Optimum CR to SC an RV8
Discussion
I've always understood that Lower (relative) compression is better than higher compression if you're going to bolt a SC onto an engine. My RV8 500 has 10.5:1 CR at the mo. is this good or bad for a SC ? Is it way too high or acceptable, or way off giving max output in terms of bang for bucks? Appreciate all opinions 
If you lower the compression ratio you will lose responce and power before going into boost. But you will be able to run a higher boost level (given the correct setup). The reason is that detonation will occure at lower boost levels with a higher compression ratio.
Given your blower setup you will probably end up with 7-9ish PSI, with a 10.5:1 cr is about as much as youd want to put through it. At the end of the day you need to suck it and see. You can always fit a larger pulley to slow it down.
Im running 10.44:1cr and using the same blower as you. Im up to 6psi without any issues so far, thats with a good intercooling system, knock detection, sequential fuel / spark, etc. (110mm pulley) I may fit the 100mm pulley I have to increase boost to 8ish and see how that goes, but for now Im over the moon with how it runs at 6psi. Off boost responce is fantastic, when the boost builds (2psi by 2800rpm) it is increadable,
Phil
Given your blower setup you will probably end up with 7-9ish PSI, with a 10.5:1 cr is about as much as youd want to put through it. At the end of the day you need to suck it and see. You can always fit a larger pulley to slow it down.
Im running 10.44:1cr and using the same blower as you. Im up to 6psi without any issues so far, thats with a good intercooling system, knock detection, sequential fuel / spark, etc. (110mm pulley) I may fit the 100mm pulley I have to increase boost to 8ish and see how that goes, but for now Im over the moon with how it runs at 6psi. Off boost responce is fantastic, when the boost builds (2psi by 2800rpm) it is increadable,
Phil
Edited by daxtojeiro on Sunday 18th March 17:17
daxtojeiro said:
If you lower the compression ratio you will lose responce and power before going into boost. But you will be able to run a higher boost level (given the correct setup). The reason is that detonation will occure at lower boost levels with a higher compression ratio.
Given your blower setup you will probably end up with 7-9ish PSI, with a 10.5:1 cr is about as much as youd want to put through it. At the end of the day you need to suck it and see. You can always fit a larger pulley to slow it down.
Im running 10.44:1cr and using the same blower as you. Im up to 6psi without any issues so far, thats with a good intercooling system, knock detection, sequential fuel / spark, etc. (110mm pulley) I may fit the 100mm pulley I have to increase boost to 8ish and see how that goes, but for now Im over the moon with how it runs at 6psi. Off boost responce is fantastic, when the boost builds (2psi by 2800rpm) it is increadable,
Phil
Phil I think you've got me confused with someone else mate my motors N/A...... But I do need your help to get it mapped on Clive's RR when you have the time Given your blower setup you will probably end up with 7-9ish PSI, with a 10.5:1 cr is about as much as youd want to put through it. At the end of the day you need to suck it and see. You can always fit a larger pulley to slow it down.
Im running 10.44:1cr and using the same blower as you. Im up to 6psi without any issues so far, thats with a good intercooling system, knock detection, sequential fuel / spark, etc. (110mm pulley) I may fit the 100mm pulley I have to increase boost to 8ish and see how that goes, but for now Im over the moon with how it runs at 6psi. Off boost responce is fantastic, when the boost builds (2psi by 2800rpm) it is increadable,
Phil
Edited by daxtojeiro on Sunday 18th March 17:17
8.2cr was the favoured standard, but the 4L cars have run 10.5 without issue.
The 500s have mostly (not all) suffered issues at 10.5. I guess the stroker engines have more sweep volume etc leading to greater detonation.
Anyway, when I looked into it in 2003, everyone was saying 8.5 max and noting above 4.6L, but charge cooling was improving alot at that time. Dennis Priddle had an excellent one he was developing.
A
The 500s have mostly (not all) suffered issues at 10.5. I guess the stroker engines have more sweep volume etc leading to greater detonation.
