Any BB experts willing to help out a dummy who thought he could just slap together a 450hp 454 on the cheap?

I'm putting together my 1st big block and I lucked into a 454HO forged bottom end in a standard mark vi L29 block for about half what others were asking for a standard gen 6. Forged crank, dimple rods, TRW 2399 small dome pistons (13.8cc). I also got the 24502611 454HO cam. Sent it to the machine shop to have it cleaned and checked out and everything looked great. Had it honed for a re-ring and I put new bearings in. So far so good.

My original plan was to use the stock L29 heads but they won't work with the small dome pistons. Because I'm an idiot or just never took the time to look more deeply into bbc stuff, I assumed I could throw some 781s that I'm always hearing about or similar on it and start melting tires. I was wrong. The 781s have a 119cc chamber and even with the small dome produce a meager 8.8:1 compression. Apparently most bbc builds increase the displacement to make power. It seems that hardly anyone uses a standard 4.25 x 4.00 bore and stroke when building one of these.

I've asked for help in a couple of different places and the standard response is: get some aluminum small chamber cylinder heads! First off, I just can't afford them right now. Second, it seems only Edelbrock makes a 100cc chamber bbc head. But, if I want to grow down the road, won't those limit me? What combustion chamber size is the upper limit for a standard bore/stroke 454? Is a 110cc chamber going to produce power? I'm not building a race car. It's just a cruiser that might see some action stoplight to stoplight. I've got some old 148 heads I thought I could use because apparently they have 113cc chambers that would bump up CR a bit but I'm not sure. They have a strange 2.17, 1.72 valve combo. Down the road I'll look into Flotek 290s, AFR 265s, Brodix RR 270s, etc if those will even work with my setup. I also read a post by a member building a T-bucket that somehow clearanced his l29 heads to accommodate similar pistons to mine. I'm willing to give that a shot if it will work while i squirrel away some dough for aluminum heads...

Any opinions, advice, criticisms are welcome! I feel like I've hit a wall here and need someone who knows better than i do to weigh in.

 

heads are where all your power is made. Down the road IS down the road.... there are many different ways to accommodate your issues. Small chambers are what makes power to up compression, big chambers need big domes. THe intake port flow number is where you want to investigate for your engine size for a 454 a 270 is the smallest intake volume you want to go with.

Let me tell you a little story about a 396 I had for a temporary replacement. The engine was a 10.25:1 narrow domed piston for closed chamber shrouded valve heads. THose heads had a 100cc chamber to get the compression up that high but they flowed for garbage. I used the CompCams LS6 nostalgia cam that I had planned to use in my 427. The heads just couldnt get the the mixture flowing. No life or excitement in that 396 at all. I got bored and dropped a 115cc Brodix Racerite 270 on it that were meant for my 427. Unfortunately the compression was going to drop to about 8.5:1. Even with the low compression It woke the engine right up with no other changes!!! Flow is the key to a happy engine,period!


For you, you need to figure out what your small dome size is and what your compression is going to be with the Edelbrock heads. You have to figure out what your final horsepower goal is and what your end goal is. Low torque stump pulling good for parking lot cruising or high horse power that will be more fun on the highways. If you buy the smaller combustion chamber heads between 100cc and 110cc that will give your 9 to 10.5:1 compression then you wont have to mess with the heads again if you are staying in the 500 hp range. YOu can vary your power levels with your cam selection after that. The problem you are going to have is how unsatisfying the stock heads are. No matter which ones you grab unless you find a small combustion chamber and hog them out a little to get them to flow. I dont know what your piston shape is and what the old cylinder head shape was so you are limited to edelbrock becasue there are no other quality head manufacturers out there that make that small of chamber.

Those 148 heads will get you by from what I have read. You should get a valve job done to them and get the spring seats enlarged and the valve stem seals machined for Viton seals. Have the cam in mind so you can get the machine shop to set them up for the right height and pressure. If you decide you want some good heads like Brodix or AFR then you will also have to get bigger pistons. Another option is shaving the heads but a very experienced shop has to do that to match the intake manifold angle .....its a precise adventure to do it.

If this is temporary and you are tight on cash go with the 148 head and a steel shim gasket if you can find one. Thats the other thing is finding a gasket to give the proper qwench so you dont lose compression as well

 

Thanks for taking the time! These are all things I hadn't considered before I dove in. Rather than dump money into the 148s that could be better spent towards a future head upgrade, I'm going to try my hand at clearancing the stock L29 heads. They will work with my cam with minimal modification if I can get them opened up to accommodate the -13.8cc dome. Which I think I can. Unsurprisingly I get caught up in wanting a project done now, rather than saving and waiting to buy a pair of heads tailored to my build. We'll see how it goes.

