3TC oversized valves

[brucey]

I'm getting some cylinder head work done at the moment and I wanted to see if it was worth putting 1mm oversized stainless steel valves in (42mm intake & 37mm exhaust), instead of reusing the stock valves. Increase in area works out to be 4.7%. The 2TG has 44.5mm intake and 38.5mm exhaust valves so it couldn't hurt to put bigger valves in a 3TC.

It's a 2TC head and it's going to have some port work, clean up, 3 angle valve seats, new seals and stiffer valve springs. The engine is for street use; the setup is going to have Genie extractors, 2" exhaust, twin Dellorto DHLA40 twin carbs, and a wade camshaft, 280 advertised duration (30/70) with 0.449" lift (profile 1147BS).

Initially I was going to go 3mm+ oversize (44mm intake & 39mm exhaust) but it's going to cost $200 more to put in new valve seats ($25 each), and maybe that valve size is not really needed with the camshaft duration I'm going to use. Also, there could be piston valve clearance issues with the stock 3TC pistons. The cheaper option is to use 1mm oversize valves and the existing valve seats can be used, machining costs already covered in the porting and valve angle cut work. The head builder can cut an additional angle on the back of the valves to improve flow. The new stainless steel valves (from BRD or Paradise racing) will have an undercut stem, so that could improve flow over the stock valves.

So I was wondering if it would be worth putting in 1mm oversize valves? Would I expect an increase in the power/torque curve to make it worth while? Valves seem cheap at around $125 at set.

[Rodger]

Yes it is worth buying the oversized valves. It will help.

If you know the history of the 2T head and it has not been shaved before (just plained flat) then you could take 1mm off safely to raise the compression ratio whilst you have it apart. You can get some good lift numbers even with stock pistons and from memory my 2T with stock pistons cleared easily 9.5mm lift. That cam reads like what I used to run in my 2T-2T-B motor (not the TRD parts motor). This acheived 74.5Kw at the wheels, drove real smooth and reved to 7500 with double valve springs and twin Mikunis.

Regards

Rodger

[MorGo]

Don't waste your money in bigger exhaust valves;the stock valves/port flow well.42 mm intakes fit on stock seats and ports can be made to flow enough for 200 hp if porter knows what he/she is doing.The port needs extensive work at that level;not possible if the quides were not removed for porting.O/S intakes are not essential but do help.One thing to keep in mind when going to O/S valves is that there is the danger of valves hit each other with wilder cams! Do check how close they are with both valves having say 4 mm lift (the overlap).

[brucey]

Yes it is worth buying the oversized valves. It will help.

If you know the history of the 2T head and it has not been shaved before (just plained flat) then you could take 1mm off safely to raise the compression ratio whilst you have it apart. You can get some good lift numbers even with stock pistons and from memory my 2T with stock pistons cleared easily 9.5mm lift. That cam reads like what I used to run in my 2T-2T-B motor (not the TRD parts motor). This acheived 74.5Kw at the wheels, drove real smooth and reved to 7500 with double valve springs and twin Mikunis.

Regards

Rodger

Where did you source your 1mm+ oversized valves from? My machinist had a quick look in his catalogue but it only had stock size listed. BRDracing only have stock valves and 45mm intake 39mm exhaust. And Paradise Racing want $210 for their oversized valves with the postage included. There's +3mm oversize from Street Sport Industries for $155.95 including postage, which could be tempting.

[brucey]

Don't waste your money in bigger exhaust valves;the stock valves/port flow well.42 mm intakes fit on stock seats and ports can be made to flow enough for 200 hp if porter knows what he/she is doing.The port needs extensive work at that level;not possible if the quides were not removed for porting.O/S intakes are not essential but do help.One thing to keep in mind when going to O/S valves is that there is the danger of valves hit each other with wilder cams! Do check how close they are with both valves having say 4 mm lift (the overlap).

So you would say it wouldn't be worth going +3mm oversize valves (44mm intake & 39mm exhaust) for a NA street engine with mild camshaft (280 duration)? I would of thought it would benefit over the rpm range; and with the increased capacity of the 3TC it would help. Though I could see it could cause lower port/throat velocity at lower rpms, reducing the power.

[brucey]

Had a look for a similar engine to the 3TC, and there's the Mitsubishi/Chrysler 4G51 engine that came out in Sigmas and Galants. Its cylinder head is a hemispherical design and the displacement is 1850cc (81mmx90mm, borexstroke). The valves are 43mm intake and 35mm exhaust. I guess there are many variables, but the valve size could give a ball park figure.

