boost vs. comp....can i beat the system?

keakua · 06-24-2002, 05:47 PM

alright, here's the deal, I'm trying to get the best of both worlds with a relatively high comp. and high boost engine that runs on pump gas. i recently blew a hole in a piston on my stock bottom end leaninging it out. so i rebuilt it with forged pistons, 331 crank, and o-ringed, arp stud edelbrock heads making 10.25:1 compression. then i might of got a little greedy adding 2.5" 10 rib pulleys on my vortech S-trim (hoping for @18#s boost). i've completely redone the fuel system to easily support but i'm pretty sure that with this setup i'm going to have to run the avgas if i really want to stomp on the gas and put the tremec to work. i was wondering if anyone ever heard of water-injection to lower intake charge and reduce detonation? i would love to not have to get a bigger pulley and lower the boost to avoid the $5.00/gallon avgas. can i beat the system? any suggestions or opinions are greatly appreciated. thanks
shane

Current setup: 88 conv, 331 forged cat crank, JE pistons, vortech 10 rib S-trim, ported edelbrock heads, .580" custom lunati cam, extrude honed ported cobra intake, 70 mm t-body, Pro-M 77, 42# inj., dual walbro 255lph in tank pumps, putting it down through a full griggs GR-40R suspension, and nitto drag radials and then some

Unit 5302 · 06-24-2002, 07:00 PM

Should be able to get high octane gas for about $3.50/gallon. 10.25:1 compression and 18psi? Are you intercooled? Yes I've heard of water injection, but I'm un-knowledgable on how effective it is.

BilLster · 06-24-2002, 07:08 PM

water injection wouldnt really solve your problem you need to lower your initial compression and then you can raise the boost and use some type of boost retard i.ve run 25 lbs of boost on 104 chevron pump gas before things started to detonated but the btm was at full retard so maybe if i lowered the initial timing
i never run more than 8 lbs on the street but i have a adjustable wasted gates so i can crank it up if a rice mobil wanst some fun .

so a smaller pulley on the street would be your way to go.

also remember all boost isnt the same another intake might give you more power but lower boost # depending on the gauge your running.

and have you looked at cuttimg you own gas i can buy race gas by the 45 gal drum its a lot cheaper and three of use split the cost and mix it with pump gas for the strip. they also sell it in 5 gal pails but its not worth it if you have the space.

keakua · 06-24-2002, 10:03 PM

no, its a vortech so no intercooler. i was looking into the aftercooler they sell, but probably would end up sacraficing power and changing pulleys before posting the money for the aftercooler. i have boost retard that worked good enough with the stock pistons and 12#s of boost, but i'm not sure how its going to work with 18#s. do they sell wastegates for superchargers? i know for turbos but i've never seen one for blowers

MiracleMax · 06-24-2002, 10:35 PM

Hmmmm.... I wonder what the dynamic comp ratio would be? the highest I've ever seen was about 16:1, but the return on investment wasn't worth the effort, after about 14.5:1 the gains are so small that its not worth it worth it with a gasoline engine.

As I remember the heads required a seperate cooling system. which indicates to me that the heads were running really cool (well relative to the block) and probably sucked more power away than what the 16:1 was worth.

If I also remeber correctly every point you bump the compression up its worth about 4% more power. However reducing chamber volume is also a gain of diminishing returns (especially in a SC'd app), you end up reducing chamber volume which displaces some of the fuel and air you'd pump into the engine.

Rather than pumping up the static compression ratio, you might consider increasing boost?

keakua · 06-24-2002, 10:50 PM

i'm actually considering lowering boost as the 10.25 comp is pretty high for a blower. i love the throttle response of a high-comp engine, so I would rather not cut the piston to lower comp, and i'm trying to figure out a way to keep the 18#s of boost without detonation on pump gas

Stroked408 · 06-25-2002, 09:14 PM

Bottom line boost and that high of a compression ratio just do not mix period.

You have a stout bottom end just lower compression down to 8.8 or 9.1 and then run the boost.

10.25 with 18 pounds of boost is asking for trouble,Turbo Pro 5.0 cars do not run compression that high,you might hear of them running 8.8 as the high.

keakua · 06-25-2002, 10:17 PM

after 8 months on jack stands i'm not sure i can bring myself to ripping it all out to cut the pistons. probably will end up lowering boost if there are no other options. any other suggestions?

06-24-2002, 05:47 PM	#1
keakua Registered Member Join Date: Jun 2002 Location: phoenix, az Posts: 20	boost vs. comp....can i beat the system? alright, here's the deal, I'm trying to get the best of both worlds with a relatively high comp. and high boost engine that runs on pump gas. i recently blew a hole in a piston on my stock bottom end leaninging it out. so i rebuilt it with forged pistons, 331 crank, and o-ringed, arp stud edelbrock heads making 10.25:1 compression. then i might of got a little greedy adding 2.5" 10 rib pulleys on my vortech S-trim (hoping for @18#s boost). i've completely redone the fuel system to easily support but i'm pretty sure that with this setup i'm going to have to run the avgas if i really want to stomp on the gas and put the tremec to work. i was wondering if anyone ever heard of water-injection to lower intake charge and reduce detonation? i would love to not have to get a bigger pulley and lower the boost to avoid the $5.00/gallon avgas. can i beat the system? any suggestions or opinions are greatly appreciated. thanks shane Current setup: 88 conv, 331 forged cat crank, JE pistons, vortech 10 rib S-trim, ported edelbrock heads, .580" custom lunati cam, extrude honed ported cobra intake, 70 mm t-body, Pro-M 77, 42# inj., dual walbro 255lph in tank pumps, putting it down through a full griggs GR-40R suspension, and nitto drag radials and then some

