dome top pistons - how to order?

[inline6]

Did a sonic test on my block and we won't be able to go to 89 mm as I had hoped. Based on the numbers, I'm looking at 88.5 mm max. That means the compression ratio is going to be too low for the cam (~ 10 to 1). So, I need to put a dome on the pistons.

 

So, how do I do that? I can easily calculate how much of a dome I need (in cc's)... But, how do I specify such a thing? I'd like to go with JE...

 

Have no clue how to proceed. I'm guessing that they have several L series pistons in their database, but I really have no idea how to specify exactly the contour that I need with valve reliefs, etc. Shooting for 11:1 compression ratio... Anyone know how I should proceed? How do I specify what I need to JE?

 

Garrett

[duragg]

Why can't you shave the head a teence?

 

I just bought 87mm ITM flat-tops which are vanilla.

 

Somebody like ROss or JE might be able to tell you.

[z-ya]

First choose the CR based on what fuel you will be running. Pump (93) gas stay with 10:1 or lower. This is especially true with an E88.

 

If you need to raise the CR, cut the head and or use a thinner gasket. Then shim the cam towers accordingly. Making custom pistons for an 88.5mm bore and valve reliefs for an E88 will be difficult. Even after making them you will need to check valve to piston clearance and may have to machine the valve reliefs more. You have to account for rod stretch at high RPMs when checking both valve to piston and piston to head clearance.

[inline6]

First choose the CR based on what fuel you will be running. Pump (93) gas stay with 10:1 or lower. This is especially true with an E88.

 

If you need to raise the CR, cut the head and or use a thinner gasket. Then shim the cam towers accordingly. Making custom pistons for an 88.5mm bore and valve reliefs for an E88 will be difficult. Even after making them you will need to check valve to piston clearance and may have to machine the valve reliefs more. You have to account for rod stretch at high RPMs when checking both valve to piston and piston to head clearance.

 

 

Hi Pete,

 

What you say makes a lot of sense... I was talking with Dave Rebello yesterday and he we saying pretty much the same thing.

 

But, I was running a F54 flat top block with the head previously (something like about 10.1:1, right?), with a Euro distributor - the Euro distributor advance spring(s) and the vacuum advance (in combination with a Crane Hi 6 Capacity Discharge ignition) with 17 degrees initial, and 36 total, and I had no detonation on the 93 octane we have around here. That was with a stock cam...

 

Now I have this monster cam I'm about to use (HUGE overlap)... which is the same one Zredbaron is using. I dunno. Seems like I should be able to run 11:1, but I'd like to have some quench. Rough measure of the combustion chamber says that .080" off the head surface still won't give me any quench (squish) to speak of, yet the compression ratio looks like it goes up to near 11.5:1 at that point. I'm thinking 11.5:1 with no quench is going to be trouble. Ughhh. Why am I finding out now that the E88 is not the best head to use?

 

Because of this, I am toying with the idea of creating a mold of the cyl head combustion chamber and seeing if JE can make something from it.

 

Welding the head is another option, but my engine builder doesn't want to send the head off for welding... According to him, there is all kinds of badness that can happen: valve seats loosening, guides loosening, head shrinking, warping in all kinds of directions...

 

If I had a job number for a JE piston that would give me some quench with an E88 head, I'd sure be happier.

 

I'll be using the Kameari chain tensioner, so I shouldn't need to put shims under the towers. But that is a minor point.

 

Rod stretch... I was planning to run .024" piston to deck. Yeah. That is what reading the forums here and having no real world experience of my own with building these engines will do for you. I'll be running about 7700 RPM max.

 

Gotta make some decisions soon.

