GS/8g/Hyundai 4g64 piston comparison

[96rsstbrwd]

Well now I have a spare 4g64 block lying around and began considering my options, a rebuild is in the works. However, I've been noticing more chatter on the 3G/8g boards for the past few years about the Hyundai version of the 4g64 (g4cs) and there seems to be a bit of grey area when it comes to compression ratio. I have a few questions...

1. What is the actual compression ratio of the 89-91(six-bolt, dohc/8V-sohc) and the 00-01(seven-bolt, dohc) Hyundai Sonata 4g64/g4cs pistons when paired with a Mitsubishi head?
2. How do they compare to the standard GS/8g pistons?

*I've found conflicting numbers ranging from 10:1 to 12.5:1 when mated to the Mitsubishi heads. Both the 1g/2g and 3g/Evo 8+ guys are saying that the Hyundai heads have a larger or higher capacity 'valve-cup'(not sure what to call it) in the combustion chamber. Which would compensate for the Hyundai high compression piston, but when the hyundai pistons are paired with a Mitsubishi designed head it would cause a much higher compression.

I'm trying to find what combination would be the most suitable for a decent higher compression n/a setup. I'm aware that the *discontinued* GS pistons have a 10:1 ratio while the sohc Mitsubishi version can go from 9:1-9.5:1. I'm just wondering how the Hyundai pistons would compare to the GS pistons in actual compression ratio, seeing that most of the sources I've found are conflicting.

If anyone has experience with the Hyundai pistons and possibly pictures of the piston shape so that we could compare it to other options, it would be very helpful and appreciated!

[master_visionary]

I understand that question from a mathematical point I would like to know as well

If this gets answered in detail it should be stickied

[96rsstbrwd]

I found pics of the 89-91 sonata 8v pistons. They are on parts dinosaur.
http://www.store.partsdinosaur.com/product2526.html

[mko]

these are 6 bolt pistons. you need to machine the wrist pin hole to 22mm in order to work with 7 bolt rods,

your best bet is 99+ sonata 2.4L Dohc pistons

[mko]

The difference in compression comes from the different head. The Sohc head will give you 9.5:1 CR while using the same pistons with DOHC head will give you 10.0:1 CR. Using Hyundai head will bump the CR even more.

8g pistons will give you 9.0:1 with SOHC head and 9.5:1 with DOHC head. I read on Club3g that using Kia Optima pistons drops the CR to 8.5:1.

[Exhaust power]

Oops thought it was all about 8gs for a sec!

[master_visionary]

As some know I am rebuilding my 7g so a f few clarifications if y'all would

These Kia pistons are 8.5:1? Would this be too low for the boost capabilities of a 16g?

Now since these Optima pistons drop the CR 1:1 if I mate these with the dohc head
which raises the CR 0.5:1 am I correct to assume this would create a 9.0:1 CR?

[mysticj]

The G4JS pistons are nearly flat top with a -3cc dish, when place in a 94-98 4G64 there are different compression ratios based on which head you use. The SOHC and DOHC heads will yield 11.5:1cr while the Hyundai 92-98 DOHC heads will yield around 12.1:1cr.

[master_visionary]

I don't think they would be that high

[w/oarctic7g]

Don't doubt, he's done his homework. A complete g4cs bottom with a g4cp top should be a nice combo. Avgas will be the fuel of choice though.

[Galanttuner10]

Visionary.... 1gs have a 7.8:1 compression ratio and 2gs have an 8.5:1 ratio. On a stock 1g bottom end right now we have a 6776 and 32 psi all day. FP3052 back on it now with 32 psi and it spools so quick. A 16g spools so fast on a 1g bottom end, a 2.4 with 8.5:1 would be good, 9.0:1 would be ideal for a daily IMO.

[96rsstbrwd]

I found a ton of info here: http://www.dsmtuners.com/forums/blog...tor-build.html

He even has pics of the 4g64 (64sa/95+) pistons!

This 4g64 came originally from a 1995 Galant LS it came with the SA pistons. Which is exactly what I was looking for. The 64SA pistons have a 15cc dish to them. With the 47cc head They have 9.5:1 CR. Just like the stock 4g64 longblock from 1995+ since the 4g64 SOHC head has the same cc as the 4g63 head in the 2nd half of the 1990s. See how much more dish the SA pistons (left) have vs. the n/t 4g63 pistons (right).

He also goes on with more info on the variations of different heads.

But still because of the displacement increase coupled with a g4cn 1.8L hyundai DOHC head which has a head chamber volume of 43cc, my compression will be 10:1. Here's a great calculator to use:
http://www.dragsource.com/index.php?...s&calctoview=6
Deck height is zero. And composite headgasket thickness is 1.2mm.

So...

