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351W Cobra R Wanna-Be

3K views 24 replies 6 participants last post by  PSIG 
#1 ·
I'm gathering parts to build a 351W/ T5 to swap into my 67 Country Sedan 10 passenger Station Wagon. It currently has a 289 2V with FMX automatic 3.00:1 9" rear. I'm not looking to go racing but I would like to have enough power to get out of my own way. When driven gently, I'd like to break 20mpg on the highway. Daily driven in light city traffic and a couple cross country road trips a year. Would like to be able to pull a small popup camper on occasion too. I have been reading up on the 351W built for the 1st gen Lightning and Cobra-R and figured this might be a good way to go. I am on a paper thin budget so most all parts are going to be sourced from the junkyard.

Here's my Junkyard shopping list so far:
-351W roller(F4TE )
-Explorer GT40P heads (I'm aware of the header issues.)
-Explorer upper Intake (Welcome to B.C. Broncos! The best source for Early Bronco Parts for your 66-77 Ford Bronco has an adapter to the 5.8 lower)
-Explorer Serpentine and front dress.
-Mustang 5.0 Engine harness and EEC
-Inertia Sw, Sensors, misc.

The Lightning had really low compression (8.8 : 1). What would be the best way to bump it up 9.5 -10:1, flat top pistons or am I stuck machining the block or heads? Is an extra point and a half extra CR really worth it? Any cam suggestions? T5 tranny, 3.00 rear, 4,277 lbs (slightly lighter than the Lightning). I don't have the current tire size on me.
 
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#4 ·
The 3.00 rear gear may be pretty tall to run with an overdrive. You would probably want a real mild cam to make enough torque at a low RPM with the OD. With your trans gear ratios, rear gear ratio and overall tire diameter you can calculate engine RPM at any speed, so you can use that info to help plan your power band needs, which should help inform your cam choice. If you have a cam you can work the other way to help determine a more ideal rear gear for the engine power band.
 
#6 · (Edited)
The current tires are P215/75R15 on 15" steelies. But when the funds become available, I'd like some 18-20" wheels. I know I need mainly the low down torque and probably won't use 5th except for the Freeway. Generic RV Cam or am I better off shelling out a little extra for a custom grind to suit my specific combo?
 
#5 ·
If I mill the heads, I'll have to mill the intake along with it to get everything to match up right? Shorter push rods? I'll have to look at the serpentine brackets on the Explorer but I think some are bolted to the heads. Wont milling cause a misalignment with the bracket?

How much should I expect to pay to get the heads (and Intake if needed) milled along with freshened up? Anyone know and reputable shops in Corpus Christi? South East TX?
 
#7 ·
As-stated, the cam is very important to getting both the power and mileage, and with regular fuel. The cam timing causes greater cylinder pressure with the 'smaller' cam, and why it uses lower CR than when used with the hotter cam, and why the hotter cam can use greater CR. The point is, unless you are willing to always pay for higher-grade fuel along with your compression increase, you must make a very specific choice of cam. Nothing 'generic' about it.

My suggestion is to use the stock F4 roller and compression, or the Lightning roller and shallower-dish pistons to get the stock Lightning compression without milling, unless you are prepared to do calculating for cam/CR planning. Use care here, as it's a proven combination, with only minimal gains for your application (and some potential downsides) by changing it.

David

PS: The Explorer serpentine is cast for the shorter 5.0L block, and will require some fabrication to make it work properly on the 5.8L.
 
#10 ·
28" tire, 3.00 rear, .68 5th Gear at 70 Mph= 1714 RPM. Is this too low? I fully understand that cam selection is crucial. When I said "generic" RV Cam, I was simply referring to an off the shelf Edelbrock, Isky, etc, cam suitable for towing, RV's and such as opposed to a custom ground cam specific to my exact engine build/ drivetrain/ weight/ performance needs.
 
