I'm getting started with a 496 stroker BBC build for my 72 LS-5. I'm not looking for anything wild, just gobs of torque.

I have a local shop doing the short block using a 74 block. They will be installing 4 bolt main caps for the middle three. The crank, rods and pistons will be forged. I am getting a set of 74 781 heads from another forum member.

Any input from anyone on intake/carb/cam/exhaust?

Bob K.

 

Eddy Air gap intake with plenum divider removed.
Holly Type 950 Carb, we use AED
The cam I have designed for the OEM headed BBC that a few member have is
.600/.570
229/241
109 Sep

It has plenty of vacuum for accessories and with stock heads it has made a best of 589HP and a worse of 560. Torque is over 600#/ft with great throttle response. You will want a 2.5 " exhaust and 2" headers.

He it is idling:

 

As the 500" Cadillac came with an ordinary QuadraJet any 750 cfm carburetor will be more than enough for up to 6000 rpm figuring a volumetric efficiency of 85%. I would consider an Air Gap and 750 cfm Edelbrock.

 

That's a goood combination . It makes a square motor(bore x stroke), they like to rev and NEED to breath. At least an 850 carb and a modified air gap. 2" headers should be good w/ a free flowing exhaust. I like header side mounts.

 

Do a search here for AJROTHM. He's got a killer 496 combo from Mark Jones (Vortecpro) that has proven to be cross country trip reliable as well as incredibly quick with PS/PB/AC.

As Mr Straub mentioned...you can easily build 600-650HP from these things and be daily driver friendly. This is way past a stock Caddy motor....which ran out of breath early also. Oval port GM heads are capable of 800 HP with work.

Do a search on Edelbrock's site for some interesting reading on dual plane intakes. With a cylinder "seeing" only one half of a carb vs a single plane where all 4 BBL's are available...you'll find larger carbs do much better.

The correct "big" carb is the trick...and tuning it. Going small on everything is a crutch to make something "idiot proof" (not calling anyone an idiot) where it couldn't possibly have an issue anywhere. Of course that also drastically limits potential and performance.

JIM

 

Good info and good advice from somebody who has real world experience- a lot of it. With 496 CI you're going to have gobs of torque anyway, unless you make a number of bad choices. So, you may as well do it with overall performance in mind rather than just build it for torque. The difference in cost is minimal and the difference in performance is big.

Regarding the part I put in bold- Jim, you're too nice of a guy to call somebody an idiot, even though you certainly could.

 

I used StraubTech cam, Edelbrock heads, Hedman Headers, roller rockers under stock looking valve covers for my 496.

I wanted to keep the stock hood so I used a repo LS6 intake and a QF 830 DP.

Almost 200 miles on it but it pulls hard.

 

Here's a true story.....I'm reminded of a good friend who had built a 540 for his C3 "by the book"....meaning everything based on "conservative" for a street motor as per what the hot rod magazines (generic) had been telling everyone for years. We met through this Forum when I was planning my 540 at the start. We never met in person until a year or two later when I was asking him how he got his to hook up? When I grabbed a gear...mine was hunting for a ditch and the tach was screaming to 7000 rpm in a nano-second. So I assumed his must be the same way and he had found a secret to make it get traction.

His combo was a 9.5 compression 540, GM/Edelbrock rectangular port heads (went a little radical there he figured), a GM dual plane intake, an 850 cfm vacuum carb, 1-7/8" headers, a 230'ish@.050 HR cam, TKO 5 speed and 3.08 gears. From our phone conversations I came to believe the carb just wasn't doing what it should. I needed to be in Dallas the next week, so I told him I'd bring up one of my homebuilt 850 DP's to let him try. This was literally an ugly pieced together carb where I had added 4 corner idle circuits etc...but it worked well. It was just to test with anyway...

He immediately handed me the keys when I got there (trusting dude huh?). We checked it over to make sure carb was opening all the way, timing was good etc and then we took off for a drive with me at the wheel. It drove fine....then we got to an open stretch where I could nail it from a roll in 1st gear. It never hesitated..and you could hear secondaries opening....tires spun about 2 ft and I slammed 2nd with another 2 ft spin...and then hit 3rd with a bark...and that was it. Hmmnnn....OK..back to his house to swap carbs.

Next drive I insisted he get behind the wheel. Same stretch of road....he nailed it in 1st and it was instant tire smoke and fishtailing...but I was proud of him...he never let out and grabbed 2nd gear with about 50' of black streaks and 3rd laid down about 10' more. He had a grin plastered from ear to ear!

So I discovered his trick to traction was to not make any power! He later chassis dyno'd it and it made about 410 RWHP...Good...but mine was making 615 RWHP at the time. He swapped the intake to a single plane and picked up 30+ RWHP. Had heads ported and milled...picked up another 20+...changed cam to a 240'ish HR...got another 20 or so. When it was all done he was still just under 500 RWHP. The low compression, cam, heads, 850 cfm carb and small headers were still strangling it. He literally used it for his daily driver at the time in Dallas commuter traffic and loved it. Took me several years to get my carb back!!!