 

G

[30 ounce]

I welded the chambers in my E-88 to raise the compression to 11.5:1 which is what Isky recomended for my cam. But we did that prior to installing steel valve seats for the larger valves. If you haven't done that yet you may want to as the brass ones are probably shot by now. You need to find a welder who will take his time and jump from one cylinder to another so as to not warp the head. Welding the chambers gives you lots of options for combustion chamber shape ie; fast burn, high quench design. My engine builder was all over it when I suggested welding the chambers as he was not impressed with the stock shape. I'm using 89mm JE pistons from Rebello and unshrouding the valves to the 89mm bore helped a lot with he flow. I think you are using a much bigger cam than me (490 lift 290 duration) so I think you'll want to be around 11:1. I'm at 5280 elevation so Isky said I could get away with an extra .5 piont.

[SKiddell]

I have got a well skimmed E88 to run at around 11:5 to 1 static but thats on UK fuel (99 RON) I accidentally ran it on 95 RON and it took 2 pistons out in a heart beat, cut through the ring lands like a blow torch.

 

That E88 Head was skimmed down to 106mm thickness, chambers were down to around 35cc's with an 86mm bore and a 1mm felpro gasket(can't remember exactly it was a while ago)

 

A lot depends on what the dynamic compression ends up (static compression combined with the cam profile etc)

 

I have seen a "theoretical" high static compression motor that has run well on pump fuel due to the cam profile EG Schneider stage IV (which has bugger all lift on overlap), conversly I ran a 320 duration cam that had over 5mm of overlap lift which was a pig.

 

Just my £0.0123693488 worth

Edited June 17, 2011 by SKiddell

[z-ya]

I have a set of Arias L24 pistons that have a dome for the E88 valve configurationn. They may be able to make you an 88.5mm set with your pin height. But, you will still need to check all the clearances and potentially have to do additional machining to the piston domes to clear the valves and head.

 

The other option is to have flat tops made, and switch to a P series head. You can shave and shim the P series to get the CR you want. You still may still need to machine reliefs in the flat tops depending on how much you shave the head and the lift you are running.

[z-ya]

Duplicate

Edited June 18, 2011 by z-ya

[inline6]

 

I have seen a "theoretical" high static compression motor that has run well on pump fuel due to the cam profile EG Schneider stage IV (which has bugger all lift on overlap), conversly I ran a 320 duration cam that had over 5mm of overlap lift which was a pig.

 

Just my £0.0123693488 worth

 

I don't know how to calculate dynamic compression, if that is what you call it. But my cam has more aggressive specs than the Schneider stage IV:

 

Intake

Seat duration 320 degrees

.050" duration 290 degrees

Valve lift with zero lash .565"

Hot valve lash .015"

Net valve lift .550"

 

Exhaust

Seat duration 315 degrees

.050" duration 274.8 degrees

Valve lift with zero lash = .565"

Hot lash = .015"

Net valve lift =.550"

 

I've got three options in mind for how to proceed now...

 

1. Send the head off to have the combustion chambers welded up. I guess I'd put modeling clay in one of the chambers and sculpt it to fit (represent the finished chamber) - so they can see where to weld. If I do this twice, I can calculate the finished chamber cc volume (immerse the finished piece in water and measure the volume), which will allow me to calculate final compression ratio before getting the work done. This would be nice - so as to confirm that I am going to land at the 11:1 I am shooting for.

 

2. Tell Dave Rebello I need domed pistons - something with a 12:1 compression ratio with my E88 with 45.6 cc chambers... specify the pin height I need, and diameter... And then when I get them, machine them as necessary to fit my chambers.

 

3. Mill the head a bunch - order flat top pistons (with adequate valve reliefs) and see if it runs worth a damn on 93 octane with this radical cam. This last option will sacrifice HP (without quench) I'm fairly certain. And, it may detonate, requiring the use of racing gas. Not cool because that stuff is expensive.

[Leon]

That cam doesn't seem street friendly at all. It will have a rough idle and develop torque higher in the powerband, making it a peakier, higher strung engine when compared to a somewhat stock L-series. To me, it seems more like a race-track only cam. Unless you plan to race this car and built the engine to sustain high rpm running, I don't see a reason to go with a high compression ratio and wild cam.

