Which carb/intake?
06-20-2014, 08:16 PM
#1
Which carb/intake? Am switching to a carb set up from GM PCM controlled EFI. Have a 24 tooth reluctor wheel.
Engine specs:
-AFR 205 heads ported, 12:1 SCR, 8.6 DCR
-Stock 3.898 bore, ARP rod bolts
-mild cam makes power through 6400 RPM.
Plan to use an MSD 6010 timing controller. Which carb/intake will best support the engine specs? Fuel pump/regulator recommendation? Anything else?
Thank-you
Engine specs:
-AFR 205 heads ported, 12:1 SCR, 8.6 DCR
-Stock 3.898 bore, ARP rod bolts
-mild cam makes power through 6400 RPM.
Plan to use an MSD 6010 timing controller. Which carb/intake will best support the engine specs? Fuel pump/regulator recommendation? Anything else?
Thank-you
06-21-2014, 07:25 AM
#5
Kind of a tough combo. For that RPM range one might suggest a Performer RPM. But, with your compression ratio, the lower volumtric efficiency of the Victor Jr. in the lower RPM ranges would likely be a benefit in preventing detonation.
Another thing to consider with that compression ratio is cam timing. With your typical EFI cam, the late intake valve closing will help limit your cranking and low RPM cylinder pressures, but if you have a camshaft that is optimized for a single plane, Victor Jr. style intake, your cranking and low RPM cylinder pressures are going to be pretty high.
What are your cam specs?
Another thing to consider with that compression ratio is cam timing. With your typical EFI cam, the late intake valve closing will help limit your cranking and low RPM cylinder pressures, but if you have a camshaft that is optimized for a single plane, Victor Jr. style intake, your cranking and low RPM cylinder pressures are going to be pretty high.
What are your cam specs?
06-21-2014, 08:35 AM
#6
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Most likely it made power through to 6400 with a factory style EFI intake, if that is where peak power was made I doubt the cam is anything too 'mild' especially as dynamic comp of 8.6 to be calculated from 12:1 static, that would say it must be a reasonably decent stick.
With the carb intake you can expect peak power to carry another 3-400 revs easily. I'd like to see what a carb setup can do with a decent set of AFR heads, but still cam spec's are going to be handy to know to see if they are in the ballpark of being suitable for carb intake manifold.
With the carb intake you can expect peak power to carry another 3-400 revs easily. I'd like to see what a carb setup can do with a decent set of AFR heads, but still cam spec's are going to be handy to know to see if they are in the ballpark of being suitable for carb intake manifold.
06-21-2014, 09:48 AM
#7
Cam specs are
.581/.583, 224/228, 112 LSA. Installed on the 112 ICL Checked & installed w/ an adjustable timing set. I don't know the lobe design ,but do know that they are not XER lobes (thankfully).
Planned to Map the MSD 6010 similarly to the timing used on the EFI tune. I have EFI live & did tune the formerly used GM PCM. So, the max timing during WOT is known @ between 12.8 & 13:1 AFR with fuel injection. Am a complete newb when it comes to carburetors & have assumed that it will be similar.
Can we use same max WOT timing @ 3-400 more RPM or should I reduce it by a half to one degree?
Which fuel pump/fuel regulator?
.581/.583, 224/228, 112 LSA. Installed on the 112 ICL Checked & installed w/ an adjustable timing set. I don't know the lobe design ,but do know that they are not XER lobes (thankfully).
Planned to Map the MSD 6010 similarly to the timing used on the EFI tune. I have EFI live & did tune the formerly used GM PCM. So, the max timing during WOT is known @ between 12.8 & 13:1 AFR with fuel injection. Am a complete newb when it comes to carburetors & have assumed that it will be similar.
Can we use same max WOT timing @ 3-400 more RPM or should I reduce it by a half to one degree?
Which fuel pump/fuel regulator?
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06-21-2014, 10:41 AM
#8
For timing, check out this thread sticky:
https://ls1tech.com/forums/carburete...iming-set.html
And, read through the combos in the carb data base sticky:
https://ls1tech.com/forums/carburete...-database.html
Those threads will give you an idea of what other guys are doing. I will say though that timing is dependent on combustion chamber and compression among other things, so your combo is going to be unique to some degree due to your heads and compression ratio.
