R33 Rb30 Conversion

[Sydneykid]

Hi Joel, I like it when the guys go and do their own research. It's much better than me telling you stuff, that you will forget tomorrow. If you do the work, you may not remember the answer, but you will always remember how to find out if you do forget.

The answer is that the optimum squish zone will result in improvements in Economy, Emissions, Performance and Response. Because there is a much higher chance for the fuel and air to burn completely. Since it takes out some unburnt fuel, it also improves the bore lubrication (no washing) and therefore engine life.

One of my favourite quotes comes from RaceTech Inc;

"On many engines, a squish or quench area is used to negate combustion in certain areas to avoid knock. By having a matched area where the piston and combustion chamber come in close proximity at TDC, the gasses are kept cool enough so that they will not ignite until the piston has moved down the bore and cylinder volumes are increasing. This keeps the rate of pressure rise below the knock limit. Some people are dismayed when they install a thicker head gasket to lower the CR and have knocking worse than before. This is because they have negated the designed-in quench effect. A large squish area also tends to promote increased chamber turbulence which is important for mixing and power at high rpm."

There is plenty of other squish zone reading around, a couple of guys in the US wrote a mega thesis on it a few years back. Do a search, it's there somewhere.

[ENTYSU]

Ok here is what I have so far.

Sydney kid.. Would you be so kind as to have a look at the cam belt setup and let us know if this is how you did your's or if this is the best way to do it?? Thanx

File is 86k.

Hey Joel ... all seams all right just for a few things .....

1 . why not go a copper head gasket std head gaskets cant hold high boost pressure ..... ?

2. a compression ratio of 7.1 is perfect for turbos just think of it as the more air and fuel you can cram into the cylinder the more bang you get ......

my car runs on around 7.5.1 comp and loves the boost ...

and remember the higher the comp ratio the less off a wack youll get when u hit boost itll more feel like a v8 at 9.1 ...... just letting you know due too experience in the engineering side ...

[GiJOr33]

standard head gaskets are fine if you O-Ring the block.

7:1 comp is pretty low, must feel like a dog when you are off boost. You are right though, it will be happier with 2bar of boost compared to a 9:1.

[Cubes]

Hu?

I've used a multi-layer metal headgasket that has its middle layer with a O-ring around the bore, it saved me $80 compared to using a stocker head gasket with a machined O-ring in to the block. Every little $$ counts when your at Uni and on $200 p/w. I havn't been out for a long long time, which is good for the studies though.

The comp ratio is around 8.2:1 by my calcs and Andrews calcs.

The only issue with the RB30 forged pistons is the comp would have been around 7:1, perfect squish but crappy comp. I didn't want 7:1. Every one told me not too.

Lowest I was told to go was 8:1. At the time I wasn't aware of Squish hence why we ended up settling on Wiesco RB25DET 14cc dome pistons that gave us around the 7.8-7.9 comp. Then shaved 20thou off the block to bring it up to 8.2:1. Should have done another 20thou or even 40thou.

Im unsure sure how it will affect the engine as I can't find any results on the net of how a engine has performed after its squish has changed by 3 fold. By the looks of it the difference is minimal, well from the little i've found on the net.

Remember for every .5 of a cr you dorp you need approx another 2.9psi to achieve the same final compression.

Drop to 7:1 and that means you will have to run an extra 6psi to make the same power if you were running a 8:1cr. So realisitically using the measurement of "I can run 2bar no problems now" is pretty usless as the final comp. ratio after the boost has been pumped in and compressed is the same.

[Sydneykid]

Hi Joel apparently you asked ..............

Sydney kid.. Would you be so kind as to have a look at the cam belt setup and let us know if this is how you did your's or if this is the best way to do it??

Did I answer that?

[Cubes]

hehe I can't remember, I could go through all the posts again but havn't got time. I've left a law subject essay to the last minute. Too busy stuffing around with the RB30 last weekend.

I really didn't have much choice in the matter as the Dayco 94407 was the only belt I could track down. The powergrip I was told didn't exist.

But out of curiosity how have the RB30DET's you know of been done?

Found an what looks to be an issue when using the stock RB20/25 exhaust manfifold on the RB30DET.

Pic 1.

The RB20 setup. Note the how water galley that is situated at the top of the block sitting a few mm down from the deck. It extends from the front of the block (end of the water pump) to the back of the block. (6 small of welsh plugs)

Pic 2.

The RB30 setup. Note the how water galley that is situated at the top of the block sitting basically flush with the deck.

