1600 with hemi-cut heads - worth building?

[Neil Davies]

As you might have seen here, I've just started stripping down one of my 1600 motors for my semi-daily driver Beetle and found it has hemi-cut heads.
It has a Scat C35 cam, 40 IDFs, 1 5/8" merged header, full flowed case, deep sump, and was re-built many years ago for my brother when he owned my car for a while. We have no idea why it has these heads - it was a long-block that he had rebuilt.
It always ran hot, and we had to run decklid stand-offs, but it went fairly well. The only reason (other than the hot running) it came out of the car was that my 15-second 1600 out of my race car became available!

So I'm wondering what to do.

Option one - do I just rebuild it, cleaning up the heads a little (you can still see machining marks!) and try to pay as much attention as I can to ignition, jetting etc in order to get it to run cool? I have been following Rick M's road trip motor thread and was wondering if the heads could work on a decent 1600?

Option two - do I just chuck everthing in a box under the bench and look at my other 1600? I know the bottom end was grumbling on that but it always ran really strongly! Don't really want to give up on this motor though - seems like such a waste!

Option three - I could even rob the heads of my other 1600 and use those on this motor, but that leaves me with the 1600 that needs a bottom end rebuild also requiring heads, and I was hoping to have that engine for the wife's cabriolet as and when that makes progress.

Option four - the wildcard. Would the hemi-cut heads work with a turbo? I've got a header, a little turbo and a 40 DCOE sidedraft that are sitting there doing nothing... I couldn't get it to work properly on a 1600 before, but that was down to ignition, which I know how to solve now!

I haven't got anyone local to machine the case for my STF 2276 yet, or the cash for a gearbox(!) so this was going to be a bit of a stopgap, and also serve as a practice build as I've not really touched a motor for 8 years or so.

Opinions please - what would you do?

[dyno don]

Heck Yes its worth rebuilding... The hemi chamber is a" Universal Application" design and I have had a few 1600 hemi chambered engines. Main key is tune up...  If you have read your homework then you know you will need to run more timing, and am assuming your old engine ran warm/hot in part due to lack of it. Always read your plugs and NOT after idling..!! Best way is to run engine on a load at peak rpm then shut off/put in neutral/ and pull a plug and be sure after the engine has warmed up NOT to strip your plug threads. INSIDE the unsulated area should look clean and slightly tan/brown. Good Luck..!! 

[hotrodsurplus]

Okay this is going to get long winded.

I drank the semi-hemi Kool-Aid in the late '80s. When I rebuilt the 1600 in my Thing in 1993 I paid extra big bucks to have my heads hemi cut at The Source. I followed the rules and advanced the timing and, if you can believe it, leaned out the main. Again, this was under recommendation from The Source.

What started out as a crisp and cool-running stock engine turned into a wet dishrag. Throttle response sucked. Acceleration sucked. Top speed sucked. It was obviously too lean--so lean that the electrodes turned white, and this in the pre-ethanol '90s. I jetted back up to stock. Still pale electrodes. Ended up going in the other direction than The Source and jetted way fatter than stock to get color in the electrodes and to keep the thing from melting down on the highway.

Not to say it was great on the highway. It always ran hot. The oil light pretty much stayed on when the engine idled after I got off the highway. If I sustained 70mph for any length of time or if I tried to push the car up a hill the engine would overheat so badly that it would lose power. 

In 1998 I ended up burning up a set of rings on a set of Kolbenschmidt pistons that were NOS in 1993. I replaced the whole set of P&Cs. The valve guides were also toast so I a valve job...again. It still ran poorly. The irony is that people would marvel at how 'good' it sounded. I have to admit that it idled smoothly. 

In '00 I took a job with a company that had a chassis dyno and full-on test equipment (the same dyno used in the VW Trends Dyno Days--I didn't work for VWT nor would have I admitted it anyway). We strapped down the car and tested it. The air-fuel ratios were all over the board. All of the numbers were consistent on leakdown tests. I could get the numbers closer by swapping pilot jets, mains, and fiddling with the timing but not without creating a huge flat spot right off idle.

By this point I knew that the lack of quench/turbulence and low CR were making the engine harder to tune. So I pulled the damn engine apart AGAIN and flycut a big whack out of the chambers to bump the CR back up to stock. I had to shorten a set of pushrods specifically for the job.

It would accelerate faster (slightly) but it would also get hot faster. Air-fuel ratios were still all over the board. Bear in mind that this engine had an untouched 34pict4 (stock for the car), another un-touched 34pict3 (with a Beetle emulsion tube), and a known good working stock distributor.  So frustrated I was with the whole experience that I stopped driving the car in about 2001.

I took it out of mothballs in '09. The first thing I did was buy a set of new heads from Darren G and had him flycut the steps out of them. With 48cc chambers and .055" deck I think the static CR is about 8.12:1 (going by memory here). I used a set of Kaduds that RK Smith sold to me a few years prior and I put a shorter curve on a Mallory unlight distributor.

