VC 460 compression ratio 10-1?

BLACK DEATH · 03-14-2020, 03:12 PM

We cc’d a stock Gx390 head today and it was about 41 cc with the quicky setup we did.
It wasn’t a 100% accurate setup, but it was close enough to see its around 41cc.
Now I really am confused on how they are getting 10-1.
I may have to message vc on their fb page that they run. See what I am missing.
We partially welded a up a 16hp duromax head and I am getting around 32cc.
With the calculator above it puts the compression close to 15-1.
That’s a lot of compression, good thing is I can slowly grind away to my compression liking.

sho305 · 03-14-2020, 05:39 PM

Curious here too. The stock piston has that relief too, the one I cut off to fit the long rod. Or are you guys all also running flat tops?

raydhd · 03-14-2020, 05:41 PM

The long rod VC 460 has a flat top piston with zero deck clearance.

BLACK DEATH · 03-14-2020, 08:11 PM

Sho, on the vc460, it’s a flat top and pretty close to zero deck and no valve reliefs . Mine was .003 in the hole but it makes no difference in compression readings even if I put it at 0 deck.

sho305 · 03-15-2020, 07:06 PM

I see. I think with my VC460 long rod in the 420 and cut piston it is supposed to be the same thing. I didn't check the piston or deck height since pistons vary, its within .010 of what Vegas said to cut it. It looks very close to deck by eye but I did check to see if it was out of the hole and it is not. It pretty much takes it down to the dish height, and I went a few thou more to clean up the dish and make it pretty on the grinder. Like I posted before I changed to the thick gasket from Vegas instead of the thin copper one that came stock in it. But I only cut my head .050 as I run regular gas, and off the top of my head figured those changes (change to flat top, higher to about deck height, but thick gasket) would keep the compression from growing much. It would spark knock with the stock clutch at low rpm before (before the long rod/piston mod), but when I swapped the clutch it is higher engagement and it stopped. And I have the smaller timing key 6 degree or something. I know most of you cut .100 on the head and run premium. This combo seems to work well on regular but engages at over 2K rpm I would say or it would knock. The old stock clutch would catch at low rpm 1500 maybe and I could hear it. So I tried to get it warm and hear it now and it wont do it. This would be nice time to have the UT2 timing advance.

scottykify · 03-16-2020, 07:40 AM

On my stock VC460 I run the VC adjustable coil mounting bracket so I can change the timing pretty easily. and last time I ran it at 5 degrees advanced it was pinging from pre ignition with 91 octane fuel at high load around 4000rpm. and it sucks to start with the pull rope! the big onboard stock starter/generator needs a very tight belt to turn it over without slipping so I believe the compression is a ways up there. I was going to try 2.5 advanced next time around to see if that will fix it but I havent got that far yet.

BLACK DEATH · 03-17-2020, 05:56 PM

Ok I talked to Geoff Warner on fb. He posted a different calculator that got closer to 10-1, depending on head gasket thickness. Here’s the calculator below, 10-1 with a .55 gasket. I guess the gasket u get will decider the true compression.

https://goodcalculators.com/compress...S7Xt7pqkcjZ3lk

BLACK DEATH · 03-17-2020, 05:58 PM

Quote:

Originally Posted by scottykify

On my stock VC460 I run the VC adjustable coil mounting bracket so I can change the timing pretty easily. and last time I ran it at 5 degrees advanced it was pinging from pre ignition with 91 octane fuel at high load around 4000rpm. and it sucks to start with the pull rope! the big onboard stock starter/generator needs a very tight belt to turn it over without slipping so I believe the compression is a ways up there. I was going to try 2.5 advanced next time around to see if that will fix it but I havent got that far yet.

Incase re check your valve lash it may be off. I’ve added an 8* key and never really remember a hard pull start condition. The pinging yeah can be because it needs higher octane

raydhd · 03-17-2020, 06:03 PM

This seems to give a better Idea of the CR with altering the head gasket or head volume.

BLACK DEATH · 03-18-2020, 07:18 PM

Sure does raydhd

03-14-2020, 03:12 PM	#11
BLACK DEATH Gone Wild Join Date: Dec 2009 Location: Corpus Christi, TX Posts: 1,644	Re: VC 460 compression ratio 10-1? We cc’d a stock Gx390 head today and it was about 41 cc with the quicky setup we did. It wasn’t a 100% accurate setup, but it was close enough to see its around 41cc. Now I really am confused on how they are getting 10-1. I may have to message vc on their fb page that they run. See what I am missing. We partially welded a up a 16hp duromax head and I am getting around 32cc. With the calculator above it puts the compression close to 15-1. That’s a lot of compression, good thing is I can slowly grind away to my compression liking.

