I would call some cam makers and talk to somebody on the phone. If you tell them what you have to work with, they may come up with a good grind in a few days time. You have a custom engine, get you a custom camshaft to go with it! my .02

 

Thanks

Still looking for someone who has used a 6.635 rod in a 9.8 deck 454 bbc 3.76 stroke.Did they use a dome or flat top piston and what was problem issues if any!

 

I never did do it, I thought about doing that same thing though. I think it would be a slick setup. My 454 runs so well that I just never had a reason to tear it down. I am sure that somebody has done something like that tho. You are right tho, getting enough compression could be tricky because the same stack height will be a bit less compression with the little bit shorter stroke but the 4.31" pistons may make up for some of it. Do you know off hand the chamber size of the heads?

I use this calculator alot, http://www.doverusa.com/compression-ratio-calculator.htm

Over on the left is a piston compression height calculator too that I have used alot in the last year or so. Maybe somebody else will chime in for ya.

It sure does sound like a cool setup you got planned there. If the compression turns out a little too high, you could run a bigger cam to compensate it. If it were a little too low, you could maybe mill the heads a little. my .02

Do you know off hand the chamber size of the heads?

 

Still looking for someone who has used a 6.635 rod in a 9.8 deck 454 bbc 3.76 stroke.Did they use a dome or flat top piston and what was problem issues if any!

The length of rod, stroke length and piston compression height works out to 9.785", leaving .015" piston to deck height on a 9.800" block, so that works out.

Can't answer any more questions without more info from you. What compression ratio are you looking to achieve?? What is the head chamber cc volume??

What trans, and converter stall??

I don't think the two Kendig's on a ram, using oval port heads, is going to be all that great a combination. Just a big mismatch.Hard to say without more info as to how many modifications have been made to the 781 heads, compression ratio goal, and rpm target.

 

781 heads

I think the chambers are 113.0.Haven't done anything to the heads yet.What cc dome do you think is best suited for this build.Thanks for your help also.powerglide 1.76 with 5000 stall.

 

All 781 castings are in the 118-122cc range unless they have been milled. Have you(or someone) measured them at all?? This is a big factor in determining compression ratio, you can't pick a piston without knowing. Still can't say what size dome until you give the compression ratio you are looking for, or the fuel you intend to use??.

How high do you want to rev it??

You could feed us a lot more info about this project.

Is is a crawl through deep bog, or a zip across the top mud race??

 

439 bbc

Probally alky fuel.Rev to 6500-7000 rpm (would like more but not sure on bbc)Heads are still stock 781's.Plan on going to a bigger intake valve, say a 2.25 with 1.88 ex.Hoping to run on top of mud,not thru it.Also heads are open to change.Can do whatever they need.If milling or porting is needed, so be it.I am looking at a set of 18cc domes in a forged piston.I think the comp. ratio will be somewhere between 10to1 and 11.1.Will measure cc on heads in the morning and get back with you.Thanks again for all the help.

 

If head is 118cc, an 18cc dome only gets you 8.9-1, figured with the .015" deck height and an .041" thick gasket. Going to take a 32cc dome just to get you to 10-1, because of your small cubes(short stroke). Zero decking the block with a 32cc dome will get you to 10.35-1. 47cc dome and zero deck is 12.1-1. It is going to be hard/take a big dome to get any compression with that huge chambered head with that small stroke.

If you are going to run alky, why run so low a compression ratio?? 13-1 will make a lot more power.

I don't think the twin 1250 Kendigs are going to like this combination at all, especially on alky. Can you even get the needed parts to convert them to alky, or even E85?? Two 750 Holleys would be a much smarter move.

With the 781's it is going to take a lot of porting and milling to get things to where you will make decent compression and serious power. I would be looking at an aftermarket head and not even considering wasting time on the 781's. If you could find a closed chamber rectangular port head it would be a better place to start than the 781.

Why are you not building a 496 to start with, instead of hampering yourself with the small cubes of the 439?? Seems like you are unwilling to rev the 439 like would be needed to get real power using a Ram(8500 rpm).

 

If you are going to run alky, why run so low a compression ratio?? 13-1 will make a lot more power.

Why are you not building a 496 to start with, instead of hampering yourself with the small cubes of the 439?? Seems like you are unwilling to rev the 439 like would be needed to get real power using a Ram(8500 rpm).

Makes no sense at all. If I were going to run against others in the same arena, I would be doing some detective work and asking questions about the combinations the fast guys are using. I'm pretty sure they ain't using 439 cubic inch motors. And if they're running alcohol, I'm also pretty sure they ain't doin' it at less than 13:1 SCR. Don't try to re-invent the wheel. Build what the fast guys are building. One other thing, unless this is claimer class racing, I'd bet that you are the only person thinking oval port heads.

