Higher compression without boost

[ejin4499]

So I've been doing a little reading and was wondering about some ways to raise the compression in our engines. I've heard of using q45 pistons to get it up to 10:1. I was wondering if the people who have made the vg34 conversion could post any hp gains or gas mileage gains that they might have gotten from the upgrade.

 

I've also heard of "decking" the heads and using a thinner head gasket but I'm skeptical of the compression gains from that. Anyone have any personal experience with that?

Edited January 31, 2012 by ejin4499

[MY1PATH]

what's to be skeptical about? thinner gaskets and milling down the heads both decrease compressed volume thus increasing Compression ratio. Thinner gaskets like SEC Pro Copper tend to leak around the coolant passages over time. they are great for race engines that see frequent tear downs but for longevity noting beats an oem factory gasket (260k still no leaks). leaving milling as the best option for long term reliability.

removing 1mm from the head will net you a 9.88:1 compression ratio in a vg30 and 9.85:1 in a vg33, do not forget to check the valve reliefs to be sure they are still deep enough. Your valve timing will be retarded aprox. 2 degrees from lowering your compression height by 1mm. this will shift your torque band up a little but can be compensated buy using adjustable cam gears.

 

MPG's... typically if you up CR by 1/2 point for every 10% increase in displacement your MPG will stay the same or possibly improve. Gains will also be had if an vehicle was under powered and lugging.

A vg34 is just over 20% but the CR is up by 2/2.

 

Mr. 510 has been getting about the same MPG with his VG34 as he did with his vg30.

Edited January 31, 2012 by MY1PATH

[ejin4499]

what's to be skeptical about? thinner gaskets and milling down the heads both decrease compressed volume thus increasing Compression ratio. Thinner gaskets like SEC Pro Copper tend to leak around the coolant passages over time. they are great for race engines that see frequent tear downs but for longevity noting beats an oem factory gasket (260k still no leaks). leaving milling as the best option for long term reliability.

removing 1mm from the head will net you a 9.88 compression ratio in a vg30 and 9.85 in a vg33, do not forget to check the valve reliefs to be sure they are still deep enough. Your valve timing will be retarded aprox. 2 degrees from lowering your compression height by 1mm. this will shift your torque band up a little but can be compensated buy using adjustable cam gears.

 

MPG's... typically if you up CR by 1/2 point for every 10% increase in displacement your MPG will stay the same or possibly improve. Gains will also be had if an vehicle was under powered and lugging.

A vg34 is just over 20% but the CR is up by 2/2.

 

Mr. 510 has been getting about the same MPG with his VG34 as he did with his vg30.

As always I can count on you to provide an answer that is both thorough and research/question provoking. If I were going to use the jwt s1 cams that provide .440 inches of lift how would I figure out if the valves would clear my pistons? All assuming a vg33 with stock pistons and bore with a head that was milled 1 mm.

[MY1PATH]

The 3.3 pistons have really deep reliefs so hopefully you get lucky.

One method is to put a layer of soft clay on one piston (you can leave the other pistons out for now) and install the head and timing belt with really soft springs on the valves so you can feel the valve on the piston instead of the spring resistance. NO SPARK PLUGS. Use your old gasket as it is pre-crushed and you only want to crush you new one once (actual install). After 2 full revolutions, or after you find resistance disassemble and look at the clay on the piston.

where ever the valve pushed on the clay will be depressed. the lowest part of the clay should be .050" thick. if it is thinner than that or you have bare metal showing the valve reliefs needs to be cut deeper.

 

Clean the parts thoroughly, some clays can be very corrosive (like play dough)

 

there are other methods, but I like that one. maybe someone else will chime in.

[Tungsten]

A few points to make here:

1. Milling heads on a VG is a STUPID idea and using a thinner head gasket is even more retarded. Not only is there potential for something to go wrong but you will throw the timing way off and as MY1PATH said, you will have to now use adjustable gears.

2. If you use high lift cams, they will create parasitic drag on the engine and you will actually lose more low end power. The stock 3.0 cams already have a pretty aggressive profile.

3. If you want to use high CR pistons then go for it but at that point you may as well build yourself a better engine.

[silverton]

 

Mr. 510 has been getting about the same MPG with his VG34 as he did with his vg30.

