First impressions-G head VS Swirl head on my van!

[turbovanman²]

Well, after getting her running, I set the timing at 16 deg, S2 cam advanced 10 deg, won't run straight up-same as with the Swirl head, I drove her home with a mixed tank of 94 octane and 2 gallons C16, same as the track where I was having detonation issues, boost set at 13-14 psi. So, on the way home, shes a bit doggy off the line but boosts fine, she seems to have a bit more midrange than before. So numerous times, I stomp it from a rolling start, it spikes to 20 psi then settles at 13ish psi, it pulls hard at 20 then softens up. NO pinging and it pulls to redline-6000 rpm whereas before, it would sign off 5500 or less. First few times, she's line so I have to stop a few times and turn up the fuel pressure-this head likes fuel, alot more than my old Swirl. After driving home, jury is still out, its a different beast thats for sure, it idles rougher, only have around 12 inches of vacuum, before solid 15. I will turn it up some more and see what happens. I also notice the EGT's are alot higher, around 2-300 deg over before.

[Una]

EGT's higher due to not enough fuel pressure yet, maybe? Err, come to think of it, have you changed the advance tables in the computer yet? The swirl needs more advance, not enough advance would give you higher EGT's.. Did you say you set the base ignition timing at 16? Wow.. heh, guess that might do alot of the advancing..

[turbovanman²]

EGT's higher due to not enough fuel pressure yet, maybe? Err, come to think of it, have you changed the advance tables in the computer yet? The swirl needs more advance, not enough advance would give you higher EGT's.. Did you say you set the base ignition timing at 16? Wow.. heh, guess that might do alot of the advancing..

The cal is still for the Swirl. Awaiting an updated cal. It doesn't really have any power at 12 deg! After I reset the fuel pressure, my dawes was yellow with the odd flash to green-perfect.

[Garret]

Something else has gotta be up if you got that low of vacuum, even with that cam it should be higher

[Frank]

Ya, not a good back to back comparison because the timing does need to be set in the cal for the G-Head. In addition, I am wondering if that 5500rpm limit you had before was due to knock pulling timing out??


Frank

[powermaxx]

12" of vac at what altitude? Yeah, somethings not right. I pull 15" up here in Denver. I run the G-head on the GLHS on 91 octane at 25-27psi with zero detonation/pinging. (I run 100 at the track just for safety since it stays at that boost level longer than I can do it on the street )

[Frank]

Well he is running larger valves and a S2 cam.

[bill2]

...Now knowing the spark is more aggressive with a slow burn head...

When i went from a 782 to g head on t2 electronics, i disliked it enough to swap back to the 782 in just a few weeks. No matter what i set base timing at it was very poor throttle response off boost. Later i wound up using a 3bar/+40cal with very aggressive timing. After a while i swapped back to the g head, and it was a night and day difference. Keep the "g" .

[Frank]

Yep! Especially since you have a cal coming with the proper aggressive timing.

[Una]

Yeah, the cal Paul at TU did for me on the dyno for my G head was amazing. I had so much off-boost power and throttle response, it was amazing. Spark curve is EVERYTHING.. I actually had the wastegate arm pop off the turbo on my Daytona with that setup, it was still plenty driveable.

[1FastCSX289]

Yeah, the cal Paul at TU did for me on the dyno for my G head was amazing. I had so much off-boost power and throttle response, it was amazing. Spark curve is EVERYTHING.. I actually had the wastegate arm pop off the turbo on my Daytona with that setup, it was still plenty driveable.

I just swapped to a g-head from a swirl. I programmed some more timing in and I notice no difference in throttle response.

[Una]

You can't just randomly add more timing. Paul did mine on the dyno by analyzing torque peak and watching for knock sensor activity. Got the timing peak in just the right place. He really should go by Mr Wizard in my book.. Guess he's lucky he's not local to me, I'd be knockin on his door all the time.

[turbovanman²]

Well its not a true back to back test but still, I have driven my swirl head van around for 3 years so it IS different,

I don't think it was spark knock pulling the timing out, it never made power over 5500, no matter what I did to it.

I just need Shelgame to do some research for me and write me up a new cal, If I wait for Paul, it will be next year,

The alky is hooked up, will play with it tonight, will run 94 octane first them play around with 87 later. Heck, I might even give it some more base timing as I have ZERO knock, its pretty cool. The track tomorrow will be the ultimate test.

[daytonaturbo87]

the proper timing makes a difference, but not that huge of a difference. I read a chrysler tech sheet from the 60's that had a dyno run done on it with a big block back in the day. They dynoed it to see what kind of a difference the timing would make. It said that from the factory chrysler retarded the timing 6* from ideal. On a big block v8, it made a difference of less than 10hp, and all before 2000rpm, after 2krpm it made almost no difference. The extra timing is more for extra throttle response at tip-in. Of course things are different when you're boosted, but I wouldn't expect a 10HP difference if the timing is a couple degrees from being ideal.

[Frank]

the proper timing makes a difference, but not that huge of a difference. I read a chrysler tech sheet from the 60's that had a dyno run done on it with a big block back in the day. They dynoed it to see what kind of a difference the timing would make. It said that from the factory chrysler retarded the timing 6* from ideal. On a big block v8, it made a difference of less than 10hp, and all before 2000rpm, after 2krpm it made almost no difference. The extra timing is more for extra throttle response at tip-in. Of course things are different when you're boosted, but I wouldn't expect a 10HP difference if the timing is a couple degrees from being ideal.

That is true when you are running identical style combustion chambers, however the difference between the Swirl and G-head is the combustion chamber. They operate (aka mix fuel and tumble the air) differently and the chamber volume is different. When used with dished T2 style pistons, the compression ratio drops by about 0.5 to 0.8! In addition, the pressure at before combustion is about 20-30psi lower depending on the cam. Because of this, you have a less efficent motor at the same timing and geometry. Since the nature of the less efficency is due to slower burn times of the fuel mixture, you need to increase the timing to properly line up high pressure with the maximum folcrum points of the rod to crank. OF course you can raise the ignition up also since it doesnt knock due to the lower pressure and it not reaching the flash point conditions of the fuel mixture.


Frank

[show-off]

Since the nature of the less efficency is due to slower burn times of the fuel mixture, you need to increase the timing to properly line up high pressure with the maximum folcrum points of the rod to crank. OF course you can raise the ignition up also since it doesnt knock due to the lower pressure and it not reaching the flash point conditions of the fuel mixture.Frank

Frank,
Did you just make that up? lol

[Rattlesnake]

Frank,
Did you just make that up? lol

Com'on Mark, you're playing right?

[Frank]

LOL. He is just giving me crap. It took alot of carbs to think and write that response! LOL.

[turbovanman²]

LOL. He is just giving me crap. It took alot of carbs to think and write that response! LOL.

Only a couple thousand more to go, hehehehe,

[Frank]

Shhh!!!!