Max engine RPM

noob question (at least on this board) on engine RPM.

Setting asside the torque vs. hp debates...

What are the practical limits on engine RPM?
What kind of parts will get you what kind of engine RPM levels?

From what I know so far..
higher rpm requires, stiffer, lighter springs to close the intake and exhaust ports in time for the next piston stroke.

light weight valves with a 3 angle grind.

light weight rocker assembly. (with girdle?)

light weight tappets and push rods.

Larger intake and exhaust ports, with smooth flow.

aluminum heads to dissapate heat better then iron.

light weight pistons and con-rods.

Good spark, timing and advance electrical systems.

Assuming a baseline rpm of 6,500, what do I need to get to 7,000? 7,500? 8,000?

Thank!

 

[John]

Hi Ian and welcome to the forum.

When you're talking about high-rpm engines you've got the right idea.

For the short block, you are probably better off with a forged rotating assembly with as lightweight of pieces as you can get... the lighter they are the easier it will be to wind it up there. Also, splayed 4-bolt main caps on the block might not be a bad idea.

In addition, with a shorter stroke and longer rod, it makes high rpms easier on the engine (less rod angularity, less instantaneous piston speed, and generally lower rotating mass).

On the camshaft, you probably won't get a hydraulic lifter (roller or flat tappet) cam to run that high, so go with a solid-lifter cam.

To avoid valve float, you'll probably need either really stiff valvesprings or a rev-kit. Valve float is a bad thing.

Just for added assurance, I'd use ARP bolts everywhere.

 

How do I know what parts will enable what RPM levels?

I've played e-mail tag with edelbrock and their answer was basically - "tell me what parts you want and I'll sell them to you" Basically not very helpfull.

 

With the small block ford, it's all about finding and upgrading the weak links.

Late model production 5.0 blocks are known for being weak in the main webs. The alternatives are:

Early 289/302 blocks

Mexican 302 blocks

SVO sportsman blocks

Boss 302 blocks

SVO, Dart and soon World race blocks.

The race blocks are the best bet for RPM over 7,500, but all of those can be better than the late model blocks.

Next is the valve train. This isn't rocket science, if you want high rpm, you need a solid cam and big valve springs.

The Rocket science is making a high rpm hydraulic roller, or a high rpm valve train that will fit under low profile valve covers.

Next is oil. While the stock oil system is probably fine on a dyno stand or at the drag strip, if you want to corner and run high rpm, a dry sump system is best. A good baffled pan with an Accusump might work also.

The last requirement is a strong rotating assembly. Ford did pretty well making the stock pieces strong. Stock rods and cranks have survived 600hp n2o injected engines. Better aftermarket pieces are a good idea for peace of mind, but properly prepped stock pieces should survive 7,500 rpm unless the engine suffers from detonation.

That is what you need to survive high rpm. Making power there is another story. This is where the valve job and port sizes come in. You will also need a pretty big cam to make power at high rpm.

You don't need Aluminum heads. There are good iron heads that will flow enough to make power at high rpm and heat disipation isn't an issue.

You don't need light weight valves, rockers, pushrods or lifters. Those all help, but in a solid lifter valve train, bigger springs will make heavy parts work (for a while).

You don't need a light weight rotating assembly either. If all of the parts are strong enough, they will handle the extra weight that is being swung around. Light vs strong is a ballencing act. When you get to 10,000 rpm, that is where aluminum rods might be needed for weight savings, but that is way out there.

I'm probably going to have a Dart sportsman block, Cola 4340 non twist forged crank, 4340 forged billet lightweight I beam rods and lightweight forged pistons. My valve train is still up in the air.

I am going to run a wet sump oil system with an accusump. My rev limiter will be set for 7,000 unless I know I'm not going to be turning.

 

[ QUOTE ]
How do I know what parts will enable what RPM levels?

[/ QUOTE ]

The best way is to look at dyno sheets of engines that have the parts you are considering.

The scientific way is to calculate port velocity based on the cross section of the port, engine displacement and piston speed.

Why don't you tell us what you are planning?

 

I'm exploring either a GT40 or an Ultima in a few years. (need to pay off school loans first) Right now I'm learning what I can on engines, aero, brakes and suspension systems. Also doing track schools with the local BMW chapter.

My goal for the car is a weekend road trip and track day car. I'm not into drag racing, just road.

Since the most likely gear box is a taller Porsche G50, a torque motor would probably match up well. Ironic that the gearbox may cost as much or more then the engine, especially if I want custom or race gear ratios in the box.

Since this board has more then a few knowledgable folks on it, here I am.

I live in Iowa, which after N.C. is a Mecca for circle track racing and the associated engine builders. I haven't spoken to any yet, as I want to learn what matters and what generally works first.