The engine to the heads is the same but the difference between the two configurations is incredible. It jetted easily. The car flat-out kicks ass. I can run 87 octane with a splash of 89 but I know if I got sharper on the jetting or ran a set of IR carburetors I could run 87 exclusively. I have pictures of the GPS sitting at 78mph on a 95-degree day at about 2,000 feet above sea level. Oh yeah, in the meantime I also lifted my Thing and installed what's basically a patio cover on it so the wind resistance is even greater. Can I get it hot? Of course. The difference now is that I have to actually try. But for the most part I can fly along at 70 to 73mph effortlessly (rated top speed for a Thing WITHOUT the surrey top is 68).

I've since rebuilt two stock 1600s with the same heads but with 34pict3s and stock distributors. Both haul ass and run cool (one in a '67 convertible). They're nothing like my engine was with semi-hemi heads.

I know two people will achieve two results but I'm pretty confident that I tuned my SH engine to the best that it could run (I had the benefit of working with/learning from several people who truly understood engine dynamics and some who knew the vagaries of Volkswagens). I'm sure some may have seen things differently and others could have achieved better results. But in the end would it have been worth it? I personally think that it's better to start with a good design than try to address the shortcomings of a flawed one.

The whole SH thing left a super bitter taste in my mouth but I have to admit one thing: they taught me A LOT about engine dynamics. All wasn't lost either. I traded those heads for a virgin, never-cut, perfect-saddle, dual-relief Type III case. So I got that going for me.

I'm not telling you what to do. I'm just telling you my experience.

[Neil Davies]

Don, Chris, thanks for your replies. I've also posted the same question on UAC and received an interesting response from Dan Ruble, who pretty much echoed Don's thoughts. However, he did mention about deck height and the quench area, so I thought I'd measure up a bit last night when I was over at my garage. Looks like I've got around 26 thou  of deck in the top of the barrels, PLUS a 60 thou AND a 40 thou steel spacer in the head too! I've not measured the head cc yet, but surely this amount of deck height isnt a good thing!

As I've found that it has 87mm P&Cs, I'm leaning towards using the heads and 1.25 rockers off my old 1600 out of my race car, and making one decent engine out of the two. I'll cc the heads first though, just out of curiosity!

[hotrodsurplus]

However, he did mention about deck height and the quench area

Hey Neil, I commend you for doing your research.

Regarding quench and deck, by its design the SH eliminates quench area. Without quench area for the piston to act upon the deck is largely irrelevant for anything but establishing static compression ratio.

My engine had/has a .055" deck. Of course with the SH chambers it had basically zero quench area to induce turbulence. Flycutting the heads created a quench band around the perimeter of the chamber but it was so tiny that I would hardly consider it beneficial.

Looks like I've got around 26 thou  of deck in the top of the barrels, PLUS a 60 thou AND a 40 thou steel spacer in the head too!

Come again? You mean to say that it has steel shims between the barrel and the heads? I admit I haven't seen it all and that's a new one to me.

As far as the height goes, if some is good more is better and too much is just right! 

Provided those chambers measure about 56cc (as mine were) that translates to 6.47:1 CR on a 1641 with a .126" deck. A stock cam reduces the effective CR a tick more than a full point. That's like Model A Ford effective CR. And you could run those things on paint thinner.

As I've found that it has 87mm P&Cs, I'm leaning towards using the heads and 1.25 rockers off my old 1600 out of my race car, and making one decent engine out of the two.

That may be a better option. What chamber volumes do they have? Has the step been flycut from them? Going by the way mine runs with 8:1 static CR on low-octane fuel with a splash of midgrade I would imagine that you could get away with 8.5:1 on full midgrade and possibly slightly higher on high-octane pump. It would feel snappy!

If the deck is .026" and all of that shim was between the barrels and heads when you pulled it apart then I'd say you could get away with a more common .030" copper shim between the barrel and head. That would give you .056" deck which is pretty safe if you don't know how solid the bottom end is.

[Torben Alstrup]

Don, Chris, thanks for your replies. I've also posted the same question on UAC and received an interesting response from Dan Ruble, who pretty much echoed Don's thoughts. However, he did mention about deck height and the quench area, so I thought I'd measure up a bit last night when I was over at my garage. Looks like I've got around 26 thou  of deck in the top of the barrels, PLUS a 60 thou AND a 40 thou steel spacer in the head too! I've not measured the head cc yet, but surely this amount of deck height isnt a good thing!

You have a 60 thou AND a 40 thou steel ring between the cylinders and the heads   Or is the 60 thou a step in the heads.

