Big cams vs vacuum
07-15-2010, 05:32 AM
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Big cams vs vacuum
I'd like to see or hear how much vacuum are your engines with
bigger than stock cams making at idle?!
bigger than stock cams making at idle?!
07-15-2010, 06:20 AM
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Re: Big cams vs vacuum
Trick question. It also depends on displacement, EFI or carb, in gear or neutral if automatic, and idle rpm. Better for you to just tell us what you're hoping to accomplish.
07-15-2010, 06:42 AM
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Re: Big cams vs vacuum
OK! I have 353 SBC with CC XR288-HR cam.
I'm having some serious too rich idle situation and my tuner thinks that
vacuum is too low.
This is exactly what is happening:
https://www.thirdgen.org/forums/tech...ew-engine.html
So, I'm wondering if 70-73kPa MAP reading that I'm having is too low
vacuum for this cam!?
I'm having some serious too rich idle situation and my tuner thinks that
vacuum is too low.
This is exactly what is happening:
https://www.thirdgen.org/forums/tech...ew-engine.html
So, I'm wondering if 70-73kPa MAP reading that I'm having is too low
vacuum for this cam!?
07-15-2010, 07:16 AM
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Re: Big cams vs vacuum
FAR FAR FAR too much cam for ANY sort of EFI, and for most 350s in general. As I posted in that thread. Again, try a cam with 224/230-112. Notice how nobody is disagreeing with me? That's a good clue right there.
07-15-2010, 08:46 AM
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Re: Big cams vs vacuum
I know that it's a big cam, but this is by no means my daily driver. I can live
with 1000 rpm idle, rough idle, and not very "happy" engine in low rpms.
Do you think that this cam is so big that it can't work on my engine?
with 1000 rpm idle, rough idle, and not very "happy" engine in low rpms.
Do you think that this cam is so big that it can't work on my engine?
07-15-2010, 08:55 AM
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Re: Big cams vs vacuum
Yes. If you want more power than the 224/230-112 can provide, then get some AFR heads. If you're still not satisfied, add nitrous. Or decide right now to just add boost, and choose AFR heads with larger chambers. They offer your choice of 65 or 75 cc chambers.
COMP's XFI-268-HR13 would be fine with AFR heads and occasional nitrous. It might be a hair too much overlap for boost.
COMP's XFI-268-HR13 would be fine with AFR heads and occasional nitrous. It might be a hair too much overlap for boost.
07-15-2010, 09:52 AM
#7
Re: Big cams vs vacuum
Agreed, way to much cam for a superrammed 353 motor. It would be ok on a 383 but even then slightly large.
You can get it to run with a high idle speed 1000-1200 rpm perhaps but that cam wants to go to 7K rpm and superram craps out at 5500-5800 depending on porting or not. Those heads probably wouldnt support the high rpm of that cam either, even if you had a miniram intake on it.
Guys have run that cam on ported LT1 motors with good success but those heads can be opened up more than 113's. Its a very big cam on a stock cube motor.
Local guy has a car here that runs pretty good with a big cam. Its stock shortblock l98 with AFR 190's and stealth ram intake. Comp cams 280xfi cam. Idles very good at 750-800 rpm or so. Seems to have good brakes too. I was impressed.
Need alot of timing at idle and some more rpms to get vacuum up. That usually helps.
You can get it to run with a high idle speed 1000-1200 rpm perhaps but that cam wants to go to 7K rpm and superram craps out at 5500-5800 depending on porting or not. Those heads probably wouldnt support the high rpm of that cam either, even if you had a miniram intake on it.
Guys have run that cam on ported LT1 motors with good success but those heads can be opened up more than 113's. Its a very big cam on a stock cube motor.
Local guy has a car here that runs pretty good with a big cam. Its stock shortblock l98 with AFR 190's and stealth ram intake. Comp cams 280xfi cam. Idles very good at 750-800 rpm or so. Seems to have good brakes too. I was impressed.
Need alot of timing at idle and some more rpms to get vacuum up. That usually helps.
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