1jz vs 2jz heads

[chris davey]

Just found this info. Someone has finally done the flow tests of 1jz and 2jz heads. Looks like it really is just an upgrade for a 1jz to be a 3 litre after all and not some crazy Japanese trend to outperform 2jz’s. Who would have guessed? *looks at Norbie*

It has been a very common rumor on here for a long time that the 1JZ head flows better than the 2JZ. This has lead to alot of people doing the 1.5JZ swap or atleast wanting to. Over the last few weeks I have been building a 1JZ, including porting the head, for a customer. I flowed the head on our SF-600 flow bench before and after I ported the head.

A stock 2JZ flows about 238in and 154ex at .400 lift. A stock 1JZ head flows 215in and 133ex at .400 lift. After I did a good street port job including reworking the chamber the 1JZ head flowed 230in and 152ex at .400. This should put to rest the idea that the 1JZ head is better than the 2JZ, because the fact of the matter is that it is not better.

Erin

Link: http://www.supraforums.com/forum/sho...d.php?t=339560

[takai]

Uh hold on, that guy is saying that there is NO benefit of doing a 1.5JZ conversion. The whole thing with doing a 1.5JZ conversion is that you can put a 3L bottom end on the car without having to change over all the head and intake, especially if you have already done work there.
Basically its a quick and easy stroker kit.

I havnt known, or seen, any 1.5JZs in the other direction, i.e. 1JZ block with a 2JZ head.

[chris davey]

He is saying that people with a70 supras who want a 3L turbo (that don't blow HG's) engine are better to go with a 2jz rather than the famous 1.5jz

[JustCallMeOrlando]

Or more to the point, people doing the 1.5JZ conversion because they think that's the best combo are doing it for the wrong reason. Those other people who do it for that extra 0.5l while keeping their existing turbo/inlet are doing it for the right reasons.

[Norbie]

Which is exactly what anyone with half a brain has known from day one. The "superior 1JZ head" rumour can once again be attributed to dumbarse yanks talking about things they don't understand.

[MR 1JZ]

Ive heard its an old wives tale developed by the yanks from ages back...as already stated..

its simply a means of retaining what might be awesome cams/headwork/turbo kit/plenium and computer with a bigger and stronger bottom end...

id definitiely do it before i did a whole 2J conversion...

in fact next year ill be undertaking either a built 1J with aftermarket rods and pistons...or a rebuilt stock 2JZ...

rather than waste a thread with some JZ heads in presence what would you guys reccomend?

[chris davey]

I would make the decision depending on how your setup goes now with the lower compression 1j and big boost. If it is fine for the track and your driving style then I would say built 1jz. But if you want some more low down power then a stock compression 2jz is going to be a big difference to a low compression 1jz.

[MR 1JZ]

haha I saw that edit

thanks for the good info as always chris

[gianttomato]

Meh....I'm going to say it.

I told you so.

Only benefits are:

1. the extra 500 cc capacity, and
2. you get to keep all your 1JZ stuff if you already had a pretty built one.

[Billzilla]

So what were the flow figures at a more useful lift, e.g. 0.050" and 0.100" ?
Flow at max lift is nice to know, but by itself doesn't tell more than a small part of the big picture.

[chris davey]

This was his response to that

Obviously I would not have gone through the trouble of flowing it at only one lift. I was using peak lift as an example that 1J is 20cfm down compared to the 2J.

Erin

But if the 1jz head is down that much at max lift wouldn't it be down a bit through the whole cycle?

[Billzilla]

But if the 1jz head is down that much at max lift wouldn't it be down a bit through the whole cycle?

It's likely, but not always the case.
Since the valves spend a almost all their time at part lift and only a very small fraction near max lift, it makes more sense to compare flows at smaller lift valves.

[Mr DOHC]

dont 1 and 2J's have max .360 lift, maybe at 360 lift they produced the same amount but the 2J was able to continue to flow better past that point.

i know on my 18RG i had the cams made b4 i got the head flowed {about 18 months later} on both sides i have 465 lift, and as u can see i dont really need more than 400 lift, but saying that, it makes the difference between the inlet at 500 and the exh at 500 look much larger, re: exh must be X-amount smaller ect ect


inlet port
lift, cfm, hp
100, 33.46, 57
200, 72.85, 125
300, 114.28, 196
400, 128.56, 221
500, 135.70, 233

exh port
100, 30.60, 52
200, 59.99, 103
300, 88.92, 152
400, 111.42, 191
500, 114.28, 196





does that guy have a ful spectrum of flows, i.e. at 100/200/300 ect ect

[gianttomato]

I can only speak for the 2JZGE head but the flow plateaus out by about 350 thou lift.

Sorry about the small pic size but I'll be buggered if I can find my full size pic. Flows were done at 10 inches water vacuum.


The big power motors aren't using 360 thou lift cams.

Like Bill said, flow at max lift is only a small part of the story, but I just can't see anything magical about this 1JZ head.

[Mr DOHC]

they did some decent work on the exhaust there GT