going blower is different than going turbo
^that

Switching from one boost method to another (generally, and assuming the same boost level) keeps a few things, such as:
1. intake manifold (probably)
2. ignition (but not the actual advance or curve)
3. oil system (except as needed for turbo supply/drain)
4. rods, pistons including CR (no, everyone doesn't agree)
5. crank
6. main caps
7. block
8. head bolts/stud quality

But a few things will definitely change:
1. cam duration, split, lobe height
2. head flow
3. in/ex flow bias
4. the entire exhaust system, including primary tube diameter
5. rocker in/ex bias
6. stall speed

There will also be differences between centrifugal (Vortech, Pro Charger) and positive (GMC, Kobelco, Autorotor, Sprintex), especially stall speed

With turbo:
cam? equal or less exhaust duration?
Head flow? Increase intake to match exhaust?
Exhaust? Hapel makes over 1000hp with 2.5" hot side and straight dump out of turbo
Flow bias?
Rockers? 1.6 intake/1.5 exhaust?
stall? Have to deal with what I got. NOS off line if need be.

How far off am I by guessing

I looked at a set of Pro comp small block heads just today at a guys shop whom I know. They were actually pretty nice castings. WAY better than the last Edelbrock junk I looked at! Only real issues was the valve spring height and the VJ was a bit inconsistent. A quick VJ and they went 245 @ .500, 248 @ .600. Just an FYI...

When I buy Big Block heads they will most likely be Speedmasters.
265cc versions are 400 a pop bare.
210cc versions I've seen for right at 300ea. bare.


Blowing my wod on these sb heads though.
Left Todd a message telling him I decided to go full workup on the exhaust side of the heads.
Wait another week and I may give in and go all out on both sides. LOL

I really, really don't need to though if I'd just pony up $500 for a turbo instead of the supercharger.

Why else did I pay $599 for a Chinese Mig/tig/arc combo welder a few month's ago, and now it sits?
This one:
http://www.ebay.com/itm/MIG-180-Amp-Weld...g-/152420938829

I did order these a couple days ago for my 73 Ford F100 and both have shipped......
Sniper EFI master kit and Fi-tech fuel command center(800hp fuel flow).
I plan to turbo it in the next couple years.

Only cost $200 more for the sniper which is good to 650hp and power adder/ignition control ready instead of the 400hp version of Fi-tech which can't be upgraded according to their tech line.

Don't be totally anti overlap when you go turbo...

True, it's the intake part of OL that hurts, Vizard has recommended some really short intake durations with none.

Turbine sizing will play a big part in camshaft pick.. A guy from TF racing said to me once, remember that your engine is naturally aspirated until the turbo supplies more air than the engine can use..

I wonder what opening up the throat, blending the seats, and de-shrouding/blending the combustion chamber would net?

Simple mods for anyone.

Be VERY careful opening the throat. Its a percentage of the valve size to keep the VENTURI EFFECT and if opened to big can trash a set of heads real quick.


google it.


http://sciphile.org/lessons/bernoullis-principle-and-venturi-tube

Couple notes on many of the above posts.

When we're talking ideal blower cam, vs. ideal turbo cam... it's not to say that the same can't work pretty well for both. A lot of the turbo cam has to do with the exhaust turbine wheel size, the A/R ratio of the housing, and foot print (T4/T6). So it's hard to just speak in generalitys to know if you have a "good turbo cam". My first custom turbo cam had 4 degree's less exhaust duration then intake. My second custom turbo cam has 5 more degree's exhaust then intake. Just different school's of thought on what works, from two different people.

What's funny is the cam he has listed above is not all that far off from my custom turbo grind. (Same intake duration, 5 deg. of exhaust, and 2 degree's of lobe sep.) I would NEVER spend the money on a new turbo cam if I already had that in possession in a blower motor that was being converted. If you were building a heads up world record competing machine... then yes... worry about it. If you're just trying to make a bunch of boosted power... then you're in the ball park.

As for the heads, remember that a boosted motor deals with a lot higher pressure ratios then a N/A head. Both pressure coming in the intake, and pressures to help the exhaust side out. Now a turbo motor really gets plugged up with the turbine itself, so making a killer exhaust port really isn't a big concern because it's not your bottle neck. The blower motor can get it out and benefit from a good exhaust port.