It looks like it is way too close. Especially being where the lower exhaust manifold bolts are the water galley has a rise that flattens outhence fouling the manifold.

The RB20t block definately has a LOT more clearance.

Pic3.

Misc pic.. Came across that poster a while back in a Wheels Mag.

It states - "Nissans new Godzilla on wheels aims to slay the Sierra. And its here soon"

Lol they obviously wern't too worried about the V8's back then..

Pic4.

My 91' R32 Bathurst GTR.

Have a read of this peoples.

http://www.racehelp.com/article_racing-10.html

It contains some interesting info regarding quench & piston design among other things.

<span style='font-size:9pt;line-height:100%'>It appears that for a high reving engine which is classified as 6500+rpm the quench or squish gap/clearance is around the .050-.055".</span>

This is due to the standard cranks felx & pin flex etc..

Well apparently according to one engine builder.

[riceline]

sent an email to gates in USA a while ago

"I'm trying to locate a particular belt of yours somwhere in Brisbane.

The one I am after is the Gates POWERGRIP GT2 p/n 1200 8MGT 30

it measures 1200mm long, 8mm pitch on teeth, 150 teeth.

If you would be able to tell me where I am able to purchace this belt

it would be greatly appriciated."

Reply

"Either Consolidated Bearing Company or Powergrip Industries in Brisbane

should be able to help you out with this one.

Best Regards,

Peter"

hope that helps anybody

[MonstaS4]

I too have emailed gates australia regarding the Powergrip belt. Two issues.....the belt needs to be cut down from 30mm to 25mm (factory width), not sure who can do this.

Secondly, The powergrip GT2 belt has a lower temp rating than a cam timing belt.

I asked if there is an equivelent to an RB30 belt, but 1200mm long. The response from gates is as follows....

I have just checked with our global database and it appears you are in

luck. T306 is the same profile as the T175 (RB30 belt) and is 1200mm

long with the 8mm pitch and has a top width of 23mm.

We currently have the T306 belts available and the list price is

$120.65

The T306 may be the way to go? I haven't ordered one yet, so cannot confirm the above.

[Cubes]

Why bother..

My head was fitted for $200 that included checking valve clearances drill and tapping a hole above the water pump. Installation of two tensioners ($90each) and then the installation of the Dayco 94407 $38 cam belt.

[Sydneykid]

hehe I can't remember, I could go through all the posts again but havn't got time. I've left a law subject essay to the last minute. Too busy stuffing around with the RB30 last weekend.

 

I really didn't have much choice in the matter as the Dayco 94407 was the only belt I could track down. The powergrip I was told didn't exist.

 

But out of curiosity how have the RB30DET's you know of been done?

Hi Joel, we mount the tensioner high and generally use a standard idler in the standard (low) position. But when we machine the head and/or the block (to get the compression ratio where we want it) we use a second tensioner in the idler position. We use the Dayco 94407 belt.

Hope that helps

[MonstaS4]

Point taken Joel. I hadn't looked into the Dayco option yet. Dirt cheap really. How does the quality of the Dayco compare to a Gates though? Obviously the cam belt is crucial to long term reliability.

[GTR-Ben]

Ok I finally have some photos.

Here is the engine. Still have to repaint the covers and do the belt etc.

Included pics of the Silvia in many bits.

http://ben.nismo.org/My%20Previous%20Skyli.../RB30%20Silvia/

[GiJOr33]

It's good to use VCT up to a certain horse power level (maybe 250rwkw???) with the standard turbo or a mild turbo upgrade, then after that you ditch the VCT and go with adjustable cam gears to get better results from different cams and bigger turbo kits.

[OVL-747]

just a note to some ppl

a mate has just done a lot of work building his engine for his vlt

its a stock n/a 3l bottomend , fully prepped though , and a 25 head , vct welded up.

now it was made apparent to him and many others that bolting a 25 head to stock vl bottom would result in approx 8.3 comp , well after many hours work , we cc'd it all and it turned out to have about 64cc , which gave a comp ratio of bout 8.8:1 , too high for a performance engine as timing would be stupidly low.

i know most ppl using this great thread are using forgies aswell , but just check out some things before going ballistic on ur new engine.

anyway we are now going forgies for this engine , etc etc etc

good luck to all who do the conversion , its a top idea

andrew

[Sydneykid]

just a note to some ppl

a mate has just done a lot of work building his engine for his vlt

its a stock n/a 3l bottomend , fully prepped though , and a 25 head , vct welded up.

