"Another" Flathead Question, bore vs stroke

I have already read the tech articles on flatheads and my site search function is not working right now so I can't find the answer I need.

I am about to start a rebuild on a flathead and had initially intended to use a big stroke, either 4.125" or 4.25" and from what I've read, I shouldn'd go any larger on my bore than 3.3125". So the question is, would the extra say 20 to 30 cu from stroking the engine make that big of a difference over using a 4" crank? Really, how big is too big on these engines in bore and stroke?

I "want" as high a horsepower, streetable engine as I can run, 3x2 intake, 3/4 cam, aluminum heads, etc. This will be going into a '50 Ford Tudor sedan, S-10 T-5 and 8" ford rear end w/ 3.55 gears.

 

The gain in cuin from the Ford 3-3/4" to the Merc 4" is 16 cuin (239 vs. 255) With that the extra 1/8" stroke with a 4-1/8" crank will be 8 cuin more than the Merc, crank. If you think the 1 cuin/cylinder gain will help much I don't think you'll be able to feel it in the seat of your pants. Better off ditching the 3-2's and install a blower that you will be able to feel in the seat of your pants and the woodie you'll gain in the front of your pants. I installed the Joe Abbin Roadrunner blower kit on mine 4-1/2 years ago and never looked back.....it made a hell of a difference with my Merc motor w/4" stroke. I replaced the 3-2's on mine with a Holley 600 four barrel when I installed the blower.

Just my $0.02 worth which is viewed by many as not much.

 

The old timer that built my engine said, " you'll gain a lot more by making a flathead breath, than you will by adding stroke"

 

The 3 5/16 bore is very safe. Most good late blocks will safely go 3 3/8, with of course some risk. 3 7/16 is getting shaky...except maybe for 99 blocks. Consider the bigger bore.
Anything over 4" stroke starts getting real pricey per cube, as noted above, and you have high piston speeds, greater sideloads on pistons, and such evils to contend with.

 

3-3/8" bore by 4-1/8" is about all you'll want to do. Anything more than that on either the bore or stroke and you're talking about really flirting with trouble, and TONS more money. Not worth it unless you're really rich or trying to set some kind of speed record.

Even the extra 1/8" stroke from 4 to 4-1/8" isn't worth spending money on really. But, if you have a 4-1/8" crank, you can use it without having to modify the block.

Take a look on my web site. That 32 has a hot flathead in it we built. 3-3/8" x 4-1/8". Spalding Flamethrower ignition. Winfield SU1-A cam, 3 Strombergs, Offy heads, 8:1 compression. Had more power than needed and never ran hot. Just my 2 cents....

Matt

 

Adding cubic inches to a flathead without increasing its ability to breath is an exercise in expense (as noted above). The flathead is limited on volumetric efficiency and adding cubic inches WITHOUT dramatic improvements in breathing ability is really compounding the problem. Blown 49 suggests adding a blower; adding a blower will in the long run be less expensive than Stroking to 4.250 and then trying to modify ports,valves camshafts etc. to feed the extra cubic inches. Navarro destroked a 239 and added a blower; by doing so he improved the volumetric efficiency of the engine and went faster on less cubic inches. The more cubic inches you try to feed through those convoluted ports the less efficient it becomes. Think about how a 3&5/16 by 4 with adequate ports and valves would breathe with a blower as compared to a larger cubic inch deal and the cost advantage becomes more clear.

 

To clarify my reason for this question. I had initially planned on rebuilding a Ford flathead. I went and looked a an engine a friend told me about at a local machine shop. Guy had some work done and changed his mind, been sitting for a couple of years, etc.... Long story short, it turns out it was a Merc engine w/ a 4" crank. I couldn't pay him fast enough. Good block, magnafluxed, cleaned and no cracks, new valve seats, bored .060 over, new valve guides, new cam bearings, a 4" crank, a 3-3/4 crank he had lying around, stock heads (unmolested) and a crate of misc. bolts and stuff.

I had planned on having to replace the crank so going to a 4-1/8 or 4-1/4 wasn't unresonable, just a couple hundred bucks in the stroker kit. So now I have a 4" crank, how can I get the same displacement? Larger bore...

So, a blower is an option, it will just delay the build a while longer, the initial cost is higher.

Bruce says a 3-3/8 bore should be okay, a few others seem to agree, but most say no. What are the extra costs involved with going to a larger bore?

Fox, love your combo, it's perfect for the couple. You should write a tech on carb set up, there are always questions on the 3x2 stroms.

