What size Carbs for 471 stroker FE

[A98Coupe]

I'm currently having my 427 S/O motor rebuilt to give more torque & power in the useable rpm region for Street and mild competition. My motor was a fairly stock 427, LeMan crank & rods, 0.524inch cam with 245 duration @ 0.050 lift. It has iron medium riser heads topped off with a Blue Thunder 2x4 with 2 x 390CFM Holley carbs. CR was 9.8:1. It pulled 450hp @ 5,500rpm before strip down.
The changes I am making are as follows:
- RPM steel crank 4.125" stroke - should give 471 cu inch for +30thou bore.
- SCAT H-Beam 6.700" rods
- Diamond pistons - flat top or slightly dished to give 10.5 ~ 11.0:1 CR
- Comp Cams 294S cam, 0.605inch lift and 248 duration @ 0.050

The big question is how big should I go on the carbs without affecting throttle response & driveability? I was very surprised how much power the 'tame' 427 spec. achieved with 2 x 390s, so I am thinking that 2 x 450CFM Holley 4160s should give good results and maybe 2 x 600CFMs will give more WOT torque / power but poor throttle response?
Any advice would be appreciated before buying the carbs.

[Mdman352]

Carburetor Size Calculator

[601HP]

These answers will be interesting!

Keith Craft and Barry Robotnik are FE engine builders and are often on this site. Their opinion will be worth a lot to you.

David

[ERA Chas]

Forget calculators for 471 cubic inches.
What's making the little carbs 'work' is the crappy stock MR heads. At 471, those heads will be a major restriction and defeat the purpose (and expense) of expanding the engine size. The BT intake is also being wasted. It's over-qualified for your current job. You'll easily make 600HP instead of 500 your way.
Preferred method is get a set of stage II or III Ede or BT heads from the vendors here. 2.250" intakes wouldn't hurt either.
With better heads that cam will work with at least 600's and properly set-up, will have great driveability and top-end too. Get the carbs from the recommended carb shops on here and they will have correct bleeds, boosters, cams and all to work well.
I ran 650's (at 427 inches) with a bit more cam and Lovehamr runs 750's on a 482 with great results.
No street-driving problems and a better use of money spent.

[601HP]

ERA Chas hit the nail on the head, especially the better heads suggestion on your stroked engine.

I tossed my iron heads years ago.

I have an itty-bitty 427FE with KC Stage II heads, and 2.25" valves. My cam is a roller with specs a little larger than those you mentioned.

I've been running a pair of tweaked Holley 600's for years, and this engine is strong and driveable. I'm waiting for a pair of tweaked 750's from one of the engine builders on this site (he suggested the 750's based on my engine's characteristics).

David

[blykins]

Two 450's wouldn't cut it. I would go with at least 600's, if not some 725-750 cfm carbs. I've ran (2) 1850 style 725cfm carbs on a 428 with a Tunnel Wedge and it loved them.

Your heads and your cam are going to be a bottle neck. Don't expect the peak hp rpm to be much higher than your previous combination.

[ERA Chas]

Originally Posted by 601HP

I have an itty-bitty 427FE with KC Stage II heads, and 2.25" valves. My cam is a roller with specs a little larger than those you mentioned.

Nearly my exact combination-only Shelby stage II's, Tunnel Wedge and flat tappet cam.

[601HP]

Originally Posted by ERA Chas

Nearly my exact combination-only Shelby stage II's, Tunnel Wedge and flat tappet cam.

Mine:
11.0 to 1.
.639" lift on the intake.
.667" lift on the exhaust.
252 & 262 duration at 0.050".

It ain't much at 2,000 rpm, but hold on and make certain you're facing straight ahead at 4,000!

David

[bret a ewing]

Just a suggestion, spec your air cleaners appropriately, otherwise proper CFM will not be realized no matter what carbs you use.

[Barry_R]

If you're using the factory progressive style throttle linkage - you should - a pair of 750s will drive as if you have a single 750 double pumper. Ford used a pair of 600+ cfm carbs on stone stock 428s in the 60's - you are 50 cubes bigger.

At LEAST 600s and I would personally opt for 750s. I have a ton of these running on the street with good manners.

[A98Coupe]

Thanks guys. Good advice. It looks like I should go for the bigger carbs. However, I didn't really want to go to the expense of Stage II or III Ede heads at this stage, given that my Medium Riser heads have been fully ported and polished and matched to the BT intake. Also, I'm not really going for top end hp, but more neck breaking mid-range grunt.

