Jump to content
HybridZ
fear_me

pistion/deck height misinformation

Recommended Posts

alright, i have fond information on here that i feel is a little bit misleading.

 

You will need .015" deck height

 

this means that the piston will be above the deck 0.15", correct?

I was just talking to the tech line at Ross and i was told that you do not want to be above the deck, you want to be even with it. Only if the head was couter bored, meaning it hade a 87mm cicle cut into it, then we would go above the deck.

 

for those that don't know i was looking to do:

f54 block =207.87 height

f54block = 87mm bore

vo7 crank =83mm stroke

l24rods = 133mm length

piston = 34mm pin height

= 8cc dish

this equals 8.5 to 1 comp.

 

Now the gentleman that i talked to said the pin height should be 33.38 and use a flat top piston with a 3cc valve relive cut into them.

 

So my question is why does the piston need to stick above the block? and why does the guy that deals with pistons for a living say different?

 

~Andrew

Share this post


Link to post
Share on other sites

The guy at Ross is apparently failing to factor in the depth of the head gasket. I can only assume that he was wrong because of the existence of VERY thin head gaskets for V8s. You don't find those super thin gaskets on L6's, so we have our pistons pop up over the deck to get the piston closer to the head (which is a good thing for quench).

Share this post


Link to post
Share on other sites

With my setup it would have put my piston at .063mm above and i told him that my gasket was 1.27mm he did say wow that was a thick gasket but still that it should never go above the deck.

So one of the reason that this is ok is because we have such a thick head gasket and it will help in quench.

 

I also told him this would be a turbo and was asking why i was staying with such a low comp... i was told the guys now a days are running around 9 to 1 with turbo!

but they only wanted 577 for the pistons, 158 for the rings, and 60 some for the pins. he told me no need to go with special pins cause my 15psi is not that extreme....

should i ask for someone else, or try a different company?

 

~Andrew

Share this post


Link to post
Share on other sites

Your source at Ross, being a sales rep/customer service rep, etc, for a custom piston manufacture, should know better than that. jmortensen summed it up rather well. If the Ross rep you are dealing with still insists such a thing is wrong, definitely ask for another rep/engineer that knows what he/she is talking about. Piston pop-up is fine so long as there are no mechanical compromises, i.e. rings getting to close to the deck etc.

 

Every N/A L-28 built after, (I think it was 8 of 1980 or there abouts, someone else here will have the exact manufacture date the change was made), any how, the engines with the P-79 head and flat top pistons, the pistons pop up OUT of the bore between .020” and .025” from the factory. So long as the head gasket is thick enough that there is approx .016” clearance between the cylinder head and the piston, all is well and in fact, quite good.

 

Here is an assembled short block with the OE flat top pistons, OE rods in an OE block, and the block was NOT decked. The piston pops up out of the bore .023"

 

DSC_4360.1Large.jpg

Share this post


Link to post
Share on other sites

sorry i had wrong information in my last post, my deck hieght will be .63mm, with a head gasket of 1.27mm this will leave me .64mm or .025" which if it is good to have .015 then i have a little bit of a breathing room it looks like.

I will call wiesco and try to talk to someone else from there and see what they say.

 

Thanks for the help

 

~Andrew

Share this post


Link to post
Share on other sites

from that post i got saw this from braap:

As Bryan eluded to, when you are building your engine, you either want squish, and all of it, or if you can’t acquire squish, you need more than .100†clearance between the top of the pistons and the chamber of the head. Between .050†and 100†is a nasty detonation zone. Between 050†and the .022†clearance that Bryan is talking about and the anti detonation tendencies of squish are realized and the benefits of added static compression can be realized.

 

Since i will be at .025" i am good, closer would be better but i am good.

 

Thanks guys, maybe the title should be change to ross guy not knowing what he was talking about :)

 

~Andrew

Share this post


Link to post
Share on other sites

Hi everybody.

I decided to write here because I'm building my 240Z and I have one question about the engine.

I have N42 block and P90 head. I'm going to use forged pistons and LD28 rods.

Megasquirt, turbo and intercooler is coming too.

But anyway... This is my answer:

What is the ideal piston to head clearance with boosted engine?

I'm going to run 1,5-2,0bar boost.

