Quote:
Originally Posted by vq35SMASH
so heres the deal, im on track for a decent power upgrade to my BONE STOCK BLACK TOP sr. so far ive got a s15 t28, dwerks 550's, Z32 MAF, HKS wastegate. on the way for the rest is a enthalpy tune, tomei procams, turbo SS lines, and a new exhaust manifold since im already there. and my question is this, my friends love the phrase "since your already there might as well...blah blah" and i have a old head off my old RED TOP sr thats been laying around for quite sometime. would it be benificial for me to p&p and do new springs seals and the whole laundry list of possibilities to the head and just put that on when i put the rest of the crap on? if so what would be the best course of action of stock stuff to leave and aftermarket stuff to upgrade too, and cane even a REDTOP head work on a BLACKTOP lower for a s13??
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That statement is definitely one we always hear, but most people throw it out there with good intentions. For instance, I would say that since you have an S15 T28 and plan to tune for better power, you might as well get some rocker stoppers... I don't know nearly as much as 4x4le & co. but I know for FACT that they will agree.
As far as P & P goes, I didn't get one because my builder said that it's pretty easy to weaken the head if you're not careful- and there was no one they trust locally to do it. I am telling you this just to keep in the back of your mind; and I don't know enough to speak beyond that.
** If you are not planning to rebuild the bottom end while you have the head off, why spend money on anything more than you need to complement your mods? In otherwords, leave your current head on and build the spare over time so it will be ready for when you do a full rebuild.
Cams (Take what I say here with a grain of salt): Like 4x4le said above, upgraded cams may not always be the best choice. They may give you more power up top, but at the cost of losing low end... It's a balance. The S15 T28 is pretty small-output turbo by comparison; and when a lot of the Japanese companies tune with them, they either use 256/11.5 Poncams, or leave the cams stock. This is because you want to match where the turbo and the cams make effective power. If you look at a dyno graph, you will see that smaller turbines start to run out of breath in the upper mid - higher rpm... so when you add higher lift/duration cams; you run the risk killing the power band in an area where the turbine is designed to give good response.
Here is one of my old dyno graphs:
S13 SR20DET-
Turbine- APEXi AX-53B70R P20 (slightly bigger than S15 T28) @ 1.15bar (17psi) boost
Fuel- Sard 850cc injectors, 255lph pump & Sard adjustable FPR
Other- Z32 MAFS, FMIC, full exhaust, Rocker stoppers, Power FC
Cams- STOCK
Yes, it's a strange-looking graph; but it illustrates the point. Throw hp out, the focus is on the torque (light blue line). Notice where the good torque is... in the midrange (4500 - 6500rpm). Notice how smooth the curve is; and also that it drops off past about 6300-6400. An S15 T28's curve will look similar to this. If you add "too much cam," that curve will potentially narrow & shift to the right; so all that torque that you made before x-rpm will be gone at the expense of a narrower upper range due to the design characteristics of the turbo. Fuck max hp- a smooth, wide torque curve IMO is what matters. There is a whole bunch of other factors here that I am not even remotely smart enough to speak on... so I will stop here lol.
SOOO- for cams, I would recommend either 256 Poncams or leave them stock. The added bonus with Poncams vs. Procams (besides being better suited to a T28) is that they plug & play without need for upgraded springs, retainers etc.
Save all the bang & buck for when you are ready for a full rebuild~