I've been working on my '81 F100 300-SROD-soon to be 3.50 open (9" rear end) setup to try and solve some Carter YFA problems. I have a good handle on that situation but it has me thinking about the next evolution of this engine.


I am trying to avoid the "slippery slope" that leads ultimately to a full rebuild. This engine has 130K miles, still doesn't burn a drop of oil, and do not want to do a bottom end until it absolutely has to be done, and for what I'm thinking it should be no problem.

Also, bear with me. I try to review what I write so it's simple and easy to understand, but it doesn't always work out that way. If something isn't clear, please ask. I also really try and do my homework so between what I read here and my shaky shade tree mechanix education can usually have something where I understand what's needed - or think I do!



Stage 1:
I already have:
> Offy C
> 1.14 2100 carb
> 2 efi exhaust manifolds.
> I have & need to choose from either a Walker Y pipe, or some factory duels - at least the front part of it - Walker Y is easier/cheaper, but duels potentially better flow.
> I need to port the exit of the efi mannys a little bit, send them out for heat coating
I'll get this together and installed. It should be a good boost w/o breaking into the engine.


Stage 2: This is where I could use a review and/or a reality check, because it's more involved.
> Head: I have a complete 240 engine and will harvest the head, send to machine shop to install bigger S.I. valves, have the head decked only as much to clean it up, and maybe some home shop port cleanup (yes, I'll read up on it again here for tips and how-to).
> Cam: I think a cam should be put in at the same time to make use of the bigger combo of valves and Stage 1 mods; this is where it starts to get slippery.




Questions:

> If I use the S.I. valves then can buy a Comp Cams kit with the stock length springs, right? I see 2 sizes - 4.750 & 4.810; as I'm putting an early head on a later engine, does it matter?

> I'm thinking either the Comp 252 or 260 cam; thoughts?

> If S.I. are not available, can use regular Chevy valves, but have to use taller springs, yes? Is it as simple when talking to the Comp Cams person tell them to include appropriate length springs for this cam?

> pressed in vs screw in studs. Should I and why? Again, length has to match valves? I'd think the machinist would be all over this as far as advice, what to use, etc.

> Roller rockers? worth the trouble and expense for a build like this, or just use regular stamped? Best deals? I read how BBC sets are used and the stud size is either 3/8" or 7/16".

> OK, last - cam bearings. If I'm putting in a new cam, then bearings too? That's tougher to do with the engine in the truck, and I'm worried about foreign debris getting in the engine. The PO has had the head off to replace the head gasket, and the oil pan off to replace that gasket also. While the pan was off he cleaned it all up good and the oil stays clean for a long time.




I'm not sure what else to add right now, but that's the basic plan. I'm getting lined up to do Stage 1 in maybe 2-3 months (gotta get an exhaust gameplan!). Stage 2 is later, but have to think about the whole system and what would work best with everything and will start ordering as money allows.

FYI future use. This truck is setup as the factory did it with the SROD trans (3 = OD4th) and a 2.46 open 9" rear. I recently located a rebuilt 3.50 open 3rd member and it will be installed soon - like next week. I was actually thinking of doing a 3.25 locker, but hard to find used and new no problem, just drop $$$. I've got $130 into this open 3.50; it was a craigslist find.

I do not like this transmission. By all accounts it's a POS, and the linkage is loose as a goose. I have to remove the shifter and modify to make room for an A/C underdash evap, so at that time I'll replace the plastic bushing at the base of the shifter - I located one on ebay and have it on my workbench. That's all the work I want to put into this transmission because I have a plan.

I have a very good, SVO World Class T5 with a 2.95 first gear currently sitting behind my hot rod Rambler with a '70 AMX 390. That engine is being upgraded and I'll also do the trans too to something like a TKO 500 or 600. I've been watching used, but that's another story. Point is I'll put that T5 in this truck. I have a good grip on what it takes to do it and that's not a priority at all right now, but that's where this is going.

 

The only issue I see here is that as an engine wears, it all wears together. So, now, if you refresh the top end and make it all top notch and tight, it's going to put extra strain on the bottom end and make it show it's age. 130k isn't too bad though, so you might never see any issues.

I've never had an issue with the Walker Y-pipe, but I don't really think they're the most efficient design. I know I'd ultimately like to have an exhaust shop make me a custom Y-Pipe, but for now, I'm quite happy with it.
As for true duals, those would definitely have a lot of fun factor, but you're doubling the cost of your exhaust setup (two cats, mufflers, etc. ) and there isn't a lot to be gained from it.

