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Old 02-16-2007, 09:56 AM
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Building a BB Chevy. I want 500HP

so I have an old Mark IV 454 block thats already .060 over. I have one closed chamber head and one open chamber head, both with the stock size valves. I have it all at the machine shop right now. he has some old head cores laying around and can match either the closed or open head. If this motor doesn't need bored, then i'm going with the closed, since the pistons in there now are flattops, which i think will give me close to 9.5 to one (haven't ran it through the compression calc yet, just going by what the machinist said). If it has to be bored, i could go with either head and just buy the pistons accordingly to get my 9.5:1. Am I going to be able to make 500HP with a minimum (without boring) of 468 cubes, 9.5:1 compression, stock oval port heads (closed or open), stock valves, and a big nasty cam? Really don't want to do a roller cam just because of $$$$. I was thinking the comp 292 cam. I have a Wieand Stealth intake, and an 850 street demon carb, but might upgrade to a Victor Jr at some point....
Thanks in advance for any advice!
Tom

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Old 02-16-2007, 11:33 AM
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To run that cam, you're gonna need more c.r.
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Old 02-16-2007, 12:51 PM
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If you go to http://www.21cgt.com/FMWebCatalog/default.htm and put your info in. It will give you an idea on comp ratio.
The 292 cam calls for 10:1 cr the 280 calls for 9:1+cr and the 286 needs 9.5:1cr (I think the 292 would be big for you). I would call comp cams or any other manufacture and get their suggestion (also check out their xtreme energy cams).
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Old 02-16-2007, 03:01 PM
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I like the 292H cam in a SBC but never ran one in a BBC.

Most likely will need more than 9.5:1cr to run that cam. I run 11:1 cr with a sbc using that cam with pump gas. 10:1 CR should be a good value to go for, but 9.5:1 isn't that bad when used in a 454.

In a 350, that cam has no torque under 3000 rpm but comes on like crazy from 3 to 7K. With a 454, you will need at least 3.73 gears and a 2800 rpm stall with an automatic, and headers. And don't forget the stronger springs and rockers.

500 hp should be easy to get with that cam. However, bigger valves and a little bowl work would help a lot.

With a good set of aftermarket heads, a 350 can make about 450hp with that cam, so 500hp with a 468 should be easily obtainable if the engine is set up right (valve train, exhaust, intake, carb, ignition, et.)

And remember to use diesel engine oil with your new cam.
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Old 02-17-2007, 10:58 AM
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Thanks for the info guys. Sounds like I need to spend some more $$$ to be able to run the 292. I might step back one size on the cam. You guys aren't having trouble at 10 or 11:1 with pump gas? I guess my biggest decision right now, since the block and heads are at the machine shop, is which heads and pistons/compression ratio to run. I plan on running stock cast iron heads for now, then stepping up to aftermarket aluminums later. Should I shoot for 10:1? My machinist was talking between 9 and 9.5, but will obviously do whatever I tell him. I'm having him put the short block together and just do a valve job on whichever stock heads I end up running, then I'll put the cam and the rest of the motor together myself. I plan on racing this thing at the local 1/8 mile track but keeping it street legal at least at first. I am going to run a 400 tranny with a 2500 or so stall and 4.10 gears in the stock 10 bolt for now, just because someone gave me the gear set with a limited slip carrier. Eventually, after saving up more $$$ I'll probably do a mini tub, 12 bolt or 9" rear end with a spool or locker, aluminum heads and a 100 shot of nitrous, but first I need to get this short block built. I've done several SBC's, but this is my first BB. The last sb I built was a 383 with sportsman II heads with 9.75 cr and a comp 268 cam, and I wish I had gone bigger with that cam. It is in a boat though and I was worried about bottom end. It runs great actually, but doesn't have that nasty cam cackle that I wish it did. Anyway, any suggestion on pistons and heads would be appreciated!
Thanks
Tom
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Old 02-17-2007, 11:52 AM
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As someone else (454C10) has eluded to, make sure you use a motor oil with a ZDDP additive which is crucial for breaking in a flat-tappet camshaft in any engine.

