Flat Top Pistons

[reverendzed]

OK I need some help!  Just discovered that the guys who rebuilt my motor didn't put flat top pistons in it, the whole thing is turning into a @!%$&%$# fight!

 

The guy is trying to tell me that it isn't possible to put flat tops in an L28 that it would 'blow the head off' (however we know that's not true)  but he failed to tell me of this 'problem' when I gave him the rundown on what I wanted.

 

(1) can anyone tell me if any of the L28's came standard with Flat tops?

(2) Does the head combination make a difference as to whether you can run flat top pistons?

(3) does anyone have a remedy for my HUGE disappointment?  I told the guy that I'd probably only get one go at doing the motor (cash flow!) and now I've been dudded, think I might just sell the whole thing! I feel like I can't get a win at the moment!

 

anyhow if anyone can help with the first 2 points I'd appreciate it.  Thanks in advance.

Rev.

[XRQTR]

Possibly with one of the closed chamber heads, but are you running a larger bore or thinner head gasket or anything else out of the ordinary??

 

Just did a quick run down on the calculator and all of them except the E31 10.21:1, come in under 10:1 static comp, using the standard crank and rods just with flat top pistons.

[C.A.R.]

I'd like to know what the current Static CR is first, Dave...

What head are you using? N42?

 

Best give me a call mate.

[Zedman240®]

In a previous zed I had a F54 block and P90 head with flat top pistons....the way I know is because I stripped and rebuilt that L28! The N42/F54 block and N42 head combo comes with dished pistons. If you use a N42 head with a flat top piston F54 block, CR ratio's are too much for pump fuel and avgas has to be used.

[reverendzed]

I guess what I'm trying to fathom is why the Engine Builder wouldn't highlight any percieved problems e.g F54/N42 combo before the engine was done, my thoughts are that they figured I'd never find out!  WRONG!!! :-\

[XRQTR]

Rev if you've been charged for ti then kindly ask for a refund of that portion of the bill, if they refuse then break there knee caps, I'm free at the moment if you need some help 

[XRQTR]

sorry hit quote instead of modify 

[C.A.R.]

I've just driven Rev's Zed, & there is nothing wrong with it!

Pulls like a train after 3500RPM...

[reverendzed]

Thanks Lurch, I just changed my undies, had a cup of tea and realised that if it's still pulling strong after 5500rpm it certainly has enough to keep me entertained.  Pretty awesome how through a club like ours we can help one another out, I appreciate it Lurch.

[Glen]

If its performing well now then nothing is lost but.....If your "A" plan was flattops and he couldnt do it he should have rang you and told you about plan "B" instead of going ahead and doing it. At least you both would have been on the same page.

 

I can certainly see why you would be disapointed and then the mind boggles as to what else was/wasnt done. If i were you id be sorting out your 5500rpm flatspot and getting your dizzy (can make big difference) matched aswell. Then throw it on the dyno as im sure you will be pleasanlty surprised.

 

BTW i will be running N42/F54 combo with flattops with the required headwork to make 10-1 comp.

[reverendzed]

yeah Glen, a bit dissapointed more in the integrity of the guy than performance.  When I mentioned 5500rpm it was more that's about where we had to throttle off because of the area we were driving, it still had plenty more to go in the RPM range which is great.  It's a little 'doughy' down low due to the cam but as soon as that baby hits 3-3500 RPM there's no holding her back!  Good luck with your engine build I'm sure it's going to be great.

[Toecutter]

Hi Dave,

 

Sorry to hear about that but if the cars driving well it should'nt matter. People should really be up front about these things. Theres alot of dodgy mechanics about.

 

I did'nt really get a chance to catch up properly with you at the last BBQ as I was all over the place but as I was hoping that I could chat to you about your experience and costs having this motor built.

 

I look forward to talking to you in the new year, hopefully before the Threadbo trip.

 

Cheers,

Sulio

[Toecutter]

This might be a bit of consolation re your flat tops on your N42 head...