03-14-2020, 05:39 PM	#12
sho305 Vegas modded 420 Join Date: Jun 2009 Location: West MI Posts: 15,443	Re: VC 460 compression ratio 10-1? Curious here too. The stock piston has that relief too, the one I cut off to fit the long rod. Or are you guys all also running flat tops?

03-14-2020, 05:41 PM	#13
raydhd VC 460 CLONE GONE WILD Join Date: Oct 2014 Location: Ray BY The Bay NJ Posts: 10,633	Re: VC 460 compression ratio 10-1? The long rod VC 460 has a flat top piston with zero deck clearance.

03-14-2020, 08:11 PM	#14
BLACK DEATH Gone Wild Join Date: Dec 2009 Location: Corpus Christi, TX Posts: 1,644	Re: VC 460 compression ratio 10-1? Sho, on the vc460, it’s a flat top and pretty close to zero deck and no valve reliefs . Mine was .003 in the hole but it makes no difference in compression readings even if I put it at 0 deck.

03-15-2020, 07:06 PM	#15
sho305 Vegas modded 420 Join Date: Jun 2009 Location: West MI Posts: 15,443	Re: VC 460 compression ratio 10-1? I see. I think with my VC460 long rod in the 420 and cut piston it is supposed to be the same thing. I didn't check the piston or deck height since pistons vary, its within .010 of what Vegas said to cut it. It looks very close to deck by eye but I did check to see if it was out of the hole and it is not. It pretty much takes it down to the dish height, and I went a few thou more to clean up the dish and make it pretty on the grinder. Like I posted before I changed to the thick gasket from Vegas instead of the thin copper one that came stock in it. But I only cut my head .050 as I run regular gas, and off the top of my head figured those changes (change to flat top, higher to about deck height, but thick gasket) would keep the compression from growing much. It would spark knock with the stock clutch at low rpm before (before the long rod/piston mod), but when I swapped the clutch it is higher engagement and it stopped. And I have the smaller timing key 6 degree or something. I know most of you cut .100 on the head and run premium. This combo seems to work well on regular but engages at over 2K rpm I would say or it would knock. The old stock clutch would catch at low rpm 1500 maybe and I could hear it. So I tried to get it warm and hear it now and it wont do it. This would be nice time to have the UT2 timing advance.

Today
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03-16-2020, 07:40 AM	#16
scottykify Not Yet Wild Join Date: Sep 2019 Posts: 48	Re: VC 460 compression ratio 10-1? On my stock VC460 I run the VC adjustable coil mounting bracket so I can change the timing pretty easily. and last time I ran it at 5 degrees advanced it was pinging from pre ignition with 91 octane fuel at high load around 4000rpm. and it sucks to start with the pull rope! the big onboard stock starter/generator needs a very tight belt to turn it over without slipping so I believe the compression is a ways up there. I was going to try 2.5 advanced next time around to see if that will fix it but I havent got that far yet.
scottykify Not Yet Wild Join Date: Sep 2019 Posts: 48

03-17-2020, 05:56 PM	#17
BLACK DEATH Gone Wild Join Date: Dec 2009 Location: Corpus Christi, TX Posts: 1,644	Re: VC 460 compression ratio 10-1? Ok I talked to Geoff Warner on fb. He posted a different calculator that got closer to 10-1, depending on head gasket thickness. Here’s the calculator below, 10-1 with a .55 gasket. I guess the gasket u get will decider the true compression. https://goodcalculators.com/compress...S7Xt7pqkcjZ3lk

03-17-2020, 06:03 PM	#19
raydhd VC 460 CLONE GONE WILD Join Date: Oct 2014 Location: Ray BY The Bay NJ Posts: 10,633	Re: VC 460 compression ratio 10-1? This seems to give a better Idea of the CR with altering the head gasket or head volume.

03-18-2020, 07:18 PM	#20
BLACK DEATH Gone Wild Join Date: Dec 2009 Location: Corpus Christi, TX Posts: 1,644	Re: VC 460 compression ratio 10-1? Sure does raydhd

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