One thing my machinist told me when putting in larger valves is that there's really no reason to do it if you're not going to port it and open it up. Otherwise, you just increased the diameter of your valve without increasing the flow area. So, if you want to go larger valves, definitely make sure to open it up.

A 252 if you want it a little more modest, torquie, and fuel conscious and a 260 if you want to get a little bit more out of your setup. If you're going to be putting in larger valves, and using the higher compression 240 head, I'd lean toward the 260. As for the springs, maybe give Comp a call and see what they say.

Not sure on the Chevy valves. I've heard of people doing it, but haven't read up on it much.
I'm going with screw-in studs for mine, but I'm also doing a bit more with the build, so it'll have a bit more stress on it. The screw-in is MUCH stronger. My machinist cut and threaded the head for screw-in for about $125, and then it was another $30 for the ARP rocker studs.

Roller rockers are always nice, but they really shine at high RPMs, which is something you're probably not going to see much of. So, they're expensive with little return value.

You can inspect the cam bearings and make a decision then. If you see a brass/gold color on them, then they're worn and should be replaced. If they're shiny silver, then they're still good.

My Bronco came with a 3.00 and an SROD. I can't imagine a 2.46! I imagine there's almost no oomph. The 3.50 is going to make a huge difference. My wife's Bronco before we sold it had a 3.55 (8.8") and that thing was ZIPPY. You're going to have a new truck on your hands. Plus, with the overdrive, it'll still keep things modest on the open road.

I'm not a big fan of the SROD transmission, which is why I pulled it and replaced it with an NP-435. It's light weight, aluminum, and like you said, loose and sloppy, and still was after I had it professionally rebuilt (not the best use of my money).
A 5 speed sounds like it'd be great. You'll lose a little bit with the 2.95 first (since the SROD is a 3.34), but with the 3.50, it'll still be a lot more than the SROD and the 2.46 rear you have now! Sounds like a good setup.

 

Hey AB, thanks for the feedback. I hear ya about the engine wearing together, which is why I'm apprehensive about opening the engine up for any reason other than to fix something like a leak.

For now, I'll do the stage 1 as outlined. I'm leaning to the Walker Y pipe, it's simple to set up and I already have it. Still figuring out what to use for the rest of the exhaust system.

I see fairly often on Craigslist new take off exhaust systems from modern truck and cars, and some are reasonable $$$. I figure if I get a system off a new truck with a bigger engine, it'll be quiet, plenty of flow for my needs, and best of all economical to install. I've got one now trying to chase down, but having a hard time getting response from the seller.

And yes, I expect the 3.50 rear to wake that old truck up a bit. The SROD will stay in there for awhile, but I'm keeping an eye out for the bellhousing and other bits I'll need for the T5 install.

 

There's just a couple of things I'd add to AB's write up. The first is regarding the roller rockers. Rr's allow you to test and know if the roller tip is contacting the valve stem in the center, and not causing sideways pressure. Knowing this allows you to 'adjust' with p.rod length.

The other thing is that Ford changed the valve length in about 1985. That is why SI shows the different sizes.

Each cam manufacturer recommends a specific spring tension for each cam, and so knows and recommends that spring with their kit. With that spring will come the installed height of the spring, which is achieved with shims.

The sbc 1.94/1.60 valves are a tenth of an inch longer than the oem Ford valves. So, even after shaving my block and head, I still needed [I]longer[I]push rods.

 

How about this for Stage 2: Instead of going the big valve 240 head route, just do a Comp cam 252 full kit? (https://www.summitracing.com/parts/c...view/make/ford) That would complement the intake and exhaust mods, be easy to install, and shouldn't stress the engine too much to affect reliability.

Sound like a plan?

It's much better already with the 3.50 rear end mod and the Redhead steering box. I'll live with the SROD slushbox for the time being until after the engine mods.

 

There is no reason you can't do a top end rebuild if the short block is in good condition. Do a compression test and install a mechanical oil pressure gauge. If you've got good oil pressure and good even compression go ahead with the mods you want to do.

And as far as the 240 head goes. I would swap on the 240 head even if you decide against larger valves. The small bump in compression will help out. But the way I feel about it, is anything you can do to increase the head flow is going to benefit you. Go with the 1.94/1.60 valves. And either have a shop do some porting in your bowl areas or do a home port job on it. If you don't want to do a full port & polish then focus your attention in the bowl areas. That is where you will see the biggest gains when porting the 240/300 heads.

