Hey guys-

Just last night i purchased a modifiyed six. its bored 50 over and has 390 pistons with a cam. And it also has 10:1 conpression. It was originally carborated will fuel injection work with this conpression well and will i benifit alot from port and polishing the head? the motor was in a 85 truck and iam going to put it in my 92. and help is appreciated.

 

Someone has to have some input.

 

Try asking this question at fordsix.com. They are a little more performance oriented sometimes. Goodluck on getting answers.

 

sounds like its gonna scream for a six

 

u should pick up a EFI head, they have a fast burn combustion chamber. in all reality, if u can...keep it carb'd, the EFI will be a pain in the posterior.

 

Yes port it out, the head holds this engine back, as long as you can supply it with fuel you'll gain some top-end outta this engine, but be careful how much you port it cause you could lose it's bottom end and lose this engines sellin point. Pop on your efi manifolds off your 92 or else get some headers to, then make sure you get a 4barrel for it. She'll run goooood after all that.

 

Thanks for the advice guys. The motor currently has a aluminum intake with a 4barrel I just wanted to keep the efi for better starts in the winter. I was also going to purchace a chip to help it out. Should i install the mustang injectors like everyone talks about doing here?
I have found a engine builder who comes highly recommended around here to do my head work. He also has a engine dyno. I hope i can see some good numbers out of this motor. Any ideas?

 

Since the efi heads have the different combustion chamber I should take the head of the 92 and have the work dont to that? Is it really that big of a difference?

 

Check with him and make sure crank sensor and stuff will all work first, but it will probly be better with the 4 barrel, as far as winter starts, get a carb with an auto choke, pump the pedal a couple times and it will start right up just like the efi, Our old '86 Dodge 360 would fire right up just as quick as you could turn the key with only one pump of the gas pedal and without even being plugged in. EFI are worse in the winter in my opinion, they have to be plugged in.

 

how many horses is this guy gonna be pushin?

 

That's a bit of compression for a street motor. I hope it's a big cam to bleed off a little cylinder pressure (that means the head had better be done up right too). You'll have to play with the ignition curve to get it not to ping. As far as EFI goes, this motor will likely not run well at all with the stock FI setup. Compression will raise heat, which raises nitrogen oxide emissions. Combine that with a naturally lean cruise mixture, and things will get pretty hot under the hood quick. And enough cam to make that kind of compression kosher with commonly available pump gas will throw the computer for a loop. There will be input from various sensors not in line with mapped operating parameters. Won't run right.

If you want it to work right with EFI (cold-start driveability is indeed better if it works properly, as is mileage...) consider a MegaSquirt controller.

You slap an EFI head on there if it's the larger chamber head on there now, and you'll bump compression up to the 11:1 range. What you will have then is a popcorn machine, and a time bomb. Not a daily driver.
All that said, the stock head really holds these motors back. By all means, port the sucker. For the sake of easy tuneability, keep the thing carbureted. Needs a header. No question. And a 3" sewer pipe after the Y-pipe.

Desktop Dyno says 209 hp at 3500 to 4000 , 333 lbf at 2500 with stock head flow numbers, valve size, small-tube open header (much like 3" exhaust), Crane 260 cam, single-plane, 600 CFM carb. I think DD's manifold selection sucks. Doesn't tell the whole story. Nonetheless, its estimates are remarkably in the right ballpark. With the 272 Crane cam, nothing else changed, we're looking at 224 hp @ 4000, 320 lbf @ 3000, and a marked decline in low-end torque output, but more on top. To give you a little idea of how much the head is holding things back, here are the same 2 cam profiles using flow numbers from a stock smallblock Chevy head (common 882 casting), 1.94+ 1.6 valves (these valve sizes will fit in 300 head...), all other data the same...

Ready for a real eye-opener? This ain't just paper math, folks. This is just the way it is:

260: 275 hp @ 4500, 354 lbf @ 3500

272: 297 hp (w00t!) @ 5000, 349 lbf @ 3500

Any questions?

Note: With the 272 cam, although peak torque figures are close here, low end torque still sucks bricks thru a straw by comparison. The 260 torque "curve" is nice and flattish from off-idle.

Of course, the cylinder pressure with 10:1 and the 260 cam is a hair on the ridiculous side for pump gas...never mind power output, I want to know cold-crank compression figures!

 

It can be made to run on the stock FI, on the Dodgetrucks.org Forums the guys are running 408 Ci strokers, one guy has a 450 horse one running with a Mopar perf PCM, 58mm throttle body, headers, and I can't remember the injector size. It can run, he just has to find someone who can program the computer for that cam and the fuel requirments.

 

thanks guys for the great respons's. I have made the decision to go with a carb. Whose header will give me the best performance. Iam deffinetly goin to go with the 272 cam with bigger valves and definetly some port work. What should i run for a ignition setup. Will I have to do anything to the factory wiring due to the fact it wont be running the fuel injection anymore. I also have the A4od tranny. I plan on doing the swap in January some time when work slows down. This truck should fly!!!

 

get an MSD ignition

 

That definately sounds like a hot setup. I'm just hoping with my next 300 (my new truck) that it won't have the mystery rattle that plagued my original one and i'll be able to build it up some.

Here's to ya! Good luck!