Club Cobra - What size Carbs for 471 stroker FE

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Quote:

Originally Posted by A98Coupe (Post 1221929)

My worst nightmare has been realised today!:eek: 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.

Quote:

Originally Posted by RodKnock (Post 1221950)

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. :LOL:

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

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

Quote:

Originally Posted by ERA Chas (Post 1221969)

Apologies A98-mea culpa. But....:mad:

Hmmmm, I say it's time for a workup.%/ Diagnostic Workup | Alzheimer's Association

I guess it's time to take the Rsimoes forum suicide pill...........:o

Quote:

Originally Posted by ERA Chas (Post 1221992)

I guess it's time to take the Rsimoes forum suicide pill...........:o

Don't feel too bad - my first thought on reading his update was that the thread was going off the reservation also.

Since he is rebuilding anyway - most of the issues sound solvable. At least the motor hadn't let go and holed the block or something.

ERA Chas,
No hard feelings! My emotions were running high yesterday when I found out the 'bad' news about my block. I agree, the thread was changing tack from the original carb size issue, but I felt I needed to share my grief somehow.

Barry R,
Thanks for your advice. My engine builder (not the original engine builder), also said that the block is useable with a bit of work, but I would be concerned about spending a load more cash making it into a 471 stroker knowing that the block has been damaged in the past. I need to hear what the original engine builder has to say about all the issues before deciding what to do.

To the original question, on carb sizes, I was surprised by the answers.

471 cid at 6000 rpm would pull in 818 cfm at 100% volumetric efficiency.

You didn't say how many rpm you planned to turn nor do we know how good the ported heads can flow.

I would have thought the existing carbs might have been enough. Certainly they are marginal, but may give excellent low end and response for the street.

I'm not arguing against the answers from the experts, but thought I might learn a thing or two here. Why so much carb?

On the block, the groves from the H beam rod strike is most likely below where the rings run with the 3.78 stroke. However when you stroke it to get 471 that may not still be true. This block may be fine for the original stroke, but not for a stroker crank, without major expenses. Maybe you can run a 3.98 stroke, but not a 4.125 stroke.

You could be better off with a new aftermarket block and sell this one to someone needing original parts for a restoration project.

I hope my random thoughts might be helpful. I feel your pain here.

Quote:

Originally Posted by olddog (Post 1222050)

To the original question, on carb sizes, I was surprised by the answers.

471 cid at 6000 rpm would pull in 818 cfm at 100% volumetric efficiency.

Why so much carb?

Because whatever carb sizing formula you are using is woefully inaccurate, and most likely based on poor assumptions regarding flow measurement. Carbs are rated at a predetermined amount of vacuum drop below the plates in order to define a comparative value. The vacuum drop rating number (1.5" on 4 bbls) was derived from limitations of the flow testing equipment, and not from any particular engine driven value. That number really has only a passing nominal relationship to the air handling demand of the engine.

Ford and others were quite cognizant of this even back in the 60s when tehy installed multiple carbs on otherwise modest engines.

Barry,

I wasn't using a carb sizing formula. I just converted cubic inches to cubic feet. A 4 cycle engine takes 2 revolutions to complete all 4 cycles, so multiply by 1/2 the rpm. This is what the pistons displace, on the intake stroke.

471 CI / 12^3 CI/CF * 6000 R/M / 2 R = 818 CFM

I do understand that it is possible to achieve more than 100% VE, using the momentum of the air to pack the cylinders.

I'm thinking, from what you explained, that the rating of a carb is at a certain manifold vacuum number, and the testing equipment wasn't the best. Therefore the rating of a carb and what will actually flow through it are not necessarily the same, especially in multi-carb applications. Am I understanding this correctly?

I have always wondered why certain engines had carbs that appeared to be way too big. The 340 Dodge Dusters with 3 two barrels, for instance. I suspected the factory put them there so you could install headers, port the heads, up the cam, and you were ready to go, without violating any racing rules. I had always assumed they would have made the same power with smaller carbs, but maybe not.

Anyway thanks for your time and sharing your knowledge.

My MR had a pair of 715's from FOMOCO

B i l l