As for fuel system, if you already have a high pressure pump for fuel injection, you could like use that with this set up if you use a return line. If you don't use a return line, you will want to go to a low pressure pump.
For a return line system, the Holley 12-803BP regulator is kind of "the standard" and it is a great unit:
http://www.holley.com/12-803BP.asp
If you need a new fuel pump, a lot of guys, including myself, have had great luck with the Aeromotive Street/Strip pump:
http://aeromotiveinc.com/products-pa...l-pump-38-npt/
What kind of car is this? gear? trans etc?
https://ls1tech.com/forums/carburete...iming-set.html
And, read through the combos in the carb data base sticky:
https://ls1tech.com/forums/carburete...-database.html
Those threads will give you an idea of what other guys are doing. I will say though that timing is dependent on combustion chamber and compression among other things, so your combo is going to be unique to some degree due to your heads and compression ratio.
As for fuel system, if you already have a high pressure pump for fuel injection, you could like use that with this set up if you use a return line. If you don't use a return line, you will want to go to a low pressure pump.
For a return line system, the Holley 12-803BP regulator is kind of "the standard" and it is a great unit:
http://www.holley.com/12-803BP.asp
If you need a new fuel pump, a lot of guys, including myself, have had great luck with the Aeromotive Street/Strip pump:
http://aeromotiveinc.com/products-pa...l-pump-38-npt/
What kind of car is this? gear? trans etc?
06-21-2014, 11:50 AM
#9
For timing, check out this thread sticky:
https://ls1tech.com/forums/carburete...iming-set.html
And, read through the combos in the carb data base sticky:
https://ls1tech.com/forums/carburete...-database.html
Those threads will give you an idea of what other guys are doing. I will say though that timing is dependent on combustion chamber and compression among other things, so your combo is going to be unique to some degree due to your heads and compression ratio.
As for fuel system, if you already have a high pressure pump for fuel injection, you could like use that with this set up if you use a return line. If you don't use a return line, you will want to go to a low pressure pump.
For a return line system, the Holley 12-803BP regulator is kind of "the standard" and it is a great unit:
http://www.holley.com/12-803BP.asp
If you need a new fuel pump, a lot of guys, including myself, have had great luck with the Aeromotive Street/Strip pump:
http://aeromotiveinc.com/products-pa...l-pump-38-npt/
What kind of car is this? gear? trans etc?
https://ls1tech.com/forums/carburete...iming-set.html
And, read through the combos in the carb data base sticky:
https://ls1tech.com/forums/carburete...-database.html
Those threads will give you an idea of what other guys are doing. I will say though that timing is dependent on combustion chamber and compression among other things, so your combo is going to be unique to some degree due to your heads and compression ratio.
As for fuel system, if you already have a high pressure pump for fuel injection, you could like use that with this set up if you use a return line. If you don't use a return line, you will want to go to a low pressure pump.
For a return line system, the Holley 12-803BP regulator is kind of "the standard" and it is a great unit:
http://www.holley.com/12-803BP.asp
If you need a new fuel pump, a lot of guys, including myself, have had great luck with the Aeromotive Street/Strip pump:
http://aeromotiveinc.com/products-pa...l-pump-38-npt/
What kind of car is this? gear? trans etc?
Street/road course car; originally completed in 03 from a 99 NB Miata. GM Viper spect T56, Ford 8.8 w/ 3.90 rear end. 275/50/15's on slicks. After market alloy 28 spline half shafts that are stronger than most 31 spline half shafts.
Am also considering the Accufab, carb style, TB/fuel injection set up if can find one cheap. There is one in the for sale section, but intake is for LS3 heads.
06-21-2014, 06:30 PM
#11
Long story short...After twelve nearly years of tuning through my 98 PCM, it failed, A1-Cardone messed it up after claiming they had fixed it. Then I bought an 0411 PCM that was supposed to be capatable to all GM V8's; LS included throuh 04. Spent far too many hours studying schematics & pinout diagrams, re-pinned the 0411 & then couldn't get spark from it. Also, wasted a $125 EFILive, PCM license on the 0411. So, it's time for a much less aggravating alternative.
06-21-2014, 06:55 PM
#12
Read through the timing thread. Two things stood out to me.
