Now I know " there is no replacement for displacement" , but I have always wondered about a destroked BBC. Say it has a 4.5 inch bore and 3.75 stroke. Its still 509ci. What could it do on pump gas? (93octane) What could it do with a higher CR on race gas? Would it still need big flowing heads with such a short stroke? Would it be a high rpm screamer? Could it be a fun street/strip motor, or a pointless waste of time and money?

 

Alot of guys that use big chief heads run 4.6 bores and 3.6 cranks...1100 hp on gas..high rpm shift at 9500..best of the best parts to do it though. Torque is king on the street and for that you need a big arm pump or race gas.

 

destroking stuff is normally for class racing type stuff or bonneville. if you are looking to run pump gas, you want as many cubes as you can get. the more rpm you want to turn, the less streetable you will be in terms of driveability and octane requirements. reliability of the engine falls off as well, since everything around the rotating assembly needs to also handle the high rpms. cost of parts goes way up since you need super strong materials in the parts so they can be light and still be strong enough to handle the insane gforces going on in there.

 

Unfortunatly big cubes means big heads. Its sucks when you can pick what ci you want when ordering a rotating assembly. All the same price. Then when you get to the heads. The price goes way up because you picked a big ci. Thats the name of the game though. For a guy on a budget. The price of heads is what keeps me from going 500 ci and up. Or maybe 540ci and up. Which brings back the fact of TQ is king on the street. No big money heads means no big CI which means no big TQ. Guess I'll settle for a sbc for the time being.

 

big cubes, low rpms = big heads
small cubes, high rpms = big heads
the small engine turning lots of rpm may move the same amount of air as the slow turning large engine.

imo, decide what kind of power you are looking to make and buy the heads first. then do the rotating assembly. thats where everyone messes up, is buying a super high dollar rotating assembly and not having enough money to buy a good set of heads. a billet shortblock with a set of double humps isnt going to make any power.

 

I looked for used heads for a little while, but they dont seem to be much cheaper than new ones. When the time comes. I will buy the heads first and build around those.

 

Bingo.

There is no replacement for displacment...except boost. - lol That's why nitrous motors typically run as big of CI as allowed, while boosted guys run what they can afford to keep together reliably.

Inches is inches, and rpm is rpm. No matter what the combination is(stroke > bore or bore > stroke), the same CI will require same amount of head flow at the same RPM.



The biggest crank I run with the blower is a 4" and I've been threatening to run a 3.5" w/ a 4.500 bore. Need to kill of bottom end torque on the little tires anyhow, I'll just buzz it on up. Out last blown combo was a 445ci(427+.100) and it turned around 10,200 at the lights.

 

Does a boosted motor require big heads like a NA motor would of the same size? Would a boosted motor be the exception to the rule of needing big ci for big tq on the street?

 

~14psi of boost is basically the same as doubling your displacement.

 

Depending on how much power you are trying to make but most guys tend to size the head the same as you would with a n/a motor, cross section required for the intended rpm range. I on the other hand am going with the biggest head i can fit on my twin turbo motor. We shall see what that does with the street cam. Some guys say you cant put a big enough head on a large cubic inch big bore 23 deg sbc, so on a big block it may work the same way.

There are also a few changes some head guys recommend for heads for turbo motors versus n/a or other motors out there. Port dimensions change slightly, and abit larger exhaust valve isnt a bad idea either.


And yes, smaller cubes on boost will make gobs of torque. Guys running huge turbos in outlaw 10.5 type racing or drag week type events have problems hooking up, and alot of those guys run shorter strokes to keep the torque levels down. Also have boost limiting electronics and pull more timing to cut torque out of the motor.


You can still have big cubic inches and run small heads and make good hp. Just need to know what rpms you want to shoot for and/or how much power you want to make. There are guys making 660hp on pump gas 489 big blocks with tiny AFR oval port 265cc heads. Those are small heads. 509" isnt too far away from that, you can get away with a sub 300cc head for near 700hp if done right. Rest of the combination must match from cam to intake.

My friend 87_TA on here runs 325 or 335cc heads on his 498" big block and he turns near 8K rpm on that setup with a big cam. Its likely 775-800hp, goes 9.0's at 152 in a vega.