Anyway, when I looked into it in 2003, everyone was saying 8.5 max and noting above 4.6L, but charge cooling was improving alot at that time. Dennis Priddle had an excellent one he was developing.
A
daxtojeiro said:
I thought you were the guy who had all the engine issues. Ohh, he was Jammy dodger. I cant cope with more than one thing at a time. I must go and take another pill 
Phil
This isn't good news, the worlds leading expert on megasquirt has mistaken me for the worlds unluckiest man. Somebody please help, this thread is in danger of entering the twilight zone Phil
Edited by Chilliman on Sunday 18th March 17:53
Guillotine said:
8.2cr was the favoured standard, but the 4L cars have run 10.5 without issue.
The 500s have mostly (not all) suffered issues at 10.5. I guess the stroker engines have more sweep volume etc leading to greater detonation.
Anyway, when I looked into it in 2003, everyone was saying 8.5 max and noting above 4.6L, but charge cooling was improving alot at that time. Dennis Priddle had an excellent one he was developing.
A
Thanks Andy, sounds like 10.5:1 is a non starter for a 500.....The 500s have mostly (not all) suffered issues at 10.5. I guess the stroker engines have more sweep volume etc leading to greater detonation.
Anyway, when I looked into it in 2003, everyone was saying 8.5 max and noting above 4.6L, but charge cooling was improving alot at that time. Dennis Priddle had an excellent one he was developing.
A
neal1980 said:
Im at 8.5CR with mine all seems good. Come on Chilli get it on there!
Tempted mate, but I've reached the point where I'll never get the money back although obviously that hasn't stopped me so far just to put it in perspective the car stands me in at a little over 23k in a little over 15 months.... It is fecking quick though 
Chilliman said:
neal1980 said:
Im at 8.5CR with mine all seems good. Come on Chilli get it on there!
Tempted mate, but I've reached the point where I'll never get the money back although obviously that hasn't stopped me so far just to put it in perspective the car stands me in at a little over 23k in a little over 15 months.... It is fecking quick though Chilliman said:
Tempted mate, but I've reached the point where I'll never get the money back although obviously that hasn't stopped me so far just to put it in perspective the car stands me in at a little over 23k in a little over 15 months.... It is fecking quick though
I`ll take that engine of yours off your hands. That will give you a couple of grand towards a new lower comp one. just to put it in perspective the car stands me in at a little over 23k in a little over 15 months.... It is fecking quick though 
Fully awake now Too much work and an early start with the F1 is to blame I hope!
Anyhow, dont worry about the cr, simply limit the boost to a reasonable amount. Like I said, mine is a 5.4L from V8D at 10.44:1 and runs 6psi without any issues.
Im not saying it would run as much as 8.5cr would, but as I've now maxed out my 32LB injectors and have had to fit 36LB to keep the fuelling correct, I dont think its low on power, Guestimate 430-450BHP.
I may try the other pulley I have (100mm) in the summer, but to be honest, as it responds so well at all rev ranges I may leave it at that.
I dont think the 500 issues are down to long strokes or the cr, I think its something else.
Phil
Too much work and an early start with the F1 is to blame I hope!Anyhow, dont worry about the cr, simply limit the boost to a reasonable amount. Like I said, mine is a 5.4L from V8D at 10.44:1 and runs 6psi without any issues.
Im not saying it would run as much as 8.5cr would, but as I've now maxed out my 32LB injectors and have had to fit 36LB to keep the fuelling correct, I dont think its low on power, Guestimate 430-450BHP.
I may try the other pulley I have (100mm) in the summer, but to be honest, as it responds so well at all rev ranges I may leave it at that.
I dont think the 500 issues are down to long strokes or the cr, I think its something else.
Phil
Chilliman said:
neal1980 said:
Im at 8.5CR with mine all seems good. Come on Chilli get it on there!
Tempted mate, but I've reached the point where I'll never get the money back although obviously that hasn't stopped me so far just to put it in perspective the car stands me in at a little over 23k in a little over 15 months.... It is fecking quick though Gassing Station | General TVR Stuff & Gossip | Top of Page | What's New | My Stuff