363 With Smallish Heads? Opinions

[stangman67]

I currently am running a 289 with performer rpm heads (1.90" intake) in a 67. Im running a turbonetics 62-1 with .81 turbine. For this winters upgrade, i have a budget which is roughly limited to either buying a used 331 stock block with studs and girdle with victor jr heads from my buddy, or building my own all new shortblock. I was interested in a 363 for future upgrades, but i dont know if i am worse of running my current heads. Supposedly the larger bore unshrouds the valves for better flow, but I am not sure how much. Right now i push about 12 psi non IC with water meth. For street driving, just looking for better low end. I am running a performer rpm hyd flat tappet cam, so a roller is definitely going in. I thought about added a roller to my current engine, but only seems like a matter of time till it dies. Been two seasons of beating so far, still running fine, it just runs out of steam at 5500 rpm. Thanks for the feedback if you have any advice.

 

[RangerJoe]

The 331 with the victor jr heads may make more power, but with your turbo it would be plenty to split a stock block. I think I would invest in the future and build a 4 bolt block. You can always upgrade heads later.

Joe

 

[madspeed]

Upgrade the block and run that until heads can be afforded

 

[A5literMan]

X3. Dart shortblock and add heads when you can

 

[srtthis]

The turbo car is a 347 with off the shelf high ports and it runs it's balls off! The heads in a turbo car aren't super important

 

[NIKwoaC]

Undersized heads is more ideal than an under-strength block in a boosted application. Do the 363 and then start thinking about heads once the toy savings account recovers.

The turbo car is a 347 with off the shelf high ports and it runs it's balls off! The heads in a turbo car aren't super important

Eh that logic is really misconstrued. Airflow is airflow. It's just *usually* less critical in boosted applications because you can just keep turning up the wick on the boost to overcome your induction shortcomings.

It is kinda a moot point for most guys with street cars though. I ran into a guy not long ago with a 700+ hp turbo car, and he was running OOTB Twisted Wedge 170s. He admitted that he was leaving power on the table by not having bigger heads, but a 700+ HP street car is already insane, so what's the point?

 

[85rkyboby]

@NIKwoaC Isn't it that you will see lower boost readings with bigger heads, compared to the smaller heads. Although the decrease in boost pressure your power does go up?

 

[revhead347]

I agree with everyone above. The 4 bolt main block is more important that head flow right now. The turbo will make up for the smaller valves.

Kurt

 

[stangman67]

This is what I was looking for. Also, I forgot to say my shortblock budget included selling my current turbo for a hurricane series from turbonetics, only cause it will fit all my piping.

 

[srtthis]

Undersized heads is more ideal than an under-strength block in a boosted application. Do the 363 and then start thinking about heads once the toy savings account recovers.



Eh that logic is really misconstrued. Airflow is airflow. It's just *usually* less critical in boosted applications because you can just keep turning up the wick on the boost to overcome your induction shortcomings.

It is kinda a moot point for most guys with street cars though. I ran into a guy not long ago with a 700+ hp turbo car, and he was running OOTB Twisted Wedge 170s. He admitted that he was leaving power on the table by not having bigger heads, but a 700+ HP street car is already insane, so what's the point?

what i think most people see is a loss of boost when they put big heads on a car.

so a 363 with a set of high ports making 17lbs or a 363 with neal 202's making 17lbs

that neal headed motor might be able to make 22lbs total with the wastegate shut
that high port motor motor should be able to make 35lbs with the wastegate shut.

not many guys on the street will be running race gas to be able to run that much boost. but they will be able to run 12-15lbs. ass seen above the big headed motor will be flowing a good bit more CFM at that boost level.


so at the end of the day what would you rather have big heads and less boost or smaller heads and more boost?

 

[rbohm]

@NIKwoaC Isn't it that you will see lower boost readings with bigger heads, compared to the smaller heads. Although the decrease in boost pressure your power does go up?

remember that boost pressure is actually back pressure, so when you add flow capability, you actually reduce the back pressure, and thus get more power, but you do see a lower pressure in the system.

to the OP, since you are on a limited budget, spend you money where it will do the most good for your application. since you are running a supercharger, and want more power, you should be investing in bottom end parts that increase reliability, in this case the aforementioned dart block. you dont want the block splitting apart just when you get the power level you want.

 

[NIKwoaC]

@NIKwoaC Isn't it that you will see lower boost readings with bigger heads, compared to the smaller heads. Although the decrease in boost pressure your power does go up?