So moral of the story is if you're going to do it...put together a strong combo for what you're wanting to do and maximize the parts you're using...but select right parts first. Heads are where the power is....don't choke them on either side and put the right cam with it and you'll have power as well as street manners. "Think small...get small". It's all in the combo!

JIM

 

615 RWHP ! Nice ! On pump gas ??

 

Are you considering a h-roller and did you ask the builder to make it internally balanced?

 

Oh yeah...that was the very first iteration. It made 732 flywheel HP on the engine dyno, 615 RWHP once in the car.

Later made 825 flywheel HP with some head porting, cam and intake change.

Somewhere between these two it made a little over 700 RWHP.

Later made 871 flywheel HP with a different cam, intake porting and oil pan change.

Now makes 1140 RWHP with a 2.5 point drop in compression, smaller cam....and two little turbos!

All on pump gas!

JIM

 

Yes, We are going with a roller can and it will be internally balanced.

Bob K.

 

RPM air gap, 850 double pumper, Straub hyd roller and as much headwork as you can afford, 2" headers, 3" exhaust..

Should be a pretty decent running ole car..

 

427 , what was your compression in NA trim ?

 

11.56

jim

 

781 heads have about 120 cc chambers and it takes domed pistons to get the compression up. I've been told that the stock heads flow about 255/199 cfm. From what i've seen in builds in the 454 - 496 ci motors is that they need higher flow. The 781 and like heads are an excellent choice for heavy cars, and cam be made to work well with just some minor changes. I would up the valves to 2.19"/ 1.88" this will give you a good cross section are under the valve. and allow the heads to move some more air. The exhaust ports are all ready big so they need no work there. The intakes are about perfect for this valve size.

big ci motors make cam durations that would make a 427 sound radical be mild in a 496. An H-roller with 240 intake @.050 would be a good mild build.

What compression are you ending up with?

 

I plan on being able to use regular gas.

I won't be able to visit the shop until next week. He is a big believer in building engines that are designed for the street if that is what you want.

I think that the compression ration will be about 10:1.

Bob K.

 

This is a really good combo, and I have built many similar, but have not had a chance to dyno them.
Are you running square port heads, and are the exhaust manifolds stock, or do you have to run headers to get those numbers.
I would really like to compare notes.
Mine is a 496 with GM 990 square port open chamber heads
I am running stock exhaust manifolds, but they are opened up so they are at least as big as the exhaust port, and I neck the exhaust pipe up to 3" as close to the flange as I can so it has dual 3" exhaust.
The cam is a hyd. roller 232@ .050 int. 242@ .050 exhaust with .620 lift. 110 LSA
The intake is a dual plane weiand team G that has the divider milled out of the plenum.
The carb is a Barry Grant 4150 flanged that flows 1040 CFM mechanical secondaries. 4 corner idling.
This combo runs really good, and the car screams, in fact it is hard to keep the fan belts on it revs so quick.
This particular engine is in a 70 SS454 Elcamino with 342 gears and a turbo 400 trans on 275 BFGs

 

Headers will bump the power up 40HP and 30#/ft over corvette manifolds. The 12 degrees longer on the exhaust gives the exhaust time to get out. This is a huge help to the manifolds since they don't flow as well

 

Hi Chris, not sure I would make a "blanket" statement to that effect?? It all has to do with EVERY other piece included in each build. They are ALL different.

Here's a post showing numbers back some time ago (2009), I have more similar but not available today.

Headers vs. Cast OEM Manifolds??

We're talking the Vette's here, but I can give you a recent test on a '72 Chevelle LS-5 that was built as a 489" stroker using the factory manifolds and headers. Both tests were done without mufflers to keep it valid!

This was a 9.5:1 build, Comp Cam's retro-hydraulic platform, and 100% stock-appearing! Correct block, heads, intake, manifolds, and Q-jet!

The first test was using the headers, unit produced 471 HP @ 5500 RPM and 523# Torque @ 4200 RPM. We felt these were decent numbers considering there was minimal head porting and almost no attention to the intake manifold!

The subsequent pulls with the factory manifolds, producing 463 HP @ 5700 RPM and 541# Torque @ 3600 RPM, was somewhat impressive as well considering the manifolds were untouched, no porting/grinding whatsoever! We gave up about 7 HP but gained almost 20# Torque with no other changes!

(Add) We were not "chasing HP" on this build, we picked the pieces and let the chips "fall where they may" so to speak!

The customer, to this day, is extremely happy with the build! Moves his 4000# Chevelle fairly easily! And is absolutely "maintenance-free"!!

I was going to place this in an existing post but didn't want to "hi-jack" that one! I get a number of questions about this specific area (headers vs. manifolds) during the course of the year!.

Thanks, Gary in N.Y.

This build was many years ago, still runs perfectly to the best of my knowledge.

Thanks, Gary in N.Y.

P.S. Have done numerous similar builds for many members up on this site! As stated above, it was for a Chevelle, but the Vette manifolds are much more efficient. The HP number aren't "staggering" (on these type builds) but most builds along these lines are 100% stock-appearing also!