If the latter is what is, you have 2 options IMHO.
1. Shim the cylinder to a deck height of ,042 - ,045 deck. Loose the shim. Machine the step out of the heads so you get a flat squish surface at the outer diameter. aim for 8,1 - 8,2 CR for medium grade fuel.
2. Let the cylinder "stay" at 0,026". Machine the step in the head down (also cut for 87 mm I.D.) so you get a semi "0" deck and let ½ of the safety deck be in the heads instead of the cylinder.
Both solutions will give you best possible burn pattern from what you have.

T

[Neil Davies]

Thanks for the replies guys! Yes, unbelieveably there were two steel shims on top of each barrel! I've never seen that before either! When the first one fell out I thought it was a copper shim, then two fell out of the next hole... Definately steel, and mic'd up at 40 and 60 thou.

I'm going to have to get the heads off the other motor and check them out - when I'm back in school next week I can laser cut an acrylic disc to use to cc the heads. I'll get some photos of the chambers on both sets of heads too - the hemi cut didn't even look to be central in the chamber!

I'll be rebuilding the bottom end just to make sure - now I don't know what I'm going to find!

[rick m]

I have .040 deck in my SH heads and can get away with it based upon the chamber to head configuration. I have eyebrows in my pistons. I am set up for 8.4 CR static with 7.3 dynamic. Will do a video of the motor running and being driven when I get the motor broken in. 2275cc engine size.

RM

[Neil Davies]

Morning all! FINALLY got around to cc'ing the heads last night, and found a whopping 41cc in the combustion chamber. It would seem that the steel head shims are to replace the step in the head that has been machined out.
Thanks to www.johnmaherracing.com and Johns wonderful calculator, with 26thou deck height in the cylinder and 100thou of shims, I've worked out that this gives 7.8:1 compression. If I take out the 40thou shim then I get 8.6:1 CR.
My dad is of the opinion that we throw it together with 8.6:1, advance the timing and maybe up the cam a bit - we found it was a C25, not a C35 as we thought!
I'm still none the wiser about building this!

[andy198712]

hmmm, sounds fly cut and hemi cut to me....?

my vw heads that were hemi cut cam out at 60cc....

[John Maher]

Neil, going back to the original question: "1600 with hemi-cut heads - worth building?"
Based on the latest piece of info you supplied, the answer has to be 'NO'.

IMO you have the worst of both worlds.... a flycut hemi chamber and the need to run a ton of deck height to arrive at a reasonable CR. Combustion efficiency will be poor. As a result you'll have to run a lot of timing. You'll also be more prone to detonation than a conventional chamber and tight deck combination. The only saving grace is you're working with a relatively small bore.

Sack those heads and save yourself some grief.

[Torben Alstrup]

Neil, going back to the original question: "1600 with hemi-cut heads - worth building?"
Based on the latest piece of info you supplied, the answer has to be 'NO'.

IMO you have the worst of both worlds.... a flycut hemi chamber and the need to run a ton of deck height to arrive at a reasonable CR. Combustion efficiency will be poor. As a result you'll have to run a lot of timing. You'll also be more prone to detonation than a conventional chamber and tight deck combination. The only saving grace is you're working with a relatively small bore.

Sack those heads and save yourself some grief.

X2

[Neil Davies]

John, thank you for your reply. I'm going to take your advice and leave this engine to one side, and strip my other 1600 to build one good one out of the two. This other one I know has got decent heads! Thanks again to everyone for your advice!
Neil

[rick m]

Torben pointed out part of the process I incorporated into my open chamber heads. I set them up so the chamber actually cups upward above the ID of the cylinder wall so there is no possible way of the piston hitting anything with "O" deck in the bore. I could actually have run a .020 copper head gasket instead of my .040 copper gasket that I used, based upon the shape of the chamber.. The tighter the quench area, the better the burn.

I was able to back off my timing from the previous bathtub style chamber when I was running "O" deck in the bore and a .060 copper gasket. I also was able to take 4 degrees of timing out of the motor and it is running cooler and had more pep. It is currently at 30 degrees total advance at 3000 rpms.  I am going to back it down another 2 degrees to 28 total and see how it likes it.

If you listen to the video I took with my camera phone on one of my motor posts, you can hear by the sound of the motor going through the gears it is no slouch on 91 octane pump gas. I have the link here for you to check it out.  Forgive the shaky hand. The phone was in my left hand as I held the steering wheel.
<a href="http://www.youtube.com/v/mup_kkzvCkw" target="_blank">http://www.youtube.com/v/mup_kkzvCkw</a>

Everyone told me the motor would not work with the size heads I am running and a smaller cam.  Well, believe what you want. Proof is in how it runs. If you refer back to my pictures of the open chamber design I am running, it is apparently defying a lot of opinions on the subject.  I did spend about 3-4 months studying combustion chamber design with some V8 guys, some of whom were mechanical engineers.  Apparently their suggestions on the design, cam timing, reduction in overlap at lower rpms, etc., etc., had some vailidity to it for a street motor application and where I wanted my power at.  :-)

RM