ok so a quick overview of my setup, 88 iroc-z, 305tpi with 60k on it, world class t-5, pro 5.0 shifter, centerforce clutch, fully ported slp runners, plenum and intake manifold base all gasket matched as well, gutter air box, a/c smog pump and A.I.R. delete, stock heads and cam, new plugs wires cap and rotor, hedman headers and ypipe, high flow cat. and flowmaster cat. back exhaust system. I still have the stock 305 chip as well. my question is: what should i save for next? keeping it within a reasonable budget. (400-600 bucks) i was thinking maybe cam but i dont know if it would be worth it with the stock heads. 1.6 roller rockers were another option but at 240-300 bucks i dont know if thats the most cost effective route to making more hp. i recently read you could gain 10-15hp just out of performance pulleys so that could also be an option. i do have a basic nitrous setup also that i ended up taking out when i did my swap just because i did a half a** job installing it and didnt have the proper set up. (i really need a tpi fogger plate, bottle heater, purge kit, and nitrous pressure gauge to really make a nice setup). any ideas?! and id LOVE to get a proper tune so if anyone knows to a shop in NJ that can tune these cars let me know and ill definately do that instead of any of these other mods.

 

Could buy tuning software and hardware and learn to tune yourself. Perfect time to start is on a bolt on stock motor. Less chance of hurting everything but if its a 350 running on 305 chip then id definately put in the proper tune. Especially with bolt on mods already on it.

Pulleys help a tiny bit but i think rockers are a good upgrade especially if cam is small. Is it a L98 spec cam? 1.6's can be had for less than 200 and give good hp gains with tuning.

Two biggest gains on my car have been intake manifold mods and headers/exhaust.. 1.6's did add some power to. 10 at the tires running lean but more if tuned right

 

Do the springs while youre at it if your present ones are tired the 1.6s will do them in. power gain right there.
Then tune away.

 

I've had success installing even a fairly aggressive cam with ported stock L98 heads. You need to install springs to support the cam and check for max lift on the heads to see if you need to swap the retainers or have the spring pockets or guides machined. The stock TPI can support 350HP with the right combination of heads, cam, and headers. I have personally seen 325HP with ported stock heads. That's a 100HP increase over stock with minimal investment. You will of course want to retune the ECM for this level of modification.

 

i knew the general consensus would be a good tune. ive read over the "intro to prom tuning" thread over and over so i do have a pretty good handle on what i would need to start tuning as well as how to burn new chips. the problem i run into is what i should change exactly. i know every motor is different but the only thing i would really make adjustments to is the fuel air mixture if thats even possible. i just dont understand the concept of what it take to perfectly tune an engine. thats what makes me hesitant to dive into tuning. i will definitely look into some 1.6 rockers. any suggestions as to which ones i should buy? preferably a tried and true rocker on the cheap? nothing fancy.

 

I know a stronger spring would be a good investment but would it be worth it to buy a new set of springs for the stock heads if I'm planning on buying a new set of heads within the year? A nice set of springs that I could transfer over to a new set of heads would be the ticket however I don't want to put money into my stock heads to fit bigger springs or by porting them when I plan on buying new heads soon anyway. Could you suggest a set of springs that would transfer into new heads and still benificial to the new heads without needing machine work to the stock heads?

I tore down the 350 to the block (leaving the crank and pistons in) when I bought it to inspect it and then rebuilt it with new gaskets and the parts I mentioned in the original thread so I am familiar with most mechanical aspects of an engine but I left the heads alone so I'm not to familiar with them. Some detailed feedback would be greatly appreciated in this area.

 

My whole issue with a new cam is that I kind of want to buy new heads and cam together instead of buying a mild cam to compliment the mild stock L98 heads and then getting bigger heads and having to rebuy a more aggressive cam. Also, could you briefly explain how to check for max lift on the heads? Shouldn't the max lift be the same for all stock L98 engines? I definately want to keep the tpi setup so I'm glad your optimistic about a tpi making 325hp without breaking the bank on a forum with an unlimited amount of tpi haters. Lol!