 

439bbc

Thanks Guys, So far I am building this out of parts me and a friend have laying around the shop.Haven't spent no serious money on this project yet,trying to get the best out of what we have at hand.I do have a 219 head but unable to find a match to make a set.If I could, this would help me on the comp. ratio. I have not purchased the pistons yet so I'm still open on what would be the best for what I have.Will the bigger domes still work using the 6.635 rod that I have at hand? What valve size do I need in those 781's to make those work and how much porting?Also you are right about the other racers having much bigger cu. in. motors out there, but my experience watching them, they are not staying hooked up and having a hard time staying out of the wall to get to the finish line.Some that I have watched make a 160 foot track into a 200 or more.Straight and hooked up all the way out sounds like a better ride! You all have been great so far.Keep the knowledge you have coming my way,and just maybe I'll hit on a good low budget build after all options are sorted out.

 

Rod length has nothing to do with whether the dome clears the head or not, only dome shape effects that. If you are stuck with the 781 head, the bigger 2.25" intake and 1.88" exhaust valves will be needed, and a good amount of porting to the short side radius of the intake port, the bowls on both intake and exhaust ports, and the bump in the exhaust port(head bolt boss bump). Since you are stuck with this head, jack the compression as high as you can to help make up for it, looks like you need at least a mid to upper 40's cc dome to get anything decent for compression. You need to be prepared to rev it, 7000 rpm won't even be close to enough, think 8000 rpm minimum, should be easy with aluminum rods and steel crank.

I know my cousin has tried the smaller motors like this in his mud racer(454 in his case), but he now has a 588ci 970 hp Shafiroff Racing Engines motor in order to be competitive. He races MRA with a Lime Green 4WD '73 Vega wagon on a chevy truck chassis, called The Swamp Thing.

Are you running 2WD or 4WD??

 

439bbc

Running four wheel drive in a gutted 88 toyota p/u body.Carbon fiber wheels,corded cut tires.Cutting weight where ever I can to help out the smaller cube motor.Sounds like alot of head work to get those 781's up to doing their job.Glad I got all winter.If I can get to a 12 or 13 to 1 ratio,what would I need to be looking for in a cam.I do have some billet solid roller cams that could have a regrind done on them.If I don't go with the alky,2nd choice is the drt fuel by Vp.

 

I'm thinking cam in the area of 276-285° dur @ .050" lift, .750"+ valve lift.

You running different size tires front and rear, and different gear ratios front and rear, or all equal size stuff??

I forgot to mention my cousins Vega wagon is all fiberglass, US Body Source body.

 

439bbc

39.5 rear tires and 11.00x38.5x15 on front.We are thinking the same on cam.thanks. Is your cousin running a tube frame also? Sounds like he has already got a pretty cool ride.What kind of times is he doing on what type track?About forgot, 456's rear and 410's frt.

 

39.5 rear tires and 11.00x38.5x15 on front.We are thinking the same on cam.thanks. Is your cousin running a tube frame also? Sounds like he has already got a pretty cool ride.What kind of times is he doing on what type track?About forgot, 456's rear and 410's frt.

I know he is using a mid 70's truck frame, a tube chassis would bump him up a class. Quickchange rear, Dana 44 front, IIRC something near 4.88 rear and 4.10 front, but he plays with ratios up or down in small increments in the rear Quickchange depending on the track conditions. I think 38" and 35" Boggers but not sure on the actual sizes. I know he has it set up for the fronts to be turning a small percentage higher ground speed compared to the rear, to keep it pulled straight down the track. 300' track, I think 4.3 second area for times but it has been a while since I talked to him about it and I may have this wrong.

I can find out more if you like.

 

439bbc

Wow, 300 ft. must be dirt drags.I am thinking about using a chain drive instead of a transfercase.Saves on weight plus you can change gear ratio's,make frt. full faster,etc.A few years ago only the rails where allowed to run them but that is slowly changing around the country.Chain drives are fairly simple to work on and cost a lot less to repair.Got my tunnel ram in today from summit and not what I ordered.Wanted the 1981 and they sent the 5981.Not sure what the difference is other than the 5981 sells for $84.00 less than I paid for the 1981 in their own catalog.There has to be some kind of difference since one is higher than the other.Can't find no specs. on the 5981.Guess I'll figure it out Monday on the phone with them.

 

Wow, 300 ft. must be dirt drags.I am thinking about using a chain drive instead of a transfercase.Saves on weight plus you can change gear ratio's,make frt. full faster,etc.A few years ago only the rails where allowed to run them but that is slowly changing around the country.Chain drives are fairly simple to work on and cost a lot less to repair.Got my tunnel ram in today from summit and not what I ordered.Wanted the 1981 and they sent the 5981.Not sure what the difference is other than the 5981 sells for $84.00 less than I paid for the 1981 in their own catalog.There has to be some kind of difference since one is higher than the other.Can't find no specs. on the 5981.Guess I'll figure it out Monday on the phone with them.