Most of the catalogs (Jeg's, Edelbrock, etc.) are pretty vague as to what parts are needed to get what power and rpm levels. They just want to sell parts. If I can start with a junk yard truck block and get 400+ HP and 7K rpm, I'll be a happy camper. should be more then enough for a ~2,200 lb car.

I've also wanted to build a motor to see what it's about. I'll need a good machine shop for the metal work, but I want to do the bulk of the part selection and assembly work.

I'm probably going to buy desktop dyno as well so I can play with different engine setups. Anybody have any thoughts on this software?

BTW, I'm a mechanical engineer and a statistician, so analytical techniques and theory are straight up for me. Also re-build a few Briggs and Straton's in my youth and do all non-computer related maintenance on my '99 BMW 540i 6-speed.

 

If you are a junkyard scavenger, the Mexican block would be a good choice. They have thicker main webs and main bearing caps.

In their lifter valley they will say "hecho en mexico". If you can find a used block that has not been bored out, you will have a pretty strong block.

I have seen a couple of these on ebay pretty cheap.

If you do your own scavenging, you can get it dirt cheap, but you have to find it first, they are fairly uncomon.

The other junkyard route to 400 hp is the 351 Windsor. When stroked to 393 or more cubic inches, they will make lots of torque and will not need to rev very high to make that power. The 351 block is also stronger than the production 289/302/5.0 blocks.

The 351 is bigger, heavier and won't rev quite so high, but it's easier and cheaper to make a 400 hp 351 than a 7,500 rpm 302.

Do you want EFI or carburators? That's the biggest decision you have to make before you can come up with the right combination.

 

[Howard Jones]

At 1.3 hp per inch, 400hp 302, you are near the limmit for a 70k mile street motor on 91 octain gas. This power level can be done with a hyd cam and 10 to 1 compression. The big deal is going to be the heads. Spend as much as you can on the best heads you can afford. At this time that is AFR's. You can save a lot of money by using a holley and a rpm performer type intake instead of a 8 barrel FI setup and make the same power. This type of motor will make best power at about 6500RPM's. Plan on spending at least $10 per HP.

Now at 1.66 hp per inch, 500hp, you are getting serious and as mentioned above a solid lifter roller cam and roller rockers are in the picture along with the 2.02 intake valve version of the really best head avaiable. 91 octain is becoming a problem and it will not last 50k miles. Call this one a low 7s rpm motor.

1.8ish to 1, 550hp-575hp 302, is a near full on race motor and will require that level of care. This kind of power will be hard to achieve at 10 to 1 compression levels and no matter what you buy for heads they are going to need pro port work. Needless to say you are long past production blocks, crank, rods, etc. and the cost is nearing $20k This is a 8000rpm motor and IMHO not much use on the street.

625 hp 302, 2 to 1 motor, 12 to 1 CR on racegas, rebuilds measured in 100 of hours and really,really, more than $20k.You have now spent at least 4 times as much as the 1st one to get a lot less than twice the power.

725ish hp 302??, NASCAR roadrace spec, $50K, 9300rpm, 3 hour motor. The carb alone will cost what it would cost to build a nice stock 302 and that last 500rpms will cost several 1000 bucks and require really serious engine building talent. This motor is more than 10 times the cost and less than twice the power of the first one. I built my car for less than this motor would cost.

More than that? BOOST and Bottle 1 run motor.

Build the first one. More power? Stroke it or use a 351. Same ratios/$$$$ apply.

 

[Ian K]

Lots of good advice.

Here's my current thinking (as with everything, subject
to change):

SVO R302 4 bolt block (if I'm sinking this kind of money,
I'm a little leery of a 2 bolt with stud girdle)

331 stroker kit (I am leaning towards DSS) with forged
rods (maybe look for longer rods if possible), DSS forged
lightweight pistons, forged crank.

AFR 205 heads ported/polished

shaft rocker system, big springs, solid lifters and
solid flat tappet cam (DSS's lightweight hydraulic valvetrain
sounds interesting though)

ARP bolts/studs all around

Dry sump

Electromotive TEC3 with Weber styled throttle body intake,
crank trigger/distributorless

I figure I can set a redline of 7200 - 7500, and push it
to 8000 on occasion.

Looks good on paper at least /ubbthreads/images/graemlins/wink.gif

Ian

 

[Howard Jones]

The problem with roller rockers is lack of oil when first cranked over. In the case of a hotrod that sets for several days between uses the top end of the valve train will really dry out. Even if you crank it over with the spark tuned off you still have spring loads right away. All this is not good and is the main reason solid roller lifters fail in street motors.

