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How to figure out compression ratio, 98mm titan pistons in vg33


Comrade_Charlie

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Ok I have a set of Nissan Titan pistons(8 of them), My plan is to put 6 of them into a vg33 bored out to 98mm(which is what the stock titan pistons are, 98mm), on the stock vg33 rods with a vg30 crank, oil pump and oil pan.

 

I beleive the compression height on the titan pistons are slightly shorter than the stock vg33 pistons. I cant find the site where I got that info from. I know the vk56 compression height is 31.something mm and the vg33 is just about that.

 

But how do I find out what the exact compression ratio will be, I will be making a custom headgasket for this since its being bored out from a 91.5mm to 98mm. So if it will be to high with a stock thickness I believe I can make a thicker one.

 

 

And another question

The wrist pins on the vk56 are bigger than the vg33s too. the vg33s is 20.98, and the vk56 is 21.99. Can the rod be resized 1mm bigger, or will it make the rod too weak? this engine will only see probably 10psi of boost, the pistons are cast so I dont want to run too much boost through it, if it gets built.

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Here is an online CR calculator

http://www.discovery-carhire.com.au/widget/compcalc.php?mode=calculator&unitmode=metric

 

91mm to 98mm I thought this would be too much but I did a quick google (not that you can believe what is posted on the interweb) but I found this statement a few time on different forums

 

"Turns out, the VG33's have some super thick cylinder walls, about .300" thick. As a comparison, the VG30 has roughly .177" thick cylinder walls. This means, you could actually bore your VG33 out to around 98 mm and still nearly retain the same thickness as the VG30 cylinder walls. This gets you right under a 3.8 liter VG (3,756 cc to be exact)."

 

Re the rod size question - if there is enough meat then yes on my L30 build I put RB30 bushes into the L28 rods = almost 3mm had to machined to press in the nice bush - however pin dia was still 21mm just that the RB30 bush was a good bush. I would not to that again - only a few $$ more and some H-Beams could have been purchased with good bushes from the get go.

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Ok I have a set of Nissan Titan pistons(8 of them), My plan is to put 6 of them into a vg33 bored out to 98mm(which is what the stock titan pistons are, 98mm), on the stock vg33 rods with a vg30 crank, oil pump and oil pan.

 

I beleive the compression height on the titan pistons are slightly shorter than the stock vg33 pistons. I cant find the site where I got that info from. I know the vk56 compression height is 31.something mm and the vg33 is just about that.

 

But how do I find out what the exact compression ratio will be, I will be making a custom headgasket for this since its being bored out from a 91.5mm to 98mm. So if it will be to high with a stock thickness I believe I can make a thicker one.

 

 

And another question

The wrist pins on the vk56 are bigger than the vg33s too. the vg33s is 20.98, and the vk56 is 21.99. Can the rod be resized 1mm bigger, or will it make the rod too weak? this engine will only see probably 10psi of boost, the pistons are cast so I dont want to run too much boost through it, if it gets built.

 

I use this guy right here:

http://www.csgnetwork.com/compcalc.html

 

It's pretty good. You can first get your block bored to 98mm, find suitable rings from Total Seal (might as well!), and then pop your pistons in and find out what the max height of the piston is at TDC using a degree wheel. That will give you the distance between the deck and the piston crown, which will be your piston deck clearance (not taking into account that there is piston rock... but that's a non issue here). You would need to know the compression height of both pistons to make an accurate comparison of deck clearance. the easier way is to just get the deck clearance yourself via depth guage, post-bore.

 

Then you need to measure the piston dish volume or dome volume. if it's a dish, you can fill the dish with a graduated cylinder/burette. if it's a dome, you need to find out the volume of your bore multiplied by a 1 inch stroke. then you put your piston in your bore, with the crown exactly one inch down from the top, and fill it with a burrette to find out how many CC's that will give you.

 

then you take your "cylinder bore * 1 inch stroke" calculation and subtract your "cylinder volume @ 1 inch actual piston depth" volume and you will have the volume of your dome.

