Horse Power

could i get 150-155 hp out of my 250i6 without puting 255 v8 pistons in it?
they guy in this article guesstimates he's pushing out 145 HP
http://www.fordsix.com/tech/engine/old_250.php

8) it isnt the pistons that matter that much, it is the compression ratio. as long as you match the compression ratio he achieved you can make the same power he did.

Thanks, can you give me some tips on how i can match his compression? in the post AOD tranny i listed some mods i'm going to do.

I don't claim to be a machinist or engine builder so I keep it simple.

There are a few alternatives to the 255 pistons. My 250 uses AMC 258 pistons which have a useful D-shaped relief about 3X the volume of the oem's. This helped keep the CR to street gas/tuning with head and deck work.
The HSC type Ford four pistons I believe are another used.

The muscle of the 250 is it's wide torque curve, simple mods maximize this and finish at piston mods, overbore and ...


Powerband

If you can't achieve a high compression ratio with new pistons, the cylinder head is all that's left. High compression without detonation is the key to efficient horsepower. Plane the cylinder head, "edge" the chamber, cut Singh Grooves, and if you have the ability, add "PowreLynz" (basically screw threads) to the intake ports. All of these mods in combination will greatly reduce the engine's tendency to detonate and allow you to run the cheap gas on your higher CR.

I know what Singh grooves are, but really: "PowreLynz"??? Surely you aren't going to tell me that cutting something like big screw threads into the intake ports is going to make the intake charge spin or something? Sorry, but all that "tornado" stuff does is induce turbulence via a series of high/low spots, which isn't always a good thing. Especially in the intake port.

Edit: googled powrelynz, and now I think even less of it. Basically the same thing as a rough-finished port. Makes me think of somebody paying to have their head passages polished, then paying again to have them roughed up (in a fancy way, but still).

I gotta agree, that goes against just about everything there is to say about increasing flow speed.

From what I've gathered, the best thing for a street engine is an intake port that has had a basic cleanup done - remove casting lines, any bumps from the molds, and smooth out the curves and transitions - but leave the surfaces "rough" like with an 80-grit stone or rougher. 95% of any gains will be from reducing the profile of the valve guide boss, and making sure that the short-side turn from the port to the valve doesn't have sharp turns. Polishing them mirror-smooth is only good for serious high-rpm engines. And purposely putting a bunch of cut grooves in there just seems silly, imho.

Now, back to combustion chambers and compression...

Thanks for the backup, fellas. Gotta keep the info good around here

jamyers":6ay2kvao said:

From what I've gathered, the best thing for a street engine is an intake port that has had a basic cleanup done - remove casting lines, any bumps from the molds, and smooth out the curves and transitions - but leave the surfaces "rough" like with an 80-grit stone or rougher. 95% of any gains will be from reducing the profile of the valve guide boss, and making sure that the short-side turn from the port to the valve doesn't have sharp turns. Polishing them mirror-smooth is only good for serious high-rpm engines. And purposely putting a bunch of cut grooves in there just seems silly, imho.

Now, back to combustion chambers and compression...

Click to expand...

8) even polished ports are not the best for a race engine. getting port flow right is.

as for raising or lowering compression as needed, milling the head will raise the compression, and if you go a bit far you can use a thicker head gasket to reduce compression. and yes you can also use a thinner head gasket to raise compressio also.

Howdy Back All:

At the risk of hijacking this thread-

Hey Pinhead- I, for one, appreciated your insight on the Signh groove idea, and am wondering what data you have on the "Powrelynz". That's a new one on me. But with Ford, I never say never or always. Oops, I just said it. I'd like to build two identical head some day. One with the groove and one without. And then compare.

250coupe- The purpose of the 255 pistons is to eliminate the huge deck clearance in a 250s block. My 250s deck height was .150" not counting the head gasket thickness. The problem is the huge deck clearance make for a very lazy quench effect and hurts combustion efficiency.

