Dished Piston, Open Head vs. Flat piston, Closed Head?

[Xnke]

I'm looking for a cylinder head for my 3.0l, long rod, street motor. I have an open chamber E88 head here, and can get a P79 head for relatively cheap. I have a ridiculously tight budget. I also have a good amount of time on my hands. Power goals are modest at 200HP.

 

Anyway, My dilemma is thus: to save on gas costs, and still make some half decent N/A power, I chose ~9:1 compression. My planned engine:

 

LD block, bored to 87mm, sleeved if needed. (I have sleeves and boring is cheap 'round here)

150mm 4G63 rods

L28 crank ground out to 84mm

Z22S pistons

Delta Cams .490/280' bumpstick

 

Thus, I have cast piston with a ~9cc dish. the dish kills the quench properties of the P series heads, and has a CR of 9.3:1 with an E88 head. I want to run 89 octane, because of availability, with the option to run 93. I don't want to be trapped on 93 octane.

 

Before someone comes up and starts a cylinder head war, Don't. I've searched all over these forums, and can't find a good answer. Usually, I just find where a poster started a thread, and folks fought over it.

 

Is it worth it to get custom flat-tops and run a P-series head from a performance vs price standpoint?

 

Is the open chamber head+dished piston combination drivable on 89 octane at a CR of just over 9:1?

 

Keep in mind I'm not going to be boosting this engine. I plan to run twin SU's until I can afford a good set of triples, probably Webers or OER's.

 

A clean discussion on the performance difference between the E-88 open chamber head (Apparently, no one wants this head for performance, but I don't see much difference from the N42 except valve size) And the P-79 closed-chamber head FROM A COMBUSTION CHAMBER STANDPOINT is what is desired. Porting is to be assumed, although nothing really nutty. I'd like to avoid welding on the head.

 

Hopefully, this thread doesn't end up being dumped in the tool shed due to a silly argument over the "Q word".

[z-ya]

All that machining to use the LD block is going to cost you. And all that crank work is going to cost a lot too. After all of this work, what you end up with will not be any better than a well built L28.

 

Since your goals are only 200HP (at the crank I am assuming), I would suggest the following configuration:

 

L28 block bored 1mm

ITM Flat top L28 pistons

Stock L28 Crank

Stock L28 rods

Felpro head gasket (1mm)

Mild street cam

P90 or P79 head

Mild port work (clean up)

Port match intake manifold to head

Header

 

This should yield an 8.9:1 CR, which with a P series head should allow you to run on 89 octane with a modest tune.

 

My concern is with all that machine work and part mix and matching. What will be the reliability of the end product? Yea, it will be a great conversation piece, but you can build rock solid L28 using the configuration above that will perform as well or better. Plus you will save a lot of $ in the end.

 

Just my opinion...

 

 

Pete

[rsicard]

I'm looking for a cylinder head for my 3.0l, long rod, street motor. I have an open chamber E88 head here, and can get a P79 head for relatively cheap. I have a ridiculously tight budget. I also have a good amount of time on my hands. Power goals are modest at 200HP.

 

Anyway, My dilemma is thus: to save on gas costs, and still make some half decent N/A power, I chose ~9:1 compression. My planned engine:

 

LD block, bored to 87mm, sleeved if needed. (I have sleeves and boring is cheap 'round here)

150mm 4G63 rods

L28 crank ground out to 84mm

Z22S pistons

Delta Cams .490/280' bumpstick

 

 

 

Thus, I have cast piston with a ~9cc dish. the dish kills the quench properties of the P series heads, and has a CR of 9.3:1 with an E88 head. I want to run 89 octane, because of availability, with the option to run 93. I don't want to be trapped on 93 octane.

 

Before someone comes up and starts a cylinder head war, Don't. I've searched all over these forums, and can't find a good answer. Usually, I just find where a poster started a thread, and folks fought over it.

 

Is it worth it to get custom flat-tops and run a P-series head from a performance vs price standpoint?

 

Is the open chamber head+dished piston combination drivable on 89 octane at a CR of just over 9:1?

 

Keep in mind I'm not going to be boosting this engine. I plan to run twin SU's until I can afford a good set of triples, probably Webers or OER's.

 

A clean discussion on the performance difference between the E-88 open chamber head (Apparently, no one wants this head for performance, but I don't see much difference from the N42 except valve size) And the P-79 closed-chamber head FROM A COMBUSTION CHAMBER STANDPOINT is what is desired. Porting is to be assumed, although nothing really nutty. I'd like to avoid welding on the head.

 

Hopefully, this thread doesn't end up being dumped in the tool shed due to a silly argument over the "Q word".

