Can a 1g head be on a 2g

[trickirickey]

im doing a stroker kit and rebulting my head and my friend says i should take his 1g head and and use it ### i wouldnt have to bore the the valve openings but and other thing is i have cams and i was wondering i could use them i was getting duel valve springs and titaum valve and etc. so inform me people

 

[VelocitàPaola]

im doing a stroker kit and rebulting my head and my friend says i should take his 1g head and and use it ### i wouldnt have to bore the the valve openings but and other thing is i have cams and i was wondering i could use them i was getting duel valve springs and titaum valve and etc. so inform me people

Yes, they're almost completely compatible. In fact, using the 1G head on a 2G is a common upgrade.

 

[JDNSBR]

Head studs are different so you are going to have to do some boring and switch them out.

6bolt is 12mm
7bolt is 11mm

 

[ericbev]

Use your 2G head. What cams are you reffering to? Boring valve openings?! Try and re-type all that using complete sentences and further elaborate on what you are trying to find out.

 

[95blackGsTurbo]

You really should search this. It will give you all the information you need to know...What headbolts/studs to use, what you need to change electronically to get it to work...stuff like that. It will bolt up but the CAS is different.

 

[ericbev]

People always assume the 1G head is an upgrade because its bigger. The size of the ports isnt everything guys. There is alot more to it. Jim and Eric know their stuff. Using your 2G head makes things alot easier to boot.

What sort of scientific proof has "look at it" been turned into? What makes you think that you will gain HP with a 1G head over a 2G head just because the intake runners are larger?

The larger runners on a 1G head have a much larger angle into the valve, this actually slows the air entering the cylinder chambers. Generally on a port job of a normal head for racing they raise the chambers not lower them so the entry into the valve is a straight as possible. The angle into a 1G head is horrible because the port is so low already in the head.

The HP increase from a 2g head to a 1g head is from the Cams, and Intake manifold. If your using aftermarket cams and plan on buying a SMIM don't put on a 1g head because you'll end up with no gain and a head that has horrible port design.

Most major racers now using DSM's are using a 2G head and 2g style intake manifold and raising the runners in V8 styles so the air is hitting the top of the valve as straight on as possible. Air flow has nothing to do with the size of the chamber and EVERYTHING to do with the shape and design.

Putting a 1g head on a 2g block is the OPPOSITE of what you want to do. Replace your 2g block with a 1g block and keep your 2g head. Have it ported and port raised and add a set of HKS or Comp cams with a SMIM. This will provide you with a much more potent street engine.

Originally Posted by AMS Eric #2
Use the 2g head!! The castings on 2g heads are far superior to 1g castings. They have more alluminum in the lifter bulkhead to reduce flexing and less problems with casting shifts than 1g heads. The intake ports are smaller yes, but they do not seem to be a restriction of any sort. The Evo 8 heads have the exact same intake ports and we are making 600+ whp constantly on completly stock unported ones. Our shop car's intake ports arent opened up that much at all and it makes over 800 awhp.

Use the 2g head. It will save you money and WILL outperform a 1g head/intake, much to everyones dismay.

 

[trickirickey]

I already have 264 intake/ 272 exhaust HKS cams in my car will they work with the 1g head you guys are giving me mix reviews

 

[ericbev]

Yes they would work. Use your 2G head.

 

[bird man]

listen to eric. You can make just as much power from your 2g head with less to worry about later on.

 

[Listen2myBASS]

you could, i wouldnt, just because of the bolt size question, ive had bad boring experiences...

 

[ericbev]

Boring what? Are you going with oversized valves? Explain more.

 

[VelocitàPaola]

He's talking about boring out the head studs to 12mm...

 

[Talesin]

Short version, the 1G head flows better. It has larger passages overall, and IMO is an upgrade. It requires a bit of work to make everything fit, and get all of the sensors where they need to go.
The 2G head will 'just work', but is more of a restriction than the 1G.

The cams will work with either. 1G stock cams are an upgrade to the 2G stock cams (when not going to performance cams) due to the increased lift they provide, just on a side note.

 

[luvmygst]

Short version, the 1G head flows better. It has larger passages overall, and IMO is an upgrade. It requires a bit of work to make everything fit, and get all of the sensors where they need to go.
The 2G head will 'just work', but is more of a restriction than the 1G.

The cams will work with either. 1G stock cams are an upgrade to the 2G stock cams (when not going to performance cams) due to the increased lift they provide, just on a side note.

DO you have the flow numbers for a 2g and a 1g head? Im curious avout how m uch better. I have a hard time thinking that it works better than the head design they use on the evo. Im doing a 6 bolt 2g head myself.

 

[ericbev]

Short version, the 1G head flows better. It has larger passages overall, and IMO is an upgrade. It requires a bit of work to make everything fit, and get all of the sensors where they need to go.
The 2G head will 'just work', but is more of a restriction than the 1G..

Airflow is not the No. 1 criterion. Bigger is not always better. Port volume, runner shape, mixture velocity and cross-sectional area are extremely important.

This straight shot design jim was referring to allows for a line of sight from the inlet directly to the front opening of the intake valve. This typically gives a lower flow value but because it is straight, it attains higher velocity of fuel/air entering chamber. The single biggest factor affecting flow quality, is flow velocity. It also creates a turbulent spin or swirling in the combustion chamber, yielding a more efficient and more complete burn

A head design with an intake port shape that compromises flow in favor of creating more combustion chamber swirl and redirecting incoming fuel droplets away from the cylinder walls, allows a nice balance between flow and combustion, and typically makes more power than just having "more flow".