I hadn't discovered the taller by .085" 255 pistons when I had my last 250 block done, so I just decked the top of the block .070" and milled the head .030" to compensate for the thicker aftermarket head gasket.

If you're going to use an aftermarket performance cam with longer then stock duration that will help to bleed off some of the cylinder pressure that comtributes to pre-ignition. Smoothing the chambers and piston helps by minimizing carbon build-up and reflects heat better.

Also tuning your carb and ignition will minimize knock, and gearing to avoid lugging will also help with the problem.

On your original question, I'm goin to go to the HP calculator (Also a compression calculator) and run the numbers on my current 250. I'll get back to you on what it says.

Adios, David

Howdy Back again:

I just ran numbers on my 250. With setting of 80% efficiency at 4,500 rpm with a 9.2:1 CR the HP came out to 156.

By upping the RPM to 5,000 it was 173 HP.

My butt-o-meter verifies those numbers.

My 250 block has stock type dished .030" over pistons, decked block .070" (Still not enough to get a decent quench effect), a Comp 260 cam.

The head is a D8 that has been ported, milled, port divider welded in, three angle valve job, back-cut intake valves, and modified to direct mount a wide base two barrel. With carbs I've used several Autolite 2100s, all with 300 cfm or more and currently a Holley 2300 500 cfm. I use a recurved Duraspark II distributor with an MSD coil.

I used a Clifford 6 into 1 header with 2" exhaust, an SROD 4 speed and an 8" read with 3.00:1 gears.

I reread Jack's overview of his original 250. The bottleneck in his system was the Carter YF. It is rated at 187 cfm- no where near enough flow to explore the potential of the rest of the engine. I think with a more appropriate carb that engine would have come alive.

If you haven't already, click on our website and check out the CR calculator. It's kinda fun. Just click on the address below my signature.

Adios, David

jamyers":1eymna2p said:

I know what Singh grooves are, but really: "PowreLynz"??? Surely you aren't going to tell me that cutting something like big screw threads into the intake ports is going to make the intake charge spin or something? Sorry, but all that "tornado" stuff does is induce turbulence via a series of high/low spots, which isn't always a good thing. Especially in the intake port.

Edit: googled powrelynz, and now I think even less of it. Basically the same thing as a rough-finished port. Makes me think of somebody paying to have their head passages polished, then paying again to have them roughed up (in a fancy way, but still).

Click to expand...

The PowerLynz don't make much sense for high-flow, high-power applications but there is some evidence that they can help THERMAL efficiency if one is seeking maximum economy. The theory of getting the puddled fuel back into useful condition (vaporized) seems valid to me.

I haven't discarded the Singh groove idea either
Joe

I'm not trying to bash anybody, and I think there's likely merit in Singh's grooves, but I still don't think there's much to something like PowerLynz that wouldn't be accomplished by stock-roughness port walls. If you want to get fancy, reshape the ports then roughen them back up. Shape seems to be where it's at anyways.

I'd think that even better, get the quench height / distance down where it can do some good, like .035. My Buick engine is set up with (iirc) 9.2 static CR, 7.5 dynamic CR, with the quench height between .030 and .035, and it runs strong on cheap 87 octane and lots of advance.

I'd think that a piston swap might be a good idea if you didn't want to mill the head and deck the block in order to get the quench where you want it.

Lazy JW":2sb4sxzs said:

The PowerLynz don't make much sense for high-flow, high-power applications but there is some evidence that they can help THERMAL efficiency if one is seeking maximum economy. The theory of getting the puddled fuel back into useful condition (vaporized) seems valid to me.

I haven't discarded the Singh groove idea either
Joe

Click to expand...

Exactly. Gaining thermal efficiency means one of two things: same power with less fuel, or more power with the same amount of fuel. The detonation resistance comes along with that. Powre Lynz has absolutely nothing to do with air flow. It's all about wet flow.