 

Thanks guys for the info. I would like to say 7500rpm would be ideal for me, but wouldnt that all depend on tire size, trans and rear end ratio? 10.5 tires are it for me now. Also Im assuming all these motors are using aftermarket blocks and not some GM truck block. How much power and rpm could a GM block handle? I dont want to fill it since it would need to stay cool on the street. I'd be limited to about 505ci also. right?

 

buuuaahahahahaha! - I'm pushing over 1200hp reliably on a GM 2-bolt main low deck bbc block. We're pushing over 2000 out of a GM tall-deck truck block. - these ain't no stink ford blocks!

Boost or spray will exponentially increase any engines tq output.

I'd say keep searching on the heads. Just a few months back I bought a pair of fully ported Pro1 355's w/ ferrea valves, triple roller springs and Ti retainers for $1k. They've had a chunk spent on them in machine work alone; having had the ports moved up 3/8" to move some serious cfm. - If you can find one GM 077 "winters snowflake" aluminum head, I have one to go with it that I'd let go very reasonably. I know for a fact they are capable of 753hp on 468ci @ 7623rpm(lol).

 

WOW! 1200hp on a 2 bolt. I'm assuming there concreted. How well would it hold up not concreted?

 

Likely have mid and front plates too? I never wanted to deal with those on a street driven setup. I just like regular motor mounts

 

Partial filled block(just to the freeze plugs), and yes engine plates @ both ends. - I will be running plates on my street car, but will be using some urethane bushings(think control arm bushings but much smaller) to bolt the plates to the chassis.

Motor has been 5.35 @ 128 @ 3050lbs with a single carb and big plate kit, has also been 5.09 @ 136 @ 2650lbs with a smaller kit. - Both runs made with a way wrong converter(for our blower combo). We expect to see high 4's on one kit and hopefully 4.7x's with both guns blazing on our new TSI nitrous converter.

 

Shagwell, I wish I had half of one of the cars you have. So at what point is it a good idea to switch to motor plates?

 

Thanks. I wish I didn't have half what I do, that way I could actually afford to really play. - The little lightweight stang is going up FS. Never planned to keep it as long as I have.

I'm honestly not real sure on the power level where plates become reccomended/required. I'd guess around 750-800hp. - It's much easier to work around block plates than mounts, thus anything I'm going to build up much recieves plates.

 

I never paid that much attention to motor plates before. I didn't realize they left you with more space.

 

shaggy...got some pics of the plates in an f-body. Thinking of doing it over winter at the power level I'm at these days. I'm assuming it's just welding some 1/8" inch angled plate into the car on the frame rails and calling it good?

 

I'd be interested in seeing plates too. I REALLY should have them I guess as I plan on approaching over 1000hp next year...hopefully if all goes well. I figured i was in the 700-850 range depending on boost and using poly mounts. No issues so far

 

heres my motor plates

 

So does your water pump just seal against the motor plate then? Also is the rear plate between your bell housing and engine? Does that keep the converter from going onto the input shaft as far as it normally would?

 

The Indy Drag Racer's auction in the winter has alot of good buys that go across the block.You would need to come early equipped with all the mic's and knowledge to scope out what parts are worth bidding on writing down the lot numbers.Some of the stuff is distress sales on new parts.(heads as a example). Just do a search for that title do the up and coming dates.And don't waste you time coming with like $1,000 thinking your going to be a player.Yrs ago a motor with mainly parts from that auction was a national winner in 9.90 car in London,Ont.

 

yes you have to put a gasket for the waterpump between the motorplate and block. The midplate goes between the trans and engine, you`ll need longer trans bolts and engine dowels. when you buy a torque convertor u have to specify if you have a midplate and how thick is it so they could build it into the torque convertor where it bolts into the flywheel.

 

If you already have a converter for NO midplate, and want to go midplate, can you just get adapter spacers for the bolt flanges on the converter to take up the space? 1/4" or so?

 

Orr - If you run a typical .090 steel or even an .125 thick mid plate you can get by with running a couple washers between the flexplate and converter. - Even w/ converters built for a mid plate I've had the need to run spacers to get the engaugement spot on.

xpndbl3 - Basically, yes. Mine also attaches to my strut bars though. Not the best pics, but the jist of it.

block plate:




mid-plate:




daverr - Looks clean, how many inches and how big of hair drier?

 

413" sbc with a 101mm .

 

NICE! - That should roll.....