supercharging question about compression

Drowzysleeper · Post by **Drowzysleeper** » Thu Apr 19, 2007 5:39 pm

i have heard a few times now that 10.5 to 1 compression would be ok to supercharge. i always thought that higher compression would be bad to boost. can anyone clear this up for me. any help would be great.

Clayton · Post by **Clayton** » Thu Apr 19, 2007 5:52 pm

the lower compression you go the higher boost you can run

Spork · Post by **Spork** » Thu Apr 19, 2007 6:03 pm

Maybe I have been miss guided (at this point, several times), but based on what I've learned about the topic, I tend to see that as just running in circles :dunno: low compression + high boost = high compression + low boost... eventually you reach the breaking point (of the weakest componant) of the motor and it will blow no matter which way you build it. the difference lies in the tuning: lower compression allows for a larger margin of error when tuning, while high compression means you have to tune much more precisely in order to prevent detonation and catastrophic failure.

But I've never really understood the logic in lowering compression just to add more boost, always kinda seemed like 'two steps back, then two steps forward' to me, I suppose it makes some sense for a daily driver since you need it to be as reliable as possible, but for real 'race' motors, I don't see any point. But the whole point of supercharging is to add low-end (thats basically the advantage right) so why build for lower compression and lose torque, just to use a supercharger to get it back to the stock numbers... then you need to go and buy a bigger pulley so that you can see real power gains. :dunno: someone correct me.

rickles8099 · Post by **rickles8099** » Thu Apr 19, 2007 6:42 pm

Spork;37156 wrote:Maybe I have been miss guided (at this point, several times), but based on what I've learned about the topic, I tend to see that as just running in circles :dunno: low compression + high boost = high compression + low boost... eventually you reach the breaking point (of the weakest componant) of the motor and it will blow no matter which way you build it. the difference lies in the tuning: lower compression allows for a larger margin of error when tuning, while high compression means you have to tune much more precisely in order to prevent detonation and catastrophic failure.

But I've never really understood the logic in lowering compression just to add more boost, always kinda seemed like 'two steps back, then two steps forward' to me, I suppose it makes some sense for a daily driver since you need it to be as reliable as possible, but for real 'race' motors, I don't see any point. But the whole point of supercharging is to add low-end (thats basically the advantage right) so why build for lower compression and lose torque, just to use a supercharger to get it back to the stock numbers... then you need to go and buy a bigger pulley so that you can see real power gains. :dunno: someone correct me.

all my understandings too but ill add this little equasion:
supercharging a fwd honda = pointless

on a fwd car (like 95% of hondas) you dont want low end torque because you'll just spin the tires. its better to have high end torque. now if we were talking about supercharging a rwd car, its totally different because of the physics in taking off from the line.

v-tecivic · Post by **v-tecivic** » Thu Apr 19, 2007 6:45 pm

spork has it explained pretty good. from what i've read also, everybody always says to get a good tune for the best reliability of the motor when running a higher compression. if its your daily driver and you don't see yourself getting another one anytime soon, a lower compression build could give you a little more comfort in case something goes wrong. a higher compression will obviously give you more power too, but with a smaller margin of error with the tune.

Spork · Post by **Spork** » Thu Apr 19, 2007 6:56 pm

rickles8099;37161 wrote:all my understandings too

v-tecivic;37163 wrote:spork has it explained pretty good.

thank you, I feel slightly more sane now.

continue with the discussion!

Post by **stolle** » Thu Apr 19, 2007 7:18 pm

supercharging a 4 cylinder is pointless think about it takes torque to spin the SC
4 cylinders dont have much torque when you throw lower compression in, it lowers the torque even more when your engine is trying to spin up the SC making low end even worse (believe me i rode in SC honda with a built low CR y8 it was slow as hell). it takes hp/torque to make hp/torque with a SC since we dont have a lot to start off with you wont end up making much in the end. not to mention when your just driving around the SC is always producing boost putting even more strain on engine components. a turbo on the other hand uses a byproduct of what the engine wastes anyway its pretty much free HP and the fact that boost isnt being produced when your cruising you get just as good of gas mileage as you did n/a or better. with a moderately sized or small turbo you can have the best of both worlds mid range for moving through traffic and a little more high end for acceleration giving a honda what it needs most TORQUE and better drive ability ie: you wont have to tag redline to get some ass out of your car...

90CivicEx · Post by **90CivicEx** » Thu Apr 19, 2007 8:55 pm

I would go turbo before super chargeing anyday on a honda

Drowzysleeper · Post by **Drowzysleeper** » Thu Apr 19, 2007 10:24 pm

well see i wanted to go turbo on my ls hatch then i picked up another ls the is basically a mild n/a build. it has 10.5 compression crower stage 2 cams and springs and retainers. so for 525 i thought it was a decent deal. i was thinking that most turbo apps i have seen had lowered compression, so i figured it would be kinda bad to go turbo. on the other hand i have read about being able to supercharge a motor with higher compression. so if its possible to boost my motor with a turbo i will probably do that. also this will not be my daily driver. would the cams i mentioned be ok for boost? i know they have turbo cams.

Spork · Post by **Spork** » Thu Apr 19, 2007 10:36 pm

well, like we've said, higher compression will net you more power down low, so 'in theory' it would be more suited for supercharging than lower compression. as far as 10.5:1 compression for turbo, all of the VTEC b-series motors run 10+:1 compression ratios, and they get boosted all the time. But, you just have to make sure you get a good tune so you don't blow it up.

and as far as cams go, I believe the major rule of thumb is that you want to avoid overlap, higher lift and longer duration are alright, but you don't want a lot of overlap (all the intake and exhaust valves open at the same time)... at least I believe thats the way you want it, it's been a long week, and I still don't feel like I am thinking completely straight.