The problem is that many engine oils have dropped this ZDDP additive from thier additive package ... including many of the "diesel oils". Newer engines with roller cams don't need it, and the EPA is forcing oil mfrs to drop it because the zinc plugs up catalytic convertors when the engine begins to burn a lot of oil.

There have been a lot of discussions here at HR.com on the subject of ZDDP.
ZDDP discussions

I am at the point that the next cam I buy WILL be a roller cam.
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Old 02-17-2007, 12:39 PM
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500 is possible, but you will need the right heads. I would look for a set of 049 or 781 heads. Just any set of oval port heads will not get you what you are after. I think sticking with 9.5-10:1 and going with a little smaller cam would be a good idea. In order to get a solid 500 hp, you will need to get heads like the ones above along with getting some 2.19 1.88 valves installed. I would also recommend getting some clean up port work done on the heads. As for the cam, I have a couple of recommendations depending on what you are willing to do with the converter. If you are set on the 2500, I would not recommend going wtih anything larger than the XE274H (230 236 @.050 .552 .555 lift). The only thing about this setup is that unless you get some pretty serious port work done on the heads, I dont think 500 hp will be attainable. In order to get the 500 hp you are after, I would recommend something like the comp xe284h (240 246 @.050 .547 .578 lift) along with a 2800 stall. Comp recommends 9.5:1 compression with this cam along with a 2800+ stall. I think that this cam with a little porting and larger valves in a set of 049 or 781 heads in a 9.5:1 468 will get you the 500 you are after.

Here is a motor my friend built that will show you what it takes to get the power you are after.

461
9.5:1 compression
ported 781 heads with 2.19 1.88 valves (flowed 290 cfm, so they had some decient work done on them as far as porting goes)
victor Jr intake ported and port matched to heads (I would recommend a dual plane with yours)
comp hyd roller cam 242 248 @.050 ~.600 lift

This motor made 560 hp @ 6100 RPM and 560 ft lbs on an engine dyno.

Adam
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Old 02-17-2007, 12:58 PM
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049 is what my open chamber head is. Those things are like 120cc chambers though. It would take a pretty sizeable dome to get any compression with those, but I have heard that they flow good. I could go for 9.5 with the 049 heads then step up to the aluminum heads later and get 110cc chambers to get me up a little higher. Not sure i really want to do things twice, but I know drag racing is going to require lots of wrenching anyway. Maybe i'll should pop for a roller cam setup. How much more $$ does the roller cam and required lifters run as compared to flat tappet? decisions decisions....... No matter what I do, I think a 468 in a 70 Nova with a stall and a 4.10 rear end is going to be alot of fun! I'll check what my closed chamber head casting number is. BTW, my closed chamber head is a 3904390 which mortec shows as a 98cc head.
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Old 02-18-2007, 09:38 AM
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Wow! Thanks F-Bird 88! Sounds like some sound advice! I agree with doing it right the first time. I haven't done any bowl work before, but I have read up on it and I have done some porting in the past, so I'll give it a shot. There is a wealth of information available on the internet! Open chambers it is, and 24.5 domed pistons as well. Once I get a mate to my 049 open head, which my machinist says he thinks he has, I'll take them back home, do the bowl work and porting, then take them back to him for the bigger valves. I'll have to find out what he'll charge me for machining out for the bigger valves.
Thanks again, I'll keep you posted!
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Old 02-18-2007, 11:28 AM
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You should calculate the dynamic compression ratio (DCR) to find the best static compression ratio (SCR) to use. DCR is calculated using rod length, stroke, and advertised intake closing point (not at 0.050" lift). There are a lot of free, on line, DCR calculators to use.

