Elgin grind 964 timing for low end torque

[smurfbus]

What I have read here on pelican is that most recommend the middle of the range cam timing for these but most are NA engine comments. I was thinking of dialing the most advance cam timing that does not affect overall performance. The normal 964 range ends at 1.39mm but I read camgrinder wrote "on some cases 2.0 is good for low end".

So what is the max cam timing advance for 930 with carrera 35mm heads ( or opened 38mm 930 heads ) with BBheaders and big turbine turbo hx40 (with 18cm2 turbine housing.) Intake is stock pancake with 38mm openings. Muffler is opened borla or zork.

I dry tested the valve piston clearance at 1.5mm cam timing and I could turn the engine over at 3mm extra valve lift so clearance is not restricting more advance!

Any ideas or words of wisdom? The car did not make good boost before 4000 IIRC so Id like to help the spool with cam timing. The turbo pulls hard at 7200 rpms so I would like move the torque lower to get better street performance, but where is the limit?

[Tippy]

Not sure on your cams as I'd set them retarded for bigger top end, but something caught me eye. You said your HX40 didnt spool well below 4k. With a 0.84 divided housing, mine spooled really quick.

Ideally, I think a 0.70 divided housing spool with the gas pedal and still have enough breadth to not choke top end.

After all, it's a "P" trim turbine.

[smurfbus]

It sure flows nice on top! I have the biggest housing on it 18cm^2. These cant be compared but this chart is floating around for comparison.

9cm^2 - .48 A/R
12cm^2 - .63 A/R
16cm^2 - .83 A/R
18cm^2 - 1.00 A/R
22cm^2 - 1.15 A/R

I wish I could get my BB MODDED for true devided flow. I can always try smaller housing 12,14 or 16 but I chose this one for least backpressure so if cams would make it spool earlier it would be fine for me.

The engine did have problems so Im not sure its that bad after new piston rings and pistons in correct position and so on...

[Tippy]

I machined a 1.00 and a 0.84 myself. Bought new P trim housings from Pure Turbos. Took about 2 hours a piece.

[Tippy]

BTW, I have a 23 or 25 cm housing on a bench. That thing has to be close to 2.0AR!!!

I think those estimates you posted are conservative?!

[smurfbus]

Too bad this pic does not show turbine side. The difference is much bigger there

[smurfbus]

I had to dig it up for a pic. Its One heavy MF. Spark plug for size comparison

[Tippy]

I remember now, it's a 26cm T4! It's almost as big as the compressor housing.

[Alan L]

I'm running 1.8mm on my Elgin cam - on the advice of Chris. Can't say what other numbers would give me, but I have lost no bottom end, in spite of opening ports to 38mm. And I have more mid/top.
Alan

[smurfbus]

Are yours 964 grind too? SC uses around 1.8mm as stock. I pm'd camgrinder for advice as he has good knowledge on these issues.

[camgrinder]

Originally Posted by smurfbus

Are yours 964 grind too? SC uses around 1.8mm as stock. I pm'd camgrinder for advice as he has good knowledge on these issues.

Factory 1.26mm is 2 degrees retarded from straight up. In a low compression cis turbo
this setting can be laggy as you described. 2.0-2.2mm puts it a couple of degrees advanced and should pick up the bottom (off boost and spool a little quicker)

[smurfbus]

Thank you. This is the first time this high numbers are mentioned and I will try them for sure. I will adjust the cams for 2.2 and do a once over with both sides clearance test just to be sure there still is 2mm for exhaust and 1.5mm for intake. Too bad I found two twisted injector blocks/flanges so I can't report in a while but stay tuned. I might have to go EFI before I can test these values if I cant find 38mm injector blocks for cheap.

[Tippy]

John, how much top end will pull out? I heard 964's are good to ~6500? So advancing may get you close to an SC/3.2 powerband, no?

[smurfbus]

Well now I feel like I could boost 1.2bar till 8000rpms. It just pulls hard and I had my limiter at 7300. I'm happy to lower my rpm limit to say 7000rpms after this rocker failure that the limiter did not catch when the pedal stuck at WOT. Good lesson to always install the cluster blanket /shield back before driving.

[camgrinder]

Originally Posted by Tippy

John, how much top end will pull out? I heard 964's are good to ~6500? So advancing may get you close to an SC/3.2 powerband, no?

Maybe 100 -150 rpm. Where you will notice it more is after peak HP. With the cam advanced the power will nose over sooner instead of a gradual taper. Earlier Intake valve closing point in most cases is an rpm limiter. Especially with boost.

[Tippy]

Wow! Only 100-150 RPM would be worth the extra grunt. ***Mental note***

Thanks!

[356911930]

John, here is the question that has been nagging many of us when it comes to street cams and the 930 engine. Mine is a 3.0L 1976. Can you give us some stats as for as low/mid range and top end performance between the SC cam and the 964 cam dialed in at 2.0mm - 2.2mm?

Thanks,

Rahl

[smurfbus]

After many days of checking different timing values I ended up with 1.96mm. 2.2 was fine with cyl 1 and 4 but after installing all the rockers cyl3 and 5 had interference. I went back to 1.5 and that being fine tried 2.1 which was fine without checking extra lift so I dialed 1.96 and tested rotation with 2mm extra lift on all valves. That seemed to be ok. I'm waiting for my sprocket alignment kit so I may need to do it once more though and you all (those who have done this) know its pretty hard to get the sides equal, huh. It kills me to see the numbers change while torqueing the bolts.

It was strange to find out the cam would not turn under the cyl3 intake rocker at 2.2mm even when the rocker elephant leg was fully rewinded

[smurfbus]

A follow up for this thread. Im pretty happy about how it runs now. I can easily cruise on 4th at 1200 rpms and pre boost is almost like NA engine. It still has uumph too. Short 1st to 2nd clip from yesterday. I have carillos and apr studs plus I lowered the limiter to 6700 so Im not afraid to keep it spinning until it has gained the speed : ) before shifting.
https://youtu.be/M_dXraWMKYQ

[smurfbus]

Rear view of some sprints: WOT at beginning, 6 min to end for busy people. Only little flames but maybe they would show when dark.

https://youtu.be/DiXmWfQeVnk