#14 · (Edited)
i have had a few behemouth old wagons so i can relate to what you are saying.

it "should" get up to speed with a good basically stock 351 with the 3.00 gears and 5 speed trans but obviously it won't have impressive acceleration . The ideal rpm for maximum mph is what you need to determine so you can determine what rear gear is going to achieve that, and off the top of my head, im guessing that with your 3.00 gears and if you have a .68 5th gear, you would need to be going around 70 mph to achieve that, or in other words, somewhere around 2000 rpm is going to be the most efficient for a nearly stock build and your weight of vehicle.

with the high water temp and multi fire ignition, you can run really lean fuel ratios and a direct port injection instead of a throttle body injection s also helpful

an under drive pulley system or under drive water pump pulley will also help a little and so will electric fans . lincoln, taurus and contour fans are all xlnt and can be modded to fit and are cheap at the junk yard . a fan controller will also help.

increasing compression will also help, however, you get to a point where you can no longer use the cheapest gas so it can become a bit of a trade off.

also try to set the quench/squish to .035" to .042".

heres a free online calculator in vase you havent tried one

RPM/MPH From Gear Ratio Calculator by Wallace Racing
 
#15 ·
I was playing with various calculators the other day and came up with about 1750 RPM at 70mph with .68 5th gear 3.00 rear, and 28"tires. According to this calculator 2000 RPM I'll be at 81 mph. Perfect for the interstate road trips. I can always down shift to pass. What determines the ideal RPM for an engine or how do I build to suit a given RPM? I plan on running factory EFI intake off a 2001 Explorer 5.0. It has MPFI not the old TBI. As far as multi Spark Ignition I wanted to run the EDIS ignition out of the Explorer to have total computer control over the spark. The MS would be controlling it all.
 
#17 · (Edited)
nope, 1750 is not the most efficient rpm for your combo because your car weighs so much . this is what im trying to tell you . the lighter your car, the lower the most efficient rpm will be.

experience or a dyno determines the best rpm . on a dyno it shows up under the bsfc which is the brake specific fuel consumption column.

if it was me, i would use 3.25 or 3.43 gears for your app.
.
 
#16 ·
Honestly I would go with a 3.50ish gear at least. I have a completely different setup as I am shooting for a fast car, but I run a t5 and 3.80 gears and would like to be lower especially in 5th gear. Now I'm on a 302 in a lighter car. The OD would make it drive perfect and the 3.50 gears would be best bang for your buck and put you at a better cruising rpm. Even with my lower gears I have to be doing 70-80 for the car to feel like it's in a decent spot and it's not a hot engine. Just stock roller bottom, TF heads and a Fcam. Also I am only running a 25-26" tall tire vs a bigger tire on a bigger car like yours. That would solve your acceleration and would be in a sweet spot for cruising in 5th.
 
#18 ·
Sooo... no amount of cam will help? If I do wind up doing a rear gear swap it will be a little down the road. Just always seemed funny people swapping out their trannys for OD to "save on fuel", only to swap out rear end to wind up right back where they started. Guess I'll see 1st hand how funny it really is?!?
 
#19 ·
I would wait and see what feels right to you as you make your changes. The BSFC is primarily controlled by cam timing and resulting VE, and where in that best range depends on the engine, weight, gearing, tires, and especially drag at speed, which change where in that range it runs. It is interesting to note that the trucks using the F4 stock roller cam (all roller 302/351 trucks and Explorer) have similar OD gearing, and default to a 3.27 or similar gear, though the tires are a bit taller also. ;) Remember, with a T5 3.35 1st gear, your 3.00's will act like 4.05's at the stoplight.

It can often rest on personal preference, and I had a car with T5 and stock 2.75:1 gears before I swapped them. At 4200 pounds and 26.6" tires, it was a very happy car for general driving, and was happy at cruise to hit 5th at 45 mph with it's healthy torque. Not necessarily best for economy, but happy. When I swapped to 3.50's, 1st was now too low for casual driving, and I defaulted to 2nd to leave stoplights, while often hitting 5th on 4-lane roads around town. If that was your car, which gears would you choose? It's necessary to plan in order to avoid problems, but this may be a 'tweak'. That's why I think you might consider holding-off, and make some cloudy future decisions when you get there, and know the issues and rewards of that reality. My 2¢.

