Squish and rpm

[bugguy1967]

I think the 1.7 heads have about 60-65ccs. I have some in the garage that I could use to verify.

I would advise against decking the case so much. Turn the cylinders and mill out domes in your pistons.

No one has touched on how a tighter deck will actually perform in your engine because they're all different.

But you say your engine runs fine, cool, makes good power, so what's the reason for wanting yo teae down?
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"A petrol engine can start readily, run smoothly and give every appearance of being in good order, without necessarily being in good tune." - Colin Campbell, "The Sportscar Engine"

[Zed999]

[bugguy1967]

Your powerband is short because your heads don't flow nearly enough for such a large engine. I think using a set of higher-flowing valves and int/ex/chamber porting will go a long way.
_________________
"A petrol engine can start readily, run smoothly and give every appearance of being in good order, without necessarily being in good tune." - Colin Campbell, "The Sportscar Engine"

[mikedjames]

Why not go half way? Reduce the deck height part way , the deck height could be halved without upping the CR too much.

I still remember when I rebuilt the previous engine into an untouched AS21 case, I left in a 1mm under cylinder spacer that was because the previous case had been decked to make it flat as it was a Vege hack. I took that up my tuning hill and was disappointed I had to change down into third. Took out the spacer and reduced deck height to 1.5mm from 2.5mm and I could again go up the hill and make it to the top in fourth again.
No other changes. Thats the engine that lasted 30k miles probably because I recycled the heads and valves and one stainless valve had enough one day after 60 k miles.

.
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Ancient vehicles and vessels

1974 VW T2 : Devon Eurovette camper with 1641 DP T1 engine, Progressive carb, full flow oil cooler, EDIS crank timed ignition.
Engine 1: 40k miles (rocker shaft clip fell off), Engine 2: 30k miles (rebuild, dropped valve). Engine 3: a JK Preservation Parts "new" engine, aluminium case: 26k miles: new top end.
Gearbox rebuild 2021 by Bears.

1979 Westerly GK24 24 foot racer/cruiser yacht Forethought of Gosport.
1973 wooden Pacer sailing dinghy

[Zed999]

[Zed999]

[UK Luke 72]

Where's Alstrup?
Have we gotta sacrifice someone to summon him? 5lug maybe

Awesome discussion OP.
I have never heard of a 'death zone'.
Also I have never heard of a best CR for our engine... Some odd sounding info in this thread... I have my own opinions but they aren't as credible as some. (Tabari, Sled et al...)
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[Zed999]

[bugguy1967]

Oil temps aren't necessarily a reflection of head temps, where you would be seeing elevated temps if cr was set too high. 9.0:1 is fine for a C35. Your high oil temps may have been from the oil used, springs, or overly-large pump you used. Just speculation though. Idk what parts you used.

What valve sizes do you have? If you still have somewhere around 39x33, your heads are too small, unless they were sent to a really good head guy.
_________________
"A petrol engine can start readily, run smoothly and give every appearance of being in good order, without necessarily being in good tune." - Colin Campbell, "The Sportscar Engine"

[UK Luke 72]

Alstrup told me he'd rather run 9:1 with a tight deck than 8.6:1 and a 1.47mm deck.
That's a 69x92 type one in a bus.
_________________
2276 Beetle build https://www.thesamba.com/vw/forum/viewtopic.php?t=670744&highlight=2276+beetle+daily
2276 EFI Conversion https://www.thesamba.com/vw/forum/viewtopic.php?t=689172

[Brian_e]

[Alstrup]

Hi guys. What´s up
Havent read the entire thread, but commenting on Zed´s assumption that his CR was too high for the C35 cam.
As Bugguy is onto, it is not the static CR that is the problem. It is just about everything else. As you have already been discussing, deck height, chamber efficiency, port efficiency (a poor mix creates much higher cylinder head temps than a good mix) exhaust size, scavenging effect/efficiency, Cooling capacity/quality, ignition, is the timing precise or is it flickering 4-5 degrees from 3000& up. Proper spark? And of course improper tune, oil cooling, oil pressure control, you name it.

