SBF Dirt Track build questions

[Stranger]

Hey guys, been lurking and learning here off and on for years.

I recently got the green light from the wife to step up from production based dirt racing to a class similar to a DLM chassis with a 361 cube limit for two valve iron production based motors.
At most tracks the vast majority are running SBC motors with the occasional Ford.
There are cu. in to car weight rules.
OEM block and head castings (with some approved aftermarket castings)
OEM type stamped rockers (long slots allowed)
Holley #1850 carb mandated - converting to center hung bowls allowed. Approved tuning methods are jetting, power valve, accelerator pump nozzles and secondary springs. Anything else is NOT allowed so playing with boosters etc. is off the page.

So if I am building a Windsor based motor allowed aftermarket blocks are.

Ford M6010 BOSS 302
Dart SHP # 31364175 8.2 deck 4.0 bore 2.25 main
# 31364275 8.2 4.125 2.25
# 31355135 9.5 deck 4.0 bore 2.75 main
# 31355235 9.5 4.125 2.74

Allowed aftermarket head
World Products #5303B Windsor Junior.

361 cu.in 1088kg's 2398.62lbs min weight
347 cu.in 1070kg's 2358.94lbs min weight

So to my questions.

Is it worth the effort to go for every last cube over obtaining off the shelf rotating assembies? Budget is a consideration.

8.2 block
Bore or Stroke?
4.125 x 3.25 = 347.47
4.030 x 3.4 = 346.95

Given the limiting factors of the 1850 and stamped rockers which way would you go?

Single or dual plane manifold? (Any cast intake allowed)

Camshaft recommendations? I was thinking probably hydraulic roller to be relatively easy on the valvetrain

[mag2555]

Let me flat out say that if you do not run the 5303B heads then do not bother stepping up to this class!

[CamKing]

What size carb ?
Can you run the 351N heads ?

[fordified]

I have a new boss 302 block. The short bore in my view kills an otherwise outstanding block. Apart from an iron eagle it would be the go to race block if Ford had not cut down the bore length.

Get the Dart.

When considering bore and stroke, it depends mostly on valve size and weight of the car. For a wedge engine, the intake valve should be about 50% of the bore. If you have at least .200 to .250 clearance between the bore wall and edge of the valve then you’re in good shape.

Longer stroke should help you get out of the corner faster.

[In-Tech]

He mentioned 1850 Holley which is a 600 vac secondary. Agreed on the 351n heads hands down, bye bye class Get with Mike for a good solid flat tappet.

p.s. Anneal the rockers, elongate the slot, then cryo. The .408-A lobes from Erson are pretty darn good too.

[PackardV8]

I recently got the green light from the wife to step up from production based dirt racing to a class similar to a DLM chassis with a 361 cube limit for two valve iron production based motors.

361 cu.in 1088kg's 2398.62lbs min weight
347 cu.in 1070kg's 2358.94lbs min weight

Is it worth the effort to go for every last cube over obtaining off the shelf rotating assembies?

When asked this question, I always ask back, "What are the fast guys running?"

Budget is a consideration.

Second question I ask, "How much are the fast guys spending? Can you afford to be in contention for the win or just have fun racing in the back?"

[Stranger]

What size carb ?
Can you run the 351N heads ?

#1850 600 vac.
No , can use oe castings (not over the counter or Lunchbox parts) or Windsor Junior

[Stranger]

I recently got the green light from the wife to step up from production based dirt racing to a class similar to a DLM chassis with a 361 cube limit for two valve iron production based motors.

361 cu.in 1088kg's 2398.62lbs min weight
347 cu.in 1070kg's 2358.94lbs min weight

Is it worth the effort to go for every last cube over obtaining off the shelf rotating assembies?

When asked this question, I always ask back, "What are the fast guys running?"

Budget is a consideration.

Second question I ask, "How much are the fast guys spending? Can you afford to be in contention for the win or just have fun racing in the back?"

Fast Fords are Far and Few Between, those kind of details are generally closely kept.

I know with the Chev crowd I have heard of some big dollar motors people are pulling out the chequered book for. I spec and assemble my own motors and have been doing my own cylinder heads since the last century.
I don't have a big chequered book but I have a PHD (Poor Hungry & Determined). Struggling at the back is no fun (why I am asking here) running with and occasionally beating chequered books is my buzz.

[Stranger]

Thanks for replies guys

[billet]

361 cu.in 1088kg's 2398.62lbs min weight
347 cu.in 1070kg's 2358.94lbs min weight

First thing, not sure how much circle track racing you been around (assuming dirt since you mentions similar to Dirt late models) but the car is way way more important then the motor by far unless you're racing on some hammer down big track.

That being said on the weight of the car: Is it a pound per cubic inch type of deal? doesn't seem so since the values you listed don't work out the same. But first and foremost I would make sure you can even get to the lighter weight on the car with your budget and car before I make too many decisions.

Little more context would help

[englertracing]

What kinda tire?
Is Cleveland architecture allowed?

[PackardV8]

First thing, not sure how much circle track racing you been around (assuming dirt since you mentions similar to Dirt late models) but the car is way way more important then the motor by far

X2 - on dirt, a sorted car and an experienced driver will always beat the strongest engine with an average car and driver. But you already know that and hope springs eternal.

[fordified]

What size carb ?
Can you run the 351N heads ?

#1850 600 vac.
No , can use oe castings (not over the counter or Lunchbox parts) or Windsor Junior

Are you allowed ported heads? The Windsor Juniors would be good but so would 70 351 Windsor heads or first generation 90's GT-40 heads.

If porting isn't allowed, you're going to need someone to "massage" them with an OE finish. Someone good. The valve job would be critical and so would the valves and back cuts.

[BCjohnny]

Generally FWIW, base engine wise .....

I'd likely run the 8.2 Dart block @ 4.125 and the lightest reliable quality crank you can afford at around 3.25, although at that stroke with long rods the Ford block will also work

Longest reliable lighter weight rods you can keeping the oil ring out of the pin

Heads will be the key, and what work is allowed

If you can run the 10* N351s you'll probably have as much legal horsepower as anyone, they are after all 'OEM' castings, loosely ...... and they run pretty good unported as is

If you're restricted to more conventional 20* heads you'll really need to be able to port them, or 'cheat' a little ...... so what are you allowed ?

Cam would be whatever one of the more accomplished experts would spec, other valvetrain considerations would centre mostly around the stamped steel rockers, and what you can do to them ..... is there an rpm limit ?

[Tom68]

Heads heads heads, its all about the heads, if you don't get them right the rest is irrelevant, bore and stroke combo won't matter a lot with the 1850.