F.I. SCR issue (request advice)
Thread Starter
Teching In
Joined: Jul 2005
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F.I. SCR issue (request advice) I am in the proccess of building a F.I. LT1 355 that is projected see about 8-10 lbs of boost (Vortec V-1). Based on my calculations, the SCR came in at 9.7:1 based on the following:
52cc head chambers (clean-up cut/ 2.00 & 1.60 valves using stock seats)
4.030 bore
.039 fel-pro 1074s (4.125 hole)
-20cc wisecos
5.7 rod
3.48 stroke
deck hieght of .015 (assumed based on factory spec;I will doulbe-check how far the piston sits in the hole once the s.b. is assembled)
Accepted theory is that this CR is too high for a F.I. motor. Is DCR more important than SCR? I am researching how to reduce CR without raplacing the pistons. Here's what i've theorized thus far:
-The original valve seats were used, if I have larger seats installed to drop the valves deeper into the chamber, would that significantly increase the chamber volume enough?
-The Fel-Pros are .039 thick. Is there a thicker gasket on the market that will hold up to this moderate amount of boost?
-Can a significant amount of head chamber material be removed on the LT1 heads to reduce SCR?
This is my first F.I. build and I definatley chose the wrong pistons. -20cc was not enough to get to my target 9:1 cr, but replacing them isn't an option. If i'm stuck with this CR, then i'll just have to reduce the boost accordingly and have it tuned accordingly.
Any insight/advice would be greatly apprecieated.
Cheers,
John
52cc head chambers (clean-up cut/ 2.00 & 1.60 valves using stock seats)
4.030 bore
.039 fel-pro 1074s (4.125 hole)
-20cc wisecos
5.7 rod
3.48 stroke
deck hieght of .015 (assumed based on factory spec;I will doulbe-check how far the piston sits in the hole once the s.b. is assembled)
Accepted theory is that this CR is too high for a F.I. motor. Is DCR more important than SCR? I am researching how to reduce CR without raplacing the pistons. Here's what i've theorized thus far:
-The original valve seats were used, if I have larger seats installed to drop the valves deeper into the chamber, would that significantly increase the chamber volume enough?
-The Fel-Pros are .039 thick. Is there a thicker gasket on the market that will hold up to this moderate amount of boost?
-Can a significant amount of head chamber material be removed on the LT1 heads to reduce SCR?
This is my first F.I. build and I definatley chose the wrong pistons. -20cc was not enough to get to my target 9:1 cr, but replacing them isn't an option. If i'm stuck with this CR, then i'll just have to reduce the boost accordingly and have it tuned accordingly.
Any insight/advice would be greatly apprecieated.
Cheers,
John
Thread Starter
Teching In
Joined: Jul 2005
Posts: 46
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Is there a calculator I can use to determine desired SCR based on a given boost number? I was told that I should keep the compression below 9:1 on any F.I. application for detonation.
I understand that "boost" is a relative measurement to detirmine CFM, based on pathway resistance. Shouldn't I be more concernend about impeller speed and rpm to calculate the cfm? Wouldn't that be a more accurate measurement? My goal here is foremost to aviod blowing my motor to pieces and find the best combination for my motor. This is the longblock:
-LT1 2 bolt block w/ ARP studs
-Factory crank turned .010 under (rotating assy. balanced from pulley to flexplate)
-Clevite H series bearings
-Eagle SIR 5.7 rods (549 grams)
-Wiseco "Tru-Forged" -20cc pisons (655 grams w/ the pin, lock and rings)
-Ported LT1 heads w/ 2.00 1.57 Manley Pros 52cc chambers)
--Intake 251 cfm @ .500 exhaust 194 cfm @ .600 (measured without a pipe)
-The poweradder is a Vortech V-1 non-intercooled pushing 6lbs on the factory combo
I understand that "boost" is a relative measurement to detirmine CFM, based on pathway resistance. Shouldn't I be more concernend about impeller speed and rpm to calculate the cfm? Wouldn't that be a more accurate measurement? My goal here is foremost to aviod blowing my motor to pieces and find the best combination for my motor. This is the longblock:
-LT1 2 bolt block w/ ARP studs
-Factory crank turned .010 under (rotating assy. balanced from pulley to flexplate)
-Clevite H series bearings
-Eagle SIR 5.7 rods (549 grams)
-Wiseco "Tru-Forged" -20cc pisons (655 grams w/ the pin, lock and rings)
-Ported LT1 heads w/ 2.00 1.57 Manley Pros 52cc chambers)
--Intake 251 cfm @ .500 exhaust 194 cfm @ .600 (measured without a pipe)
-The poweradder is a Vortech V-1 non-intercooled pushing 6lbs on the factory combo
Thread Starter
Teching In
Joined: Jul 2005
Posts: 46
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I ran 6 lbs (non-intercooled) on the stock LT1 set-up without any issues. The factory pistons were perfect and sparkplugs were fine. I never noticed any detonation issues either; that was at 10.4 to 1. Combination Motorsports can supply me with a set of Cometic .051 thick MLS set for $130 if I absolutely need to go that route.
