Hello everyone.
I have a VG33 coming from an xTerra.
The only mod I would like is raising the CR, with custom pistons.
I would like to raise it at the maximum possible, running on premium gas of 95 octane, without knocking.

The general rule is that "The compression ratio of your vehicle is from 11:1 to 12:1, you can use 95. octane"
But it is true for the VG33E? I searched every forum, but I did not find anything.
I kindly ask to avoid things like "put a Chevy LS engine", or "mod it to a VG34" because I have no intention to change anything else than the compression rate throught custom pistons.
Thanks in advance.

I would like to correct the word "rate" in "ratio".

I answer to myself, this forum seems dead. I wrote an email to Top-End Performance, that is actually the only one selling forged pistons for VG33. This is the reply:

We have a maximum of 11.5:1 and that is quite high for 95 Octane...
I would try to keep it closer to 11:1
Steve

Therefore, beside adjusting the timing, one can do one of the following:
1 - use the engine in LPG instead of gasoline at 11.5 CR. It is an excellent option, because for the much less price of the LPG. The engine would gain around 7,7% power and torque (meaning 14 hp) from the rise of the Compression Ratio, and would loose around 3-5% of power and torque from the use of LPG.
For a VG33 at 180hp this would mean an overall improvement of 4 hp. But an incredible better fuel economy, you would save, at least in my country (Dominican Republic) around 50% of the money in using the car. A huge economy.
2 - using the engine in gasoline, at 11.2-1.3 CR, but with a thin gasket, like 0.8mm gasket, then if the engine knocks one should increase the gasket height to 1.2mm. It is the cheapest way I think, to obtain the maximum CR at the minimum price (basically one more gasket).

If the 2 does not work in any way ... then go LPG

The forum isn't dead, it's just kind of an offbeat question which no one knew the answer for. Why one would want to go through all that for a 4 hp gain I have no idea, and I'm sure a change to LPG doesn't require bumping the CR. So conceptually, messing with the CR doesn't seem to make a great deal of sense. That's probably why no one had an answer, because no one has done it.

Also, the VG33 has a CR of 8.9:1. At a CR of 11.4:1 this would mean an increase of 2.5 points of CR.
This brings a better efficiency of the engine, and a higher Miles per Galon.
1 point of CR increase means around 5% better efficiency, so mpg.
2.5 points of CR increase means around 12.5% better mpg.

In few words: using forged pistons to increase CR at 11-11.4 means CONTEMPORARY better power, better torque, a more responsive engine, better fuel economy, at a price of around 1000 dollars.
This to me seems the best Value/Cost improvement for a VG33, much better than any other option.

Other things that in my opinion are very good in Value/Cost ratio are lightweight pulleys, an electric fan, and a Phenolic Thermal Intake Spacer. They are cheap mods, with really good benefits.
The problem, with lightweight pulleys, and Thermal intake spacer is that they are not sold anymore by any online shop. That's really a pity.

VStar650CL wrote: ↑

Mon Apr 17, 2023 10:55 am

The forum isn't dead, it's just kind of an offbeat question which no one knew the answer for. Why one would want to go through all that for a 4 hp gain I have no idea, and I'm sure a change to LPG doesn't require bumping the CR. So conceptually, messing with the CR doesn't seem to make a great deal of sense. That's probably why no one had an answer, because no one has done it.

+4hp overall EVERYWHERE (low end, middle, top end) (raising 2.5 points of CR improves 7.5% power and torque, if one to stay away from knocking uses LPG then he looses 3-5% of power, the overall result is around +4hp)
+12.5% better mpg (everywhere, city, highway)
-50% costs per year in fueling

LPG is a way to have high CR without knocking. LPG does have 112 octanes.
If one does not want to go LPG, there is choice 2, the math is there, +6% power and torque, everywhere, +10% mpg in any condition.

That's all fine, but does it justify the cost of the engine work? My guess is you'll have to drive it for years to see any payoff, and that's assuming you have no reliability issues from the higher CR (not a good bet). I'm not saying you shouldn't do it, only that you shouldn't be surprised if no one else has done it.