rather technical camshaft question

[s13sr20chris]

i was thinking of optimal camshaft setups for sr20det's. obviously just bench racing like this will not prove anything but lets speculate. people with small stock turbos running max boost seem to not gain power with camshaft upgrades. i have read that is because you cant run cams with significant overlap unless your turbo has a good size turbine. to go further, i understand that once you get into crossover you can run cams as big as an na car. this leads me to think the intake cam may be outflowing the compressor(or something like that). makes sense right? sooooo, if using a small turbo(stocker or mild upgrade) why not just upgrade the exhaust cam to give the engine maximum exhaling but not messing with the intake.

[PoorManQ45]

sorry for the wasted post . Atleast I tried
Modified by PoorManQ45 at 10:06 PM 6/22/2005

[DAEDALUS]

Note, please don't rag on me if I sound like a complete idiot

+1 for the engine modeling software suggestion.

[s13sr20chris]

pmqno offense but i think that speculation is mostly wrong. i do have modeling software but the turbo stuff is weak.

[Nismo_Freak]

i was thinking of optimal camshaft setups for sr20det's. obviously just bench racing like this will not prove anything but lets speculate. people with small stock turbos running max boost seem to not gain power with camshaft upgrades. i have read that is because you cant run cams with significant overlap unless your turbo has a good size turbine. to go further, i understand that once you get into crossover you can run cams as big as an na car. this leads me to think the intake cam may be outflowing the compressor(or something like that). makes sense right? sooooo, if using a small turbo(stocker or mild upgrade) why not just upgrade the exhaust cam to give the engine maximum exhaling but not messing with the intake.

1. The cams have to be matched properly with the engine. You know this, and most people know this, but not alot of people understand it.

IE. Running 272's on a stock valvetrain motor that operates from 3000 - 7500 RPM is wasting powerband.

2. The SR engine is very picky about cam timing (similar to the 2JZ in this aspect). In my opinion running cams without cam gears is like buying un-adjustable suspension. Timing the exhaust valve opening is CRUCIAL for a smooth powerband, especially for the larger cam'd engines where you can dial out some of the overlap.

3. Stepped cams - alot of this extends from Japan. People running 264 intakes with 272 exhaust cams to maintain some low end flow with the top end from the 272. The issue I see with this is that the valve openings become scattered from the varying durations and lift patterns aren't the same. I find this to be mismatched. I don't have alot of proof to back this up but I don't think it follows the flow pattern very well as cams generally are ran in "symmetrical" pairs in most engines.

However in the SR20VE the camshafts are ran with variations in intake and exhaust durations and lifts. You might want to look there as the SR20VE is a very efficient engine and the head design has proven itself so far.

You might also look further into the differences used between the SR20VE and SR20VET engines, but bear in mind that the VET must spool the turbocharger in order to provide low in response, whereas the VE relies on it's high compression ratio.

[s13sr20chris]

yeah, i am pretty familiar with the ve as i have messed with them before but i just wonder about cams and turbo size. for example...tomei reccomends their ecm and camshafts as a set as the first stage of upgrades on the sr. that seems to contradict what engineers like mike kojima and rob cadle(as well as tuners like andreas miko) say about big cams on small turbos.

[Q45tech]

Simple you flow bench the cylinder heads [with intake and exhaust in place and model flow vs lift vs cams available.....important to correct for temperature in flow bench feed air [preheat it to 200F]......to stablize the cylinder head dimensionally.

Obviously there will be correctable errors in the exhaust flows [due to temperature] but you can get close.

Important to reverse the process to measure reversion into intake during overlap.

Then you pick the cams that fit the profile you want.