David
 
#21 ·
I would wait and see what feels right to you as you make your changes. The BSFC is primarily controlled by cam timing and resulting VE, and where in that best range depends on the engine, weight, gearing, tires, and especially drag at speed, which change where in that range it runs.
Do you think I'd be better off getting a custom cam grind suited to these parameters or contacting Comp (or another cam company) to have their guru's help selecting one of their grinds already available?

It is interesting to note that the trucks using the F4 stock roller cam (all roller 302/351 trucks and Explorer) have similar OD gearing, and default to a 3.27 or similar gear, though the tires are a bit taller also. Remember, with a T5 3.35 1st gear, your 3.00's will act like 4.05's at the stoplight.
That is one of the reasons I didn't want to change the rear gear. I knew it was lower than the FMX or AOD but never did the math.

It can often rest on personal preference, and I had a car with T5 and stock 2.75:1 gears before I swapped them. At 4200 pounds and 26.6" tires, it was a very happy car for general driving, and was happy at cruise to hit 5th at 45 mph with it's healthy torque. Not necessarily best for economy, but happy. When I swapped to 3.50's, 1st was now too low for casual driving, and I defaulted to 2nd to leave stoplights, while often hitting 5th on 4-lane roads around town. If that was your car, which gears would you choose? It's necessary to plan in order to avoid problems, but this may be a 'tweak'. That's why I think you might consider holding-off, and make some cloudy future decisions when you get there, and know the issues and rewards of that reality. My 2¢.
David
I currently drive a 99 Toyota Tacoma for my daily driver. Not sure of the gearing with its 2.4L 4 banger. While getting up to speed on the Free Way, I'm frequently reaching over to try to shift into 6th. :p
Put-putting around the neighbor hood, I often take off from 2nd. 1st when needed is only used for a brief second. It's good when I have to haul something though. I'd rather have a slightly more useable 1st gear in the Station Wagon and shift into 5th at a higher speed so I can cruise down the Interstate at 75-80 mph and not feel like I need to grab another gear.

Like you said though, I will be holding off on any gear changing. I still need to source an engine. I'm holding out for a Junk Yard Jewel!
 
#22 ·
It would be fun to spend your time and money for you, but there is no baseline (yet) for your application and how you use it. While it's good to plan a cam change before it's less convenient later, it's not a huge deal to do it when you know exactly what you want (and don't want) after you get this much of it going, and tuned to your use. While some others may have a better handle on your specific uses and preferences, I don't, so if it were me I'd analyze the results of what sounds like a good package for you already before trying to out-guess it. That's me. Do your thing.

David
 
#24 ·
While it's good to plan a cam change before it's less convenient later, it's not a huge deal to do it when you know exactly what you want (and don't want) after you get this much of it going, and tuned to your use.
David
Thanks, that's the kind advice I need. I just assumed I'd be better to do while the engine is out of the car and getting freshened up. The stock truck cam might fit my needs just fine and I could allocate the funds elsewhere.

I was unaware that Comp had any Guru's and I am a Comp dealer. As far as a custom cam goes, it never hurts to ask a cam grinder what they think, and in this case I would call chris straub at straubtechnologies.
Sorry, never bought a cam. Assumed their sales staff would have the technical knowledge to point out their best cam for my application. If I'm not satisfied with the stock truck cam, I'll be sure to look up Chris Struab.
 
#25 ·
Just for comparison, the base 5.0L roller cam for cars, and the more aggressive split-pattern F4TE "truck" cam spec's. The ~30hp SAE rated increase of the Explorer versions over others was primarily the heads and intake with this cam. The same would generally apply to the 351W/5.8L packages.

David

 
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