 

Then you can use those values (or get them from someone else) and use the calculator I linked to.

 

Someone correct me if I'm wrong on this. It's just what I've read within every race-engine building book, and I have about 3 or 4 of em that I think are very well written and will be what I use to get mine.

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Thanks everyone!...

 

I got a set of 8 off of ebay for 80 bucks from a truck with 2000 miles on it, and I believe it, these are in good condition.

 

They are dished with 4 valve reliefs, and a shorter compression height so Im hoping it will come out to 7-8:1?

 

And I think a stock t3 with be too small for a 3.8 liter, I was thinking a hx40 with custom manifolds and running 5-10psi. 5 to 10psi from a hx40 should be good LOL, huge turbo but im crazy and like used stuff.

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here are pics of the vg33 rod vs the vk56 rod. the wrist pin side of the vk56 rod is like narrower than the vg33 rod so I dont know if a engine place can machine that down to work. Because as they sit right now the vg33 rods will not fully go into the vk56 piston... take a look at teh jdm picTars. red lines is where it would need to be cut at, x being the material cut side obviously, paint brush ftw

 

vk56 rod

 

hpim1541up3.jpg

 

vg33 rod

 

hpim1543jr0.jpg

 

random picture of the vk56 piston 98mm

hpim1540eh4.jpg

 

vg33 compared to vk56

 

l_1d408e95b01e4fb493eeffa75f2ccf22.jpg

 

from left to right, titan, villager, 300zx

 

l_caacc93e709345b2935ce716c7cc1ecf.jpg

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  • 3 weeks later...

yea it was around christmas, I always have loads of candy around then, still have some on my desk, haha.

 

But I havnt done anything with the pistons yet. I found a good machine shop but my clutch on my 300zx just went out, and my 1990 maximas auto went out, so I got a whole 5 speed swap(pulled it myself with the help of 2 friends at a junkyard), got it all for 81 bucks out of a 1992. So thats at the top of my list to get running so Ill have something to drive around. and gotta get a new clutch for my 300zx. but it looks like the titan pistons should work, wristpin hole resized to 1mm bigger, rods shaved on the size to fit into the piston and balance the rotating assembly then stock rebuild with titan rings and custom headgasket, found a guy to make one for 50 bucks with a bore of 98mm.

 

what would that be in boring? 256 thousandths over?

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I will keep those rods in mind next time, I am sure they are easy to get too, huh?, but I want this to be kind of a budget build, kind of like my car, I dont know of anyone that is faster than my car for the money that i have met(I have like 300 bucks in actually increase hp parts, which would be nistune, mbc, and injectors. It is easy to make z31s go fast lol.

 

I dont know how much the titan pistons will hold, I plan on building another 3.3 later one with more money. I am simply doing this because the titan pistons came out to be 98mm, and everything looks like it will work. I have 150 bucks in buying the motor, 80 in buying the pistons. That is 230 then + machine work. It should be sick for the amount of money I spend. I have a really nice crank out of a z31 and have a whole spare motor for the cams, dist, oil pump, everything needed.

 

all I need now is custom headgaskets(found a place for that), normal rebuild vg30 parts, I still dont know the condition of the heads that were on it, the exhaust or intake has some rust in it from it being in the junkyard but it doesnt look bad, I took them off of the engine and put them on a shelf and havnt looked at them.

 

I found a "good" machine shop after searching around for a while.

 

But what all machine work would I need, I want to ask yall instead of a shop, I dont know if they would BS me and say balance everything or tell me not to balance anything... I trust people on here more.

 

-boring+honing

-resize the wrist pin holes

-shave the sides of the rods to fit into the titan piston, if machine shops can do that.

-balance what???? confused on the whole balancing thing. since the rods are being worked on I think they need to be balance, the pistons wont be machined so why balance them, if they are all from one engine?

 

Any good sites or reads on engine balancing?

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factory parts are balanced to within a certain tolerance... 5 to 10 grams, maybe?

 

for a performance application you want things balanced within a gram of eachother or close to that.

