How much of a power gain from 11.5:1 pistons?
09-22-2003, 06:56 PM
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How much of a power gain from 11.5:1 pistons?
If a stock 350Z dynoes at 250 rwhp with its stock 10.3:1 pistons. Should a 350Z with no other modes except some 11.5:1 ratio pistons put out around 279 rwhp then? I am assuming the increase in compression is directly proportional with the increase in rwhp. I doubt this is true in real life but it should be close, no?
If not, where are the loses at?
Oh, what are some of the benefits besides increase in hp?
What are some concerns to watch out for?
If not, where are the loses at?
Oh, what are some of the benefits besides increase in hp?
What are some concerns to watch out for?
Last edited by Enron Exec; 09-22-2003 at 06:59 PM.
09-22-2003, 08:25 PM
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With higher compression you will rev faster and it sounds different.. much cooler - at least that is what happens on other cars I have seen with higher compression. Also you will have more low end power/torque but the high end will suffer a tad because all that extra compression makes it harder to spin fast. I had a 396 cid smallblock motor with 12.2:1 compression and I could barely turn the thing over manually.
I doubt you'd see 29 rhwp from 1.2 extra compression points, but hey this motor is new and no one really knows what it will do. Usually you see about 20 hp (flywheel) from each point in compression, but you reach a point of diminishing return after 11:1 or so.
A final thing to note about higher compression... Cylinder head temps play a big role in whether you will get pre-ignition (pinging). A cast iron block with cast iron heads and a standard cooling system will start to detonate around 10:1, the aluminum heads lets you turn it up some, and I guess an aluminum block might help dissipate some more heat that might make it to the heads. I would guess that 11.5:1 is probably getting close to the detonation mark on a hot day with the stock cooling system, but like I said... it's a new motor and it's anyone's guess right now
I doubt you'd see 29 rhwp from 1.2 extra compression points, but hey this motor is new and no one really knows what it will do. Usually you see about 20 hp (flywheel) from each point in compression, but you reach a point of diminishing return after 11:1 or so.
A final thing to note about higher compression... Cylinder head temps play a big role in whether you will get pre-ignition (pinging). A cast iron block with cast iron heads and a standard cooling system will start to detonate around 10:1, the aluminum heads lets you turn it up some, and I guess an aluminum block might help dissipate some more heat that might make it to the heads. I would guess that 11.5:1 is probably getting close to the detonation mark on a hot day with the stock cooling system, but like I said... it's a new motor and it's anyone's guess right now
09-23-2003, 09:54 AM
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If you look at an Acrua RSX Type-S which has a compression ratio of 11.0:1. It has much more horsepower at higher RPM's. Redline is at 7,400 RPM. Low end torque is very weak. There is lots of torque and HP at higher RPM's. My RSX ran best from 6000 rpm to 8000 rpm. In general higher compression allows you to run at higher RPM's assuming the rest of the engines internals can take the higher compression. I loved my high reving RSX. I wish somebody would put in some higher compression pistons, and raise the fuel shut off to see what the 350 is capable of. I think the results would be very good. 11.5:1 should be fine on 93 octane gas. You could probable get a little more compression out of our engines if you put thinner head gaskets on. I don't know how thick they are now, but on the Acura there was a thinner head gasket available that would raise the compression a bit. All i know is that a high reving n/a engine is very reliable if built right.
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09-24-2003, 08:01 AM
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Hey Zoasis why is there only 91 octane in Blue Springs, MO? Not that I am looking, but in St. Louis I have never seen 91. I have seen 92. Most places in St. Louis sell 93. Raising compression to 11.5:1 may have slight problems with 91 octane. I have read that some people have done it in CA and have ran 91 octane with no problems, but that is in a RSX. Z,s may be different.
Running 11.1:1 will be fine on 91 octane. I would really like to see the performance change in the Z after doing that. People were changing from 11.0:1 to 11.5:1 in the RSX,s and were getting good results. They were rasing torque and I can't remeber what kind of HP gains they were getting. I don't remeber all the details, but if you search clubrsx.com you will be able to find them. If I had some money and wanted to definatley stay n/a I would consider this. You don't need different cams to get better results either. You can get better results by adding different cams which if you have the car apart and have the money may as well.
Running 11.1:1 will be fine on 91 octane. I would really like to see the performance change in the Z after doing that. People were changing from 11.0:1 to 11.5:1 in the RSX,s and were getting good results. They were rasing torque and I can't remeber what kind of HP gains they were getting. I don't remeber all the details, but if you search clubrsx.com you will be able to find them. If I had some money and wanted to definatley stay n/a I would consider this. You don't need different cams to get better results either. You can get better results by adding different cams which if you have the car apart and have the money may as well.
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