With a detonation prone BBC, you should go for about 7.5:1 DCR. And with out doing the math, I would guess that 10:1 SCR used with a 292H will make about 7.5:1 DCR in a 454. I wouldn't go below 7:1 DCR or above 8:1 DCR for pump gas.

I think the 292H will work OK in a 9.5:1 454 with 049 heads with stock valves and some bowl work. Not ideal, but it will certainly run a fairly low et.

Old 112cc, semi-open chambered, #820 BBC heads flow well. They especially have a good intake to exhaust flow ratio due to the exhaust valve being unshrouded in the chamber. The combustion chamber is much more open around the exhaust port which runs even with the edge of the head and not angled toward the exhaust valve like the 049 or 781 heads.
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Old 02-26-2007, 09:06 PM
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Sounds like I am going to be very close with my cr depending on what the cc's are exactly on the 049 heads. Mortec has them listed at 122, but how do I tell exactly? Do you fill them with water and measure the water? Whats the standard procedure? I haven't heard back from the machinist on the bore yet, but if he has to bore this already .060 over block, its going to be .100 over and then my compression is going to be a problem with the 24.5cc pistons.
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Old 02-27-2007, 08:35 AM
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I use a 1/4 inch thick flat piece of clear plastic with a 1/4 inch hole drilled at one end, squirt bottle, bearing grease to seal the plastic to the head, and a digital scale.

1cc of water weighs 1gm.

Subtract the weight of the squirt bottle before and after filling the combustion chamber.
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Old 02-27-2007, 09:59 AM
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vaseline and a cd! Very clever. I'm all over it. I have also found that fel-pro makes a bunch of different head gasket thicknesses, inclucing .020, .031, .040, .050 and even bigger I think. I think the speed pro forged 24.3cc domed pistons are the ones i'm getting. At least if he can save it at .060. I don't think that piston is offered in a 4.35 (.100 over) bore. Playing around with the cr calculator with the 24.3 pistons, and different gasket, I can get 9.6-9.8 pretty easily.

Now for porting the heads. I asked my machinist about it and he claims on a big block it wont buy you much if anything. He says on a small block yes, but not worth the effort on a big block? you guys obviously think differently right? I still need to get a price from him on machine work for the large valves. How important is porting and valve size guys??? The heads I ended up with are the 049's.
Thanks

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Old 02-28-2007, 10:16 AM
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I would also recommend getting the heads ported. As was already said, you dont have to go with anything too extreem. I would recommend finding a good head guy and having him do the port work. I dont want to assume the intentions of your machinist, but I have found that when people make comments like he did about the BBC heads, it sometimes means that they just dont want to do it. That is fine, if you force someone to do something they dont want to, it will cost you more, and you will probably not get as good of a job done. Doing it yourself is a viable option. I would try to find a old set of heads to practice on first though. Other than that, I think you could get a pretty good job done for $500-$700 depending on what you want to get done. Here are some prices to give you an idea of what you can expect to spend.

They are all from this company.
http://www.revolutionaryperformance.com

Porting - V8 bowl blend $225

Porting - V8 Econoport - includes bowl blend plus narrowing intake guide and full exhaust porting $500

Porting - V8 Stage II - includes Econoport plus gasket match intake end of runner and polish intake port $700

I have heard that, as a rule of thumb, on a relatively high performance street motor, you can expect around 2 hp per cfm of flow increase. If you assume that you will go from ~260 cfm stock to ~300 cfm with the porting and new valves, that equates to an 80 hp gain.

Adam

Last edited by firestone; 02-28-2007 at 10:27 AM.
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Old 02-28-2007, 10:23 AM
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Here are a couple of different sites with flow numbers to give you an idea as to what flow before and after you can expect.

Stock flow from chevy hi performance
http://www.chevyhiperformance.com/te.../photo_82.html

Ported from a company called BH Performance along with 2.19 1.88 valves. Scroll down a little bit, you will see them on the left side.
http://users.erols.com/srweiss/tablehdc.htm#BBChevy

Adam
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