A good port speed 300cfm head will make LESS power then a lazy port speed 300cfm head when both are boosted (within reason of course). But that is because the airspeed is through the roof on the small port when you throw a bunch of boost at it and gets choked up. The lazy port will get the airspeed more in line where it should be when you throw boost at it.

My motor has a 230@.050" / .540 cam in it. Literally the lower I shift it... the quicker the car is. Even though it has CNC ported EDDY heads on it that flow 300cfm, they were designed for N/A with good port speed, and just don't want to go a lot of RPM. I have the shift light set around 5800rpm on my car. Any lower then that and the converter flash just keeps the light on the entire run... LOL

The bottom line is... you're thinking into this way too much. Buy a cheap set of heads... put good valves in it so they don't get warped/beat up, and if you're not happy with the performance on the first day... just turn the knob up... a good sized turbo will break that block no problem... what do you care if the motor comes apart at 25psi or 30psi. Either way it's probably going to ruin the set of heads no matter how much you pay for them.

Air speed goes down with boost. Air speed is highest with less density. Intake to exhaust pressure ratios are what you base overlap on. Duration is defined by operating range(rpm)

I talked to Todd again today.
I'm going full port work on exhaust.

Off Topic:
Didnt know but he can get a turner from mopar for a decent price that lets us tune Gen 3's
kinda like the chevy guys tune ls engines.

That throws a wrench in my next build which was going to be a big block. lol

Back on topic:
What about this quote?

Some may question why you would want to spend the cash for porting when the supercharger can just use pressure to feed the same amount of air into the engine. The simple answer is that the amount of air moved by a supercharger is usually measured in pounds per square inch (psi) of boost. But this boost number is actually an indication of resistance to flow. By reducing the restriction to the inlet side by porting the heads, this immediately reduces the restriction to flow. This increases the volume of air the engine can ingest and power improves while at the same time reducing the actual boost in the manifold. Plus, reducing the boost demands on the supercharger also reduces the amount of work the supercharger has to produce, which reduces heat. The net effect is that moving 500 pounds per hour (lb/hr) of air at 10 psi requires less work than moving the same 500 lb/hr at 18 psi. The net result is more power.

https://www.google.com/amp/www.hotrod.com/articles/blown-gen-iii-hemi-centrifugal-wind/amp/

Thanks for the link.

I was only talking about blending the sharp edge into runner and into seat.
Not really reshaping or re-sizing much being the heads are pretty good it appears ootb.

BTW, I was studying all that stuff back when I was building a home made flow bench.

Had a guy from russia make me a script to calculate flow rates with a manometer.

dude, I had forgot all about doing that!!!!!

I agree obviously less dense air at the same pressure would have higher airspeed (fluid is "thinner").

But in the case of boost I don't really see it. I mean even a simple example of blowing out birthday candles. Purse your lips and blow softly doesn't get much airspeed, but push hard with your lungs/diaphragm and obviously the airspeed picks up. Bigger pressure differential = more air speed. Density and airspeed are not inversly proportional. In turbos it's multiplied together to get mass flow right? Density x speed = mass air flow rate.





The quote above is absolutely true. Like I mentioned before... when I had home ported 308 iron heads on mine vs. the CNC ported EDDY's, it took LESS boost with the eddy's to make the same power. That totally supports what was written above.... and if you were trying to optimize a world record holder on a blower/turbo limited class it would make sense.


In the case of your undersized little blower... the head will matter. No doubt. If you're interested in getting every last hp out of it... the porting will count.

But, In the case of a properly sized blower/turbo... there is no reason to spend money on the head.

I'll share some real world results on how boost is so much more powerful of a tool then anything. My buddy ran my car the last time we had it out after I had made some passes on a test and tune night. I had run the car hard at 23psi of boost. He hadn't had any time in the car so we started him off slow. Turned the turbo down to ~7psi so he could get used to driving/shifting the push button.

The difference between 7psi and 23psi was 12.40@110 to 9.55@142mph Same night, same track, same head, same cam, just add boost... for free.

My point is... if you took the money you're spending on porting the heads, and put it toward the turbo... you're going to be WAY further ahead bang for the buck. Scrap that little blower project, and just put the proper turbo on it from the start (or even proper sized blower... either one would work)... You'll be WAY happier with the results for the money, rather then spending it on porting.

I agree obviously less dense air at the same pressure would have higher airspeed (fluid is "thinner").