 

I think this is believed to be caused by the TBI...

[ejin4499]

The 3.3 pistons have really deep reliefs so hopefully you get lucky.

One method is to put a layer of soft clay on one piston (you can leave the other pistons out for now) and install the head and timing belt with really soft springs on the valves so you can feel the valve on the piston instead of the spring resistance. NO SPARK PLUGS. Use your old gasket as it is pre-crushed and you only want to crush you new one once (actual install). After 2 full revolutions, or after you find resistance disassemble and look at the clay on the piston.

where ever the valve pushed on the clay will be depressed. the lowest part of the clay should be .050" thick. if it is thinner than that or you have bare metal showing the valve reliefs needs to be cut deeper.

 

Clean the parts thoroughly, some clays can be very corrosive (like play dough)

 

there are other methods, but I like that one. maybe someone else will chime in.

Ahh and here I thought you would have some clever calculator on the internet that would do the math before I tore the engine down.

does anyone know what the clearance between the pistons and the valves is on a stock setup?

[ejin4499]

A few points to make here:

1. Milling heads on a VG is a STUPID idea and using a thinner head gasket is even more retarded. Not only is there potential for something to go wrong but you will throw the timing way off and as MY1PATH said, you will have to now use adjustable gears.

 

Whats wrong with adjustable cam gears. I thought people ran them on stock setups so they could mess with there timing anyway?

 

2. If you use high lift cams, they will create parasitic drag on the engine and you will actually lose more low end power. The stock 3.0 cams already have a pretty aggressive profile.

 

So what happens that causes the parasitic drag?

[Tungsten]

Almost no one runs adjustable cam gears on a stock setup. Messing with the cam timing in a factory setup is not recommended. The real reason milling the heads is bad is that the heads will be out of specification and who knows what that will do to the head gasket.

 

High lift cams cause parasitic drag because the engine has to work harder to push the valves open.

[ditchdiggerjcf]

Messing with the cam timing in a factory setup is not recommended.

High lift cams cause parasitic drag because the engine has to work harder to push the valves open.

I guess someone forgot to inform those NASCAR and NHRA guys.Think of all that power they have missed out on.

[MY1PATH]

Sorry buddy no clever calculator for valve reliefs, every head is built different. But here IS a calculator for you to play with. www.xenonz31.com/engines.html

The vg33 dish is about 7cc, piston is 91.5mm and the Head gasket is 92.5mm all other numbers in the calculator are correct.

 

ok, forget the whole parasitic drag crap about cams. They rotate at 1/2 the speed that the crank does and the amount of lift and duration have nothing to do with drag with regards to the lower RPM range.

The REAL reason Big lift cams reduce bottom end power is for 2 main reasons.

1) the cam is usually designed to shift the torque band up for racing purposes

2) the added availability of air at low RPM reduces the scavenging velocity of the engine. This factor is often overcome when larger pistons are used because the added draw of the piston brings the velocity back up.

 

Also wrong on the cam gears, their purpose is to locate the torque band where you want it. Yes on N/A motors they are almost never used with stock cams but with boosted motors they are used with stock and aftermarket cams to locate High RPM torque bands to match the spooling of the turbo or perhaps to get the ideal punch on a 7k rpm shift point on an engine that revs freely to 9k.

 

In a 3.3 the JWT S1 cam behaves nicely gives great highway power and picks up at about 2k rpm. It may pick up a little sooner on higher compression. MPG's can be the same but if you are heavy on the skinny pedal they will go down. Due to the overlap duration this cam features enough natural EGR to remove the actual EGR vavle and still pass cruise level smog in many places (unless having the acutal valve is required) on the other hand the idle scores will be a little harder to pass.

 

Milling the heads is NOT stupid it does not take the heads out of spec (because they should always be FLAT) and sealing will not be an issue with out wealth of 26 total head studs to hold our freshly milled heads to the OEM gasket that seals better than any other. That being said, You just have to be prepared for the extra steps required. That being said maybe, if you are afraid of these steps, you might call it stupid (hint, hint).

BTW Tungsten, If I can't set you straight alone these words are also endorsed by MR. 510.

