the.hamburglar

i have been out tuning my car the last few days and it seems as though it pulls hard from 5000-7000 but from 7000 to 8500 it seems a little dead. i currently have itr cams with a t3/t4 60 trim turbo. since i am reving my motor so high am i getting some overlap between the intake and exhaust cams. would it be better for me to get a smaler duration exhaust or intake cam to avoid this?

im thinking right now about using a b16 exhaust cam and itr intake?

highschooler

those irt cams are fine. If you dont already have 3" exhaust or intake manifold, those will help.

the.hamburglar

ya i have 3" exhaust and aebs intake manifold

tokesGTR

Smaller duration cams aren't going to make more power at high RPM's

Look at Tony1's test, the huge Skunk2 Pro1's made a ton of power on the top end over ITR cams.

the.hamburglar

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by tokesGTR &raquo;</TD></TR><TR><TD CLASS="quote">Smaller duration cams aren't going to make more power at high RPM's

Look at Tony1's test, the huge Skunk2 Pro1's made a ton of power on the top end over ITR cams.</TD></TR></TABLE>

no thats not what i mean....air is being forced into the motor through the intake valves first. if my exhaust valves are not seated (still open) as my intake valves are opening, to let the air in, im going to be losing some of that boost pressure out my exhaust (because the exhaust valves have bled it out). so if i get an exhaust cam (b16) with shorter duration, im thinking ill be able to use all the boost my turbo is producing. ie, my exhaust valves will now be completly closed as the intake valve is letting in air so ill have a more air in the combustion. it wasnt as noticable at 5psi but now that i have turned up the boost to 10psi it seems as though my top end is dieing. maybe its just me but at 10psi it feels as though it pulls the same as boost at 5psi from 7000-8500. i think this is because of the overlap im getting with the itr cams....does this make any sense? i can really notice the differnce between from 5psi to 10psi at lower rpm but at top it just doesnt seem to pull anymore.

Top Ramen

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by the.hamburglar &raquo;</TD></TR><TR><TD CLASS="quote">

no thats not what i mean....air is being forced into the motor through the intake valves first. if my exhaust valves are not seated (still open) as my intake valves are opening, to let the air in, im going to be losing some of that boost pressure out my exhaust (because the exhaust valves have bled it out). </TD></TR></TABLE>

Yes - we know what duration and overlap are. We are all talking about the same thing here.

I agree with the previous posts that the issue is probably not with your cams. ITR cams a fine with boost, although my personal experience is that GSR cams seem to be a slightly better choice at lower boost levels and the ITR (or even bigger cams) have an advantage at higher boost levels. People used to think that overlap was fundamentally bad for forced induction motors, but this is not the case.

In any event, the ITR cams should do just fine at higher rpms for the same basic reasons they work fine at higher rpms on NA motors. If you are really having a problem at the top end, the basic cause is something else. Do you have a dyno chart with the air-fuel ratio plotted? That would be a huge help.

Best of luck on your project.

tony413

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by the.hamburglar &raquo;</TD></TR><TR><TD CLASS="quote">i have been out tuning my car the last few days and it seems as though it pulls hard from 5000-7000 but from 7000 to 8500 it seems a little dead. i currently have itr cams with a t3/t4 60 trim turbo. since i am reving my motor so high am i getting some overlap between the intake and exhaust cams. would it be better for me to get a smaler duration exhaust or intake cam to avoid this?

im thinking right now about using a b16 exhaust cam and itr intake? </TD></TR></TABLE>

you would get the same amount of overlap at low rpm that you would get at high rpm. the motor is still making the same amount of rotations just quicker.

before you try changing out cams go to the dyno an try retuning instead of using the "butt dyno" if your speculations are right then try adjusting your cams, check valve clearances, and ignition and fuel maps what did you tune the car on ?

the.hamburglar

im using crome. i dont have adjustable cam gears. im now thinking about getting them. i dont really care much for low end power because im never lower than about 6200 at the track. my air fuel is good...approximatly 11.5+-0.2 in all boost. my ignition timing is enabled to retard 0.8* per pound boost. if i do get adjustable cam gears would i set them both to 0* at first and then leave the intake at 0* but then advance the exhaust cam so i closes a little sooner?

non-VTEC

take a look at your datalogs for boost.

i was having the same issue where it would feel like it was loosing power after 6500-7000rpm... it was the boost dropping off......make sure the boost isnt falling off any in the upper rpm.......

black98gsr-t

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by the.hamburglar &raquo;</TD></TR><TR><TD CLASS="quote">

no thats not what i mean....air is being forced into the motor through the intake valves first. if my exhaust valves are not seated (still open) as my intake valves are opening, to let the air in, im going to be losing some of that boost pressure out my exhaust (because the exhaust valves have bled it out). so if i get an exhaust cam (b16) with shorter duration, im thinking ill be able to use all the boost my turbo is producing. ie, my exhaust valves will now be completly closed as the intake valve is letting in air so ill have a more air in the combustion. it wasnt as noticable at 5psi but now that i have turned up the boost to 10psi it seems as though my top end is dieing. maybe its just me but at 10psi it feels as though it pulls the same as boost at 5psi from 7000-8500. i think this is because of the overlap im getting with the itr cams....does this make any sense? i can really notice the differnce between from 5psi to 10psi at lower rpm but at top it just doesnt seem to pull anymore. </TD></TR></TABLE>


i use to think the same thing back before i turbo'd my car (4yrs ago) but u have to really understand what your trying to make the engine do... the whole point of force ind. is to put more air and fuel into the cly. to create more power.. now think about the four strokes of the engine, when the intake opens and boost is pushed in, then the valve closes and then compression starts after that the spark lights off the power stroke and the piston moves down and then starts to travel back up when the exhaust valve opens.. if the valve closed before the intake opens u would have burn't exahust gases still in the cly. which would delute the fresh intake charge (good for emissions thats what a egr valve does).. if u have the exhaust overlap when the intake opens the incoming boost will blow out all burnt gases... then when both valve close your left with a clyinder that is full of fresh air/fuel mixture which will create more power per cly.. if the turbo is to small it could be possible to see the boost psi fall a little bit but a basic t3/t4 shouldn't... thats my understanding of it

tony413

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by black98gsr-t &raquo;</TD></TR><TR><TD CLASS="quote">
if the turbo is to small it could be possible to see the boost psi fall a little bit but a basic t3/t4 shouldn't... thats my understanding of it </TD></TR></TABLE>

a t3/t4 with to small a trim could die at rpms highers than 8K
to OP: whats your turbo specs

the.hamburglar

its a t3/t4 60 trim compressor, .63 exhaust a/r

the.hamburglar

the turbo is not too small and its holding steady boost from 6000k+. here is a pic



its prob just me, i need to hit a real dyno

tony413

yeah man with a 60 trim you should be good. just go to the dyno and look at the graphs