I have been told that before you build a all roller valve train with high seat pressures then plan on installing a pre start oiling system.

That motor ought to make 500+ hp. My car has about 350 and I think that it has enough to make the corvettes go backwards. Good enough for me, at least for now.

 

[Lynn Larsen]

Ian,

No first hand knowledge, but before starting an engine remarkably similar to what you describe, I consulted with an automotive engineer who is in the know on parts that work and parts that play the part, but don't quite cut it. He didn't have good feelings about DSS. He said that their stuff tends to be on par with the mass engine rebuilders: fine for standard family sedan type car, but not up to snuff for performance builds. He was especially critical of their pistons. Again, his words not mine.

Conventional wisdom also says that if the engine is going to spend much time over 6500rpm, you are better off with an internally balanced engine. Some will argue this and it becomes somewhat religous. Personally, I would not use a 50oz imbalance. If you don't go internally balanced (much easier now than it used to be) go with 28oz.

Regards,
Lynn

 

[Rick Merz]

One more thing to consider is at what rpm range you will be operating your engine at for the majority of time. If you go with a steel cam with roller lifters and roller rockers with high spring pressures the recomended rpm range will be 4,000 to 7,5000 or more. The important thing to consider is that this combo NEEDS to be ran at 4,000 rpm or more to ensure proper oiling. If you run this engine on the street at 2,000 to 2,500 rpm you will shorten the life of your high revving engine if it has a windage tray or crank scraper then life from driving on the street will be even shorter.

 

Where did that come from?

If you have adequate oil pressure and your valve springs are not too crazy, you should be fine with an all roller engine unless you put in oil restrictors that are too small.

Windage trays and crank scrapers have nothing to do with engine life unless they come loose and hit the rotating assembly.

I think you may be confused with the RPM range on a cam card. That just tells you where the engine makes good power, it has nothing to do with the oil system.

 

[Howard Jones]

Interesting,Rick, Makes sence to me. All those roller bearings need a contant pressure oil source. This is why I like a large diplacement low reving motors in street cars. If hp/cubic inch ratios exceed about 1.3 or so then its better to make the engine larger that spin it faster to get more power. With out race class rules to limit engine size this is the perfect solution to more power in a street car. For that matter even a track day car would be easer to maintain with a big inch,low tech, low reving, motor.

It should be noted that the Ford mk2's were 427's at about 550 hp. They used this combo because thet wanted endurance, low rev torque, and simplicity. Oh and that comes out to about 1.28 power to displacement ratio.

It worked then and it will work now. Build them big and simple.

 

[DBLDREW]

Well to my knowledge DSS does top notch work. I had them do the machine work for my 351W that I put in my Mustang. That was around 10 years ago the motor is still running strong with no problems. In fact the last time I had it at the drag strip (last year) it ran an 11.85 @ 118mph and that is in a ~ 3000 lb car. So I wouldn’t categorize his work as for “family sedan type car”.

 

Roller bearings need less oil than a plain bearing.

 

[DBLDREW]

Rick I’m also going to have to disagree with you. Again if we look at my motor it has a hydraulic roller cam and roller rockers. I usually will shift at 6500 but it will go to 7000 no prob and with out any valve float. So the spring pressure on my heads are pretty strong. Now this is a street car that I cruse around way more then I race so it usually revs around 2000-3000 while I’m cruising. So again 10 years and it’s still going strong.

 

Some good information in here. Thanks!

I bought a copy of desktop dyno so I can play with matching components to get a good, cost effective solution.

I don't think I mentioned it, but I enjoy a higher reving motor then a torque monster. I'm also not into drag racing, my preference is for road racing (on a track of course!) and I enjoy the satisfaction of shifting well. Hence my preference for a motor that needs to be flogged and a tranny that likes to be stirred.

So to sum up - looks like I need a:
set of heads/manifold/carb solution that breaths well
well matched cam/roller/spring combo that won't float at higher rpms
robust block with a shorter stroke, longer conrod to reduce internal forces - probably balanced internally
good combustion charateristics to have an efficient burn, probably at 10:1 compression for pump gas
good ignition system to handle higher rpms (MSD?)
Lots of other little bits to keep it together and oiled properly. (accusump, ARP bolts, windage tray, etc.)

 

Static compression ratio isn't the right target.

A dynamic compression ratio of about 8.2-1 is considered safe for premium pump gas.

The dynamic compression ratio is calculated with the rod length, stroke and intake valve closing, so an engine with 12-1 compression could be under 8.2-1 if the cam is big enough.

Here is a good calculator for dynamic compression ratios:

http://www.kb-silvolite.com/calc.php?action=comp

 

cool, thanks