7g 4g64 pistons + Stock (sohc) or 4g63 (dohc) 47cc head = 9.5:1 CR

7g 4g64 pistons + Hyundai 4g67/1.8l 43cc head = 10.034:1 CR

4g64 Sonata/Mighty Max 8v pistons + Stock (sohc) or 4g63 (dohc) 47cc head = 11.3:1 CR

4g64 Sonata/Mighty Max 8v pistons + Hyundai 4g67 1.8l 43cc head = 12.077:1 CR

But there was also a 1.6L version found in Mirages and Hyundai Elantras called the 4g61. If my math is correct, the cumbustion chamber of that head is 37.3556645 (37.4)cc

So...

7g 4g64 pistons + Mirage/Hyundai 4g61 1.6l 37.4cc head = 10.885:1 CR

4g64 Sonata/Mighty Max 8v pistons + Mirage/hyundai 4g61 1.6l 37.4cc head = 13.384:1 CR

If you ask me, anyone building a n/a setup with compression ratios higher than 10.5+ should have 6 bolt 1g turbo/ evo 8,9 oil squirters machined into their block. Ceramic coating the pistons and the head/valves would also help fight the added heat from added compression. Cool pistons are happy pistons!

I wonder how Mazda keeps their new 'skyactive' engine in check, it has a 14:1 CR from the factory!!!

[Galanttuner10]

I would never go through that much trouble for an NA build. Many DSMs run non turbo 6 bolts with no oil squiters turbo and make good power. You also forgot about the 1994 Galant GS pistons. They are 10.0:1 and they GS block has oil squirters from the factory.

[96rsstbrwd]

Its not that i forgot them, but I'm having trouble locating specs of the GS pistons. (valve relief/dish measurements)

The oil squirters are for concerns regarding reliability. After all, I'm sure there is an almost infinite number of high performance engines that don't have them. But we have the ability to machine them in at a relatively low cost, so why not?

[mysticj]

GS pistons are around -11cc. They are discontinue anyway, go G4JS and be happy with 11.5:1cr or more. If you are concern with reliability, install an oil cooler. Its probably cheaper than buying oil squirters and having them install.

[Galanttuner10]

2g style oil squirters like the turbo cars and the GS blocks have are just little jets. And like mystic said just do an oil cooler. I have a spare set of GS pistons with new rings I may put in another block but for now they are just sitting on my bench

[96rsstbrwd]

Using an oil cooler is a great idea for any engine, and I will be adding one wheather I choose natural aspiration or turbo. Using an oil cooler will definately decrease oil temps, however, they do not have as much of a direct effect on piston heat as the squirters do.

In order for any oil to reach the pistons of an engine without oil squirters, it needs to be splashed around by the crankshaft and eventually this creates a 'windage cloud'. With oil squirters, the pistons are exposed to oil much more frequently, and piston heat is decreased in a more efficient manner. For the best results, an oil cooler would help even more.

Unfortunately, 2g style oil squirters are complete crap and prone to clogging. But lucky for us, the 1g/evo style can be machined into any 4g6x block. (Even the wideblock mighty max's)

www.projectzerog.com

There are no piston oil squirters in the SOHC blocks, however, all 4G6x blocks can me made to use them. The holes for the oil squirters can be machined into any 4G6x block. First the pad will need to be machined flat and then a hole will need to be drilled and tapped for the oil squirters. It is important to have a flat surface with a perpendicularly drilled and tapped hole, otherwise the crush washers will leak precious oil pressure from the main gallery. Oil squirters are not required when doing a swap. Some argue that with forged pistons, they serve very little purpose at all. Some say they are absolutly required on any turbo engine. Using oil squirters is a judgement call and the costs/benefits of adding them should be considered by the builder.

Also found some more info about the different blocks/heads that could be useful in the Dohc swap.

www.projectzerog.com

4G61 - 1.6L (Turbo, N/A, High Comp, Small Port DOHC Head)
4G62 - 1.8L (N/A DOHC)
4G63 - 2.0L (Turbo, N/T, DOHC, SOHC, Wide, Narrow, 6bolt, 7bolt, aka: G63B)
4G64 - 2.4L (N/A, SOHC, DOHC, Wide, Narrow, 6bolt, 7bolt, aka: 4GCS, G64B)
4G67 - 1.8L (High Comp, Big Port DOHC Head)

[96rsstbrwd]

I also find it interesting that Mitsubishi found it necessary to add the oil squirters to the GS block after only increasing compression by .5:1 over the Sohc version.

[Galanttuner10]

Remember it wasn't about the compression. The GS made more power and revved higher and was tuned to run on premium fuel not 87 or 89. Because of the high performance design they used that design. Remember te GS has 2g style oil squirters and a 2g style head a full year before the first 2g was made meaning that it was a prototype if you will for the 2g 4G63T.

[mysticj]

BTW, the stock rods have little 'squirters' build into it. Oil squirters do cool pistons but also add more windage on the crank because you have more oil collecting on the crank after the oil falls from the pistons. You want cool pistons, how about ceramic coating on the piston tops? Not that expensive and you will keep all the heat in the combustion chamber, where it belongs.

Even with the stock G64 pistons and Hyundai head, that will net 10:1cr. Good for either NA or boost.