 

The thing is it really runs well now - doesn't burn any oil, good compression, etc. It goes back to the slippery slope scenario mentioned in my earlier post.

No argument there, and I think I will start on that 240 head here sometime with the larger valves and porting. I currently have 2 extra engines ('88 efi & 60's 240) and 3 heads - 240, efi, and 80s carb.

Actually, the efi head is rebuilt - stock - but that would bump compression a little bit and is ready to go. Maybe with the Comp 252 would be a good combo? Would be a compromise for sure vs the big valve 240 & Comp 260, but could put this on and forget about it for a while and get to other parts of the truck more important. Something else to remember is all this equals $$$, and right now I already have everything except the cam kit if going to either no head replacement, or the efi (other than gaskets). I can better spend that money elsewhere for a while.

edit: I forgot to address your oil pressure suggestion above. I do plan to put an oil pressure gauge in the truck as I only have an idiot light right now. I will make sure to check that first, but I have no reason to believe it isn't good because of how well this engine runs, but ya never know until a gauge is on it so good suggestion, thanks.

 

Replacing/modifying the top end of an engine with a good shortblock is not going to cause the shortblock to fail.

Here's my suggestions.

Option 1: If your engine runs good, don't even open it up. Do your stage 1 mods you listed. Call it good and enjoy it.

Option 2: Use your current shortblock. Swap on a modified 240 head and swap in some higher ratio rocker arms ( instead of a cam swap ) . Don't even mess with the shortblock at all. Tearing into the shortblock is when things really start sliding down that slippery slope.

Option 3: Do your stage 1 mods to your current engine. And then rebuild/build up one of your spare engines. This allows you to enjoy your current set up without the long down time. And you can build your spare engine exactly as you want it with no worries about hurting your current set up. And you can collect parts and do the build over time. Then when it's finished just swap engines.



Out of the heads you've got the 240 is the clear choice. The EFI head is not a good head for a modified carb engine. Shrouded valves and the fast burn chambers not the best for modifying the engine. And your 80's carb head isn't going to give you the compression boost. And depending on it's age it might have the pedestal mount rocker arms which will require push rod guide plates if you want to change out rocker arms.


Here's my opinion on the camshafts. Again this is just my opinion and that doesn't mean a whole lot. I feel any aftermarket cam smaller then the Comp 268 is a waste of money. I'd just swap in the higher ratio rocker arms over a 252 or 260 cam.

 

I know the efi head is good for mostly stock applications, but also thought it would be good for the moderate compression increase and the package like I noted above.

I do have a set of the increased ratio rocker arms new in the box and that would be an easy swap along with the intake and exhaust manifold stage 1 mod. I think I'll just look at doing the better manifolds, get it sorted out, then do the rocker arms so I don't have a mess of mods all at once.

Interesting take on the camshafts; I would have thought either of the smaller cams would help in moderate situations, but I'll consider your opinion and do some more digging. I could do the rocker arm swap and see how it affects performance; that is an easy plus reversible mod. Thanks for the ideas!

PS Rebuilding one of the extra engines is my ultimate goal and I want to plan it out for performance and longevity, but that's down the road a yr or more until I get more important mods/improvements done. Yet another reason to only do a certain amount to the one that's in there now. So, I'll stay well on top of the slope and avoid slipping down lol!

 

Unless your current head needs rebuilding, I don't see any benefit to swapping on a stock efi head. The whole purpose of the head swap would be to increase the performance. If you aren't going to use the 240 head I would just run the one that's on the engine.

The head & camshaft really all depends on what the goal is for the truck. Is it a daily driver? Work truck? Hot rod? Are you after performance, mileage, reliability or something else?

 

Yes! All of the above.

OK, it is a street truck and a daily driver, altho I'm retired so that means it doesn't always get used daily or even several days. Light truck work, I want more performance with some somewhat reasonable mpg. And I do use it to travel. It went to Michigan last month, and maybe Key West in a couple of weeks. And a possible Arizona run in Jan or Feb.

So, efi head is a no go, no problem, just a random thought. The 240 head would require a bit of parts and logistics getting it done the way I want, so that will need to be shelved for a while.

I'm really thinking the offy, 2100, efi manifolds, and increased ratio factory Cheby rockers will be the way to go, and do it in 2 stages, with the rockers added after I get the intake & exhaust sorted out.

That will work easy enough without getting too tangled up with add ons that would make a fairly simple project get out of control and hard to finish.