A comparrison of NA and TT head design

Ok so today i finaly got back around to stripping my spare NA head and i thought id share my findings and insights

1st here's the mess. Not the best of ideas using the kitchen table if you have another half and treasure your wedding tackle!

Now before i talk about design theres the ovious differences such as different cams. The exhaust cam has a ring on the end where it meets the distributor which picks up cam position unlike the TT which uses a seperate CPS sensor on the intake cam to detect cam postion.

Not to sure about the valvetrain as i dont have TT parts here to compare to.

Now onto the actual design.

1st thing i looked at was the intake ports.

Now i know it isnt the best picture in the world but they appear to be fairly smaller than TT ports but also higher up the head with a slightly steeper angle.

Then i looked at the exhaust ports.

Again not the best of pictures but it was hard to get a good shot.

They seem to be larger than TT exhaust ports which suprised me as i would of thought larger exhaust ports would be better suited for turbo applications?

Moving on to the combustion chamber design.

The NA head has about a 0.023" recessed surface that's cast into the combustion dome

For the GTE head, however, the combustion dome is flush with the bottom of the head.

The difference is IMO the GE valve/piston clearance is shared between the head and the piston resulting with the very thin HG on the NA.

On the TT however the HG is much thicker,about 1.3mm, and again IMO may account for most of the piston/valve clearance on the GTE design.

Thoughts and opinions guys?

well im guessing the .023 recess is to up compression making a sharper responce as this moter was not supposed to see anything above atmospheric pressure

That would be my 1st thought as if you decked the recess out of the head so its flat and added a TT HG you would essentialy end up with TT head, minus the few other differences.

You need to measure head chamber volumes really. Does the N/A have the different sized exhaust ports that the TT has, I forget?

Think so chris although i havnt looked at a TT head for quite some time.

Im thinking of getting the head flow tested before i go ahead and modify this 1 and see what numbers it produces

Head thickness's, top to bottom? Would the N/A skim to have flush chambers? I suspect the difference is in the casting, and the cam centreline to block face of the two heads are the same though. Have never really looked into this.

i would like to know if there is a difference in flow rate and wich is the more efficient head if anny

Head thickness's, top to bottom? Would the N/A skim to have flush chambers? I suspect the difference is in the casting, and the cam centreline to block face of the two heads are the same though. Have never really looked into this.

Havent measured the thickness but i can do when i get some time.

Id say the head would skim flush yes.

Ive heard of people state side do this sort of thing but ive never seen any actual results from it.

Would flushing the chambers make much of a difference though?

Any advantage to it?

I wouldnt put my money on the NA head outflowing the TT to be honest, the intake ports are alot smaller but unless i had 2 heads i could take away and get tested i couldnt tell you.

Nice to see some pics of one apart. I would expect the exhaust ports to be smaller, but would be great if you could take some measurements.

Is the exhaust bolt pattern different to that of the TT?

When i get some time ill try and measure them.

I also thought the TT would have much larger ports either end but going off what ive read, everyone who's talked about it, mainly on supraforums and club na-t, have all said the same thing that the NA has larger exhaust ports.

Im guessing the exhaust pattern wouldnt be that far off but it appears to be different.

If i had something like an old turbo manifold off a tt i could try it up and see just how different it is.

the exhaust pattern is different. i tryed a tt mani up to my engine and they do not fit.

I also thought the TT would have much larger ports either end but going off what ive read, everyone who's talked about it, mainly on supraforums and club na-t, have all said the same thing that the NA has larger exhaust ports.

I've read the same over the years, and from the same forums, but had always thought they were referring to the exhaust valve diameter, rather than the size of the port exiting the head.

I've read the same over the years, and from the same forums, but had always thought they were referring to the exhaust valve diameter, rather than the size of the port exiting the head.

Im not entirely 100% sure myself realy. It may well be the valves but the ports themselves do look fairly large.

Its been a long time since ive looked at a TT head. May try and get hold of 1 and take it to bits.

I have a scrap (warped) TT head you can borrow to flow test if you like?

What's the diameter of the NA exhaust port you have there? If memory serves me correctly the TT's is more of an oblong, roughly measuring W 40mm x H 30mm.