The death zone wrt deck height is from approx 1,55 to 2,8 mm. The area from "perfect" around 0,95 to 1,2 mm dependant on engine, up to about 1,55 reduces perfect squish which results in the need of more timing to get the burn to evolve enough and properly. HP wise there is not that much of a difference, but torque is measurable reduced and cylinderhead temps rise especially under load. The death zone is where the squish is not efficient at all which results in too much mix in the outer part of the cylinder not getting burned or getting burned so late in the powerstroke that it almost only creates heat in the cylinder and exhaust port. Above approx 2,8 mm. the squish is not evident and the burn begins to react somewhat like a hemi head, because now there is so much room between the piston and the flat areas in the head that the burn can evolve out of the chamber during the powerstroke. If such a situation occurs (maby turbo engines run like this) you need a somewhat advanced ignition timing, but then you can make fairly decent power, and the cylinderhead temps are LESS than if you were in the death zone.

Wrt static compression. In general my opinion is that this part of the automotive world sets the static compression too low and have too much deck. By spending the time (and maybe a little money) to optimize these two things you will already notice a significantly better and cooler running engine. That alone does not do it, but it is definitely a step in the right direction.
Of course it is cam/Bmep dependant, but Luke is correct with what he wrote about deck versus CR. The more efficient you can make the burn so it is almost all over BEFORE you open the exhaust valve the cooler the heads will be and the more static compression the engine can handle, meaning more hp, better torque and a cooler running engine.

Hope this helps.

T

[Brian_e]

[mark tucker]

[bugguy1967]

I didn't notice where you mentioned larger valves. What valve sizes are you running?
_________________
"A petrol engine can start readily, run smoothly and give every appearance of being in good order, without necessarily being in good tune." - Colin Campbell, "The Sportscar Engine"

[Zed999]

[Zed999]

[Zed999]

[Zed999]

Just for Mark as I notice he likes slapping his forehead in disbelief...

I had half a dozen engines built by a reputable builder. All great engines so I had him build one for me. I supplied a new ali case a c35 cam kit, a pair of mexi heads and 90.5 p & c's. He said get a serp pulley kit and a pair of ict's. He supplied the rest including a 76mm wasser crank.

It was a dog. It made a tapping noise. It leaked at the pulley. He was a sort of mate and I trusted him, he built me other nice engines., so... On his arvice I had the little ends rebushed. Still tapped. Sounded central to me. He said thrash it until something breaks. So I did and loosened an exhaust baffle. Relaced muffler, still tapped.

Meanwhile in an effort to contain the pulley end leak I went as far as having an og oil spiral wire cut from a pulley and fitted to my serp pulley. Much better but still leaked. Also unless rammed full of oil it had intermittent pressure loss. Hmmm.

So I shipped it back to him. He said he could find no problem to case the tapping. When it came back it went even more badly. He sent me ratio rockers that perked it up a bit. Still tapped. Jeez, I got him to build it because I didn't want to even atempt to learn about engine building!

With no other option, I took it apart to at least find out what it was.
It had semi-hemi heads, a stock cam, 4mm+ deck height, a mullered oil thrower, a stock oil pump, ovalled rod big ends and the wrong size pickup rammed part way in the hole and stting at an angle best described as jaunty. The tapping noise was either the rods or crank whacking into the case roof in three places. The case had been clearanced...1" out.
Here are some pictures.

Oil pickup as found. It's securely fixed like this, it hasn't wandered.

Oil slinger - he dropped the crank in wrong then just carried on didn't he?

Oops, missed! Look also top right at the "neat" ledge for the tang on the wasser thrust bearing.

Oops again!

Lovely heads.

After seeing all this I thought I could do better. The case and crank hung in there but the rest was replaced. My version with the 40x35, c35, higher compression, j-tubes, vs exhaust, drla40's made 135hp flywheel but as said above got too hot on a long run. I decided a bigger more ploddy engine would better suit my next bus so I sold it to beetle owner who loved it.

So the funny part - I've come full circle back to an oversize low compression stock cam engine with too much deck. This one is better simply because it's bigger but really it's not what it should have been.;

[mark tucker]

small seats with big valves do work good if done properly....(properly!!) most 40mm heads have sesta that are great for 42mm valve(type 1) I use the seats for 42mm valves for 44mm valve size as the 44mm seats are too big to get the right shapes and flow.