KSFats, breathing improvements are already planned into the build. Larger valves and relieving and porting as much as possible to increase the flow and keep the compression ration up around 8:1.

 

Blower: One advantage of this is that you can do it in stages. Build engine with cam/pistons/compression suitable for blower, add blower later when financially recovered.
3 3/8's is usually ok...look at amount of rust pitting in jackets, perhaps probe at things with sonic test, and decide whether to try it. Block could be sleeved back if you lose the gamble, but of course then you're into more money and less displacement.

 

50, here is something to think about; with your .060 overbore and the 4 inch crank you have 265 cubic inches, add the modifications you have indicated and you'll have a good street package PLUS you have left room for a future overbore and stroke increase when its time to freshen up.Sounds like you have gotten into a pretty good package deal;congratulations on your find. Put 'er together and let it "chuckle"!! fats

 

KS, I understand that the engine build up as a whole needs to be balanced, i.e. correct carburation, cam, displacement ability to breath etc. That being said, I have always been a firm believer in that, "there is no substitution for cubic inches" I need to buy new pistons anyhow, so I am going to go bigger, just how much bigger is what I'm trying to figure out.

I appriciate all the help and comments, any other points of view out there>

 

Blown49 has the right idea. Remember also, that the bigger the bore, the thinner the walls and you create more head. You don't create overheating problems.

 

I meant to say, "you create more HEAT."

 

I like the .125" bore because, as Bruce said, most will go to 3/8" so you have one more rebuild with readily available pistons.

Another expense no one has seemed to mention (I only skimmed the responses) is piston price. You can get pistons for the 4" crank loads cheaper than for the stroker 4+ cranks.

If you're going to stroke, why not turn down to the 2.0 journal size & use the Scat rods - readily available Buick bearings too.

Having said all that, you'll be hard pressed to get loads more performance out once you exceed 300 cu-in - the breathing becomes the major bottleneck - even with 1.6" valves. The funky inverted S turn the intake charge must make to get into the cylinder will be your biggest obstacle.

The cure - supercharging. As has been mentioned, $ for $ you'll be ahead power wise by sticking to the tried & true 276" (4" crank, .125" bore) and spend your money on the Roadrunner kit...

 

Good Thread! Having run big cube flatheads, blown flatheads and blown big club flatheads -- there are some things to consider on not just cost, but also block work, future rebores, etc..

Here is my combination for your motor:

1) 3 5/16 bore, 4" stroke, 49-53 rods. Unless you're running some heavy boost and high RPM, you'll be fine with stock rods. I recommend a somewhat conservative bore -- at 3 5/16, that leaves you an easy 3 5/16 + .030 and a 3 3/8 bore later on.

2) If you're running heavy boost and higher RPM (over 6 lbs or so and over 5200 - 5500) then consider some stronger rods and main cap supports or billet caps.

3) If you are buying pistons and replacing rods (high output blown motor), then maybe stroke the crank an additional 1/8 and run the H-Beam rods and Buick bearings --- better deal than trying to find 21A of 91A rods, full-floater bearings, etc.. Having a Merc crank offset ground will probably cost you $200 - $300.

3) Make Your Decision on the Blower on the Front End: If I'm going to run a blower, then I'm going to make decisions on main-cap supports, maybe billet caps, rods, piston types and initial compression ratio. If you have to buy pistons anyway - then you'll want to buy them with the end-game in consideration. I'd probably run forged pistons with a blown motor. Also, I'm going to setup my heads and my compression ratio with the blower in miind -- you don't want to detonate the thing . . . hurts lots of parts real fast.

4) Porting, Relieving, Big Valves, etc: You can spend a ton of time (if you have the skills and eqiupment) on porting, reliefs, big valves, etc..

The thing you need to consider is that "yes" . . . all this work will definitely increase your horsepower and RPM range -- especially if you're racing the thing. But - it can be very expensive and time consuming to do -- so really think about how far you want to bore the block . . . cause when you run out of bore, all your time and $$$ in port/valve work goes out the door. Personally, I don't like to sleeve 8 cylinders with a blown motor. That many sleeves just weakens too many things - just my opinion.

A blower will give you the most horsepower potential of almost anything you can do on a flathead --- so if you have medium cubes, good breathing and a blower . . . you've got the cat by the ass.

If you have any direct questions about cams, blowers and other such stuff, let me know . . . will do my best to share what I know.

Best of luck!