 

The 454HO cam is very mild, only 211/230* dur @ .050", on a 112LC.
It is designed to build cylinder pressure with 8.75CR heads.
IIRC the HO heads flow pretty well, 430HP @ 5500 is not hard at all from a 454.
A bigger cam is almost useless with that CR, and better heads are not going to help that cam vey much, and only if the CR does not go any lower.

Now the problem is "down the road". Most BBC heads have large open chambers.
If you truly want BBC high performance, you need a bigger cam, better heads, and new pistons for more compression. Taller intake, bigger Holley.
With AFRs, 10.5 CR, and a streetable 230-240* cam, you are staring at 550-580+HP.
The AFRs are worth like 60-80HP over stock castings alone.
Then there is "the-intake-won't-fit-under-my-hood" problem.

The Edelbrocks and that cam, or one 10* larger could also work pretty well.

I went with the low rise LS6 "569" intake to keep the stock BB hood, knowing it would cost me 30HP. I don't care, the hood is worth it. It's all lost past 5500.
That is the only R-intake that fits under the hood.
With an L88 hood, you can fit a L88 size high rise, or air-cap, and gain 30HP.
I kept the old school L88 heads too, knowing they cost 60HP over the AFRs. I knew I was not going after max HP.
But I still have 500HP and 550# TQ on the Dyno.
232* /239* dur tight lash Hybrid Roller, 112 LC, 10.5CR, LS6 sized cam, but more modern.
I would be at or over 580 if I changed heads and went up thru the hood.
And I am still worried about the strength of the rear end parts!

Many ways to make big power with a BBC!
You have a good strong bottom end.
Decide your "end-game" and build heads & compression to match.

 

Save your money, do your research and build it once.
You’ll waste a ton of money doing it twice and you will need all that money and then much more upgrading your drive train to handle all the horsepower and torque.
Just ask us how we know!!!

 

I have a 427/4 speed combo in my 1968 C3 and when we had it rebuilt I made a deal with a guy who owned a speed shop. He was a mechanic from way back and knew his way around the big blocks. He knew what worked and what did not. I chose to build a L88 engine (CLONE) and I put it in my Corvette with a L88 Hood and the cold air intake system. I have the wedding cake assembly on the throttle body and it works nicely keeping cool air going into the combustion chambers. I spent many months studying the various BB builds and then chose the L88 for it's power and torque. I lucked out as I met a gentleman at Corvettes@Carlisle who sold me the 1968 L88 parts like the hood and the carburetor parts. On Sunday afternoon he still had it so I bought a very rare 1968 factory L88 hood for a few hundred dollars because the owner did not want to truck it back home.

When we built my engine I saw that the Open Chamber heads used in 1969 on were more likely to have detonation issues. In 1968 they used a Closed Chamber as they had done earlier without the sensitivity of the open chambers. My cylinder heads are the Closed Chamber GM 3931063 and are 100.9 cc Oval Port heads and they allow me to run 12.25-1 Compression ratio which is what makes the power on my Corvette. We spent some serious money getting the heads cleaned up to allow then to flow better by a cylinder head specialist. I have see 0-60 times down in the 3 second range and the capability to run a high 10 second quarter. The cylinder heads along with cold air and cool fuel make my engine very happy and it will run all day on 93 octane unless the engine gets hot in traffic and then I activate my water/methanol injection system to improve the quality of the fuel (~115 octane) and the water cools down the combustion chamber.

Having the forged bottom end really helps if you are going to use any kind of power adders. I have used compression to make the power my engine makes. Aluminum heads are nice and so much more affordable today. But you still need to match them to the piston shape. With my L88 pistons at TDC the valve pockets and the pistons mesh perfectly since they were made for each other. The pistons valve pockets stick out above the block at TDC. We used Play dough in all 8 cylinders to verify that I had the clearance to run the engine up to 7k rpm but it gets tight and I have little room for any valve floating. The engine is supposed to be able to make 562 hp according to the Dyno software. The water/methanol system will provide another 20-40% more power with the higher octane, I have not measured the difference yet.

Forum member OldCarBum tells you the truth about your drive line. My car started life as a high horsepower Corvette and has the parts for the BB and it's power. I put a pair of D.O.T. slicks and then broke a half shaft the first time I side stepped the clutch. I am lucky it was not something more expensive.

