1981 EK Engine Speacs (EK 1751)

[redr2]

I just want to make sure the specs for this motor on the site are accurate as their appears to be some discrepancies btw the Prelude/Accord and the years.

1. As far as I can tell the 1981 EK engine is listed as having: 8.0 : 1 Compression ???
2. Anyone know if this is raised slightly with the addition of the 1981 EL Head ??? I suspect that it may be?

3. I have not yet pulled the CVCC head off the motor....but I believe the pistons are flat as opposed to dished or domed ??? I assume this as my 1981 EL motor are flat as a board.

[2ndGenGuy]

My 1981 Accord Factory Service Manual lists the compression as 8.6:1

And as you can see here, the pistons are slightly dished.



The EL head is rumored to bump compression. But I really have no way of confirming...

[fullthrottle_man]

2ndGenGuy's right as far as everything I've ever read/heard. The 81's got a compression bump from 8.0:1 to 8.6:1. And everything I've heard about the EL head swap leads me to belive that it bumps the compression some. Also, it gets rid of the pesky CVCC system and has a conventional 2-valve valvetrain. Using the EL head with the Weber 32/36 DGV/DFV (or Holley 5200) boosts power output. How much so, I don't know for sure. But I've heard rumors of people getting as much as 100hp out of the EK with the head/carb combo swap with a mild cam.

[79cord]

There was also the the theory that the EL engines slightly higher compression ratio compared to EK was due to its smaller combustion chamber @ bottom dead center, relative to that in the head @ top dead center for any given cylinder head.

[redr2]

Okay, here are some more things to throw out there. My new '81 EK also has dished pistons (same as pictured below).

However, my '81 EL pistons are completely flat.

I am not sure where the compression bump (if any) comes from. Does the EL have a slightly longer stroke?

See the pics:

[redr2]

pics:

[redr2]

anyone elase have any engine specs: re": compression ratios? I am hearing 8.8 : 1 on other sites

[Ichiban]

Okay, here are some more things to throw out there. My new '81 EK also has dished pistons (same as pictured below).

However, my '81 EL pistons are completely flat.

I am not sure where the compression bump (if any) comes from. Does the EL have a slightly longer stroke?

See the pics:

The EL and EK have the same stroke. My 83 EL pistons are also completely flat on top. Also, the EL head must have a smaller chamber as compared to the EK, or else all other things being equal, its smaller bore would result in a lower compression ratio. EL engines usually have a HIGHER CR than comparative EK engines.

[79cord]

The EL and EK have the same stroke.

Err, We're getting confused here.
SAME BORE, Different stroke.
EK & EL engine blocks have the same part numbers according to some partsbook references I found. Crank & Pistons varied.

Bore/Stroke
EK 77x 94 mm
EL 77 x 86 mm

EL was destroked compared to the '76-78 motors to let it rev more easily while EK stayed roughly the same (previously 93mm).

[Ichiban]

Err, We're getting confused here.
SAME BORE, Different stroke.
EK & EL engine blocks have the same part numbers according to some partsbook references I found. Crank & Pistons varied.

Bore/Stroke
EK 77x 94 mm
EL 77 x 86 mm

EL was destroked compared to the '76-78 motors to let it rev more easily while EK stayed roughly the same (previously 93mm).

Oops you're right. I was thinking of the Toyota 20R/22R engines. I remember contemplating swapping an EK crank for the greater stroke. Duh.

[redr2]

After compiling the specs here is what we know:

'81 EK 77x 94 mm 8.8 : 1 Compression
'81 EL 77 x 86 mm 8.4 : 1 Compression.

EL having the lower compression due to the shorter stroke (despite the flat pistons).

Here is what I want to confirm now:


Will the flat EL Pistons work on the EK rods ? The obvious result would be an instant bump in compression.

[79cord]

Don't forget that EK before '81 seems to have had an 8.0:1 cr.

While the EL (in Australia at least) previously 8.4:1 was supposedly increased to 8.8:1 for the '82 (EL) models (A friend having fitted '82 pistons to his '80 Accord).

[redr2]

For my case I am only dealing with the 81 motor and EL head....

Will the flat EL Pistons work on the EK rods ? The obvious result would be an instant bump in compression.

Don't forget that EK before '81 seems to have had an 8.0:1 cr.

While the EL (in Australia at least) previously 8.4:1 was supposedly increased to 8.8:1 for the '82 (EL) models (A friend having fitted '82 pistons to his '80 Accord).

[2ndGenGuy]

I would guess that it would. In fact, that thought crossed my mind when you told me yours were flat. As long as the piston height, bore and wrist pin were the same, you should be good. But remember too, the EK might have the dished pistons due to the compression bump from the longer stroke. Assuming that the rods are the same between the two motors. If the rods were the same, you could also assume that the wristpins would be the same...

If the wristpins were different, I would imagine that you could just put the EL rods and pistons on the EK crank.

[redr2]

I suspect the EK would use a slightly longer rod for the longer stroke, I hear the blocks are nearly the same.

I set mine to TDC (by eye for now) and WOW, the pistons on mine are also sticking up above the deck surface.

I had no idea these things came up that far in these motors. Now I see why a stroker is out of the question. By what I can see I am really doubting that the flat top EL pistons can be used without some sort of valve reliefs, it certainly does not leave much for clearance.

On a side not I confirmed both the EL and EK pistons use an 18mm diamater pin.

Here are the pics, for anyone interested:

[2ndGenGuy]

Wow that's pretty significant just how much those stick out! However, rod length doesn't change the stroke. Rod length can change compression, and I think that's about it. If that works in the EL head, I can't imagine there being a problem in the EK head. I doubt the cam has any more lift. Pretty sure the valves are the same size too.

[Ichiban]

Since the EK has a longer stroke, I doubt it would have a longer rod, if anything, maybe a shorter rod. It would have to have one of the three (or a combo thereof); a shorter rod, higher wrist pin height, or, taller deck height on the block, in comparison to the EL engines.

[redr2]

your right, I got it all reversed. I think the deck height is the same, I keep thinking I once heard the difference was in the rods.

As for how much they stick out, I am having that measured tomorrow. No need for different pistons at this point though. I am thinking the shaved head should bump up the compression easily from 8.8 to 1 to 10 to 1.

As for the heads, they do share a lot of parts. The rockers are the same and the EK cam will work in the EL head but the auxuillary lobes spin freely.

Since the EK has a longer stroke, I doubt it would have a longer rod, if anything, maybe a shorter rod. It would have to have one of the three (or a combo thereof); a shorter rod, higher wrist pin height, or, taller deck height on the block, in comparison to the EL engines.

[redr2]

Just FYI for those of you playing with the 1981 EK motors:

I picked up my engine today and they (engine shop) were able to measure everything up.

- pistons (.040 over) have a 5 cc Dish
- the pistons are .020 to .025 above the deck (with no head gasket)....this is on my rebuild
- The head gasket (FelPro) I measured at .060 (this is new without being compressed).

According to the rest of the specs I have acquired:

- Bore is 77 mm stock (I am .040 over)
- Stock compression on the EK is 8.8 to 1
- transmission is geared at 4.071 final drive (I use the 82-83 GK tranny)
- stock EL head (measured by Dan) comes in at about 47 cc
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