Thread: 6 inch rod 357CID SBC

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I am running a 6" rod small block Chevy, with 10.5:1 Ross forged pistons, on 6" Eagle Rods. Spinning the Crane bumpstick with Edelbrock gear drive, bumping full roller valve train, and Manley stainless race flo oversized valves in a set of 58cc 1984 MonteCarlo 305 heads, hogged out for oversized valves - bowl blended, ported and polished.

Two questions -

What is the max timing I can run this engine at. Speed Unlimited says 36 degrees, but I have read that a 6" rod motor can be run with as much as 44 degrees of timing advance because detination issues are more controlled with the increased rod length allowing the piston to remain at TDC longer, than a stock 5.7" rod - basically the geometry is changed.

My other question - I have 750 Edelbrock performer series carb and a Speed Demon 750 - which one is going to give me better performance. I've been running the Edelbrock, pleased with it, but I hear that the Speed Demon can do better. I have not tried it. The Edelbrock wants to cause the engine to stall on hard cornering, and hard braking. Can I get away from this with the Speed Demon and get better acceration perfomance?

"What is the max timing I can run this engine at. Speed Unlimited says 36 degrees, but I have read that a 6" rod motor can be run with as much as 44 degrees of timing advance because detination issues are more controlled with the increased rod length allowing the piston to remain at TDC longer, than a stock 5.7" rod - basically the geometry is changed."

Please post a source to that article, I'm a technoid and I'd like to read it. I guess the best way to determine the optimum timing in the motor would be to read the plugs. I ran into an offer while surfing recently that piqued my interest and I think I'll order it. I've spent a hundred dollars on some other things that didn't give me the return that this offer promises.
http://racingsecrets.com/spark_plug_reading.shtml

"My other question - I have 750 Edelbrock performer series carb and a Speed Demon 750 - which one is going to give me better performance. I've been running the Edelbrock, pleased with it, but I hear that the Speed Demon can do better. I have not tried it. The Edelbrock wants to cause the engine to stall on hard cornering, and hard braking. Can I get away from this with the Speed Demon and get better acceration perfomance?"

Bolt a Predator on it. They're self-adjusting from 390 to 930 cfm and can't flood the motor or starve it either because they have no fuel bowl.

Here's a paper by Ron Iskendarian on the long/short rod controversy.....
http://www.iskycams.com/techtips.html#2005

Thanks - but no thanks - I need answers from someone who knows what they are talking about. You obviously have no idea what all the hype I spewed about my block means. Any fanatic can quote scripture - I.e. point to links. I need answers, not another opinion. The question was how much total timing can I run a 6" rod SBC block at. See beginning of thread for specs. The other was which is better for performance (out of the hole stop light to stoplight) the 750 Edelbrock or the 750 Speed Demon.

I am an engine builder as a hobby. It took me two years to design and build the 357CID SBC that is in my Wrangler. The vehicle does 0-60 in 5.2 seconds and weighs 4300 pounds. My 350 makes about 430hp according to Al's Custom Engines, with all the custom machining I have done. Every little thing you do when building an engine from scratch makes a difference. 5 - 7 hp here and there all adds up in the end to big power gains.

Your question had to do with what total timing you could run with your particular combination and since every combination is different, even with a motor using the same parts as you are, I suggested continuing to dial in advance until you encountered detonation. You can detect that easily by reading the plugs, if you know how to read plugs properly.

Your other concern had to do with the inability of the motor to continue to operate properly in tight turns and sudden stops, which would be a function of fuel sloshing in the bowl. If you have no bowl, you have no sloshing.

Now, I feel a little stupid for trying to help you in the first place, since you already know all the answers.

The links provided don't even address the ability to run higher compression on pump gas without detonation - by using longer rods. All they were talking about is where the hp gain is - low vs high rpm - and torque vs hp - I already know that, or I wouldn't have engineered the bolck to run 6" rods. I built a torque monster of an engine. My powerband is very flat. I am looking for substantial claims of other than 36 total degrees of timing can be run on a 6" rod motor with results. Is this fact or fiction. I have a variable timing module installed - and my Unilite is out getting set up with 28 degrees of total timing on the distributor, all in at 3K.