Generally speaking, yes. Boost is a measure of resistance to flow, not flow itself. By itself, your boost gauge tells you very little about how much air and fuel is actually going into the cylinders.

Of course a turbo builds exactly as much boost as you tell it to, so it's a little different than a supercharger in that regard.

 

[NIKwoaC]

what i think most people see is a loss of boost when they put big heads on a car.

so a 363 with a set of high ports making 17lbs or a 363 with neal 202's making 17lbs

that neal headed motor might be able to make 22lbs total with the wastegate shut
that high port motor motor should be able to make 35lbs with the wastegate shut.

not many guys on the street will be running race gas to be able to run that much boost. but they will be able to run 12-15lbs. ass seen above the big headed motor will be flowing a good bit more CFM at that boost level.


so at the end of the day what would you rather have big heads and less boost or smaller heads and more boost?

If you're asking me, I enjoy RPM. I'd much rather take a motor that shifts at 6500 than one that shifts at 5500, even if they make the exact same power in the end. So I would usually err to the side of higher flowing parts, though it becomes purely personal preference, because any way you slice it you can make insane power with a turbo for a street car even with mild heads.

 

[srtthis]

If you're asking me, I enjoy RPM. I'd much rather take a motor that shifts at 6500 than one that shifts at 5500, even if they make the exact same power in the end. So I would usually err to the side of higher flowing parts, though it becomes purely personal preference, because any way you slice it you can make insane power with a turbo for a street car even with mild heads.

yea turbos def make stupid amounts of power.... a 347 high port turbo motor shouldnt make more power than a 450" sc1 headed nitrous motor. but 155mph and knowing we can get 157ish out of it at 3250lbs vs 150@ 2805lbs thinking we could get MAYBE 151-152 out of it really shows how much more power a turbo makes over the other combos

 

[85rkyboby]

remember that boost pressure is actually back pressure, so when you add flow capability, you actually reduce the back pressure, and thus get more power, but you do see a lower pressure in the system.
quote]
Would the more boost(i.e. back pressure) with the smaller heads be more beneficial to low rpm driving? Like how it is with low rpm on a 2 1/2" exhaust compared to 3". I understand you want more rpm with turbo, I was just wondering. Thanks @rbohm & @NIKwoaC

 

[NIKwoaC]

@85rkyboby No, not necessarily. Remember, gauge pressure is not directly correlated to how much air/fuel is actually entering your cylinders, in other words, it is not directly correlated to how much torque/power you're making. In the same way as described above, an engine with a very highly flowing inlet/exhaust may make the exact same torque/power at a given RPM as the same size engine with a very poor flowing inlet/exhaust running a higher boost pressure. In both cases, the power adder (super/turbo) is moving the same amount of air into the cylinders, but the poor flowing engine represents a higher restriction, which results in higher boost pressure.

It's for this reason that "how much boost can I run" type of questions can never be answered directly. It is heavily, heavily application dependent.

This is all speaking in generalities. Like anything else, there are a lot of variables that come into play that we're ignoring here.

 

[85rkyboby]

@NIKwoaC I understand now. I had some things backwards. Thanks for the knowledge

 

[rbohm]

@85rkyboby No, not necessarily. Remember, gauge pressure is not directly correlated to how much air/fuel is actually entering your cylinders, in other words, it is not directly correlated to how much torque/power you're making. In the same way as described above, an engine with a very highly flowing inlet/exhaust may make the exact same torque/power at a given RPM as the same size engine with a very poor flowing inlet/exhaust running a higher boost pressure. In both cases, the power adder (super/turbo) is moving the same amount of air into the cylinders, but the poor flowing engine represents a higher restriction, which results in higher boost pressure.

It's for this reason that "how much boost can I run" type of questions can never be answered directly. It is heavily, heavily application dependent.

This is all speaking in generalities. Like anything else, there are a lot of variables that come into play that we're ignoring here.

couldnt have said it better myself.

in the end its all about the flow of air. remember that an internal combustion engine is basically an air pump. the more efficiently you can move air in and out, the more power you are going to be capable of making. a perfect example of this;

years ago car craft magazine built a supercharged small block chevy using stock heads and they set the blower up to build 9psi boost. after they tested the engine, they swapped heads to a set of aftermarket dart heads out of the box, and no other changes. boost pressure dropped to 5.5psi, but horsepower jumped by something like 80hp.