250 inline 6 mild perfromance upgrades?

[69stang250]

Hey, I'm a little new to engine performance mods so bare with me.

When I was 18 I bought a 69 mustang fastback to fix up with my dad and with intention to remove the inline 6 and swap it for a v8. We ended up restoring it with the inline 6 instead because I took an instant liking to it.

I want to get a bit more of a punch out of the inline 6 but I want to keep it as original as I can (which means no new aluminum heads). I’m not looking for the fastest it can go but even if it could move off a little quicker at a stoplight that would be awesome. Although, I don’t want to abuse the engine and risk destroying parts. The engine was just tunesd up and had the valves grinded recently. I’ve changed the spark plugs and plug wires and replaced the coil with a high performance coil. I’m also about to remove the mechanical fan and place a dual fan shroud on the radiator. I bought a decarb kit and replaced all the gaskets. The engine is also running on synthetic oil with lucas oil stabilizer. The exhaust is kind of a cheap dual out with an empty muffler pan just to get a rumble sound. Any advice or suggestions are really appreciated. Thanks

 

[rocklord]

Purchase the Falcon Six Porformance Handbook, read it, then reread it.

The Handbook will help you determine what you can do to increase performance/efficiency.

One of the first things you want to change out is the distributor. Upgrade to the DSII, adding the recurve springs. This will give you a hotter spark.

Eventually, you may want to purchase a later model head (casting codes beginning with D7, D8,E0, or E1) for the larger valve, hardened valve seats, and larger volume intake log, and mill the intake for a direct mount 2Bbl. The new carb can be hidden by the stock air cleaner.

By the way, welcome to the forum.

 

[JackFish]

One simple thing I did in the beginning to my 200 was install a timing chain with a four degree advance.
It really helped pep up the bottom end, but you might lose a mile an hour or two off the top end, how much time do you spend at WOT?

 

[Gene Fiore]

One simple thing I did in the beginning to my 200 was install a timing chain with a four degree advance.

A timing chain with cam advance capability is not available for the 250...only way to advance the cam on a 250 that I know of is with an offset crank key.

 

[MustangSix]

Adding a Pertronix or Duraspark electronic ignition will noticeably improve idle and drivability. A recurve with a set of lighter springs to bring in the advance earlier might help a little. The log head has "lazy" chambers and the huge negative piston-to-deck height on the 250 only makes it burn slower, but be careful. The lack of quench makes the engine a bit detonation prone too, so too much advance to quickly can cause light throttle pinging.

Removing the fan and adding an electric fan puts five or six more horses back into the drivetrain. A set of headers won't hurt either. There's only another 6-8 horses there, but combined with the rest, it begins to add up.

I picked up a bump in power by pocket porting the head. The exhaust bowls are really bad. I think you could easily gain 7-10 hp by blending the seats and removing all the lumps and other flow impediments. Your car may or may not have air injection bumps in the exhaust ports, but those could be ground out. The intakes are hard to work, but there's some definite gains to be had there as well.

The last thing might be to add a direct mount 2bbl. The 250 is badly under-carbureted and can use the extra CFM. The Autolites seem to be a good match for a stock engine.

 

[MPGmustang]

Welcome to the Forum!

the 250 has alot of potential, to push it little more is very easy, take the head (or get a 78+ head), mill it down to 50-52cc (keep them even) chambers and port the intake bowls where the valve comes out, the exhaust only take 50-75% of what you took from the intake, this helps MPG and it's very cheap (aim for 65%-75% exhaust flow compared to intake flow). Going to a bigger carb is really the best thing you can do, if you go camshaft you can do a 2-1bbl adaptor and be up to ~110hp at the tires, or just the head a direct mount 2bbl will do ~95 with the stock cam and valve train. with both, cam and direct 2bbl, will push you to the 120hp+ if you go with a header and dual 1.75 or single 2.25 pipe(s).

An electric fan will unlock alot of rev, not just higher rpm' but the whole range, it increased my mpg by 2 in city and I've seen up to 5-9mpg more on the road. if not running AC, ur stock 65amp alt is safe with a 1800-2400cfm fan (or combined CFM with your dual assembly) will be plenty put a 160t-stat in and set the electric fan to turn on from the t-stat housing around 195* and off at 185* range. you'll notice the fan turn off on any freeway cause it don't need it, increasing mpg more. (not to mention it be WAY easier to spin tire compared with the mech fan...)

the ignition I agree with MustangSix, Pertronix or Duraspark with electronic igniton will help alot in power and MPG, not to mention idle and start up.

if you went engine rebuild, Zero deck the block, resurface the head for 9.3 CR and put in stock 7cc dished pistons with a 260or264 112 cam with max lift. it will be smooth and you'll feel a big difference, I esimate it to be around the 135hp and torque to be around 160+ (which is what you feel on the line and would enjoy more)

Now if you're going for passing power on freeway, that's a different animal, basicly it's gearing for the Inline6 and what has been mentioned, I recommend a thourgh engine rebuild and either an AOD or a t-5 with 3.8gear 8inch rear end. OD will be around 2800rpm @ 70mph and passing will be in the sweet spot around 4000rpm.

IMO the i6 is peculiar, at 65-70mph I get 2300rpm and 21mpg... at 85mph I get 2900rpm and 25mpg go figure, using a 3.2 rear gear currently think it should be 3.5 or 3.8 and I'll get 25+mpg at 65-70 due to less wind at the slower speed and better engine effecincy...

it depends on how stock looking you want it, you can get decent numbers out of a 1bbl, but it will have to be a later 1bbl like a carter YF (I got 114hp on my very warmed up 200)

all in all, the engine will be easier to maintain, the car will be more of a joy to drive and less of a cost in the long run. IMO all I mentioned is easy to do, just ask questions if you don't understand or want more details, it's better to measure twice cut once, or ask twice to rebuild/modify once and do it all at one time.

Good Luck!
Richard

 

[JackFish]

One simple thing I did in the beginning to my 200 was install a timing chain with a four degree advance.

A timing chain with cam advance capability is not available for the 250...only way to advance the cam on a 250 that I know of is with an offset crank key.

I've offset the timing on my engine with a stock timing chain.
You just move it by a tooth, or two, and degree it to verify.
I've compared the gearsets with the JPI double roller, and they are exactly the same.
I used the double roller, and then just duplicated the setup with the stock gear.
Mostly because the chain in my double roller set was getting slack, and I challenge you to find just a replacement chain.

 

[bmbm40]

69 Fastback is one of my favorite Mustangs. What transmission do you have?
Definately get the Manual, it is a great resource and the DSII is a must no matter what you do as far as other upgrades. These are good tips from the guys here for the DSII, electric fan and headers for a mild increase. If you can find a late model head and do the 2v conversion with some porting and milling that is the plan I have for my 250 and i have researched this extensively. Plus I can mod the head at my pace and then do the swap hopefully in one day so no extended down time for the Bronco.