Wow chain drive? Being into motorcycles my whole life I find the idea to be very interesting!
Among the benefits you listed, what does frt. stand for? I like the idea of getting more power to the wheels due to less drag of the differential. Sorry you got the wrong part- definitely call them up

 

Chain drives

Well to start off frt. means the same as front.Chain drives are neat little set ups.You can find them for sale at Power Pro Racing products (power pro racing.com). After checking into my motor options more, you all saved me some costly mistakes.Still going with the dual kendig carbs. on the tunnel ram,but I think 47cc or larger dome pistons with some milling of the heads and alot of porting with 2.25 intakes and 1.88 exhaust just might get me in the ball park.Looking at 14.1 to 15.1 cr. And back to Vp's DRT racing fuel.The 781 heads might still have to be changed to some good flowing aluminum ones.Oh! and I meant make the frt. (front) pull faster.

 

Decking block and milling heads,

How much can you deck the block and mill the heads on a stock 454 bbc using 781 heads? I've got to get somewhere around a 14to1 cr.I like the quick rpm the 3.76 stroke crank will give,but I'm having trouble getting my compression ratio where it needs to be.Would be happy at a 13 to 1, but would like higher.

 

How much can you deck the block and mill the heads on a stock 454 bbc using 781 heads? I've got to get somewhere around a 14to1 cr.I like the quick rpm the 3.76 stroke crank will give,but I'm having trouble getting my compression ratio where it needs to be.Would be happy at a 13 to 1, but would like higher.

About .020-.025" on the block, .060-.080" or so on the head unless you angle mill them. When going to max milling like this you will likely have to hand clearance and fit the domes in some areas to avoid crashing them into the head. Big milling like this will also require milling the intake face and intake bottom, and angle milling will require milling the heads intake face back to the correct angle.

That "quick rpm" comment of yours sends up a red flag to me, it is an old BS wives tale same as the ones SBC 302/327 lovers spout. An engine can only rev as fast in gear as it can move the mass of the vehicle it is installed in. To put this BS theory to a test, think about this, and I'm using extreme examples to illustrate a point...both with say 4.56 gears - How fast is your so-called quick revving 3.76" stroke engine going to rev in Uncle Elmers dump truck with 5 yards of gravel in it??...pretty slow, right?? Now put a stock 4.00" stroke 454 in a 2500lb Vega...it will blow the tach needle off faster than you can move the shifter. See my point on how short stroke/quick rev ideas are shade tree BS?!!

How fast an engine free revs in nuetral is meaningless, all that matters is how it revs in gear...it is power to weight that determines how fast an engine revs with any given rear gear set. Make more power, engine revs faster even if gearing remains the same.

 

Short Stroke vs. Cubic Inches

So are you saying that more cubic inches is where its at?If Say I use a 4.250 stroke crank instead of the 3.760, and put both in the same exact vehicle,the 4.250 stroke will get its rpm's up off the line just as fast as the 3.760.I guess the only thing going for the 3.760 that I have is its hardened steel forged.What your saying does sound right.So far it looks like the 3.760 crank is hampering this build and needs to go on the auction block or I better be prepared for lots of extra machine shop work to use it.Thanks for the eye opener.

 

So are you saying that more cubic inches is where its at?If Say I use a 4.250 stroke crank instead of the 3.760, and put both in the same exact vehicle,the 4.250 stroke will get its rpm's up off the line just as fast as the 3.760.I guess the only thing going for the 3.760 that I have is its hardened steel forged.What your saying does sound right.So far it looks like the 3.760 crank is hampering this build and needs to go on the auction block or I better be prepared for lots of extra machine shop work to use it.Thanks for the eye opener.

Yes, the more power(torque) it makes and the sooner it makes it is what jumps the tire speed up quicker.

 

cu. in.

Looks like its back to the drawing board.How much clearance issues are associated with the 4.750 crank and can this be used in a stock 454 block?

 

Looks like its back to the drawing board.How much clearance issues are associated with the 4.750 crank and can this be used in a stock 454 block?

4.250" crank, or actually 4.750" crank??

4.250" crank goes in pretty easily, might need a little clearancing at the oil pan rail and the bottom of the bores where each the rod swings through the area, depends on what rod is used(stock, aftermarket I-beam w/capscrew, H-beam). It isn't hard with a carbide burr and sanding rolls on a die grinder, just takes some time checking one rod at a time. Same as with most any stroker, small or big block. Grind for .050" clearance between parts and block.

4.750" won't fit in a stock block at all, you need a Aftermarket spread pan rail, priority main oil passage block to do that.

 

http://victorylibrary.com/mopar/journal.htm

That is an article on crank journal overlap and is worth reading imo because the effect on the strength of the crank. The longer stroke simply cannot rev as high as a shorter stroke due to piston speed. I guess volumes could be written in favor of either, my preference in the 3.766 crank and the most gigantic bore you can possibly get. That is my vote, take it for what it is, my opinion. There are benifits and downfalls to both approaches but most people agree that the bigger stroke is nice on the street and screamin high rpm is for racing. A 439 turning 8000 rpm would breath just much as a 878 cube motor at 4000 rpm in a perfect world.

You building a race car right? If you had an aftermarket 4.5" bore block with that 3.766" forged crank in it you could have 480 cubes (492" at .060 over) just like the stroke monster but still rev like crazy. Bigger bore lets ya have bigger valves in the heads too. Again this is all just the way I might do it if I could build a race car, so take it for that