06-24-2002, 07:08 PM	#3
BilLster Registered Member Join Date: Oct 2000 Location: Ontario canada Posts: 446	water injection wouldnt really solve your problem you need to lower your initial compression and then you can raise the boost and use some type of boost retard i.ve run 25 lbs of boost on 104 chevron pump gas before things started to detonated but the btm was at full retard so maybe if i lowered the initial timing i never run more than 8 lbs on the street but i have a adjustable wasted gates so i can crank it up if a rice mobil wanst some fun . so a smaller pulley on the street would be your way to go. also remember all boost isnt the same another intake might give you more power but lower boost # depending on the gauge your running. and have you looked at cuttimg you own gas i can buy race gas by the 45 gal drum its a lot cheaper and three of use split the cost and mix it with pump gas for the strip. they also sell it in 5 gal pails but its not worth it if you have the space. __________________ 89 with 331 t3'/t4 hybrids. upr Suspention worked out finnaly . 9.89 144 mph .

06-24-2002, 10:35 PM	#5
MiracleMax Registered Member Join Date: Apr 1999 Location: Hayes, Va, USA Posts: 798	Hmmmm.... I wonder what the dynamic comp ratio would be? the highest I've ever seen was about 16:1, but the return on investment wasn't worth the effort, after about 14.5:1 the gains are so small that its not worth it worth it with a gasoline engine. As I remember the heads required a seperate cooling system. which indicates to me that the heads were running really cool (well relative to the block) and probably sucked more power away than what the 16:1 was worth. If I also remeber correctly every point you bump the compression up its worth about 4% more power. However reducing chamber volume is also a gain of diminishing returns (especially in a SC'd app), you end up reducing chamber volume which displaces some of the fuel and air you'd pump into the engine. Rather than pumping up the static compression ratio, you might consider increasing boost? __________________ 2002 5M GT (99% stock) 1991 5M LX (30% stock) patiently awaiting my satin silver 07 Mach 1, and don't forget the shaker

06-25-2002, 09:14 PM	#7
Stroked408 Registered Member Join Date: Jun 2002 Location: Southwest Posts: 131	Bottom line boost and that high of a compression ratio just do not mix period. You have a stout bottom end just lower compression down to 8.8 or 9.1 and then run the boost. 10.25 with 18 pounds of boost is asking for trouble,Turbo Pro 5.0 cars do not run compression that high,you might hear of them running 8.8 as the high. __________________ Deeper,Harder,Faster Stage Deeper Launch Harder Go Faster

06-25-2002, 10:17 PM	#8
keakua Registered Member Join Date: Jun 2002 Location: phoenix, az Posts: 20	after 8 months on jack stands i'm not sure i can bring myself to ripping it all out to cut the pistons. probably will end up lowering boost if there are no other options. any other suggestions? __________________ 88 Conv Vortech S-trim 2.5" 10-rib pulley, 332 stroker w/ Cat forged crank, forged JE flat-tops, forged rods, 10.25:1 comp, DSS girdle, edelbrock heads, Omega valvetrain, Lunati custom cam, extrude honed Cobra intake, 70mm T-body, Pro-M 77, bypass valve, dual Walbro 255 lph in tank pumps, an -8 fuel hose, aeromotive fuel rails/regulater. 42# inj, MSD ingniton/boost retard, JBA headers, flowmasters, full Griggs GR-40R suspension (K-member, torque arm, panhard bar, subframes, strut brace) Centerforce clutch, Tremec, Auburn posi locker, moser axles, Baer brakes/rotors, 17" cobra R wheels, custom body/roll bar

06-24-2002, 07:00 PM	#2
Unit 5302 Registered Member Join Date: May 1999 Posts: 5,246	Should be able to get high octane gas for about $3.50/gallon. 10.25:1 compression and 18psi? Are you intercooled? Yes I've heard of water injection, but I'm un-knowledgable on how effective it is.

06-24-2002, 10:03 PM	#4
keakua Registered Member Join Date: Jun 2002 Location: phoenix, az Posts: 20	no, its a vortech so no intercooler. i was looking into the aftercooler they sell, but probably would end up sacraficing power and changing pulleys before posting the money for the aftercooler. i have boost retard that worked good enough with the stock pistons and 12#s of boost, but i'm not sure how its going to work with 18#s. do they sell wastegates for superchargers? i know for turbos but i've never seen one for blowers

06-24-2002, 10:50 PM	#6
keakua Registered Member Join Date: Jun 2002 Location: phoenix, az Posts: 20	i'm actually considering lowering boost as the 10.25 comp is pretty high for a blower. i love the throttle response of a high-comp engine, so I would rather not cut the piston to lower comp, and i'm trying to figure out a way to keep the 18#s of boost without detonation on pump gas

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