbs at 3000 rpm and max horse power peak at 3300 rpm?

I am not concerned about idle but I just want lots of mid range torque with low hp.
I want this to out run my Bronco2 2.9L automatic

1. Power and torque are equal at 5252 rpm, irrespective of if its a Modle T or a Lamborghini.

2. If it can't do 3000 rpm, the rule still applies!


It is impossible to do a 300 lb-ft at 3000 rpm 250 engine unless you have about 280 hp at 4200 rpm. A 250 six can never do that at those revs without a postive dispalcement supercharger or an XR6 turbo engine with bost modulation. The best you can hope for is 300 lb-ft at 4000 rpm, and 280 hp at 5500 rpm with independent runner Weber down draft carbs, ex 911 T, or sic CV40 Mikunis.

To do what you are suggesting requires a 300 cube I6, stroked with a offset ground or welded steel crank to about 330 cubes. Then it would do 300 lb-ft at 3000 rpm, and 280 hp at 4200 rpm with an idependent runner Weber 40 or Mikuni CV, HS, RS 40 or HSR 42 system.

The engine follows the abdiactic cycle, and they only hope you've got is to get a slightly wilder, modern cam from FSPP, Clifford, et al.

I promise you that if you run to the strictures above, you'll get no loss in torque on the standard 250 in any point in the power curve. An engine is just a pump.

If you go for the longer 5.99" HSC rods, and a sub 270 degree cam with the rules above, and you get a good exhast, you'll be really happy. The engine will not be detonation prone even with higher compression.

The best torque will happen with a single or dual small 2 stage carb like the 32/36 on a Cliffy/Offy adaptor, or direct mount 2-bbl Holley 2300 plate like what the Schendahl Bros suggest. You could alternatively use the Mustang Geezer dual carb idea, and get a great low end torque curve. The problem is that the rev range will then be widened, and will widen the distance between the maximum torque and maximum power revs. That will increase the rev range.

What you are angling for is the right amount of low speed torque.

The head mods which maintain the existing internal port sizes, but smoothen out the bends, will result in more power up high.

Pulse tuning with Weber 3 chokes will work, but the cost is making a Offy style alloy intake manifold. It will give extra power up high, but won't pulse tune very much at low speed, so it will end up creating a freer reving engine, which will give you the impression you have less low end torque. Flat head owners find there engines are stump pullers only because they won't rev easily. Any improvement in breating will give a proportional increase in power for each rpm. Don't over carb it, or it will want to rev more.


The $$$/ benefit isn't there unless you have the Weber 3 chokes on offer. The port spacings are, from memory, about 108 or 95 mm uniform, and won't line up with the offset inner intakes ports of the small 144- to 250 I6's.

 

[Anonymous]

ok i got it...
i can get a clifford 264 cam
clifford headers'
1.6 rockers
400 cfm of carb
ram air filter
independent runner setup down draft.

how hard is it to tune 3 two barrels.

 

[xctasy]

how hard is it to tune 3 two barrels

.

Oh boy, I better stop talkin..."ve haf no vays of making you stop talking, xtaxi". Addo, StrangeRanger...help!!!

you could be in need for therapy on trying to tune the triple set-ups. The twin carb numbers have been done by the Valiant Slant guys on the Slant 6 forum.

If you wanna get confused, read on....

All you have to do is decide excactly why you are doing it, and what you want.

I repeat. If its just a fat, wide, flat torque band, then just undercarb with a simple single 32/36 or 5200. If its to be the very best you can get without injection, the isolated runner 3 times 2-bbl Webers down drafts will work best, but at huge cost.

All side draft carbs are not an option on an offroader

Anything other carb choice asside from the 2-bbl Weber in a single sense will favour the top end of the rev range more, which is not what you want.

If you go for a triple 2-bbl, which I think is what you are asking, then the torque optimized option gets very complicated.

Three 32/36's wont work well due to the throttle opening being loaded past 60 percent of the throttle travel. One carb is heavy, 3 carbs are tripple the spring loading, and when the progressive section opens at 60% of the wide open throttle, it will be real heavy to shove on the gas pedal.

Two 32/36's or Holley Weber will work okay if the linkage is done. You will need to have a longer gas pedal travle to increase the mechanical advantage. The set-up will load up when the secondaries kick in at 60% throttle.You can run them in any direction if you use Mustang Geezers set up of running two carbs. No progressive carb should ever by beside a single intake port.

The Triple Holley Weber 5200 and 32/36 carbs cannot be run port to port, and wont pulse tune.

A set of three 38/38 DGAS carbs will bind in a similar way to the 32/36 nad Holley Weber, as the carbs throttles are geared. The loads are too great for a triple set up in the same way as the Holley Weber carb is, but they won't over load as wide open throttle as much. They could be run as a pulse tuned item. As a dual set-up, they may be to rich, and will hurt low end torque too much.

A specific type of downdraft carb with a specially tailoured Weber with idle and progression circuits, is a set uplike the DCNF Weber 36. That would pulse tune fine with 3 by 2-bbl set up. The carbs are found on French Simca, Talbot Horizon, Solara or Alpines in the 1980 to 1988 era. They are found in Ferraris, Maseratis and some Aston Martins.

They have a reputation of being rich at wide open throttle, but can run very lean at part throttle.

The last is the offroaders favourite. Baja Pinto 2000 or 2300 racers have used Mikunis for years becuase they give great power and are the only side draft carb which can take the knocks. A set six 40 or 42 mm numbers will be murder to calibrate unless you can get the advice of an expert, but they will pulse tune just like an EFI system.

The last option is to do like this 240 Zee guy did, and make your own EFI system via the Megasquirt system.

 

[Anonymous]

thanks Xtaxi