Maybe have some solid information when you try to advise, such as having designed your own aftermarket cams and installed them and even dyno tested them from before and after. or perhaps dealt with other engines where milling is actually required if the head pulled after 250k (damn fords)

Edited February 1, 2012 by MY1PATH

[MY1PATH]

Lastly, there are no High CR pistons for the vg30e and vg33.

If you want a cheap High CR 3.3 I THINK milling the heads and installing a fresh oem gasket will likely be it. This is based of the assumption that the deep 7cc valve reliefs in the 3.3 will require no modification. Your torque band will be shifted upward slightly but this may be fine for an automatic and a highway machine. This is the build I have planned for the wifes 94 I will also be using the European z31 cams and I expect about 200 Hp out of it. I would not bother with a higher CR with the stock 3.3 or USDM 3.0 cam because I THINK the short duration will yield minimal gains however, I THINK the S1 cam and the euro z31 cam will most likely love the 10:1 CR or close to that.

The s1 might even like 11:1 but good luck doing that without a custom piston with a 7cc pop up in the middle.

Edited February 1, 2012 by MY1PATH

[ejin4499]

Almost no one runs adjustable cam gears on a stock setup. Messing with the cam timing in a factory setup is not recommended. The real reason milling the heads is bad is that the heads will be out of specification and who knows what that will do to the head gasket.

 

High lift cams cause parasitic drag because the engine has to work harder to push the valves open.

tungsten why is it that you always have such strong opinions on different topics but so little to back it up with? Don't do it because it will be out of spec? Doing anything to raise compression with or without boost is going to take the truck out of factory spec. Out of spec is a prerequisite of this conversation. Isn't the whole point of having our trucks getting it out of factory spec and into our own specs? As well as help each other out when we take it a little to far? :/end rant

[Kingman]

Adjustable cam gears are becoming pretty common on VGs now. I put a set on my Z with stock cams and what a difference it made in the top end. Low-end was just as punchy. On the dyno the torque curve far surpassed the 4,500RPM mark unlike stock and flowed to almost 5,900RPM again unlike stock. With accompanying mods I'll bet there would be even more gain, such as a gutted plenum.

 

Messing with the cam timing in a factory setup is not recommended.

High lift cams cause parasitic drag because the engine has to work harder to push the valves open.

 

 

Oh, and the dyno showed more power. More and consistent power too with the plenum spacer.

[ditchdiggerjcf]

 

 

 

 

 

 

Oh, and the dyno showed more power. More and consistent power too with the plenum spacer.

Where did u get a plenum spacer for a vg30? I tow the bass boat with mine and could use a little more umphh. lol

[Kingman]

Meh, it doesn't do much power-wise. Shifted the torque curve down slightly but the major point of it is to separate upper and lower intake manifold temperatures to cut down on the heat soak on turbo cars.

 

They're made by my buddy up North, sold through ASCO.

http://allthingsz.com/index.php?main_page=product_info&cPath=1_12_24&products_id=34&zenid=j5voh11kufq135tg8k6fh40tc6

[MY1PATH]

"don't use throttle body spacers they slow down your throttle response"

lol JK

 

Keep in mind how the spark wires attach to the pathy manifold. a 3/8" spacer will not allow the boot to seat if it is using the manifold pin. I plan to press my pins out shave down the pin bosses 3/8" and press the pins back in.

A N/A 200sx user from z31p reported a 60F drop in upper manifold temp on a hot summer day. Its reconfigured that you remove your manifold and TB coolant lines when you us this spacer.

[Tungsten]

I guess someone forgot to inform those NASCAR and NHRA guys.Think of all that power they have missed out on.

I think you missed the fact that this is not NASCAR.

 

Adjustable cam gears are becoming pretty common on VGs now. I put a set on my Z with stock cams and what a difference it made in the top end. Low-end was just as punchy. On the dyno the torque curve far surpassed the 4,500RPM mark unlike stock and flowed to almost 5,900RPM again unlike stock. With accompanying mods I'll bet there would be even more gain, such as a gutted plenum.

 

 

Oh, and the dyno showed more power. More and consistent power too with the plenum spacer.

That Z has a turbo, a Pathy doesn't. The turbo changes the physics completely. So yes you will see a benefit of adjustable gears with boost.

