I need more RPM from my sbc. Looking for advice.

Im limited to three forward speeds so i want to increase my now 5500 rpm redline. I have a decent bottom end and would like to turn about 7500-8k with it and see at least 650hp. The car will be roughly 3100 lbs set up for road course so im trying to keep as much low end as possible. In the beginning i was looking at the cnc port AFR 220s but im wondering if either 18* or sb2.2 will be better for my needs. Or would it make better sense cost wise to just go buy a used sb2 or r07 complete engine? The only real limitation im working within is it needs to easily bolt up to a th400. Easily bolting onto a gen1 sbc block would be even better. Thanks for the help.

First things first, are you running out air from head flow or are you floating valves?  

Hate to say it, but three words.  No, no, and no.  :)

Unless you have more money than California.

A stock bottom end is getting stressed at 5500.  Better rods and a 4-bolt main will get you to 6500 maybe if you have a perfect balance, but the pushrod valvetrain will be very hard to control.  

Nascar engines get their high RPMs by raising the cam in the block to limit valvetrain weight and prevent deflection of the pushrods.  They also use a good amount of Titanium, special block castings and alloys, billet components, dry sump oiling, 18 degree heads... the whole thing costs over $50,000 to get into the realm of RPMs you're talking.  Even at that level of money, you frequently see one go kablooey during a race.  They sometimes don't last the 500 miles of the race.  I could understand something like this for a huge oval track

Not to mention, even if you successfully made it to hold together at that level, the amount of cam, intake, and compression required to get that RPM and power levels will make it a completely useless engine for anything but super hardcore racing.  It won't make any useable torque until 6000 rpms, it will overheat at any speed below about 80mph, and require race-only fuel at about $14/gal plus about $500 per 55 gallon barrel to ship hazmat.

Sorry to be debbie downer, but what you're asking from an engine that was designed in 1955 is just not going to happen.  You will need some serious aftermarket race equipment to get your goals.  SB1 won't cut it.  I don't care how many bolts you have in the main, how light a crank and how short a stroke you use, not gonna happen. You'll rip the whole bottom end out or snap a rod or crank.

Fewer gears actually means you want LESS RPMs in a lot of ways.  You need an engine that builds mountains of torque, then use gearing to attain whatever highway RPMs you want.  There are likely a host of 4, 5, and 6 speed transmissions you can slap behind an SBC for a lot less than $50,000 for a useless engine.

Let's start with what you have, what you want to use it for, and a budget.  It's possible to get 650 hp from an old SBC.  It will be expensive, and might not last long, but you don't need 8000 rpms to get it.

In reply to Patrick :

Right now im using a production iron head, 1.94"/1.5" valves, 76 cc chambers with z28 springs. I haven't even really driven it anywhere near its redline yet so i cant really say. Id guess itll be a combination of both though.

In reply to Curtis :

Ok so new question, which cylinder head would you recommend to make the biggest boom when my bottom end lets go?

Why not just get a decently built 200-4R and make sure the torque converter is exactly what you need for your application?

I don't think anyone can make a good statement on heads until we know a lot more.  Camshaft?  Compression?  Rear end gear?

Build a stroker and aim for making all of your power below 5k. Your crankshaft will thank you.

In reply to pres589 (djronnebaum) :

Because i already have the th400 with a lot of money invested, set up just how i like it. The camshaft, compression and axle ratio are all undecided because i havent decided on a top end yet.

In reply to Recon1342 :

Longer stroke is a possibility but i will still be looking to turn around 7500 - 8k rpm with it. 

The cam you need to spin 8000 is not going to like the 76cc heads. You'll likely need over 11:1 compression, which would mean domed pistons, and that's not good for flame travel.

But,

BOOST is going to like those heads, and with the right gearing, you won't have to rev as high. It will probably cost less to boost what you have, and keep the RPM at earth levels.

Two words: BOOST.

(Boost!)

In reply to SkinnyG :

Its tempting but the added weight of the turbos and plumbing is a big turn off. Even if i did decide to turbo this car, these iron heads are still going back on the shelf. They're currently installed just so i could start and move the vehicle. The 604 bottom end and th400 are mainly what i want to keep. 