I am attempting to research the effects of DCR, SCR, quench and boost to figure out what the best approach will be. I am a novice at this and am learning groups of info daily.
With my cam profile (listed below)I got 8.7 to 1 DCR and 9.58 SCR using an online calculator (assumed .020 deck height):
LT1 3314/ 3316 HR115+3
lift- .502/ .520 (@1.5)
Valve timing @.50- open close
int: 0 btdc 44 abdc
exh: 56 bbdc 0 atdc
The specs are for cam installed @112 ICL
Dur- 224/ 236 (@1.5)
Lobe seperation 115 + 3 degress adv. ground in
Since I have no idea how to read a compressor map, I cannot deduce the cfm I am producing with my v-1 S trim Vortech (a 3.33" supercharger and 6.00" crank pulley). Therefore, I assume that the DCR calculators are for NA motors; how would I calculate for a F.I. application? Should I even be concerned?
I am attempting to research the effects of DCR, SCR, quench and boost to figure out what the best approach will be. I am a novice at this and am learning groups of info daily.
With my cam profile (listed below)I got 8.7 to 1 DCR and 9.58 SCR using an online calculator (assumed .020 deck height):
LT1 3314/ 3316 HR115+3
lift- .502/ .520 (@1.5)
Valve timing @.50- open close
int: 0 btdc 44 abdc
exh: 56 bbdc 0 atdc
The specs are for cam installed @112 ICL
Dur- 224/ 236 (@1.5)
Lobe seperation 115 + 3 degress adv. ground in
Since I have no idea how to read a compressor map, I cannot deduce the cfm I am producing with my v-1 S trim Vortech (a 3.33" supercharger and 6.00" crank pulley). Therefore, I assume that the DCR calculators are for NA motors; how would I calculate for a F.I. application? Should I even be concerned?
just put some trickflow heads on it and be done.. 62cc chambers should put ya where you think you need to be, but with a .030" overbore, lowered to 9.7scr and only 8-10 psi of intercooled boost.. just keep the fuel ratio safe and dial the timing in and it as stated above would be an ideal setup not sacrificing power for overkilling your compression ratio decrease.. the higher the compression ratio even with boost the more power you will make per pound of boost, but unfortunately with readily available pump octane ratings, it is tough keeping detonation at bay.. just dial in the tune stay safe on afr and you should be as fine as frogs hair!
Chris
Chris
Thread Starter
Teching In
Joined: Jul 2005
Posts: 46
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Well the bank account is dry, credit cards are maxed and divorce papers are on the way; not really, but i'm at my limiton the large ticket items for this car. New heads are not in the plan and my ported ones flow well.
In Utah, we only have 91 octane premium and we;re at 4500 above sea level.
In Utah, we only have 91 octane premium and we;re at 4500 above sea level.
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TECH Apprentice
Joined: Jan 2004
Posts: 337
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From: Frisco TX (Dallas Area)
FWIW, I built my 383 stroker with 9.7:1 and that's should be ok for 8 psi, more with IC. So I don't see why you wouldn't be good for 10-12 psi with IC and 8 psi without. Both assume a good dyno tune (priceless) and good fuel. HTH 
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