 

[Talesin]

I respectfully must disagree. Velocity is a component of flow, as is cross-section (capacity). The 1G head has larger ports, meaning a higher potential flow. It's odd that you mention both the benefits of added turbulent swirl, and the slightly steeper entry angle of the 1G head's runners... which as far as I understand aerodynamics, will add to turbulence while not detracting from the total flow unless the runner narrows dramatically over a very short distance.

I haven't tossed one on a flow bench (as those things are a little pricey, and I don't do fabrication), but just having a 1G and a 2G head side by side... the 2G looks kinda.. well, 'economy' by comparison.

 

[luvmygst]

I respectfully must disagree. Velocity is a component of flow, as is cross-section (capacity). The 1G head has larger ports, meaning a higher potential flow..

And lower velocity.

I haven't tossed one on a flow bench (as those things are a little pricey, and I don't do fabrication), but just having a 1G and a 2G head side by side... the 2G looks kinda.. well, 'economy' by comparison.

Its wierd that alot of the high hp guys are running economy heads.

This debate can go on forever. Even if you pick up a little power on topend it's not worth the trade off of midrange power on a a sreet car, and the 2g head has proved itself past 8000rpm. I think a 2g with a good valve job and minor porting will outdo a 1g all the time. Just my .02

 

[ericbev]

The thread intruiged me enough to do some heavy research after I ate my dinner. I have come to the conclusion that there is way too much engineering put into designing a cylinder head and I will have to read on this topic for quite a while to get a solid grasp on all the factors and how they apply to the 2 different designs. The 1G vs 2G head debate has been around for a while now, so I figured I try and make a little sense out of it. This isnt intended as a flame Talesin, I am simply trying to get a better grasp on this topic, albeit it will probably make my head hurt. I encourage anyone with technical expierence and real data to chime in at will. I have a 1G head on my work bench right now. Ill see If I can ebay a 2G head for exact comparison purposes.

First off, velocity and capacity are two different things.

Flow velocity in ft/sec, is the speed at which the air flows through a tube (fancy term in aerodynamics is conduit flow velocity). Simple enough, but people often confuse flow capacity for flow velocity. Flow velocity is how fast bulk flow is travelling. Flow capacity is how much bulk flow is travelling.

Flow capacity is the bulk volume or how much air is delivered. The units of measurement are usually cubic feet per minute or cfm. When some head porting shops quote how good their work is, they quote flowbench numbers in cfm. If you took an AEM intake and measured it's flow capacity on the flowbench and then take a big ass sewer pipe and measured it on the flow bench, which would have more cfm? The bigger diameter sewer pipe of course! More volume of air is delivered. Does that mean you should put a sewer pipe on your engine?

You want the turbulence in certain areas, not just anywhere. Specifically the combustion chamber is where this is most important from what I am reading. When the higher velocity air hits the backside of the valve and enters the top of the combustion chamber, this is where this occurs (what I was reffering to above). Turbulence created in the runner, that is caused by a steep angle slows the "wet" flow and creates worse atomization. How much of a difference is there angle/cross-section/runner length between the two, I dont know? I really need to get a 2G head on my bench so I can start examining things a little.

From what I am seeing, all the dimensional factors that go into a heads design really are based off of what RPM you want the engine develop peak power at. So, this is the dilemma of the engine builder: you need enough flow capacity to make power and support the combustion for a given displacement but if you make the cross sectional area (or diameter) too big or shorten the tube too much, you get poor flow velocity and flow quality on straight parts of the tube. It really all comes down to compromising between capacity and quality, and getting the design that suits your setup the best.



Post Away!

 

[Carter97GSX]

Alright, I'm going to give my two cents on this because I'm an aeronautical engineer. As was said before, just having a larger peak flow rate (CFM) is not going to increase your power. That being said, the peak flow rate is actually the largest factor that dictates the power produced. The reason for this is simply that more air (and thus oxygen) can be sent through the combustion chamber with a higher flowing head. Head design is much more complex than just that though. You CANNOT look at a head and "see" whether it is better, flows more, makes more power, or anything like that.

Here is a list of things that affect the flow characteristics, and some information:

Runner cross section is important, and bigger is generally a good thing.

Rounder is better, as a circular runner will flow more air due to decreased surface area for a given cross sectional area and thus decreased friction.

Smoother runners are better and flow more also because of decreased friction.

The swirling of the air as it enters the combustion chamber is actually pretty important, and much too complex to be discussed here. Let it suffice to say that unless you're doing some 3-D flow modeling you're not going to have the least bit of a clue as to how the air is swirling.

I know this is counterintuitive, but you actually want the flow velocity to be as low as possible. The higher the velocity, the more friction will be present because of a steeper velocity gradient at the runner walls.

There is only one spot that the head designers WANT turbulence, and that is at the valve. This is purely to mix the fuel as evenly as possible.

Fuel atomization is ideally perfect with good injectors, but in the real world some turbulent flow is helpful in completing that atomization. You do not want that turbulence in the runners, only the cylinder.


Here is the bottom line. Higher flow rates (CFM) are generally better, and you can bet you'll make more power with a higher flowing head. You will also generally hurt yourself when it comes to low end torque, and shift the power curve around. It is entirely possible that the 1g head flows more air than the 2g head, but still does not make more power due to less efficient combustion chamber design.

I know this is another one of my long technical posts, but for the few with the patience to read it I hope it makes sense.