You can get 6500 - 7000 out of a pushrod V8 without going too crazy if you've got a solid valvetrain setup and bottom end, but it still takes some work to keep it together up there.  And going beyond 7k definitely starts to need seriously beefy valvetrain, etc. to keep it all in 1 piece.  And once you're up in the 6500+ range, oiling becomes a concern too, even if your vavetrain and bottom end can take the revs.  

pres589 (djronnebaum) said:

Why not just get a decently built 200-4R and make sure the torque converter is exactly what you need for your application?

I don't think anyone can make a good statement on heads until we know a lot more.  Camshaft?  Compression?  Rear end gear?

A 2004R would need more RPM than a TH400 because the gears are spaced further apart.  Something like 2.78:1 First vs. 2.45:1 in the 400, and second gear is similar.

In reply to rslifkin :

You're touching on the major issue there, once i add up the price of offset lifters, shaft mounted rockers, 18* or RR intake, and the heads themselves, would i be better off just spending the 10~12k for a used complete 2.2? 

In reply to bwh998 :

I'd be thinking about one of the crate LS motors made specifically for circle track instead of an SB2.anything, myself.

Then longer stroke isn't going to work.  You need to keep rotating mass to an absolute minimum.  As you increase stroke, you increase piston speed, which means the stopping and starting of that mass will rip the pins right out of the pistons.

Think big bore (easier breathing, maintaining displacement) and short stroke (less rotating inertia)  Ford 460 comes to mind.  Buick 455.  At least the Buick could be easily adapted to the TH400.

General rules:  Displacement sets the torque peak RPM for any given combination.  The old wives tale of longer stroke makes more torque is BS.  If you make apples-to-apples comparison of a Buick 455 (big bore, short stroke) to an Olds 455 (small bore, long stroke), they will make the same power and torque at the same RPMs.  The place where the Buick shines is its potential for higher RPMs because you have the bore area to support the airflow and the short stroke that won't explode into bits with a little more RPMs.

8000 RPMs in a large-displacement V8 is expensive.  Hardcore expensive.  Billet crankshaft and rods, specialty forged pistons, aftermarket block that will hold the crank in one place, significant oiling mods.  Completely get the idea out of your mind that you can do it with a production block.  Chevy did a 302 which took a 350 bore and stuffed a 283 stroke.  It barely held together at 6500.  You could get to 7500 with it, but the combination of big cam, large heads, and small displacement means you have to swing it to 5000 before it makes any useable torque.  You'll be coming out of corners wondering why you're being passed by a stock Civic.

This is why many high-strung race engines have more gears.  They make power and torque in such narrow ranges of their operation, you need lots of gears spaced closely together to keep the RPMs swinging in the right range.  Contrast that with something like a Caddy 500 with a 2-speed powerglide.  It redlines at 4500, has 2.43:1 gears, but still roasts tires and is never needs more than two gears.  If you are honestly limited to three gears, you need broad torque bands, not a peaky high RPM race monster.  If you condense your torque to a high RPM range, you'll need really deep final drive to multiply the wimpy torque and get you moving, and then you'll run out of RPMs on the straights before you hit your top speed.

Fewer gear ratios means broad torque curves.  I know you said you have good money tied up in a TH400 you like, but trust me... for the money you would spend getting an old school SBC to even 7000 rpms you could buy a sequential 8-speed planetary with flappy paddles.

Knurled. said:

pres589 (djronnebaum) said:

Why not just get a decently built 200-4R and make sure the torque converter is exactly what you need for your application?

I don't think anyone can make a good statement on heads until we know a lot more.  Camshaft?  Compression?  Rear end gear?

A 2004R would need more RPM than a TH400 because the gears are spaced further apart.  Something like 2.78:1 First vs. 2.45:1 in the 400, and second gear is similar.

Disagree.  That gearing is neglegible, and it's not RPMs he would need, its torque.  Plus, the proper TC selection will make it stall at a the proper RPM more than the gearing would.  Now, if we were talking about a 700r4 with the 3.06 first and 1.78 second (the largest ratio change of any production automatic), THEN he'd have some issues.

In reply to Knurled. :

Yeah the ls swap would definitely make more sense, but i really want to keep this one sbc. World products does have an iron smallblock thats cast to accept LS heads though...

bwh998 said:

In reply to SkinnyG :

Its tempting but the added weight of the turbos and plumbing is a big turn off. Even if i did decide to turbo this car, these iron heads are still going back on the shelf. They're currently installed just so i could start and move the vehicle. The 604 bottom end and th400 are mainly what i want to keep. 