 

When people refer to "dynamic compression" what they're really referring to is the intake valve closing event. The later the intake valve closes, the less cylinder pressure there is during low speed operation. With a later intake valve closing point, the cylinders will fill best at a higher rpm so cylinder pressure will be at a maximum at higher engine speeds. The idea is that by moving maximum cylinder pressures (also decreasing cyl. pressure at low rpm) to a higher rpm, the engine will be less likely to detonate because there is less time for the heat transfer that precludes detonation to occur.

[z-ya]

To be honest, I would go with a P90. It has the chamber shape you want for flat tops, and milling/shimming are relatively inexpensive to do. The cost will be the port work that needs to be done on the P90. But that may actually cot less than welding and shaping the chambers of your E88. And, you could probably sell that E88 to someone looking to build a hot street engine. Plus you will save on pistons and piston machine work.

 

What is the stroke you will be running?

[inline6]

To be honest, I would go with a P90. It has the chamber shape you want for flat tops, and milling/shimming are relatively inexpensive to do. The cost will be the port work that needs to be done on the P90. But that may actually cot less than welding and shaping the chambers of your E88. And, you could probably sell that E88 to someone looking to build a hot street engine. Plus you will save on pistons and piston machine work.

 

What is the stroke you will be running?

 

 

The stroke is 3.165 (80.39 mm). I was shooting for 81 mm using the stock crank (79 mm), but this is the most the crank grinder could get out of it. I am using Toyota Celica rods... They are 5.430 (measured) center to center, which is about 8 mm longer than stock. Cam redline is 7700 RPM with the springs that came with it. Stock flat tops wouldn't have taken those revs... and of course, I will be using the Toyota rods. So, custom pistons are a requirement now.

 

The E88 head has had the seats replaced with hardened ones, intake seat and valve is now 280z size. I just did a ton of port work and combustion chamber work, put in new maganese bronze guides, had them sized to fit and refaced the Manley valves (tuliped ones sourced from Nissan Comp back in the day). If horsepower is in the heads on these cars (and the money), I really hate to start over with another head.

 

I talked to my engine builder about the three options I mentioned in the post above. He suggested another option... Ordering flat-top pistons that will pop above the deck by .095".

 

I know of no one who has done this. But, he makes some good arguements. Looking at my combustion chamber, he says that he could stick the head on his mill table, and then remove material from each chamber... But, he says we'd only have to remove a little bit from say, 11:00 to 1:00 (on driver side of the chamber), and cut back the edge of the chamber a bit along the 5:00 to 7:00, or 4:00 to 8:00 locations (passenger side of head) to make room for the piston. The other locations around the chamber are already cut back enough for the 88.5 mm piston to come up into the chamber - because of the unshrouding work I have done.

 

If you look at this pic, you can see the chambers as they are now.

 

 

Note the little shelf at 12:00. That shelf is about .080" stepped down from the head gasket surface. Cutting another .080" off of the head (.017" has been cut so far from stock) will give me a flat area for quench that will be about the size of that little shelf. But, add flat top pistons to this mod, and I will probably be somewhere between 11.5:1 and 12:1 based on my calculations.

 

With the pistons in hand, we could mill a small dish as necessary under the exhaust valve area to fine tune the compression - bring it down to 11:1.

 

Another benefit is that the chambers would be modified identically across the six where material is removed instead of any casting irregularity that I might have now.

 

I'm chewing on it.

Edited June 18, 2011 by inline6

[inline6]

That cam doesn't seem street friendly at all. It will have a rough idle and develop torque higher in the powerband, making it a peakier, higher strung engine when compared to a somewhat stock L-series. To me, it seems more like a race-track only cam. Unless you plan to race this car and built the engine to sustain high rpm running, I don't see a reason to go with a high compression ratio and wild cam.