PS: Here is a link to a post I did to show my work-in-progress on the ports, reliefs on my older blown motor. I have quite a bit more to do on the guides and valves this winter - hope to have the motor running next spring.

http://www.jalopyjournal.com/forum/showthread.php?t=100009&page=2

 

Alright, suppose I start my build with a blower in mind. Run the 4" crank I have, bore it to 3-5/16 so I have a 276 cu. flathead.

1. The money I have saved or rather not spent on a new crank $700.00 to 900.00
2. Per Joe Abbin, I can run my stock connecting rods. saving another 200.00 maybe
3. I should be able to reuse my heads, but cost to machine will offset savings, ~600.00 - 200.00 = 400.00 savings.
4. Anyone see any more money to save here????

So, going with the parts I have and planning on a blower, I have over half the cost of the RoadRunner kit. So I am going to do it, I've reread my Blown Flathead book and I'll start making plans to make it happen.
According to Joe, I can expect to get ~250 HP from the 276 flathead w/ 6 psi boost and 7.5:1 compression on pump gas, 93 octane. I think I can live with that.

So, does anyone know of any other blower kits out there besides the roadrunner kit? I want to check out all my options, home building from scratch isn't going to be at the top of my list, but not excluded completely.

 

Now you're talking -- once you have a blown flathead . . . there is no going back! You'll love it!

Another option is to checkout H&H -- they are the guys who bought our Barney Navarro (so they have his blower manifold, heads, patterns, etc).. They are also in the works on a reincarnation of the traditional SCOT blower (but I imagine that will be some serious money).

http://www.flatheads-forever.com/home/

If you want the GMC look, then consider running a 4-71 blower - and talk to them about a "trimmed case" (which is where they machine all the standard wide-footprint GMC mounting flanges and profile the case to look the same on the bottom as the top side. If it was mine, I'd run a gilmer belt - as it won't slip like v-Belts. Yes, you can run V-belts and they "look" more traditional, but a 2" gilmer belt is a better way to go IMHO. ( I used to run v-belts on my SCOT blower - wanted the retro look. The only thing nice about them is that they will "slip" on a backfire . . . a gilmer may or may not!).

Checkout a complete system from them -- and post back what the options and pricing are . . . I'm sure many of us would like to know.

I'm curious what you're going to do for porting, relieving, valves and cam -- these can have a huge effect on the overall package?

Take er' easy . . . Dale

 

50, I don't have any connection with Abbins but I think it would be hard to beat his kit. The guy is an engineer and has obviously put a lot thought into his kits; Bored and Stroked will probably be glad to verify that there are always unforseen obstacles when you have to build everything from scratch especially on a street engine. Since its your first time through go with the kit and then use that as food for thought on future projects. The 276 decision is a good one; I was just thinking of it from a cost saving standpoint. Once you commit to the blown motor stick to the plan; the thoughts on porting for blown engines and naturally aspirated engines on the street are different; flow velocity with the blower is of less concern.

 

BE READY TO SPEND MORE THAN YOU HAVE BUDGETED.But it's worth it in the end. Good luck with your project.

 

"BE READY TO SPEND MORE THAN YOU HAVE BUDGETED"

Hahahaha! Just take your estimated costs and square them! It all gets easier after the divorce is settled and you've trimmed expenses by living in the backseat in your rented garage!
Best thing is to buy one piece at a time and NEVER look back or add up the receipts.

 

Now you're talkin' Talk to Joe and get his recommendation for a cam I know he has used the Isky 400jr. and the Isky Max 1 in engines he has dynoed (sp?). You'll need the cam lift before selecting your heads. I used the 400 jr. and Offy .425 heads with mine.

BTW if you go with Joe's kit it could look like this:

 

Thanks again for all the info, it has helped me make the "right" decission. I wanted to do a blown flathead from the begining but talked myself out of it, it seemed too intimidating.

Nothing against Joe Abbin's setup, I am considering it, I just like (prefer) the look of the roots 4-71 setup better. I love the 2" gilmer drive over the v-belt look, and there is too much "billet" stuff on the roadrunner kit. Again, it's all personal preference when it comes down to who's money is being spent. I've read Joe's book a couple of times and I have talked with Steve at Uncommon Engineering, I just don't have that kind of money available right now.

Cam decision is still up in the air, the Isky 400 jr, Potvin 3/8, L100, or a Schneider 278 all look interesting.

I plan to have the stock Mercury heads reworked for valve clearence and maybe milled to keep the compression ratio where I want it.

