WOTTECH wrote:Rettax3 wrote:WOTTECH wrote: I know it is way off topic here, but how bad is gasket-matching on the older MPFI heads? I know there is a lot of room for improvement on the older heads, and greater limitations to them even with major mod work, but overall, gasket-matching (with proper supportive work) seems intuitively a good thing...
On my 3400-block 3.1 turbo MPFI top-end hybrid, even with little or no boost, the engine makes very respectable low and mid-range torque, and seems only somewhat limited in upper-RPM bands by the ported gen-2 splayed-valve heads... I am also running custom headers though, so I don't know how much difference there is with that added in.
How much boost and fuel line pressure? I saw your other post in the 2.2/2.3/3.1 thread and you are basing everything on books, theory, etc. The gen 2 is only good for low and mid range. Mid range for it is 3-4k. 60V6s are good for 7k. Thats a lot left on the table in stock form, and even modified with headers and camshaft, the engine never makes good power to 6. Getting power to 5k was a serious accomplishment NA. Your turbo will move that powerband some but even if you hit 7k, its just much much lower output than a bone stock gen 3 top end. Gasket match all you want, it can't fix those intake manifolds. Extrude hone can't fix that manifold design.
Reversion isn't really the same on the intake. You have sound waves and pressure waves on both sides, but the exhaust side has a much higher pressure, making its reversion stronger. This can also help suck the intake charge into the cylinder during valve overlap if the pulse tuning isn't forced exhaust back into the chamber/past the intake valve.
Currently, I still haven't had time to mess much with the car, now that the engine is actually installed -I've probably put way less than 1000 miles on it yet, so I still consider it to be in 'break in'. Issues with my poor choice to use aluminum oil-supply lines with compression-fittings instead of flares and some wiring issues and other projects have side-lined this car from being a reliable daily-driveable car right now. I am only running a few PSI of boost until I get it past 1000 miles (hard to determine that, since my speedometer isn't compatible with the Z-24 VSS I screwed up on putting in the car
). With the compression ratio calculated off of 60degreeV-6, I won't likely be pushing more than 7, possibly 9 psi (ever), and even that will concern me until I can actually put a tune on the PCM (Venture). I have stock LH0 fuel-pressure, and thusfar have not encountered any limitations related to that -I also have not pushed my engine, so I don't know what other hurdles I will be facing in the upcoming future with it, but I do have a good idea on what to look for. So far as what I have any of my builds based on,
I've built enough engines to say I have real-world knowledge
overall, but for port-work, yes, a lot of it starts with theory, and only some of it is based in real-world experience. I do not have the flow-benches and computer-based models that some others may have, I am basically a hobby-level shade-tree builder who likes to tinker with things to make them better than what they were originally. I know full-well that the stock 3400 manifold originally on my LA1 block breathed much better than the ported mani and heads from an LG5 turbo 3.1 -I don't care. I used that top-end because I trust it more; to my knowledge
and experience, there have been a lot less problems with the older MPFI top-ends than the newer 3X00s (3500s may be excluded, I don't have much experience with them specifically). But more importantly, I used the LG5 top-end because I wanted to keep the look of the older MPFI top-end, since the engine was going into an older-era Beretta, and I like the factory-cast "3.1 Intercooled Turbo" on the manifold.
So, for me a lot of it is just preference, esthetics, and even a touch of nostalgia. If it wasn't, I wouldn't bother modifying a Beretta at all -I would sell them all off and buy something else if it only boiled-down to the numbers. I am running stock internals too, so I don't plan on seeing 7k RPM often (if ever), and I am not looking for serious power out of this build (250-275 would be fine for me), but the added efficiency of some more-than-mild port work and gasket-matching seemed appropriate, and was fun to do at the time, as was adding the roller-base rocker-arms from a 3400. Hopefully, it helped more than hurt.
But that is why I asked you, since you are an acknowledged expert on this subject...
If gasket-matching hurts an otherwise good-breathing 3400, would it hurt or help a choked gen-2 top end? So far as how the engine actually feels, all I can say is that it seems to pull almost as hard as the 3800 Series 2 Supercharged engine in my GTU in mid-range, which is saying a lot when looking at the 300+ ft-lbs the 3800 allegedly produces and the very low boost-level I have dialed-in right now, with a totally wrong tune. I've had a basically stock Turbo 3.1 LG5, and it felt quick to me, but this hybrid would destroy it for performance, I will stand on that from experience, and even without the turbo spooled, this engine feels much more responsive than a 3100 (even the wide-port J-codes). My biggest concern over my build (aside from the oil-leaks) is the fact that I put a very large turbo on an engine designed more for mid-range.