Highest compression for boost?

[trxcobra]

So I've been toying with the idea of putting a centri on my car, however it is already a built N/A setup and is somewhere around 11-11:5:1 compression. Would I be able to run a low boost setup and still be reliable on pump gas? I also have Comp #106400 N/A cams at the moment so I don't know if those would bring any issues as well.
Is nitrous my best option without having to rip into my motor again??

Thanks guys!

 

[SlowSVT]

You mean: "Highest boost for compression" not the other way around

A reliable 11.5:1 FI motor running pump gas?

Since the motor is pretty much at the limits of detonation on pump gas I would say probably 0-2 lbs.

Now worth putting a blower on this engine with those slugs in there. Is the bottom end forged?

 

[trxcobra]

You mean: "Highest boost for compression" not the other way around

A reliable 11.5:1 FI motor running pump gas?

Since the motor is pretty much at the limits of detonation on pump gas I would say probably 0-2 lbs.

Now worth putting a blower on this engine with those slugs in there. Is the bottom end forged?

haha that's kind of the answer I was expecting to get. Yes the bottom end is forged

 

[na svt]

n2o

 

[OW99]

n2o

Yes!!

 

[SlowSVT]

haha that's kind of the answer I was expecting to get. Yes the bottom end is forged

Not a huge stretch installing low compression pistons. Doing that with a blower will put your car into a whole new realm :mj:

 

[na svt]

Not a huge stretch installing low compression pistons.

Engine removal, disassembly, boring, honing, new gaskets, reassembly, install...should have it done over a weekend.

 

[AntiHeightPunk]

na svt what is the highest compression you would do on an e85 turbo car?

 

[Myersprostatus]

what about a centri on a 10.5:1 compression engine? Think I could run 10psi of boost?

 

[na svt]

10.5:1

 

[Myersprostatus]

I actually have Sean Hylands book and in it as im reading he states that he always runs a higher compression engine with a centrifugal supercharger. He states that he keeps a flat top piston whether street or race. It states he experimented with centri superchargers on 4v engines with a lower compression and the results were loss of torque in the lower RPM range with no measurable change in ignition timing sensitivity in the higher RPM range. He then goes on to talk about how he runs 30+ lbs of boost and still maintains a flat top 10.2:1 compression ratio engine.

It says lower compression is ideal for an eaton style supercharger or turbo charger, but centris come on hard at about 3k rpms and like higher compression.

 

[na svt]

I actually have Sean Hylands book and in it as im reading he states that he always runs a higher compression engine with a centrifugal supercharger. He states that he keeps a flat top piston whether street or race. It states he experimented with centri superchargers on 4v engines with a lower compression and the results were loss of torque in the lower RPM range with no measurable change in ignition timing sensitivity in the higher RPM range. He then goes on to talk about how he runs 30+ lbs of boost and still maintains a flat top 10.2:1 compression ratio engine.

It says lower compression is ideal for an eaton style supercharger or turbo charger, but centris come on hard at about 3k rpms and like higher compression.

centris don't come on hard at 3k, they make boost in a linear fashion so the pint at which the "come on hard" is determined bu the intake and cams.

It's common knowledge that centris combos can benefit from more static compression and the same goes for turbos.

PD and turbo combos will lose about 50hp/50tq when dropping from 10:1 to 8.5:1.

 

[trxcobra]

Thanks for the replies, so basically the highest compression I would want on pump 93 with boost is 10.5:1. I have no plans of tearing down the motor anytime soon so that will have to wait haha.

Nitrous would be cool but it just scares me for some reason. I guess my motor is built to handle it though, so why not haha. Wouldnt be able to spray too much anyways without blowing the t45

 

[whiteboyawesome]

Spray the piss out of it an buy a new tranny

 

[procharged 99]

Boost and E85

 

[SlowSVT]

I actually have Sean Hylands book and in it as im reading he states that he always runs a higher compression engine with a centrifugal supercharger. He states that he keeps a flat top piston whether street or race. It states he experimented with centri superchargers on 4v engines with a lower compression and the results were loss of torque in the lower RPM range with no measurable change in ignition timing sensitivity in the higher RPM range. He then goes on to talk about how he runs 30+ lbs of boost and still maintains a flat top 10.2:1 compression ratio engine.

It says lower compression is ideal for an eaton style supercharger or turbo charger, but centris come on hard at about 3k rpms and like higher compression.

Be wary of professional racers running 30 lbs of boost giving advice to street car owners (2 different Worlds). Running high compression on a centrifugal blower engine is a band-aid to make-up for its short coming at low end.

 

[SlowSVT]

Engine removal, disassembly, boring, honing, new gaskets, reassembly, install...should have it done over a weekend.

If the engine does not have a lot of miles on the bores you can get away with a flexi-hone to scratch the cylinders for ring break-in which is possible to do without removing the engine. Adding a blower means you will want more PWC and chances are you won't need an overbore. I would do this before just topping the engine with a blower.

 

[trxcobra]

If the engine does not have a lot of miles on the bores you can get away with a flexi-hone to scratch the cylinders for ring break-in which is possible to do without removing the engine. Adding a blower means you will want more PWC and chances are you won't need an overbore. I would do this before just topping the engine with a blower.

As much as I would love to do this, I simply don't have the time or money to go through the motor like that on top of a blower set up. I would rather just leave it as is for now.

What would be my main worries with a nitrous setup? I would probably only run 100 shot or so until I swap transmissions or build mine down the road

 

[SlowSVT]

As much as I would love to do this, I simply don't have the time or money to go through the motor like that on top of a blower set up. I would rather just leave it as is for now.

What would be my main worries with a nitrous setup? I would probably only run 100 shot or so until I swap transmissions or build mine down the road

Good call

 

[OW99]

What would be my main worries with a nitrous setup? I would probably only run 100 shot or so until I swap transmissions or build mine down the road

With only a 100 shot you only have to worry about puddling in the intake from spraying too low a rpm and spark being too advanced.
2-2.5 degrees retard per 50hp increase is the rule of thumb.
Spray higher than 3,000rpm is also.
The fuel pump should be sized to what your car makes on spray.
In tuning you should tune to the leanest cylinder to make sure there is no detonation. Nitrous should have the same wot a/f ratio as na. But richer is better than leaner. But that shouldn't be an issue with just a 100 shot.