W/ EFI, timing @ idle can be as high as 42* depending upon amount of air in combustion chamber. There are multiple tables that alter that timing based on temp, cranking, TB position, etc. So, that 42* could be 18* under certain conditions. W/ the MSD & carb, it needs to be close to correct in the MSD table & then adjusted w/ vacuum advance. Looks like carb'd engine is more sensitive to low engine speed timing.
Second, around 26* max is peak timing @ WOT, 94-102 KPa MAP; anymore will cause pre-detonation. I saw carb'd stock cubed LS1's, 5.7L getting away w/29*. W/ EFI, the max spark is based on MAP & RPM. Does the MSD 6010 accept a vacuum line for MAP or is timing solely RPM based @ WOT?
I do have a wide band 02 sensor & plan to connect knock sensors to something that will indicate knock to me. So, I will be able to alter timing & fuel based on A/F ratio & knock. Will be interesting to me to see how much WOT timing the carb'd engine will take.
W/ EFI, timing @ idle can be as high as 42* depending upon amount of air in combustion chamber. There are multiple tables that alter that timing based on temp, cranking, TB position, etc. So, that 42* could be 18* under certain conditions. W/ the MSD & carb, it needs to be close to correct in the MSD table & then adjusted w/ vacuum advance. Looks like carb'd engine is more sensitive to low engine speed timing.
Second, around 26* max is peak timing @ WOT, 94-102 KPa MAP; anymore will cause pre-detonation. I saw carb'd stock cubed LS1's, 5.7L getting away w/29*. W/ EFI, the max spark is based on MAP & RPM. Does the MSD 6010 accept a vacuum line for MAP or is timing solely RPM based @ WOT?
I do have a wide band 02 sensor & plan to connect knock sensors to something that will indicate knock to me. So, I will be able to alter timing & fuel based on A/F ratio & knock. Will be interesting to me to see how much WOT timing the carb'd engine will take.
06-21-2014, 06:57 PM
#13
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I'd seriously consider a cam swap if you are wanting the carb to perform well.
If you go somewhere around 232/238 111+3 this will work better with a carb intake, and dynamic comp should remain similar, although I'd personally select lobes that lower DCR anyway.
And being a road race deal a 750 carb will probably be fine.
If you go somewhere around 232/238 111+3 this will work better with a carb intake, and dynamic comp should remain similar, although I'd personally select lobes that lower DCR anyway.
And being a road race deal a 750 carb will probably be fine.
06-22-2014, 05:54 AM
#14
W/ EFI, timing @ idle can be as high as 42* depending upon amount of air in combustion chamber. There are multiple tables that alter that timing based on temp, cranking, TB position, etc. So, that 42* could be 18* under certain conditions. W/ the MSD & carb, it needs to be close to correct in the MSD table & then adjusted w/ vacuum advance. Looks like carb'd engine is more sensitive to low engine speed timing.
Second, around 26* max is peak timing @ WOT, 94-102 KPa MAP; anymore will cause pre-detonation. I saw carb'd stock cubed LS1's, 5.7L getting away w/29*. W/ EFI, the max spark is based on MAP & RPM. Does the MSD 6010 accept a vacuum line for MAP or is timing solely RPM based @ WOT?
https://ls1tech.com/forums/showthread.php?t=1675175&styleid=27
06-23-2014, 09:48 AM
#17
As for the intake, I am not sure which intake the "mid rise" is referring to. What is the actual part number?
06-23-2014, 10:45 AM
#18
I would say no to the vacuum secondary carburetor in a road race car because I would think you would want full throttle control for precision. Vacuum secondary carburtetors simply do not offer that.
As for the intake, I am not sure which intake the "mid rise" is referring to. What is the actual part number?
As for the intake, I am not sure which intake the "mid rise" is referring to. What is the actual part number?
06-24-2014, 12:26 PM
#20
Thanks for the heads up & the cam info. Car's been down all season. So, I'm gonna just get 'er goin for now & then look into a different cam in the late Fall. I'm very leary of getting an agressive lobe that likes to destroy lifters; a conversation for another day.
Got a pile of parts now & am gonna begin the swap to a carb. Starting a carb swap thread to add to the archives.
Thanks again men. You're advice is well appreciated.