Best regards,
Chris a.k.a ctmccloskey

 

Yeah...be careful what you wish for!

My friend George took his 69 BB to the dragstrip, once.
He kept street tires on it, to be "safe".... but 10" wide Nittos....
and A GM ZZ 427, 480HP and 490 ftlbs, 411s, and a TKX 2.87 first gear....and....

He got three runs in before "it felt funny" and he stopped.
One factory half-shaft twisted 45* or so, like a pretzel!!!!!!!

 

As Leigh said, that cam is small and designed to be pump gas friendly and have decent manners. Heads are where you make your power. The Edelbrock heads are a good piece. But we need to hit the brakes for a moment. Do you know what your in/out of the hole specs are for the piston? Any idea what gasket you’re looking at running? If you don’t know this, you need this info before you go any further.

Example:

Assume the following just for consistency. .037 thick head gasket, 4.370 fire hoops on head gasket and assume the pistons are .015” down in the hole, with a 119 CC combustion chamber. That puts your compression ratio right around 8.8:1. Putting a 110 cc head on it bumps the compression to 9.5:1 which would probably be the highest I would want to run with that cam without knowing all the particulars IE how much advance is ground in etc.

Now assume the block was zero decked. This is when the block was decked to bring the pistons to .000 with the deck. This will raise your compression to 9.1:1 with 119 cc heads or 9.8:1 with 110 cc heads. That’s a pretty drastic change in compression for such a small change. You can get similar changes messing around with head gasket thickness and also the diameter of the fire ring.

You want roughly .040 -.050 quench with the head gasket. Get tighter than that you run the risk of pistons kissing the head etc. get too big of a gap and your compression goes down and you’ll have spark knock issues. Sounds counterintuitive but having too much quench will make a motor have detonation problems.

Hope this helps

 

less compression would decrease the risk of knock. KNock is pre-ignition from hot spots and higher compression. Usually an issue with higher compression, more ignition advance and cast heads. Aluminum heads will allow a higher compression and more advance than cast iron before you get pre-ignition and it can be mitigated by dialing back timing or adding a higher octane either through higher octane gas, octane additives or a water-meth injection set up. I run 93 octane, have 11:1 compression, brodix 115cc heads, 36* advance all in and vacuum advance and started out running an octane additive to be safe and backed it off to find if I had any knock. I dont run an additive at all now but will at the track to prevent higher RPM heat related knock just to be safe. It is what your engine needs as yours may not like what mine likes. No 2 motors are exactly the same

 

Brodix makes a 110cc head in a 270 volume intake runner now but currently arent available at Summit. They sell them each so you can buy one at a time which helps with cash flow

 

Thanks for all the input gentlemen! My piston to deck height is .020. I would like to run the 3933148 heads if i can. With a 113cc head and .039 gasket I'm getting 9.33:1. The 113cc is a guess though. The only info I've found on these 148 heads has them at 113cc. But that is if they are indeed from 69. Apparently these heads were made until the early 80s for trucks. The date code is A15*9. The Brodix 110cc heads sound like a great option once I can afford them.

 

I also uncovered an old set of closed chamber 206s that came off a 396. They would need quite a bit of work to get them back in shape but the closed chambers are really cool.

 

Is that in the hole or out of the hole?

 

avoid closed chambered heads. Those shrouded valves block air flow and they cant breathe worth a ****. THats why everyone makes open chambered heads now. the difference in performance is night and day. I know because i swapped heads and nothing else and went from, a dog that would only spin the tires if i revved high and dumped the clutch and that was just for a few feet with 10.25 compression closed chambered heads to my brodix heads and dropping to 8.5:1 compression and the tires would breakloose if I just down shifted and matted it. No other changes, not even much of a carb tune...they are that much better. Its all about efficiency and those chimney style heads aint got it

 

The Brodix heads would be night-n-day better than any stock head. It's all in the ports & chamber shapes. +60+HP!

If you are thinking of maybe going that way in the future, don't waste any money on some other heads now.

Just save up, and do it once! You'll be money ahead in the long run.


These are some very heavily ported SBC race heads, and they were good heads to start with. But now it makes 770HP at 8000 rpm! You could almost stuff a deck of cards in those ports. The walls are near straight! They had to epoxy up several leaks after the porting went thru the walls. The pushrod holes have brass sleeves, etc. But they work well now! Sorry don't have any BBC race head pics.