Helpful suggestions would be good at this point, not a history lesson on rod length.

o.k., here's a helpful hint. If you want to run high compression on pump gas, there are three areas of concern.

1. Squish. Piston crown to cylinder head clearance of 0.035" to 0.040" will optimize your combination to reduce the tendency toward detonation by jetting the fuel mixture across the combustion chamber to maximize mixing and also to eliminate a dead combustion space above the piston where cooling water will keep that space cooler than the rest of the chamber/head. I've seen some fellows run as tight as 0.018" squish by angle milling the piston crown so that as the piston cocks in the bore, it will still clear the head at TDC.

2. Camshaft. Altering the intake closing point will alter the amount of fuel/air charge that is trapped in the cylinder on the compression stroke. Using short timing on the cam with a high static c.r. will result in very high cylinder pressures which won't work with pump gas. Conversely, long timing on the cam with a low static c.r. will result in very low cylinder pressures and a motor that won't pull the hat off your head.

3. Aluminum heads. Generally speaking, you can run about a full point more static c.r. with aluminum over iron due to the heat rejection capabilities of aluminum.

Furthermore, you'll notice that I didn't say a word about those silly-ass 305 heads you're using. I'm really trying to be a nice guy.

I sometimes add links to my answers because you're not the only one reading these posts. There are over 3,000 members on this forum and maybe some of the newbies will be educated better if I include links to expand further on what I'm talking about.

Hey try this......

keep bumping the timing till you hear it ping then back it off 2 degrees....

I have to disagree with the theory about a longer rod can accept more timing....

The longer the piston dwells at TDC the more chance it has for detonation to occur....

Trick is to run as much timing as you can to get the job done but....the more efficient the engine is you can make the same amount of power with less timing....

You really have to do your own experiments with timing just to see what the engine like or can handle....

Several of my engines I run different size weights on each side of the distributor and 1 light spring....nothing on the other side...depending on traction.

If traction is not a concern I will lock the distrubutor down at full total advance.... ( so it runs the same from turn key till shut down any where from 38-52)

dr, I think we lost gpzilla somewhere along the way. Was it something I said?

Earth to gpzilla, Earth to gpzilla, come in please

The 305 heads are the exact casting number that Lunati used in their horsepower tests. I performed the exact same machining process on those heads that Lunati did with the exception of 1.60 exhaust valves. The valves are Manley RaceFlow undercut valves. Check out the link to see what Lunati taught me:

http://www.hioutput.com/tech/343hp/343hp.html

I am using an Edelbrock RPM performer intake, and a Mallory Unilite Photocell Distributor, with MSD 6AL, MSD variable timing module, and Blaster coil.

Sure I could have shelled out a couple grand for expensive aluminum heads. I liked the tip about the angle machining of the pistons. I hadn't heard that one. I am running 10.5:1 compression and have .040 head clearance at TDC with the gaskets installed.

I zero-degreed the cam to be sure it was on the mark. With the Edelbrock gear drive it was, had I used a chain, I would have needed to adjust it.

Here's the cam I am running -

Crane HR-276-2S-12 IG

intake @ 325 is .488 with 1.5 rockers
exhaust @ 339 is .509

Cam timing is:

.050 @ 0 BTDC closes @ 34 ABDC max @ 107 ATDC DUR 214
open @ 48 BBDC closes @ 6 BTDC max @ 117 BTDC DUR 222


So back to the original two questions.....

Edelbrock 750 or Speed Demon 750 which is going to give me better accelleration?

What's the max ignition timing I can run on this engine, with 28 degrees built into the distributor? Or should I just set it at 36 degrees at 3000 RPM and dial in the other 6 degrees and see if it makes a difference or causes detonation?