now it was made apparent to him and many others that bolting a 25 head to stock vl bottom would result in approx 8.3 comp , well after many hours work , we cc'd it all and it turned out to have about 64cc , which gave a comp ratio of bout 8.8:1 , too high for a performance engine as timing would be stupidly low.

i know most ppl using this great thread are using forgies aswell , but just check out some things before going ballistic on ur new engine.

anyway we are now going forgies for this engine , etc etc etc

good luck to all who do the conversion , its a top idea

andrew

Hi Andrew, I have done this conversion more than once and the compression ratio is 8.3 'ish always. I suggest you get them to check it again. Standard compression ratio on an N/A VL is 9 to 1 with 58 cc combustion chambers (SOHC 2 valve). If you do the mathematics you will see that with 64 cc combustion chambers (DOHC 4 valve) there is no way you only loose 0.2.

If you want to post the dimensions you used I can probably verify where the error is in the calculations.

Secondly, who says 8.8 is too high for a performance engine anyway?

See that car at the bottom, it has over 1,000 bhp (now that's a real "performance engine") and it runs 9.3 to 1. I would argue that 8.8 to 1 is too LOW, in fact I have many times.

I suggest you read Joel's posts of 23/3/04 and prior, he covers the reasoning behind this very well.

Hope that clears up any misconceptions

[GiJOr33]

yep... 9:1 for me as well!

[OVL-747]

sydneykid

thanks for ur advice mate , i respect what u say , i have read many a response from u and u seem like a very knowledgeable chap

i will let him know the points u have made.

my mate works for tighe cams , he is an engineer , i dare say he did his calculations correct but who knows.

anyway , we planned for a cr of bout 8.2-3:1 , while using custom zorst manifold , gt35 or 30/40 dunno which one , custom inlet etc etc , anyway i will see what he says , also will try and grab the specs and post em up

thanks again

andrew

[Cubes]

OVL..

I don't know exactly as I'm still reading in to it but here's my best shot.

Try to ignore the static compression ratios, thinking of them as only a base compression ratio that means in practice very little when you start to fiddle with cam timing, after market cams, turbo efficiency range etc.

It comes down the the dynamic compression ratio.

Rememeber this. For every .5 of a CR you drop in static comp you will be required to pump in another 2psi to make the same power/dynamic compression. Approximately that is.

Lets see what this looks like on paper.

An RB30DET with a static CR of 9:1 on 1 bar of boost makes 260rwkw.

An RB30DET with a static CR of 8.5:1 will require an extra 2psi (makes it 17psi) to achieve the same dynamic compression ratio hence 260rwkw.

Only real difference is that the RB30DET with a static comp of 9:1 will have better response, fuel economy and spool the turbo a little earlier.

Say you were to drop to 8:1. You would need an extra 4 psi (hence 19psi) to make the same power as a RB30DET running a 9:1cr with 15psi of boost.

Work the turbo's efficiency range in to this with a required power goal/ fuel used etc and you will find the 9:1cr is pretty much on the mark.

Running a higher static comp also leaves the door open for much better performance for when you or if you decide to slap a set of cams in it.

I've started to realise there is so much more involved when looking for a certian amount of power. So many variables that all work hand in hand to achieve the most responsive, fuel efficient engine.

I'm sure we have all read or heard at some stage or another that when you cam up an engine it is best to up the compression ratio. And why.. Dynamic compression ratio.

Having to pull timing out of a higher comp engine simply states that the burn is more efficient. It isn't a bad thing.

All this has started to make sense when I have heard tuners say with stock RB25DET's they tend to pull a little bit of timing and tend to richen it up a little if running on the limit around peak torque. Peak torque you will find occurs around where the engine is running at its highest VE (RPM of which most air is able to fill the cyclinders) hence at the peak torque the dynamic compression ratio is at its highest.

Do a bit of googling.. Definately worth the effort if you are building up a motor.

[JNR24]

Guys,

I have noticed in the RB25 Workshop manual it says to first Torque the head down to a small number... like 25-30pounds all round...

Then torque to 70-75 (100Nm) and then back to 0!!? then back to 101Nm??

Why?

Doesnt this create unnessacery stretch on the head bolts, and doesnt the gasket loose its "mojo" (tensile)

Do you guys tension the head a diffrent way?

Cheers,

Trev

[OVL-747]

joel

i am aware and i understand what ur saying

just that we cc'd it correctly and found a slight variant of what we have read elsewhere.

looks though we will use it as is , we figured that half a point of comp wont be to detremental.