The difference a bit of head makes

[Chris bugster]

https://lh3.googleusercontent.com/-e3ijb_j-OhY/UrggCBnGmWI/AAAAAAAADKs/pRrwG3ELXxg/s912/7.jpg

Two power runs, a year apart. The difference in the the engine is that the earlier run was with standard vw 040 heads with only hi-po single springs. The second run is with fully ported 40x35 heads and a jump from 8.5 to 9.0:1 compression and a set of 1.25 rockers. The cam is a scat c35. Carbs are 40dells with 34 vents and exhaust is a cheapy 1 3/8 that will soon rust through. Power readings are with a standard size pulley and twin quiet packs.
I was shocked at how much power it made and at such high rpm.

[Zach Gomulka]

Looks like it was still pulling. A 1 1/2" exhaust should make a nice improvement. What size is the engine?

[Chris bugster]

1835cc- oops sorry

[Zach Gomulka]

I had a very similar 1600 that made 93hp @ 6300. It would be interesting to see the difference on your engine with the larger exhaust and another 500rpm
People don't give the C35/Engle 110 enough credit. With the right parts it can make power over 6k rpm, our dyno sheets prove that.

[Chris bugster]

It looked the engine was still pulling to me too, but the dyno guy said it wasn't so shut her down.
Zach, how much of an improvement do you guess a 1 1/2 exhaust is worth?
The cam looks so small on paper that I coudn't believe it wanted to go that far- must be the heads.

[modnrod]

Good tope end added on, very nice!
Did you do the heads?

[Zach Gomulka]

Wild guess... 5-7hp. There are others that would know better than I do. I just know a 35.5 exhaust valve goes best with a 1 1/2" primary. Would be very interesting to see the actual results.

[spanners]

I would say the chart is bang on for the engine spec, its all in the heads as the saying goes, the power dies suddenly as shown, but thats airflow dying, you can get 36 vents in 40's and that would extend the range and increase the power, the h.d singles were a good move, my 1835 circuit engine spec was 45 dells on 38 tubes, 044 40 x 37.5, 10.8 c/r,  bug pack dual springs,  Engle 130, 1.25 rockers, 1-5/8" primary into a cone silencer, full ARPM dry sump system, but here's the good bit, a 69mm Scat CAST crank, and yes i tried for 10 years to kill it in racing at up to 7200 rpm, it has many many race hours and an oil pressure dive/ regrind on it, its still going strong, power is a guess, but at 140/145 is a good guess judging from its race results. good luck with squeezing more hp from yours.

[Chris bugster]

The power doesn't drop off suddenly as the graph suggests. The first run was done further and the power remains at over 120 to 6500rpm. This run was done to max power only.
The heads are home grown.

[modnrod]

The heads are home grown.

Then I reckon they grew very well.
 

[Chris bugster]

The actual labour came from our (Jas's) hands but the info is pure Cal-look lounge

[markvo]

The horsepower and torque should cross at 5252 rpm

[Chris bugster]

They will cross if you convert from metric to imperial values.

[Whyshchuck]

Oh, my engine. It's nice to see it. Thank you Chris.
New CR is 9.8 not 9.0.
I'm sure Jas will present effects of his work here (All heads' photos I have are presenting them unfinished).

[jaqo]

Hello.
During this upgrade I took into consideration some tips and tricks I got here from Torben and few other guys and I also analysed some information from JPM about port size etc. It really worked well.

What I did was:
-decreased the deck height
-flycut the heads to bump up the compression ratio to 9.8:1
-installed 40x35.5 mm valves
-I changed the shape of combustion chamber around the valves
-ported the heads and intake manifolds - I tried to stick to Johannes advices about port to valve size. As you can see the heads required welding around the intakes (at the top and bottom)
-installed scat 1.25:1 rockers with correct geometry etc (had a lot of problems with scat lash caps - they literally seized - some material problem)
-changed steel pushrods to hd aluminium ones
-installed some short velocity stacks
-removed all imperfections from the carbs (casting, butterfly bolts etc)
The heads still have bugpack hd single valve springs but I calculated that the bigger weight of the new valve plus lashcap is not a problem because of the difference in weight between new aluminium pushrod vs. the old steel ones. It still has stock size exhaust with heaterboxes.

The dyno plot you see ends so rapidly because the the operator just let go the throttle. With 34mm vents the power curve is still above 120hp up to 6500-6600rpm. I recently spent some time jetting the carbs etc and I think that it now has a lot more power up to 3000rpm and maybe a little more peak power (it was a little beat to lean on 32mm vents)

Amazing thing is that the engine runs very cool and is very resistant to detonation - I almost can't make it to ping with pump gas (98 octane) - I tried as much as 40 degrees max advance (!!) and it couldn't heat any detonation.

[jaqo]

Some photos - this are made during the work so the parts are not finished - unfortunately I don't have any photos of finished parts.


butterfly bolts had to be trimmed:


As you can see the port size is big but it still gained a lot of low rpm power:


Rocker shafts and end caps had to be machined down on a lathe to achieve correct clearances:




Thin silver line shows how much material needs to be removed around the intake valves


You can`t see it here well bu the wall around the valve is angled