Has anybody had any experience in putting larger valves in an NA 3TC and found there was/wasn't much gain, or even hindered performance?

[MorGo]

Of course the bigger valves help (if done properly) but they are not the first thing limiting the hp.Stock valves are big enough for 180 hp but that takes much more cam and compression than you have.
Just mill the head some 1,5 mm and have the block deck milled too;blocks warp,not the heads.
Demand the flowbench results of the head;have seen too many "professional" ported T-heads where there wasn't done anything but polishing the easily accesible parts..

[brucey]

Of course the bigger valves help (if done properly) but they are not the first thing limiting the hp.Stock valves are big enough for 180 hp but that takes much more cam and compression than you have.
Just mill the head some 1,5 mm and have the block deck milled too;blocks warp,not the heads.
Demand the flowbench results of the head;have seen too many "professional" ported T-heads where there wasn't done anything but polishing the easily accesible parts..

Got your flow bench data from the "T-Series heads" and plotted a graph of cfm versus lift:

http://www.toymods.org.au/forums/tec...ies-heads.html

Lift in mm

t-seriesFlow_mmlift.jpg

Lift in inches



Interesting that the ported 2T head with the stock valves (41mm intakes) flows very similar to the stock 2TG head (44.5mm intakes). Then it out flows it with 42mm intake valves, with the whole curve shifted up a little, as well as more flow above 0.3" lift.

Looks as though the 2T head with 42mm intake (1mm+ oversize) valves make a noticeable difference over the stock valves. For example at 0.45" there's a ~10cfm difference. Could help with the upper rpm range.

Have any more flow bench data for larger sized valves for the 2T head?
I suppose there must be some point where the head is able to flow too much for a given engine capacity and port velocity will be reduced for low to mid rpm ranges. For the 2T ported with stock valves the cfm peaks at around 0.45" lift of 180 cfm, so the figure of 180Hp sounds about right. Seems like stock valves would be sufficient for a street engine. Though just wondering if larger valves would improve power throughout the rev range since it shifts the curve up, like what the 42mm intakes did on the 2T and the 45.8mm intakes on the 2TG did.

[brucey]

Plot for just the 2T head data for comparison:

t-seriesFlow_2T.jpg

[toyota1515]

I never waste my time with O/S valves over 1mm over stock size, just me!

[alexlegault]

what kinda gains will you see?

[MorGo]

Doing enough heads teaches what is worthwhile and what is just wasting time.Someone may have different opinion but then again,it's just a opinion..
I do what I have seen to work.

[toyota1515]

Thing is, that all comes to what kind of engine it will be, as i wont waste my time on N/A T series engines for me is a waste of $$ and time, cuz a turbo will do what i need for the intentions and the kind of powerband i used to in these engines, if i want N/A power, i surely wont use a T series engine, and go with something more modern and easy to achieve good numbers like a 3SGE,

Like you said, an opinion is just that, and they are like an ass, everyone got one, for me, a guy who just do T engines in a Turbo way, there is no reason to spend the extra $$$ when the gains will not be that significant or non existent!

Cheers!

[ctrain]

how would a 2t head go with oversized valves (43-44mm intake and 38-39mm exhaust) go on a 2t head thats going to have double valve springs, ported, stainless steel valves, fully balanced rocker assembly and with a suited cam for a turbo setup as it will be going turbo, also it will have wiseco 87mm turbo pistons 7.5 c/r and eagle rods, i can afford to get the new valve seats put in, or would it be better to stick with 1mm oversize valves

[brucey]

It seems that the limiting factor in the head flow is the size of the ports. From the mathematics the stock valves can flow enough at a given amount of lift. The port is narrower than the valve throat, so there is not much point going larger in valve size.
I had a look at a 3T head and it looks like the inlet port diameter in the horizontal direction can be taken out safely to ~36mm. This leaves around 4mm thickness in the wall between the inlet and pushrod space. A 2tg head could be taken out further I think since it doesn't have the pushrods.
Not sure what the safe limit in the vertical direction is before going into the cooling galleries. Would have to slice a cross-section of the head and find out. Removing most of the ridge around the valve guide and taking the diameter to 36mm might be safe?
Maybe making the inlet ports oval, with a 36mm width and 41mm height, a flow of 230 cfm @ 28" of water could be achieved.

Max flow of ~200 cfm @ 28" of water looks like what can be achieved safely for turbo applications:




A flow of 220+ cfm @ 28" of water has been achieved by Headway Performance, but is CNC machined with no cooling. They use 44mm intake 39mm exhaust valves.