Could I benefit from swapping out the 1.5:1 rockers with 1.6:1 rockers? I know this changes roller to valve stem geometry, but it can't be by that much. What kind of hp gain could this make if any? Perhaps several more ponies? I have enough valve clearance to facilitate this swap without having to re-check with clay.

To the dr.

You lock down between 38 and 52 degrees of advance?

That's above the 36 degrees that most Chevy rodders recommend. Now I'm interested.

What allows the engine to run with so much ignition advance? That is what I want to know. Is my .040 over SBC 350 built in such a way with the cam etc... that I should consider bumping the total timing up to say 44 degrees on 93 octane pump gas ?

If so I can put 8 degrees on the crank with the 28 degrees in the distributor, all in by 3000 rpm and then dial in the rest with my MSD module and see if it runs better with up to 44 degrees of total advance?

Guess like you say try it till it pings and back off.

How about the carb question - 750 Edelbrock Performer or 750 Speed Demon. Which one would you run for an ET if that was your choice, and why?

gpzilla, what is the piston crown configuration, dished or flat. If dished, how many cc's? If flat, how many valve reliefs?

I'm trying to figure your ACTUAL static c.r., 'cause flat-tops with 4 cc's of valve reliefs, 58 cc chambers and 0.040" squish is gonna put it at 11.3:1

Same combination with 10 cc's of piston dish will put it at 10.48:1, so if you're using flat-tops, you're kidding yourself.

Just curious, did you consider the 12558060 Vortec heads? The reason I'm asking is because Lunati taught you to use a 305 short block with 305 heads, not a 350 short block with 305 heads.

The Vortecs are available from Scoggin-Dickey under part number SD8060RAGP all set up for 0.600" valve lift and complete with valves, springs, retainers, keepers and guide plates for $366.47 each. I'll bet you've got more than that invested in your 305 heads and the Vortecs will outflow them and they have a more efficient combustion chamber.

Posted by the dr...
" keep bumping the timing till you hear it ping then back it off 2 degrees...."

While I agree with the dr to a point, I would argue that detonation may have begun 3 or 4 degrees before you could actually hear it.

Posted by gpzilla...
"makes about 430hp according to Al's Custom Engines"

I'm not disputing Al's claim, but don't you think he's gonna tell you what you want to hear in order to justify all the money he's extracted from you. Have you had the motor on a dyno?

I have $410 (includes guide plates and studs) combined in the heads plus cost of valves, springs, shims, and locks.

Yeah I could have bought a set of Dart heads ready to run. But 3 years ago some of the nice heads weren't available.

I had Ross make the pistons they are flat-top with a dish and valve reliefs which equal 10cc total each piston, set-up for 6" rods.

With a .040 gasket it should be real close to 10.5:1. If I had not had them cut the dish the pistons would have yielded 11.2:1 (which I wasn't sure I could get away with on pump gas).

My wet compression test (forgot to prop the throttle open) is 210 PSI on all 8 cylinders. That is wet or dry - doesn't matter.

The only thing I had Al's custom engines do was machine the back of my Edelbrock cam gear to accept a torrington bearing press-fit. He was a patient guy, and gave me some pointer during my build. He's a professional race engine builder and owns and operates his own shop, so I know I was getting info from the best source.

I am spinning a set of 33x12.5 Firestone Destonation tires on 3.55:1 gears and getting a 0-60 time in just over 5 seconds. This I know from my Nordskogg digital gauges which are calibrated with a marked mile.

My engine has not been on a dyno, but the numbers speak for the engine. I have to be cranking out that much power to get a 0-60 time like that on a 4300lb vehicle. Don't even ask me about 1/4 mile time. A Wrangler is a short wheelbase flying brick, at 95mph the wind resistance is too great. I put four overhead off road lights on top and dropped my gas mileage by almost 2 miles to the gallon. But is sure is fun to smoke Vettes and Stangs and anything else that will play.

So - Edelbrock 750 or Speed Demon 750?