 

In the 350 TPI engines I have built, using stock heads that I ported myself, I used an SLP cam that by most standards is considered a rather aggressive cam. It is designed for "extensively modified TPI". The lobes are 223/230 @.050, .513/.520 lift, 112 degrees LSA. This cam produced a slightly lopey idle(though quite drivable) and dramatically increased torque from 2,500rpm up to 5,500 where, even with port work, the factory heads and stock TPI ran out of breath. These were 300HP motors. With headers and good exhaust they could have been tuned to make 325hp. With good heads, they would have made 350HP.

To check max lift, remove the valve spring(place the piston at TDC, use shop air and a holding fixture to prevent the valve from dropping into the cylinder) and replace it with a lightweight spring, just strong enough to hold the valve closed and keep the retainer and locks in place. Then using either a dial indicator, or the depth gauge of a caliper, measure the height of the edge of the retainer with the valve closed, and again with it fully open. This will tell you how much lift the retainer, guide and seal will allow.

Be aware that the exhaust valves use press on or umbrella seals while the intakes use o-rings. They both suck and should be replaced by good quality push on seals while you have the springs off if you're doing cam and springs. Be sure to measure max lift with whatever seals in place that you're using . Then, you need to measure from the base of the spring pocket to the bottom of the retainer where the spring rides with the valve closed and open to determine installed height and compressed height of the spring. then you need to find springs. If you cannot find springs that fit the measurements, you will need to have the spring pockets machined, and or install offset retainers that raise the installed height of the spring and allow for more lift before coil bind. Keep in mind that the max lift of most any spring is .020 less than coil bind.

 

300 hp motors? Mine came with 245hp stock at the crank.

 

The 100HP increase is based on factory output of 225HP in 1987. The 325HP package requires alot of work and experience with porting. 350HP is considered the max capability of the stock TPI with ported plenum and base. In my experience, the stock heads, even with porting and machine work, won't support this power level.

Whitestripes, the SLP cam that I refer to is the same cam that made 417HP in my 355 with ported TFS G2 Twisted Wedge heads. It's no punk. In my opinion, it's about the max for duration and lift without a serious reduction in manifold vacuum at idle. The ZZX cam that I run now is 240/240 at .050, .560/.560 lift with 1.5 rockers. It is a huge cam and pushes my large tube, ported aftermarket TPI about as far as OE based TPI can go without boost or bottle. (by OE based I am excluding the First Injections system) The ZZX made 408HP from ported stock L98 heads with aftermarket hi-flow TPI parts. This cam can easily support 500HP with the right intake and heads. It works very well at pushing the upper limits of TPI.

I know what TPI is capable of because I've built them a few different ways. On the 355 I run now, I've pulled out all the stops, short of siamesing. This is because, in my opinion, siamesing changes TPI into something that is no longer really TPI. If I were going to alter the TPI, I may as well just go with something else. Especially since in my case there are no enforced legal restrictions as to what modifications I can make to my engine, and for the cost of my hi flow aftermarket TPI pieces, I could choose from a number of higher flowing alternatives(Miniram, Stealth ram, etc).

I am very pleased with the results of this project and I have enjoyed it for 14 years since the original build. It can still scare the s**t out of me, especially on the first drive after being stored away all winter. Having said this, the goal for my next engine is 600+HP naturally aspirated. Naturally, it won't be TPI.

 

I got a big gain with a TPIS zz9 cam

 

The ZZ9 is an excellent cam for ported factory heads. The ZZX, while it was originally used in a factory headed engine, is plenty of cam to support hi flowing aftermarket heads. You'll notice that the intake and exhaust dur/lift numbers are the same(even though the actual lobe profiles are unique to int/exh). The added intake duration serves to extend the intake pulse, allowing the long tubes more time to create velocity and improving cylinder filling.

 

It's been a while but I wanted to say I really appreciate the input. I think after reading your responses Ive decided to jump into tuning after the holidays, (Im on a tight budget and have a lot of gifts to buy hahaha) I need a wide and o2 sensor and an AFPR and I think I'm gunna go with this set up http://www.dynamicefi.com/EBL_SFI6_Flash.php
Any advice or experience with this system? It's seems the most user friendly and no chip burning! I wanna familiarize myself with the system and then go SFC's and some drag radials and 1.6 rockers and then heads and cam. Sound like a plan? I'm not to sure on the heads and cam combo either. I want drive ability cause it's my daily driver but I'm not expecting like 2012 zr1 quality either. The best word I could use would be "rowdy" I want something rowdy. Hahaha