bshonda

iTrader: (1)

in the motor section i notice alot of talk that goes on about DCR ratios and how important it is to get to 8.5 to keep running pump gas. and everyone should select a cam and heads setup to get you to this mark. but what i dont see is anyone talking about how nitrous will affect this ratio. if im going to get a cam and head setup for nitrous, then what should i shot for in a DCR ratio? how much does a 100 shot affect that DCR ratio? what will a 200 shot do to it? how much will more or less valve overlap change this with lower or higher lobe seperation? if i have less lift with more duration, will my DCR rise less or more than it would if i had high lift and long durartion? alot of questions i know, but what bothers me is that i cant find where anyone has ask these questions. and lastly, piano, can you come up with a chart that you could input a nitrous shot and compute what the DCR would rise too?
GO TO WORK GUYS!!!

brad8266

iTrader: (23)

1. Use some puncuation. No offense but its hard to read.
2. DCR does not change at all once the engine is assembled.
3. Nitrous has no effect on DCR, it increases cylinder pressures though.
4. Choose you cam based on how you want the engine to behave in respect to max TQ points, max HP points, rev limits, down low power, idle quality.
5. Whatever cam you choose, just spray on top of it and it will work just fine.

The general rule with nitrous cams is just to use a traditional split cam, more exhaust duration than intake.

Beast96Z

iTrader: (21)

Done and done.

Patrick G

iTrader: (14)

You choose the intake valve events for the intake side exactly like you would NA. DCR will be the same NA as on nitrous. But because nitrous burns so much faster, you'll want to open your exhaust valve about 4 degrees earlier for a 100 shot and around 6-8 degrees earlier for a a 200 shot. This usually means spreading the LSA some, advancing the cam, and increasing the exhaust duration.

IE:
If a 230/230 110LSA +2 was ideal for you NA
Then for a 200 shot, you'd want: 230/236 112LSA +4
Same IVC, Same DCR, 7 degree earlier EVO.

bshonda

iTrader: (1)

ok, so im thinkin im gonna look really stupid here, but, if nitrous raises cylinder pressure, isnt cylinder pressure in direct relation to compression ratio. i mean, the more cylinder pressure, ie in the form of forced air by a turbo or supercharger and nitrous causing a more dense charge of air, would mean a higher compression ratio, right? so the more psi a turbo pushes, the higher the compression ratio and so the higher DCR you would have, right? i know that nitrous loves compression and turbos dont, but thats why it takes so much more nitrous to do the same as a turbo or supercharger, right? if nitrous didnt affect compression ratios then why would you need to throw more fuel to it to keep it from detonating or running lean? i just dont get it i guess.

PREDATOR-Z

Patrick is correct.
But that is just a rule of thumb and not concrete. Head exhaust flow and exhaust scavenging play a big role here to determine to what extend one needs to start applying that concept (increasing split)
I've sprayed reverse splits with as much as 150+ shots will little effect on output Vs standard split of same intake duration.
So it is better to build the motor NA and shoot on top if you do not go above 150 +/- shot depending on your combo.

DCR doesn't change.
In Nitrous applications, you are feeding more O2 to your intake charge, therefore you add more fuel, by doing so you now have a bigger charge, wich will have a bigger BANG wich will make more power.
I tried to make this simple.

ShevrolayZ28

iTrader: (4)

The compression ratio is independent of cylinder pressure. The compression ratio is defined as the volume of the combustion chamber when the piston is at the bottom of it's travel divided by the volume of the combustion chamber when the piston is at the top of it's travel.

bshonda

iTrader: (1)

ok, so let me see if i understand you guys correctly. if i degree my 112 lob sep cam in at 107 which takes my DCR to 8.48, and spray 150 to it, then i still wont have to run race fuel when i spray it? complete numbers are 236/244 .579/.579 on 112+0 with a .041 gasket and 61.12cc chambers, and stock bottom end.

PREDATOR-Z

It will not fit unless you flycut, and ideally advancing more than 4* means you ground the cam wrong.
6* is acceptable but out of norm.

bshonda

iTrader: (1)

it only has .579 lift, why would i need to fly cut pistons?

brad8266

iTrader: (23)

Its more about duration, closing and opening points than it is about lift. Overlap occurs at TDC when all it takes is a little bit of lift to smash into the piston. The farther you advance the cam the earlier the intake valve opens which means that the more you advance the more lift the intake vavle will have at TDC.

TeEnAgE pHeNoM

iTrader: (6)

https://ls1tech.com/forums/showthrea...8&page=3&pp=20

To save Predator some typing!

PREDATOR-Z

Thanks man