 

As for your project, there is no need to switch over to the N-47 from the N-42. Any gains that you might realize from that swap would be to minute to worry about. Though you do have a much bigger issue at hand, detonation! An L-28 with Flat top pistons and the open chamber N-42 head, (or Z N-47 for that matter). This combination is well known for not being pump gas friendly even at a measly 9.5:1 comp ratio, they WILL detonate even with premium pump gas and a mild cam. I’ve witnessed this first hand on more than a few engines that others built and have also read about from LOTS of other people as well. Yes, the ignition timing can be backed down to help subdue the audible knock, but by doing that you are giving up LOTS of power by retarding your ignition timing. I would much rather loose a whole point of compression using amore ideal head, (P-79 or P-90), and be able to run ideal ignition timing. I.e. sacrifice maybe 3 % HP due to loss of compression ratio to regain 10-20% HP with ideal ignition timing. Don’t rip over dollar to pick up a dime. 10 degrees of ignition timing can be worth more power than even 2 points of compression.

If it were me, I would ditch the N-42 and N-47 for either a P-79 or P-90 head as either of these two heads complement the flat top pistons MUCH better and will allow you to run ideal ignition timing on pump gas allowing your engine to run a max effort.

 

I could go On and ON in this post, (as most of you already know), so instead of repeating myself here, I’ll refer you to a couple of threads that cover 6 cyl L-series heads in great detail, covering all the nuances of each of the L-series 6 cylinder heads and has been referred to as the most informative write up on L-series heads thus far…

http://forums.hybridz.org/showthread.php?t=104420

 

 

And this thread covers detonation with the L-series and squish chambers. (just ignore the little tiff about someone’s ¼ mile times discrepancy)…

 

http://forums.hybridz.org/showthread.php?t=105653

 

thread here...

 

http://forums.hybridz.org/showthread.php?t=108398&page=2

 

Sulio

[C.A.R.]

As I can't be bothered reading those threads at the minute, I'll say this;

The shape of the combustion chamber has a LOT to do with detonation - the N42/7 heads have a TERRIBLE shape & thus contribute significantly to causing pre-ignition.

 

Also the P90 for example, has massively deep chambers - designed for the turbo application.

But it does have a nicely designed chamber shape (for a factory head).

HOWEVER, because of the deeper chamber this effects port flow, specifically the short turn radius before the valve. It can be corrected but it needs some work.

Plus you have to run different valves, retainers...

 

If I was doing an all out L31/32 I'd start with a N42/N47 casting, Alum. weld the chambers up & recut a new chamber into the head to promote a better burn & squish.

 

In any case, if your building a L28 you'd be CC'ing everything, then working out the static CR from there.

THEN modifying the head chamber from to achieve a suitable CR.

[Toecutter]

Well Lurch seeing you did'nt read the thread you've pretty much summed up much of the discussion in those threads. It's interesting to read about how the shape of that squish area can affect detonation. Not that I could understand all of it but there seems to be a general consensus that a penut shaped squish area with careful carving in the right areas provides the best performance. Most of this stuff is over the top of my head but this pic below shows what the aim would be for a head with big dollars spent on it.

 

 

I'll just stick to my budget build thank you very much! 

 

Cheers,

Sulio

 

[C.A.R.]

Apart from the poor quality pics that looks pretty good to my eyes.

 

[MickyG]

Reverendzed

 

Sorry to read of your issues, although it sounds as if the resulting engine is OK even if not what you were expecting.  Given my search for a trustworthy & recommended engine builder for an L26 in Melbourne, are you willing to share the name of your builder so I can try to avoid similar issues?  (If you're not comfortable to name & shame publicly, would you PM me details?)

 

Thx

 

Mick

[kalium]

If you are after more compression, get a late model E88 head. They seem to have the same modern combustion chamber type as the P90....just much smaller.

 

Ray

[modular9]

interesting. I was after a flat topped n42/f54 combo until I thought about the following

1. crud petrol becoming more plentiful as the good stuff goes bye bye

2. Future proofing. EFI+turbo is in the future of my car.

3. Shave the head down to up the CR without destroying the bottom end if i wanted to go back to something less street/fuel friendly. ( got a spare head which is stock )

 

So I went to the builder and told him dished please. He was about to ring me anyway about the CR ratio anyway ( Excellent engine builder : Torqueteam in mansfield QLD ) so it was all good anyway.

 

So Rev i dont know how you use your car ( mine is a daily with some mods ) but if you need it to sit in traffic for 1 - 2 hours every morning I'd be happy with the CR + dished pistons.