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
Talk to somebody that does heads and see if they can work on your chambers. I know that you can get them worked to reduce compression. (it is not the goal of the porter but a side effect of re working them for different shape. ( read this on a head article somewhere on the net , from one of the magazines.) Like I said , you need to talk to a head porter and get their advice.
I however would check into getting custom made gaskets that are a little thicker if you can. I have not heard of anybody doing this however.
I however would check into getting custom made gaskets that are a little thicker if you can. I have not heard of anybody doing this however.
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?
Last edited by SiCk PuPpY; Dec 9, 2005 at 08:42 PM.