Also, today I hace also thought about having my stock crank ground to 4.125, just a thought... 286 cu is a nice number, any ideas on cost $$$?

Stock Merc connecting rods. Will these work with the 4-1/8 crank?

A main cap support.

1.600 valves, adjustable lifters? Are they really necessary (the lifters)?

Now any ideas on piston recomendations? Ross seems to be the name I hear most.

any other thoughts or ideas on internal parts? Please let me know. I am open to all suggestions.

Thanks

 

A blower will give you the most horsepower potential of almost anything you can do on a flathead --- so if you have medium cubes, good breathing and a blower . . . you've got the cat by the ass.
What he said

 

Bruce, I think the biggest money saving factor is not having to redo something. Every mod I have done to my car I thought about for a very long time, looked at all my options and made a very educated decission.

I do get rid of all my receipts, if my wife was to ever find them, it would be the "Big D" for me and I don't mean Denver...

 

The Mercury rods will not work if you stroke the crank as you will be turning the crank pins down to 2" accomplish the stroke. 21A style or Scat rods are required. Break down and buy a book or two. It will save you money in the long run. Homework pays. Wayno

 

It's billet, because it's easier to maintain repeatability by machining a hunk of aluminum than by casting a hunk. It's also stronger. You could bead blast it to soften up the look of billet - just another option.

Joe made over 300hp with a 276" & 400Jr cam - ported/relieved & re-worked Offy heads.

Once you go to the 1/8" stroke, you've defeated the cost savings. The stock merc rods won't work unless the crank is welded up first to maintain stock journal sizes. If you decide to spend the money on the Scat rods & run Buick rod bearings, why stop at 1/8" stroke? You're going to be buying custom pistons anyway...

The beauty of the 276" engine is the commonality of the parts.

Probably worthwhile in a blown engine.

I'd definitely go 1.6" valves - use SBC tuliped valves & they're relatively cheap.

As fo the adjustable lifters - no, they're not "necessary" - but I use them because I don't like having to check my clearances, then pull the head & valve assemblies for the ones that are out of tolerance, grind/shim with all the trial fitting, reassemble, etc. Quality adjustable lifters are worthwhile IMHO.

If you stick with the 276", you'll have a much larger choice of pistsons from cast to hyper-u to forged. If you keep it below 7psi, you should be fine with garden variety cast pistons.

 

Thanks for the reply, I didn't think it would work, I was just double checking. I actually do have a book or two, not with me at the time I was typing up the post. And I actually feel like I am back in school now, I've got so much homework I can't think straight.

 

Let me jump in here and ask a few questions,if I can. I watched Joe run and also picked his brain at HRR. I'm planning on using his system on a buildup that I'm working on now. My question has to do with the heads. Joe likes to machine the stock heads and I don't have any problem with that, but every blown motor that you see has alum. heads on it. If the stock heads are stronger, is everyone using alum heads because they look better or what? How about using a pair of machined stock heads and having them HPC'd for a different look, even possibly improving performance. Know what I mean, or am I not thinking correctly. Also I was going to use the single wide belt anyway so it wouldn't be the retro look anyway. Any more thoughts? Thanks CBN

 

definitely stick a blower on it before you go up to a 4.25" stroke. you got to remember you are dealing with about an 75 lb. crank and only three two bolt mains to keep it in there. the 4" will work fine for you with any style of blower.

 

Blower "Kit" prices.

• RoadRunner Engineering, kits run from $2200 to $2500. Check out the details here. http://www.roadrunnerengineering.com/

• Uncommon Engineering, kit runs about $4500. You can see some different pics and styles here. http://www.uncommonengineering.com/

• H & H kits are as follows: http://www.flatheads-forever.com/home/component/option,com_frontpage/Itemid,58/

1. Navarro Kit $5500
2. Weiand kit $3400
3. Magansun kits $3800
4. SCoT kits.. Call for price. $$$

All companies kits still require additional equipment to run. Mostly they consist of a blower, intake adapter and some type of belt drive system. Just some info I found during lunch today.

I really love the setup from Uncommon Engineering, but 4500 + is not going to happen anytime soon...

 

Joe's latest engine uses Offy heads. He got 318 HP out of it. He used to favor stock heads because he felt you could torque them to a higher value than aluminum heads & consequently get a better seal at higher boost levels. Don't know what he torqued his Offys to.

I think there's benefit to some of the aluminum heads insofar as cooling & breathing, but a significant issue is looks.

I like your idea of HPC coated stock heads - I think it would be different.