You have a 3100 lb car.  50 lbs is nothing, plus the way it adds boost means that you have effectively flattened your torque curve like Nebraska.

I wouldn't even consider SB2.2 stuff.  Maximum investment for what basically amounts to "a little bit better than LS"  I'm currently building a 6.0L LS, 11.3:1, 550 hp at around 6500 rpms on a completely stock shortblock that came straight out of a pickup at a junkyard.  No upgrades to valvetrain except springs, titanium retainers, and improved Stainless valves.  It will run on 93 octane all day, make mountains of torque from 2500 to 5500, and I expect 100,000 miles of daily driver abuse out of it.  The only real money I spent was CNC porting the heads and having them professionally set up.

And, a TH400 bolts up with the proper TC.

bwh998 said:

In reply to Knurled. :

Yeah the ls swap would definitely make more sense, but i really want to keep this one sbc. World products does have an iron smallblock thats cast to accept LS heads though...

But it will never hold together like a modern, 6-bolt, cross-drilled main will.

LS is your answer here. If you find an all aluminum donor and strap a turbo or two to it I bet you'd still be ahead wrt weight. Better design all around. Better for rpm. Better for longevity. Cheaper to deal with once you start talking real power. And swap kits mean it'll bolt in anywhere a 350 would. Easy. 

In reply to Curtis :

According to the guys on speedtalk, stroke is nothing compared to valvetrain when it comes to making revs work.  Lot of people running 400-stroke cranks and larger at 8000+.  

Heck, there are OE engines with strokes that long with 8000+ redlines. So good rods and the lightest pistons you can afford (long rods and long strokes will make this happen regardless, because of the short pin height) and you don't have to worry about the bottom end.

And as you point out, it's easier to extend the powerband 500rpm lower than 1000rpm higher. 

Keeping something with a 3.48" stroke (like a 350) together at high revs needs good bottom end parts, but it's not impossible by any means.  The world doesn't end at 6000 rpm.  Valvetrain and oiling are bigger problems than keeping the bottom end intact.  

Heck, over in the Mopar world, I've spun the 360 small block (3.58" stroke) in my Jeep to 6100 many times (including sitting on the limiter for a few seconds at a shot).  And that's on a stock bottom end with over 200k miles of wear on all the parts (stock is a cast crank, forged I beam rods, cast pistons).  It's getting close to the limits of the stock spinny bits, but it's not on the ragged edge.  Depending on usage and time spent at high RPM, people will say the stock bits will live up to somewhere in the 6200 - 6800 range.  This engine is also using basic 5/16" stud mount roller rockers and stock hydraulic roller lifters, nothing fancy in the valvetrain.  I wouldn't want to rev it higher without a better valvetrain setup though.  

In reply to Curtis :

8k isnt asking much from the bottom end, i sometimes even see the cast crank 602 crates spinning close to that. I have the 604 which uses a forged 4340 piece.

Knurled. said:

In reply to Curtis :

According to the guys on speedtalk, stroke is nothing compared to valvetrain when it comes to making revs work.  Lot of people running 400-stroke cranks and larger at 8000+.  

Heck, there are OE engines with strokes that long with 8000+ redlines. So good rods and the lightest pistons you can afford (long rods and long strokes will make this happen regardless, because of the short pin height) and you don't have to worry about the bottom end.

 

And as you point out, it's easier to extend the powerband 500rpm lower than 1000rpm higher. 

Agreed on OE engines spinning to 8000... because they are designed from the ground up to do it.  That doesn't mean you can do it in a flathead or an SBC design from the 50s.  Valvetrain is what it needs to supply the air without float.  That's easy.  The cam it takes to rev that high will kill low end torque, and he won't be going anywhere if he drops a crankshaft in turn two.  He's limited by the SBC architecture.

I'm simply saying that SBC of any flavor represents one of the highest investments possible to attain his goals.

Seriously, if he came to my shop and asked me to get an SB2.2 to spin to 8000 rpms, I wouldn't even consider it unless there was $20,000 cash on my desk first and it would have a 10/10 warranty.  Ten feet or ten minutes.  I wouldn't even dyno it in my shop because I couldn't take the downtime when it exploded at 7500 and wiped out my dyno room.  If he asked me to do it with an LS, I'd say $6000 and it will be done next week.  (disclaimer... I no longer work in that business, nor was high-rpm race stuff in my wheelhouse, but just sayin)