 

you want to have the pistons, rods and gudgeon pins balanced as an ASSEMBLY as well... so that when balanced with the crank later, there will be no vibrations

 

think about he differences between pistons, then between rods, and then with the pins installed.

 

if pistons were off 5 grams, rods 5grams, and pins 3 grams, you have say... 13 grams worth of imbalance.

 

remember, you're taking material off TWO parts. they have to be weighed. I wouldn't skip the balancing duuuuuuuuuuude!

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  • 3 months later...

hey C_Charlie.

 

any updates here? I've got a VG33 and I'm wondering whether I should use the VK56 pistons and make something big here. LOL.

 

Not entirely sure if I wanna increase my budget a bit, and kinda get the engine hot-tanked and re-size the bearings and have the rods machined to accept larger pistons.

 

Then I need nistune for sure.

 

A VG37 would be a torquey engine, that's for dang sure! I would definitely need to fix my subframe spacers ASAP on that note.

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no updates im going in for a job interview on tuesday I hope, first thing im going to do once I get some money is see if this will all go together, my vg33 block, heads, vk56 pistons, vg33 rods are still sitting in my building. But yea a turbo vg37 would be sick, id exspect it to break my t5 with headwork and cams. Im going to run a pathy 2wd trans if I can get the engine far enough back... I dont know if I want to put this in my 280z or my 300zx just yet.

 

Oh and I need to dig up the dude I found that said he can make custom headgaskets normal graphite or mls. for 50-150 bucks. He had good reviews so...

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hope the job interview goes well.

i just picked up a vg33 and i'm looking at some options.

 

I think i'm just going to stick with stock parts and clean it up, and tap the oil pump for a relocation kit, and get my accessories lined up. hopefully it all slips into the z31 fine.

 

I'm dismantling all the parts from the vg33 today and possibly the heads. I'll be inspecting it to make sure it's all good, then getting OEM nissan hg's cause the MLS gaskets at z31 parts look awesome but are out of my budget for this thing right now.

 

I'm going to paint the bare block with 4 layers or so of rust-bullet after removing the rust from the iron. And I hope to have this thing relatively complete by early July. I think with z31 cams and turbo and all associated parts, it should be a good running engine :)

 

Not sure if I want to remove the internals and have it lightly honed and re-ringed and have the bearings replaced... we'll see when I pull the pan off! I'm also looking into a lightweight KA drive pulley with the center bored out to quest size.

 

total budget for this one is 800 or so CAD. which is like 50 cents USD.

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50 cents lol. I tell you after I replaced the bearings and injectors in my 300zx it ran so smooth through all the rpms with 2 broke motor mounts... I have 2 good ones now, dont ask why.

 

I love those big exhaust studs. I got my engine out of a JY so the heads need some cleaning up, I think 2 valves have a bit of rust in them. was going to pull all the valve out any way and do that spinny-sucktion-ma-bob thingy with that magic compound stuff to make them seal properly LOL. And new valve seals. no clutch how many miles was on this 3.3 the cluster was gone.

 

What is your 3.3 out of? suv or van?

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my engine is out of a quest van. i think i'm going to use my 300zx balancer and have the center bored out. I may have to look at my RB30 balancer and put that on for now, and just get an ATi or another romac for my RB30 later.

 

I think the water pump on the 3.3 i have is the same length as the pump on the 3.0, but the pulley is what dictates where the ribs direct the belt. I noticed that the face of the pulley on the 3.0's direct the belts backward over the snout of the water pump, whereas the 3.3 pulley directs the ribs parallel, or outward with the mating surface of the pulley bolts.

 

3.0 =]

3.3 =[

 

something like that (those are not happy and sad faces)

 

the quest 3.3's are a touch different from the Frontier 3.3's... water pump being the first thing I noticed.

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When I put a VG33 from a D22 into a U11 I had the U11 crank pulley center bored by a machine shop to the bigger crank snout and just used all the accessory pulleys and brackets from the U11 engine. Worked very well.

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