But in the case of boost I don't really see it. I mean even a simple example of blowing out birthday candles. Purse your lips and blow softly doesn't get much airspeed, but push hard with your lungs/diaphragm and obviously the airspeed picks up. Bigger pressure differential = more air speed. Density and airspeed are not inversly proportional. In turbos it's multiplied together to get mass flow right? Density x speed = mass air flow rate.

I will use your car as my example...
Where is the pressure differential? Your exhaust pressure is higher than your intake pressure, so the combustion chamber never "sees" this blowing effect as your simplified example suggests. A turbo merely changes charge density. There is no "positive" change in air speed with increased boost pressure.

Density and air speed are not linearly proportional, but, given a fixed area of flow, have direct effects on each other. The more contact surface/flow area, the greater the effect.

Your mass flow equation is leaving out quite a few more details as it relates to what I was describing. I believe you are equating compressor map math to port speed. It's not that simple. Compressor maps are basically telling you the efficiency of the wheel as a centrifuge(speed in rpm) as it relates to inlet mass.

Yes, a bit off topic, but not really.

And I whole heartedly agree with you in your advice to O.P. Much better off cash wise spending the budget on the turbo than on heads.

I mostly agree.
I've been thinking more and more about going straight to the turbo route and what you say makes sense. Would also make me some cents too.

I've already committed to the sidewinder heads and the port work.
I'm not going to go back on my word even if he doesn't have the heads quite yet from the manufacture. Told the guy I wanted a pair ported, that's what I'm going to get if he is able and willing.

Just think. In 20 yrs when I'm sitting at some car show with my road kill I can say..... "These heads were ported by a Daytona 500 winning engine builder"

My next option is to forgo the blower. I can give it to my son for whom we are building a magnum headed 318. Would be about perfect for that motor. He still has to drive it a while without it so he doesn't get into trouble right out of the box. He's only 14 but will have his permit in 6 months.

I've got my eye on the billet 78/75 from VS racing. Right at $500.
That's cheap.
Dudes with LS motors are laying down close to 800hp at the tire with that turbo.
They also just released an 80mm too.

The more I think about these Chinese Sidewinders, the more I like the idea of getting them.

Now, If I hadn't bought the box of toys (diamond pistons/TS rings/rods/etc.) 15yrs ago we would be talking about BIG BLOCK heads in this thread instead.

You know the saying.....chasing good money after bad. ;-)

I did buy a single bare Big Block 210cc procomp head off a guy on ebay for $120 + $34 shipping. He accepted offer.

[img]https://goo.gl/photos/qtBwY9Ak95PvnsM46[/img]

Lets see if it actually arrives.
Gonna use it to do some practice porting and possibly cut it up with the band saw.

Are those chinese turbos? The Chinese ones that went through the rotary world, turned out to be total garbage...
I wanted to add this, in regards to overlap, the most power I ever made with a rotary was running a port with huge overlap, a bridgeport is like runner cam with 300 deg at .50...Works great with a big turbine wheel.
I got the parts in for my next 2 rotor, its peripheral port turbo motor, in effect the intake and the exhaust never close. Its really interesting, the intakes are milled in, but the exhaust is bone stock, because Mazda incorporates an anti-reversion step in the exhaust port for turbo motors... Most rotary builders grind it out, not having the faintest of clues of why its there or what its for, but they see it as flow restriction so out it goes, and the power band gets cut down..
You've given me some inspiration though, when i am done moving house and shop at the end of summer, I am going to embark on a twin turbo D-150 build with a big block...

HAHA
Ive got a few big blocks laying around.
Mopower for my ford f100?
Id like to stick the turbo in the bed and use a scavenge pump to send the oil back to the pan.

Chinese turbos have stepped up their game JUST LIKE THE CYLINDER HEAD castings have done.

Custom orders from people who know what they are doing bringing them to the forefront.

Look what came in the mail yesterday.
Procomp BB head, the one I paid $120 for off ebay.
I'm gonna have some fun with this one.


Spark plug boss is sticking way out into the chamber with super sharp edges.



Sure looks pretty.



Very sharp short side turns both intake and exhaust.



At least they barely touched the runners with a carbide and didn't touch the bowls at all. Make it easier to blend for the DIYer.




Last one.

Speaking of china.

I ordered this stuff for my SB in the weeee hrs of the morning.