 

This car has only been driven to and from and during autocrosses and track day events for the last 4 or 5 years (when running). I'd like to be able to fire it up and drive it down the street if I want without getting tickets... but, it by no means is driven on the street with any regularity. I have an M3, an S2000 and a C6 Corvette Z06 which are all bone stock that I drive around for transportation (yeah - no wife).

Edited June 18, 2011 by inline6

[madkaw]

I don't have any ideas for you, but I thought it would be an oppurtune time to throw in a picture of my EARLY E-88 compared to your late E-88.

It's just a good chance to show the difference in design between the e-88s with similiar work done,i.e biggger valves and such,

'As you can see the shelf is not there at 12 oclock. This head was only shaved .010

My chambers are around 39cc, but compression reduced with valve reliefs on the bores.

So far no detonation problems with an estimated 10 to 1 and a stage 2

[Leon]

This car has only been driven to and from and during autocrosses and track day events for the last 4 or 5 years (when running). I'd like to be able to fire it up and drive it down the street if I want without getting tickets... but, it by no means is driven on the street with any regularity. I have an M3, an S2000 and a C6 Corvette Z06 which are all bone stock that I drive around for transportation (yeah - no wife).

 

You lucky guy! I'm looking to get a new DD within the next 6 months or so, and all three of those are on my list. I've been craving the S2000 for a long time, but the M is tempting (I'm itching to drive an S4 as well).

 

Thread derailed, haha!

[inline6]

I don't have any ideas for you, but I thought it would be an oppurtune time to throw in a picture of my EARLY E-88 compared to your late E-88.

It's just a good chance to show the difference in design between the e-88s with similiar work done,i.e biggger valves and such,

'As you can see the shelf is not there at 12 oclock. This head was only shaved .010

My chambers are around 39cc, but compression reduced with valve reliefs on the bores.

So far no detonation problems with an estimated 10 to 1 and a stage 2

 

I WISH I had those chambers...

 

G

[madkaw]

I will add that a member on CZCC (steve911tt) is dealing with issues with detonation using the later e-88 head. He is limited to 30 degrees total advance. I know it's not what you want to hear , but information is always good. Of course everyones set-up is a bit different, but I think the chamber for the late 88's need the most work.

[30 ounce]

My E88 chambers look a lot like BRAAP's pictures here of a welded N42. Mine are more heart shaped (BRAAP has a flat side by the spark plug) and more unshrouded by the valves (89mm bores). They ended up being 44cc's which gave me 11.5:1 compression. I am able to run 33 degrees advance with my 490/290 cam and 93 octane fuel. Any Z head can be made to work well and the E88 is a prime choice to weld the chambers and make a better combustion chamber than any of the Z's came with. It really wasn't that expensive. Less than custom domed pistons to be sure.

[inline6]

It really wasn't that expensive. Less than custom domed pistons to be sure.

 

Do you recall the name of the place that did the welding work for you? Pistons are anything from ~$850 from Rebello to $1200 or $1300 direct from JE. If I send it out for welding, I'm thinking new guides and seats all around, in addition to the welding, plus head gasket resurfacing and combustion chamber shaping. Most of that my engine builder could do...

 

I'd like to estimate these costs vs. doing a P90 from scratch I guess. My engine builder did one of those recently, and he didn't care for the shorter valves - which put the exhaust port turn even sharper... Plus, he said something about not being able to get good quality valves for that head. He ended up having to get a custom set I believe.

 

And then, there is the option of a welded N42...

Edited June 20, 2011 by inline6

[30 ounce]

Bowers Racing in Fort Collins Colorado did my head. He sent it out to have the chambers welded but he reshaped the combustion chambers, installed steel valve seats with larger valves, ported intake & exhaust, ordered the cam & springs, trued the top and bottom and put it all together for $1500. This was when my motor was a 2.6 liter. About a year later I decided I wanted a 3.0 liter so my cousin & myself took it all apart redid everything for the 3.0: unshrouded the valves improved the exhaust ports & rechecked the flow rates to make sure we didn't ruin it.