 

Xnke: From a combustion standpoint the closed-chamber is more desireable. If you are to use the 9cc dish pistons then do so but suggest that you have them thermal barrier coated on top. Use www. kb-silvolite.com to determine compression ratio. At 9.1:1 you should still be able to run 87 octane. With the pistons ceramic coated, the combustion chambers thermal barrier coated, valve faces thermal barrier coated and exhaust ports thermal barrier coated you may well get away with a higher compression ratio and still run 87 octane (cheapest) without detonation. I have done this very thing to a Chev 454 bored .030" and stroked 0.75" gone from 118 cc to 110cc aluminum heads and STILL run 87 octane just fine. The above suggestions are on the order of what David Vizard (an engine guru) suggests. He recommends FLAT TOP pistons for flame travel in the combustion chamber. Assemble the short block less piston rings and see how much above or below the deck the top of the pistons are. Zero deck to slightly above is optimum.

[OlderThanMe]

Xkne,

If your objective is only 200hp, why do all of the custom work? You could get that HP level on an L24 with a stock bottom end and somewhat extensive head work on your head of choice.

 

L motors don't make power with a built bottom end, they need head work and a good flowing intake like Webers or SUs with a free flowing filter.

They are handicapped from the low VE of the stock ports.

 

In my opinion the only reason to upgrade the bottom end is when you have reached the extreme limits of a fully built race head and your pistons are being stretched close to their yield stress.

I have seen guys build a 3.1 stroker and then go to the dyno and make under 150hp. Then again back in the racing days an L24 made over 250hp...

 

My L26 had a 9.2:1 CR with an open E88 head and I ran 89 octane all day and it NEVER pinged once. I was making in the neighborhood of 130hp.

I have seen an L28 at ~11.25:1 CR running on 93 octane and it was a beast of an engine. The car was driven on the highways too and had relatively good gas mileage.

 

I'm not doubting your drive to innovate, just your ($)$$$/hp ratio for 200hp.

[Xnke]

Certainly, I can see the dollars/HP point. The 200HP that I want a starting point at the wheels, and I don't see many N/A L28s OR L31s doing that. The crank work isn't that big of a deal, the local shop isn't going to charge me any more than if it were a simple resize to clean up a scored bearing. The reason for using the LD block is to be different, and for the long rod reasoning. Not because long rods make more power, but because it provides longevity. Notice how all the newer engines have much longer rods than the L28? I don't know why, but I do know that by geometric reasoning, it puts less side load on the pistons. And the Mitsu rods and bearings are inexpensive, because of popularity.

 

You are correct, it is quite a bit of money. And, I'm usually broke. But I don't see it costing much more than rebuilding an L28, considering that the parts yards around here are completely devoid of anything imported and older than 1990. I go looking around in the local (and some not so local) junkyards, and there are never any L28s, or Z's at all, around here. (Bowling Green is home of the Corvette, and all the parts yards keep around is GM and sometimes a few Ford parts cars)

 

Here's the parts/price breakdown so far, mostly discards from HybridZ members.

 

L20B timing cover-Gift from GF

LD28 block-75$(can likely get an L28 block for a similar price, dunno yet.)

L28 crank-15$

Delta cams regrind-82$

Mitsu 4G63 rods-14$ for 6

 

Price to bore block-130$

Price to regrind crank-168$

Price to sleeve block with custom sleeves-free, as long as I provide sleeves. I have already cast the blanks out of a dead KA24 block, will machine to fit when school starts back. Total cost to me-about 18 hours of time.

 

Main bearings-54$

Rod bearings-51$

Gasket set-74$

Various assembly necessities-200$

 

Total cost:864$

 

That's the projected build cost, minus pistons. What would a similar L28 build cost, on average?

 

***EDIT***

 

I have decided that the regular L28 block and crank will work fine, and save a ton of money. Hopefully the member here selling me the block will let me sub out the L28 block he's got instead. If I continue to use the Z22S piston, then I can use the L24 rods that I have already, and slap a ported MN47 head on top for 9.7:1, or use my E88 for 8.9:1 compression.

[Daeron]

Five easy steps to building an L-series engine.

 

 

1. Build your cylinder head, whichever casting you choose and whatever work is done to it, and make sure you have enough valve and valve spring.

 

2. Select your pistons to be an appropriate complement to your cylinder head for combustion chamber shape and size (read: quench and compression.)

 

3. Select a camshaft based on your cylinder head, and compression/combustion decisions above.

 

4. Design engine control, fuel, and ignition appropriate to power goals

 

5. Assemble bottom end to match all of the above.

[Xnke]

Ok. So, lesse what I got to work with:

 

E88 cylinder head, pressure tested. Needs bigger valves, porting.

4G63 rods

L24 rods

L24 crank

L28 crank

L24 P30 block

L28 N42 block (87mm bore)

E88 carb intake manifold

'72 SU's

 

Things I can aquire and/or fabricate:

 

P79 cylinder head

L28 rods

round port header

twin throttle bodies + megasquirt, after the thing is running on carbs. (This looks pretty damn cool to me, from the pictures that Z-ya posted. Probably the final ieteration.)

 

So, to sum up the thread:

 

I would get better performance AND a more compatable (from an octane standpoint) from an L28 with flat-top pistons and a P79 head.

 

It would be possible to run the E88 and Z22S piston/L24 rod combination, but ultimately would be less desirable.

 

Is this the general consensus?