Barry R,
If I purchased a pair of 600+ CFM carbs from you, would they be stock or could you set them up for my application?

[601HP]

With iron heads, isn't a 10.5-11.0 to 1 compression ratio a recipe for detonation?

David

[dcdoug]

Originally Posted by 601HP

With iron heads, isn't a 10.5-11.0 to 1 compression ratio a recipe for detonation?

David

I have MR stock iron heads and 11:1. No prob on 93 octane.

[Barry_R]

When we do the carbs we take an honest shot at the calibration - they are all made custom per the application. That noted, its not unusual to need to swap jets on some of them - seems like we're often two or three numbers rich. Its a better safe than sorry deal...

[undy]

A stout cam will drop your dynamic compression ratio allowing you to run a bit more compression.

[A98Coupe]

My worst nightmare has been realised today! Just had a phone call from my engine builder who has completed his stripdown assessment and here's some of the worst points:
1) Block has been sleeved on No.7 cylinder and No.6 cylinder has twin grooves at the bottom of the bore, where a broken H-beal rod has hit it sometime in the chequered history of this block! Also, one of the main cap registers is loose allowing the main cap to move around when unbolted.
2) TRW pistons show signs of skirt collapse.
3) LeMans crank main & rod journals under 30 thou under size so that is definitely scrap anyway.
4) The valve guides were worn, and the valve collets were loose allowing valve stem movement.
5) Valve spring pressures below spec.
6) Small witness marks on the underside of the Dove roller rockers where the pushrod cups have been hitting them. i.e. pushrods are too long!
7) Oil pressure relief valve in the back of the block has been jammed closed to keep high oil pressure.

The engine had only done 3,000 miles since purchase from an engine builder in USA - whose name I will keep to myself for now, but save to say that it is nobody on this particular thread.
In summary, I paid a lot of money for a 427 side oiler which had turned out to be nothing more than a pile of knackered parts bolted together.
I shall be contacting the engine builder in USA next week to hear what he has to say about my situation.

[Barry_R]

Originally Posted by A98Coupe

My worst nightmare has been realised today! Just had a phone call from my engine builder who has completed his stripdown assessment and here's some of the worst points:
1) Block has been sleeved on No.7 cylinder and No.6 cylinder has twin grooves at the bottom of the bore, where a broken H-beal rod has hit it sometime in the chequered history of this block! Also, one of the main cap registers is loose allowing the main cap to move around when unbolted.
2) TRW pistons show signs of skirt collapse.
3) LeMans crank main & rod journals under 30 thou under size so that is definitely scrap anyway.
4) The valve guides were worn, and the valve collets were loose allowing valve stem movement.
5) Valve spring pressures below spec.
6) Small witness marks on the underside of the Dove roller rockers where the pushrod cups have been hitting them. i.e. pushrods are too long!
7) Oil pressure relief valve in the back of the block has been jammed closed to keep high oil pressure.

Might not be as bad as you think - obviously I have no idea how the package was represented to you upon sale. Still sounds like an old piece.

Old 427 blocks are almost all vintage warriors with a racing history - not many were used for genteel transport to and from the store. A well installed sleeve is rarely a problem. The marks in the bottom of a bore are likely cosmetic and should not cause any problem as long as they are below ring travel.

TRW pistons - if they are truly TRW - are really old. I discontinued that brand in the USA back in 1994 while I was running the Speed-Pro product line for Federal-Mogul. The crank at 30-30 is not my first pick, but will not cause any issues as long as its round and straight - bearings are readily available - definitely not scrap.

Loose guides and valve locks are not good - they need to be corrected, as does the valve spring pressure. Same for the pushrod length, although we've been caught by that one once in a while - Dove machining is not too consistant if you're only spot checking a few. We often disable the rear pressure valve and rely on the pump mounted relief.

Best of luck - sounds like a fixable situation.

[ERA Chas]

Sorry for your problem chap but start your own thread for it.

[RodKnock]

Originally Posted by ERA Chas

Sorry for your problem chap but start your own thread for it.

Chas is getting kinda old now, so please try to forgive him. We've tried to put him "out to pasture," but he keeps finding his way back here.

[ERA Chas]

Originally Posted by RodKnock

Chas is getting kinda old now, so please try to forgive him. We've tried to put him "out to pasture," but he keeps finding his way back here.

Apologies A98-mea culpa. But the advice I gave you was genuine and meant to be helpful.

As for you Mr. No-miles.....