 

tungsten why is it that you always have such strong opinions on different topics but so little to back it up with? Don't do it because it will be out of spec? Doing anything to raise compression with or without boost is going to take the truck out of factory spec. Out of spec is a prerequisite of this conversation. Isn't the whole point of having our trucks getting it out of factory spec and into our own specs? As well as help each other out when we take it a little to far? :/end rant

I don't know where you guys get your information from. Stop reading ricer forums. Why do you think Nissan uses lower lift cams on the 3.3? It's to increase low end efficiency.

If you are going to mess with the heads, you are going to be asking for trouble. Can you mill the heads with 0.001" tolerance? What about the bolts to tighten those heads down? Anyway, if you are going to be removing the heads, why not just rebuild the engine with a bigger bore and better pistons? I hate when things are done cheaply. Do it right or not at all.

 

Milling the heads is NOT stupid it does not take the heads out of spec (because they should always be FLAT) and sealing will not be an issue with out wealth of 26 total head studs to hold our freshly milled heads to the OEM gasket that seals better than any other. That being said, You just have to be prepared for the extra steps required. That being said maybe, if you are afraid of these steps, you might call it stupid (hint, hint).

BTW Tungsten, If I can't set you straight alone these words are also endorsed by MR. 510.

Maybe have some solid information when you try to advise, such as having designed your own aftermarket cams and installed them and even dyno tested them from before and after. or perhaps dealt with other engines where milling is actually required if the head pulled after 250k (damn fords)

MR.510 will never endorse nonsense like this, why don't you talk to him. He in fact said, NEVER mill the heads on a VG.

Edited February 1, 2012 by Tungsten

[sewebster]

The engine shop machined my heads because they were damaged somehow by previous gaskets. I didn't really think much of it at the time, and don't know how much they took off. I guess since my engine seems to work, the pistons probably aren't hitting the valves too much

[adamzan]

Tungsten you've never built an engine or done anything to the truck yourself so leave your opinion at the door. My1path has talked with mr510 in person, and he has modded his motor so he speaks from experience.

[Tungsten]

I guess you weren't paying attention then.

[ditchdiggerjcf]

I guess you weren't paying attention then.

It has been said that you basically don't know @!*% about @!*% from several members here.

[1994SEV6]

It has been said that you basically don't know @!*% about @!*% from several members here.

I don't appreciate you saying that. I've learned a lot from Tungsten and his guides.

 

Pretty much the dispute here is to mill the heads or to not mill the heads.

 

We have one person saying that you should not do this and Mr. 510's advice is to not do this.

 

We have another person saying that this is a feasible method of increasing compression and that Mr. 510 will concur.

 

This seems to be a stalemate until Mr. 510 steps in and says his own personal/professional opinion or another qualified person does.

So let's leave it at that.

Edited February 2, 2012 by 1994SEV6

[Tungsten]

I learn a lot from the experience of others even if I don't do it myself. From what I know, you should never mill the heads on a VG. Yes, there is the right way and the cheap way to get things done. Please choose the right way, it's much more economical in the long run.

[ejin4499]

I learn a lot from the experience of others even if I don't do it myself. From what I know, you should never mill the heads on a VG. Yes, there is the right way and the cheap way to get things done. Please choose the right way, it's much more economical in the long run.

There is no right or wrong only the one with the price you are willing to pay.

 

Trying to get back on topic

increasing compression can be achieved by milling the heads down a certain amount taking into account the change in timing and clearances. Another method that I have read about is overboring and using pistons from a VH45. Does anyone have any information on this or any other type of pistons that might be used in a vg33 short block. I remember reading someone from this forum did do that and posted a right up but I can't seem to find it.

 

So far from this conversation I have gathered that you have several ways to increase compression in our engines.

1. Pressurize the air going turbo or super charger.

2. Shorten the cylinder by milling the heads. Which I assume you could also mill the block and get the same result?

3. Change how far the piston pushes with a different shape

 

4. Has anyone seen a way to change how far the rod pushes the piston? Isn't this called a stroker ???

 

Found a company that would do a set of custom pistons though they don't post pricing. www.reacetep.com

Edited February 2, 2012 by ejin4499