Seeing how there hasn't been much tech related info going on here and I'm a little bored, I figured I explain some engine building tips and break some myths. I'll start from the top down and do it as a Q&A. I also don't want any BS... and I don't care if you wanted it or not.

Fuel System:

"Which is better fuel injection or a carburetor?"

While they both can produce the same peak power outputs, fuel injection has the upper hand with the air fuel ratio. Carburetors can be only be set to be perfect in a specific rpm range be let say lowend, midrange and highend. The other two ranges will be less efficient, where as fuel injection with proper tuning can hold the same air fuel ratio from 500-9000 rpm. Carburetors are fine for the majority of engines but if you are planning on taking your engine to the edge of it's limits, fuel injection is the only way to make your engine live.

"Should I use a mechanical or electric fuel pump?"

Mechanical pumps are great as long as it can sustain the proper fuel pressure required by your carburetor. EFI or forced induction setups require an electric fuel pump. Forced Induction setups also require a much bigger fuel pump than naturally aspirated setups.

Air Induction:

"Should I use a single or dual plane intake?"

This mainly is dependent on your fuel system. Carburetors can utilize both with dual planes being the easiest to setup for the street. That said, single plains can be used effectively on the street but requires careful selection of parts and tuning. Fuel injection requires the use of single plane intakes for best air distribution.

"Should I build a naturally aspirated or forced induction engine?"

It all depends on what power level your are trying to obtain and how much you want to spend. Most engines are able to produce the required power by natural aspiration with only several changes. Forced induction is mainly for all out power or making small engines more powerful. Forced induction is more forgiving to poorly matched components or engines as you are forcing the air in.

"Should I use an intake with short or long runners?"

Now this is where it gets complicated. Generally short runners are better for high rpm and long runners for lowend. Proper manifold selection requires you to think in three dimensions. Port size and runner length isn't enough to chose the right intake. You need average port and taper with over the entire length of the runner to find the port cross section. This gets into specific math formulas and specifications I don't have. While you could just put any intake manifold on but for best performance, your camshaft designer can get you pointed in the right direction.

"Why do intakes have RPM ratings? (Idle-5500/1500-6500)"

These are just general guidelines on the specific usage of the intake. Changing the engine size bigger or smaller and several engine components will change the rpm range of the intake.

Cylinder heads:

"Which is better cast iron or aluminum heads?"

It's mostly just a user preference. Iron heads will just edge out their aluminum counterparts in total output. Aluminum heads do have weight savings and better detonation resistance in their favour. Although iron heads are normally cheaper.

"Are these heads to big for my engine?"

You can never have to big* of a cylinder head (within reason). It's very easy to have too small heads, factory 302/351W come to mind. Camshaft selection is very important, big* heads require small* camshafts and small* heads require bigger* camshafts.
* - Generalization

"This head flows XXX more than this head. Which is better?"

Flow numbers at 28 inches of water should only be taken at face value and is just a general tool for comparing them. 28 inches of water is nowhere near what pressure they see during engine operation. Using a flow bench and taking it up to 40-50 inches of water will tell you if you have a "quiet" or "noisy" port. The louder it gets under the higher pressure means that the air is getting more turbulent and less efficient. These figures aren't normally released.

"Which is better canted or inline valve heads?"

Canted valve heads normally perform much better than the inline valve variants but require special pistons for valve clearance. Aftermarket heads with altered valve angles even the playing field but require special valvetrain setup.

Valvetrain:

"Which is better adjustable or fixed rocker arms?"

Adjustable is better as it can compensate for deviations with aftermarket parts as fixed rocker arms can go out of alignment if there has been any machine work or deviations from stock parts.

"Which is better, pedestal, stud and shaft mount rocker arms?"

Pedestal rocker arms are non adjustable and are the weakest due to the small retaining bolts.

Stud rocker arms are the best all around setup. They are available in adjustable and non adjustable versions.

Shaft mount rockers are the best setup for high rpm stability. However stock setups do not come close in strength to the aftermarket setups.

"Are roller rockers better?"

Roller rockers are definitely better than their regular counterparts. Decreasing valvetrain friction is always better. Roller rockers free up HP and have longer lifespans.

"Should I use higher ratio rocker arms?"

I would use what ever your aftermarket camshaft recommends. With a stock camshaft you can use them normally without a problem for a small improvement.

"What is with sodium filled valves?"

Sodium filled valves are only used on low rpm engines in hard working conditions. They can take higher abuse from engine lugging without damage. While they may look stronger than a regular valve but in reality they are hollow. There are drawbacks to their use, their weight makes high rpm impossible and they make choosing proper valve springs harder. They belong in the scrap bin with valve rotators.

"What valve springs should I use?"

You should use what ever valve springs your camshaft requires. Stock valve springs are ONLY good for stock camshafts. Incorrect valve springs selection can result in camshaft damage or severely reduced engine RPM range.

"Should I get heads with bigger or smaller valves?"

It's normally best to get the bigger valves. You won't lose any power or have driveability problems.

Part Two to come....

 

I didnt see anything about a roller cam in there, damn you nathan, what do we pay you for?!

Seriously good info. I know a little bit here and there about engines, but I think its neat to read aticles like this.

Today is a day that if I would have known you were bored, I would have picked your brain with a milion questions about my 351 project Im doing.

