Power Band

[LateApex]

When I first decided to build a 300 with a turbo, my thoughts were that the 300 has great bottom-end torque but not much up top. The turbo would kick in when the engine was out of its original power band and I'd have the best of both worlds, bottom end and top end.

Then, I found a ported head with big valves and it should support high rates of flow for the turbo.

But, will it lose the original bottom end? Is this engine naturally torquey down low because of its original head design with small valves? Will making it flow for a turbo cancel out the original advantages?

Thoughts?

Thanks in advance.

 

[freefli]

No! not in my experence.It may not lug,and crawl around under 1000 rpm as well with the ported head,but over one thou when that engine comes under load ,the turbo kick's in.You don't need a ported high flowing head for a turbo,they can be counter productive.Back in old school when Ak Miller was turbo king,the rule of thumb was.1LB boost=VE.One pound of boost equal one hp for each cubic inch displacement.300 cu in = 300 hp.Seven pounds boost = 1.5 HP per cubic in 450 hp.14 pounds boost =2hp per cubic inch.That's 600 hp from a 300 cu in engine.that's with an unported head,also a cast crank.Save your ported head,and steel crank,for a wildly camed,over carbed ,red light to red light show off machine.The most performance for the least amount of money spent,is a turboed factory fresh motor held to seven lbs boost,change your gear ratio from it's present ratio to 2.73 to one or so,and that will make that turbo work down low,pull like a freight train,keep the R's down and get you the best gas mileage .If what you want is a red light tire burner.just blip the gas,drop the clutch and stomp on it.A fresh stock motor is good for 7 lbs boost.If you want more,Then the first thing I would change would be the cam.An Isky 331-ta is hard to beat ,next is low comp forged pistons,and so and so on,untill you run out of fund's for the project.after the cam ,pistons,and ARP fastners.it becomes an exersize in deminishing return's for money spent.Have you ever heard the Old Phrase (Keep it in the Six'es) 600 Hp-6000 RPM,and it will live forever.

 

[LateApex]

Interesting thoughts; thanks.

I already have a forged crank, so I'll use it.

I planned the entire engine around the ported, big-valve head, so it's staying.

The Jaguar independent rear has 3.31:1 gears and I don't want to tear into that.

I planned the turbo selection (Holset 40) based on making 450 HP and I'll need to run 10 pounds of boost to do that, based on compressor maps and making assumptions of volumetric efficiency for this engine with an upgraded head.

I do like the suggestion of the Isky 331-ta cam. I was considering that one and it's nice to have confirmation.

Definitely going to run studs instead of head bolts ...

Custom forged pistons since it looks like my freshly-rebuilt (before I got it) block is .040 over ...

Anyone know where I can get forged rods for this engine? (Just kidding)

This may be one of those "you don't know until you try it" things so I may not really know how it runs down low until it's all working together. At least the vehicle should be around 2800 pounds.

 

[MPGmustang]

IIRC the larger valves does not help in any way with a boosted 6, maybe an 8 but not a 6. once you add a turbo to the i6 it seems that you get the best of all worlds, basicly your VE goes through the roof of 100+, and to add more 'porting' for more VE just crank up the boost. stock i6 engines are lucky to see 75% VE. but that turbo is something else.

IMO I would sell teh big valve head and go stock valves. but that's what I would do.

331-ta cam sounds great, I too would want one.

the rear gears are okay, it's best of both worlds, add a trans with an OD and you'll be extremely happy.

.040 over about at much as you want, and will raise CR by .1

overall the engine will be a power house as you have planned, it might not be as good down low but it will do good still.

 

[JonL]

IMO I would use the ported head as you will not need to run as much boost to get to your target hp, because of the reduced restriction. Lower boost means lower exhuast manifold pressure to turn the turbo as well. Lower exhaust pressure means more power, and less damming up of the heat in the exhaust manifold reducing cooling requirments. Also with the log head the exhuast and intake ports are side by side, and exhaust will heat the intake charge less reducing the risk of detonation.
2800# you say, what vehicle is this going in?

 

[LateApex]

The turbo 300 is going in a '63 Econoline pickup.

I have a manual transmission, the good ZF one from an F-250. It'll have to be cable-shifted.

Out back, there's a Jaguar rear with 3.31 gears.

The intercooling will be water-air.