Turbo BS Thread

Majority of cracked heads you find are not from people who are boosted. Number of people who are boosted with these engines still relatively small compared to the amount in service. It's possible it's just a poorly designed head with poorly supported valve seats. The common theme with heads that cracked is a lack of service. But lots of other Toyotas use the same valvetrain design too and they don't all have the issue. @Pinchaser yeah I responded quickly, echod the same information I've seen others say for years because I don't care about the topic enough dissect why it happens. But I do recognize that you and I both went to the same school of condescension and for that I have respect. But more seriously, something certainly is happening, if there were no physical change occurring there would be no reason to ever adjust the valves. If somebody wanted to I suppose they could keep removing the head and check the seat depth to the head surface measurement. I don't primarily deal with the four cylinders anymore so I have zero interest doing that. One thing about the echod information though, it does seem to solve the problem. Folks who have gotten new castings to build a head and then maintain their valve train clearances don't end up having another cracked head.

 

I don't think that would be necessary. It could be done by taking one measurement when the head was installed, recording valve clearances through the observation period, and then measuring the seat depth again when it came off. It could then be determined how much the clearance tightened because of valve wear and how much resulted from seat movement.

Valve seat retention in aluminum heads is not something I exhaustively study, but in a particular engine I have experience with, a seat insert sinking into the head occurs as a result of the seat press-fit coming loose. That same cylinder head design can also crack (not common, though) in the same way an RZ head can, although the cause is usually not obvious and assumed to be from running hot.

 

Something led Toyota to later on move away from this Yamaha derived valvetrain (was an old partnership starting back with the 3SGTE, uses the same shim sizes/diameters as their older motorcycles) setup too and move to head designs with hydraulic lash adjusters. It could be a heat related problem, but it still presents most commonly on daily driver trucks with reports of these heads cracking and people initially tearing them down to do a headgasket and then finding the cracks after sending them off to a machine shop to be pressure checked or decked.

 

Fixed

 

Poor taco has been getting neglected, but the car has been getting out a lot. Did a canyon run over the weekend. All the badass cars were out. Diesel Benz. Ferraris, Porsches, BMW of all flavors, Honda's, Subarus, gen 1 rx7, were a few. My BIL got a 718 so we've been doing more street stuff lately. One of the guys in our group had a gr86 hakone edition. That little car can fly.

 

That sounds like a lot of fun! There is a road here in Texas that I have been wanting to run for the longest time. Called Devil's Backbone. Probably the closest thing to a canyon run that is anywhere near me.

 

That's something that has puzzled me since owning my Tacoma. Many (most?) other manufacturers were using HLAs or adjustable followers/rockers in their more pedestrian engines before and after the RZ came out, not PITA shims for adjustment. Performance engines I can understand, but pickup trucks? Hydraulic buckets would have been an obvious option.

 

Probably cost savings, these engines weren't just sold in North America, they're in vehicles without EFI in some third world countries, they're in forklifts... the list goes on. To do this kind of head hydraulically it either needs to be taller or it needs some more moving parts. They took the more moving parts path later on with the HLAs on little roller rocker type levers that actuate the valves. But some manufacturers still do the static lash thing, Honda's popular K series 4 bangers that are in everything from the Civic to the CR-V have to be manually adjusted just like their engines from the 80s haha.

 

Most of these heads with bucket over shim rarely need to be adjusted. Most of the newer stuff literally never gets adjusted except out of the factory. Any good head shop can cut/rearrange valves to avoid having to buy several hundred dollars worth of shims. That or they have done it a billion times and have a box of shims , or buckets in the case of shimless. Ditching the shims for shimless buckets is also a trick on motors you intend to rev the to moon but it's not a cheap endeavor.

 

You can use the shimless buckets from a 1ZZ on a VZ or RZ... do with that knowledge what you will

 

Right outside of Austin. It's pretty in that area. I haven't done a proper mountain road drive in years. I was definitely rusty.

 

I guess not everything always makes sense, I believe there is more that we do not know, than what we know. I do so enjoy the conversations, and opinions.

I have seen loose seat inserts, but never seen an insert sink, I thought they all are friction fit, and bottom out into the aluminum cut, meaning seats cannot sink unless they are mushrooming and displacing aluminum. Sinking seats is news to me, and seems like a poor design issue.

I will say that proper valve adjustment does have benefits: already mentioned, a tight gap dings performance and overheats valves (more accurately, does not properly cool valves), and I have seen where valve clearance being too big, makes the camshaft hit the valve and valve hardware like a hammer; instead of Shoving the valve and valve hardware. At some point, noisy valve gear will get steadily worse and suddenly fail; as all the impact points get mushroomed to failure. Seen this, but was not one of my engines.

Back to the cracked head, I wonder if the head where nearest the spark plug, is so close to the valve seat, and so remote from the water jacket; that the closed valve bridges and carries heat from the spark plug, to distribute better to the water jacket. I think this is a stretch, but possibly wold explain how a tight valve would promote cracked heads.

 

I have a junk head from a 3RZ kicking around somewhere from the last build we did. It has cracks between the exhaust valves and ones extending to the plug bore (an unfortunately well up into the bore). Nothing ever presents on the intake sides other than pitted intake valves which is common in older RZs and TZs but never seems to be the reason anyone tears them down.

 

One of those cracked heads would be a good candidate for sectioning to see how close water is to all the places that porting might happen.

I can't find much specific porting info on RZ heads. Most of it consists of "just send it to so-and-so" or "it's easy to ruin the ports."

In the engines I mentioned, that's what happens. The press-fit seat comes loose and moves around with the valve which hammers it into the aluminum head. And yes, there is metal visibly displaced in the process.

 

I swapped back to a conical filter today to bring back some turbo spool and bov noises. The 3rd gen air box quieted things down a little too much.

 

Hi all. I'm looking to make the switch to a single G-series II turbo. I've narrowed down my options to
1. G25-585,
2. G25-700,
or
3. G30-725
but it's hard to say what A/R I should go with. The 5VZ doesn't rev high at all, which is why I'm looking at these turbos rated for slightly less displacement than 3.4L. My main concern is the proper A/R ratio. I don't think I should go above 0.85, and 0.49 seems too small, though tempting - again given the low redline. So the middle is 0.72. But thoughts on dropping it to 0.49?

Otherwise, the G25-585 calcs perfectly with the flowrate for stock internals limits (~16psi, or <50lb/min), but I have a feeling I'll be upgrading the rods at some point which is why I'm considering larger. The G25-700 is 7mm larger on the compressor side, same on the turbine size, and offers an extra 15lbs/min flow for +115HP capability (obviously these are estimates, but work with me). The G30-725 increases the inducer by 6mm from the GT25-700. The last two show the same compressor map. So again, given the limited redline, I think this shows I can stay with a GT25. Thoughts?

At redline of 5500 RPM, 3 bar gets me to the edge of the latter 2 maps and my estimator shows 670-690HP for if I build the engine. Again though, hard to say for me how much A/R or the slightly larger turbine on the G30 will come into play on any of these.

 

Fwiw I have a Gt3076r with .82. It spools very quick but chokes out up top. Its great on trails, almost like a SC. For this turbo I wish I did a 1.06.

I had the Gt3582r with multiple housings. .82 was the best overall, but i wanted a little more snap on the trail.

Do what you will with this info.

 

When you say it chokes out, how can you tell/what does it do exactly?

 

The 3582r pulls way harder up top. 1.03 and .82 fly up top, one more than the other. The 30r lights up quick and then lays over.

 

It does exactly what Jon just said because it does not have a big enough cross section for the exhaust. It just becomes a restriction. That's been one of the big enhancements of G2 series