 

This is my first post to here by the way. :-)

Share this post


Link to post
Share on other sites

Raami, there are numerous posts regarding engine configuration, deck height, etc., etc. First thing you want to do is a lot of searching and reading. You'll want to investigate much more before coming to a choice of components and a final build plan. Plan to invest several hours reading and pen down lots of notes to yourself. Once you've done this your questions will become more specific and the assistance will be there for you. Your ideal clearance was mentioned above, between .016 and .025 will provide ample quench to reduce detonation.

Share this post


Link to post
Share on other sites

I have done the searching alot. I haven't join here yesterday. :-)

I was just curious to know how much would it be in turbo-engine.

I was going to use 0,80mm clearance but now I think would that be too much.

 

 

The CR I'm going to use is 8,8:1.

Share this post


Link to post
Share on other sites

Raami,

Umm... 140mm LD28 rods are WAY too long to use with an L24 or L28 crankshaft.

Even using a SUPER SMALL piston pin height of 32mm, LD28 rods, and L28 crankshaft the piston will protrude 3.65mm above the deck.

 

Unless you use either the LD28 block or an L20A crankshaft then I suggest not using LD28 rods or the engine will not work

Share this post


Link to post
Share on other sites

Why wouldn't it work with the LD28 rods?

Yes I do know that the piston pin height has to be small but so what?

The wisecos I'm going to use can be machined even to 26mm piston pin height and it won't become too weak.

I do know that the LD28 rods top is way too big but it will be machined to match with the pistons.

Or is there something bad if the rod/stroke ratio is going to be 1,77?

 

 

This forum is really good to get information because here in Finland we don't have much L-engine builders. :-)

Share this post


Link to post
Share on other sites

If your pin height can go down to 26mm, then you're golden.

 

Dunno if you know about this or not, but this is the perfect tool:

 

http://www.ozdat.com/ozdatonline/enginedesign/

 

A 28.35mm pin height would put you at 0 deck.

 

Though obviously those numbers should be checked in the real world, as they're real close but not right on.

Share this post


Link to post
Share on other sites
Why wouldn't it work with the LD28 rods?

Yes I do know that the piston pin height has to be small but so what?

The wisecos I'm going to use can be machined even to 26mm piston pin height and it won't become too weak.

I do know that the LD28 rods top is way too big but it will be machined to match with the pistons.

Or is there something bad if the rod/stroke ratio is going to be 1,77?

 

 

This forum is really good to get information because here in Finland we don't have much L-engine builders. :-)

 

 

When you say 1.5-2.0 BAR (we use a decimal in the states rather than a comma) do you mean absolute or relative?

If you mean absolute then why not use a stock turbo engine?

If relative then your ring lands won't be nearly thick enough to be durable with only a 26mm pin height and you can expect to pop those ring lands the first time you detonate.

The lowest OEM Nissan pin height that I have heard of is 32mm in the VH45 engine and that is pushing it.

I just don't want you to build an engine that you invest a lot of money in and something goes wrong with it.

 

You can build it like however you want but I, and others too, would most likely suggest that you keep strength in the pistons rather than going for a slightly better rod/stroke ratio.

Share this post


Link to post
Share on other sites

Sorry for that. Let's just say that max boost I'm going to use is 1,8bar. =)

 

The only think that I'm worried about is that would the LD28 rod hit the bottom of the cylinder wall, when I use L28 crank in L28 block?

 

My friend has those rods but I haven't test it yet.

 

The pistons I'm going to use is wiseco and those are that type that you have to machine the right pin height to them.

 

The headgasket is also something that I don't have yet. I'm thinking of buying kameari metalheadgasket because my friend has got datsun A-series engine and needs gasket too. :-)

Share this post


Link to post
Share on other sites
i always thought anywhere between 0.030 - 0.040 was good for quench, and you guys are going closer to the .015's?

 

isn't that too close for comfort in the event (highly likely) of metal expansion, i.e. - rod stretch and slight piston rock?

 

 

That's what I was thinking too.

I've read that the ideal would be 0.030-0.035 but all I would like to know is that does that include turbo engine too?

I think I'll go with that 0.030.

Share this post


Link to post
Share on other sites

I've got the LD28-rods and they will work just fine after the machining is done.

I think they are strong enough because my friend has LD28-engine and it has "only" 350hp. ;)

And yes.. that is still a diesel-engine. :-)

 

The pin height that I'm going to use is about 28.9mm.

But that might change little because I don't have headgasket yet so I don't know its thickness.

Share this post


Link to post
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.


×
×
  • Create New...