Bit of a bump..

This afternoon whilst i was bored i took some measurements with the limited measuring equipment i have a home i.e. a digi caliper guage

Intake valve is 33.61mm

Exhaust valve is 29.26mm

Intake port is oblong and measures 48.54mm wide and 36.87mm in height (to its highest point)

Exhaust port is round and measures 35.50mm wide.

Headness thickness top to bottom is just shy of 5" at 4.8"

Now prior to what i said before i dont think the head will skim flat as there are coolant passages that are drilled at an angle and i suspect they would start walking very close to the combustion chamber. Also id hazard a guess that you would then need a thicker HG to make up for the piston to valve clearances as i suspect they would be to close but again im no expert on these things as im still learning but im just going off what i can see and what i know (which isnt alot )

That would be my 1st thought as if you decked the recess out of the head so its flat and added a TT HG you would essentialy end up with TT head, minus the few other differences.

What is the difference in thickness between a NA and TT HG??

Surely taking out the difference in skimming the head flush and adding a thicker HG is only gonna bring it back up to NA compression range again or higher depending on differences between NA-TT HG thickness and the difference in skimming to remove the recess...

Excuse my ignorance, i'm more of a engine builder than a mathmatician, i'm purely interested in this mate, as you know myself and Gav are looking into an NA making decent power without the need for running some sort of race fuel to compensate for higher compressions..

the exhaust pattern is different. i tryed a tt mani up to my engine and they do not fit.

How far out is it mate? Are we talking stud pattern or worse?

The NA HG is less than 0.5mm thick compared to the TT 1.3mm HG

As i said in my most recent post my opinion on that has changed after looking more closely at it.

If you were to skim the recess out then yes you would need a TT hg, perhaps even thicker HG to get it back to NA CR depending on how much needs removing but now I now dont think this would be a good idea looking at the angles on which the cooling passages are drilled.

How far out is it mate? Are we talking stud pattern or worse?

A fair bit mate sadly

The NA HG is less than 0.5mm thick compared to the TT 1.3mm HG

 

As i said in my most recent post my opinion on that has changed after looking more closely at it.

If you were to skim the recess out then yes you would need a TT hg, perhaps even thicker HG to get it back to NA CR depending on how much needs removing but now I now dont think this would be a good idea looking at the angles on which the cooling passages are drilled.

 

 

 

A fair bit mate sadly

Hmmm, what are our options to get the compressions down on a NA lump to get boost out of it mate, without early det? Can go into PM's if you like, but like I said before, i'm more of a builder and Gav is the brains and research bitch. We do have a complete NA head to go with our complete NA engine to experiment with and seems like you have done plenty of research that we could put into practice for you;)

Most of the NA-T guys use a 2mm HKS head gasket to lower the compression ratio on the NA engine, not sure what it would change it to though!

Probly drop it to around the high 8s mark i suspect.

Its impossible to tell without actualy working it out properly. I maintain though when lowering CR it should always be done through the piston and not the HG

Most of the NA-T guys use a 2mm HKS head gasket to lower the compression ratio on the NA engine, not sure what it would change it to though!

So, effectively, if we added a HKS HG (2mm), or even a TT HG, it would increase combustion chamber volume? (-head skim) I know Mig(?) did a reference as to how to work it out but are we saying the larger the volume the lower the CR?

So, effectively, if we added a HKS HG (2mm), or even a TT HG, it would increase combustion chamber volume? (-head skim) I know Mig(?) did a reference as to how to work it out but are we saying the larger the volume the lower the CR?

Yes. Although I agree with Michael that it's a bit of a nasty bodge to lower CR. If you're stripping the block wouldn't it be worthwhile fitting a set of oil squirters and TT pistons? The rods, crank and block and the same on the TT and NA.

Yes. Although I agree with Michael that it's a bit of a nasty bodge to lower CR. If you're stripping the block wouldn't it be worthwhile fitting a set of oil squirters and TT pistons? The rods, crank and block and the same on the TT and NA.

Already ahead of you mate!

TT pistons are in hand, whats involved in fitting the squirters? Are we talking drilling the block?

Would be nice to see just how much a stock NA lump will really take though.. We could be the JamieP of the NA world!