 

Good stuff Nathan, it`s very enlightning.
Hopefully some day you can explain the advantages of aluminum heads and some of the the best brands/types for a mild 351 street engine.

 

Nice reading this stuff. Same here, I know some of it, forgot some of it, and never knew some of it!!
What type of hp gains are the roller rockers capable of making on a street engine, small or big block, making about 1 hp / cu in?
Why do engines like the 426 hemi or the Boss 429 with the 'semi hemi' heads make so much power?

 

very good thread Nathan!!

 

We should have a thread just to ask our stuff to Nathan.

Nathans tech corner, Nathans info center haha something like that.

 

The roller camshaft stuff is still coming in part two.

Aluminum heads can run a higher dynamic compression over iron heads without running into detonation problems. Now which ones you need is dependent on your engine combination and how much you want to spend. Heads range from $1000 to $3500!

How much hp is freed by roller rockers is had to say as there are several designs. Some only have roller fulcrums, others have roller tips and the high end ones are damn near frictionless. Many have said Ford freed up 15 hp on the 93-95 Mustang Cobra engines with them.

From what I know about hemispherical heads is they allowed bigger valves and a straighter shot of fuel into the combustion chamber. The downside of having big valves in this setup is at low rpms, in makes it a "dirty" combustion as some on the fuel is dumped out of the exhaust. To help correct this they had to add a second set of spark plugs but it still isn't very fuel efficient.

 

Now for the continuation...

Engine Short Block:

"What type of pistons should I run? (Cast, Hypereutectic and Forged)"

This depends on the engine build and user preference. Cast and hypereutectic have about the same strength. Forged is the strongest and is required for high performance / forced induction setups. Hypereutectic pistons can run tight piston clearances. Proper piston to bore clearance is required on all pistons and very important for forged pistons so you don't get piston slap. Do not bore your engine until you already have the pistons you are going to run and give one piston to your machinist to ensure proper clearance.

"Should I use flat top, dished or domed pistons?"

Flat tops and domed pistons are good for raising compression on low compression heads and offer about the same performance. For a slight boost in performance it's best to run dished pistons as long as you can keep a decent compression ratio. Dished pistons create a more efficient combustion chamber and also trick the engine into thinking it has a longer stroke. To properly explain this goes into physics above my skill level.

"How much compression should I run?"

There isn't really much point to build an engine to have less than 9.0:1 static compression. Having less compression means you aren't using your gasoline to it's full potential. Forced induction setups require a lower compression to lower combustion temperatures otherwise you melt your pistons. Dynamic compression dictates what octane fuel you require and this is controlled by the camshaft's intake closing point.

"Are stock connecting rods good enough and what is the difference between fixed and floating rods?"

Stock connecting rods are normally pretty strong but it normally comes down to a price to performance issue. Used connecting rods MUST be resized as they do stretch during engine operation or you will have a shorter than normal bearing life. Aftermarket rods are normally the same or just a couple bucks more than the cost of reconditioning the connecting rods. However there are two different types of factory connecting rods, split and cracked. Split rods can easily be remachined and cracked ones cannot normally. Fixed rods have the wrist pin pressed into the connecting rod and floating rods have the wrist pin running on a bushing.

"Are longer connecting rods better and what about rod to stroke angle?"

Longer connecting rods were considered a way to increase performance as they held a longer dwell time at TDC. This got a slight increased flow out of stock heads. The results were minimal and is redundant with the availability of performance parts today. Rod to stroke angle is the ratio of an engines crankshaft throw to the connecting rod length. As long as you keep it above 1.5:1 you will be fine. Stroker engines normally require longer rods to keep the smaller pistons in the cylinder bores.

"Do I need need a nodular or billet crankshaft?"

These crankshafts are normally only required on all out horsepower builds and forced induction setups. Stock crankshafts are normally good for 400-500hp.

"Is external or internal balance better?"

Internal is better as it doesn't require separate parts to keep your rotating assembly within specifications. For most setups it's cheaper and more than adequate to have external balancing. Some engine setups cannot be internally balanced.

"Do I need a high volume or high pressure oil pump?"

There is so much miss information about this. You do not need anything more than a factory oil pump for 99% of engine builds. The ONLY time you run a high volume or high pressure pump is you have done modifications to the oil system on the engine. The use of a high volume pump on an engine with factory bearing tolerances on average increases oil pressure 10 psi over normal. The proper use of a high volume pump is on an engine that sees sustained operation over 6000 rpm and has larger bearing clearances to reduce bearing temperature. Always use a hardened aftermarket oil pump driveshaft as stock ones are known to break on occasion. It's just cheap insurance.

Part three with camshaft and exhaust to come.

 

Right on good stuff

 

good note about the HO oil pump... heard many a wanna-be gearhead talking about boosting the oil pressure... if it ain't broke, don't fix it...

 

Hemi heads produce more power and efficieny due to a cleaner burn and a more natural flow through the head.

 

Do ford have some sort of hemi spherical type heads?



Haha damn Nathan, ya sure are making me wait eh! lol

Good stuff though

 

The Boss 429 engine which was available in the 1969 and 1970 Mustang (known as the Boss 429). It had huge heads - they were nicknamed semi-hemi heads. The engine was designed to power Nascar racers but they had to built a certain number of these for public sale as per the rules of the day.

 

If it ain`t broke you`re not trying hard enough aka Red Green.

 

lol... i like my stuff to last!!