I currently own an '89 Iroc-Z 305 T.P.I. / 5-speed. The car has minimal mods: K&N's, TPIS Airfoil, and Accel Coil. These mods have netted me a best of 14.89 @ 94.5 mph. I'm currently in college, and will be building a nice motor when Im out of school. For now though, I want to squeeze some horses from the 305. These were the mods I had planned:

1. Holley 52 mm TB
2. CompuCam 2032: 270/276 .452"/.465"
3. TPIS Fuel Pressure Regulator
4. Taylor Spiral Wires
5. Edelbrock Aluminum Water Pump
6. 160 Themostat
7. SLP 1 5/8" JET HOT headers
8. Random Tech 3" Cat
9. SLP 3" Cat Back
10. Free Mod: Port TPI System (Upper, Runners, Lower)

I want to reuse all of the parts except for the themostat and cam on my post-college motor. (Which will be a 355" w/ 6" rod all forged assembly, TPIS Miniram, TrickFlow Twisted Wedge Heads, ATI Procharger) I need help with deciding on whether or not a cam is the right choice, or if I should just buy some 1.6 rocker arms. If I went with just the rockers, this would strike the Cam & Waterpump from the list. I want to run some consistent 13.99/14.25 times. I hope I've provided you guys with enough info. Please help me because I don't have loads of cash to be throwing around. Oh yeah, my current gear ratio is a 3.42 which is going to stay that way because when I build the nice motor, I will just throw a Moser 12 bolt rearend, therefore I don't want to waste money on the Australian Rearend in the car now. Thanks guys!

 

Excellent choice. Not only is it a good choice naturally aspirated, but also with nitrous and/or a supercharger. My best times are with 1.6 rockers:

N/A: 14.07
90-hp nitrous: 12.58
6 psig boost: 12.57
6 psig boost + 50-hp shot: 12.04

You should be able to get into the 13's N/A because my engine was set up with a supercharger in mind, i.e. 1-3/4" headers, lowered compression ratio (8.8:1), large tube runners, TPIS base, etc. Tim Burgess has run in the high 13's with this cam.




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Willie

Supercharged 1987 305 IROC-Z, Daily-Driver, Emissions-Legal.
Paxton (6-psig): 12.57 @ 111 mph.
Paxton (6-psig) & 50-hp nitrous: 12.04 @ 114 mph.
ATI D1SC (10-psig): ?

http://willie.camaro-firebird.org/

1987 "20th Anniversary Commemorative Edition" Z28 Convertible -- Super Chevy Show Class Winner, 1998.

 

The only thing I like out of those is the thermostat and the headers.
Save your money on alot of those bolt-ons like the TB. Get the higher ratio rockers though.
The best CAT is NO CAT. The only high flow CAT is a hollow tube.
Don't waste money on CAT back exhaust for a 305. The factory intermediate pipe is large enough already. Just get an electric exhaust cutout to put before the muffler.

Porting is a good idea, but not much to be gained in the TPI with free-porting. I'm not saying 'don't do it', but if you're going to port, then pocket port your stock heads. You will get much bigger gains from work on the heads. A good 3 angle valve-job after the porting costs little over $100 and will add even more power.
While it is apart is a good time to plug off the exhaust crossovers in the heads and baseplate. This will keep the TPI much cooler and add power. Same goes for the PCV to the throttle body.
Check the threads on here about porting the plenum (by Nitro Don), and from tech-central about porting the base (by madmax). Good info.
Your factory camshaft should be great for the 305 in 1989.

Have you done the free mods to your air-filter duct and air-sensor?



[This message has been edited by The ODB (edited February 24, 2001).]

 

ODB, lemme cut to the chase, you're an idiot, and I hope no one takes you seriously.
160 thermostat is a bad decision for an sbc, even worse for a computer controlled SBC.

electric cutout? catback allready to big?

I think we have a troll on our hands

 

don't take me seriously then, do it your way. That just makes me look better.

 

C'mon guys. We don't need to be like that! I will get exhaust because 1: I want the sound. 2: Later I will build an engine that will take full potential of the exhaust. 3: I have to replace my fuel pump, and there is no point in putting the stock exhaust back on. As for the catalytic converter, we have emissions check where I live. So, taking the cats off is not an option. I will however order my headers without the air tubes so that I can take my smog pump off. After talking to my mustang buddy, he suggested ordering 1.6 rocker arms for now, and saving the money I would spend on the water pump, cam, and gaskets for the new motor. As for the 160 themostat, maybe that is too low of a temperature. I do know that I want a themostat that will open a little earlier because my car is on the verge of overheating during our HUMID ohio summers.

 

2Ball,

Just thought I'd throw in my 2¢...

Save your money on the 52mm TB. You won't realize any real gains from it on a 305 until you overcome the other restrictions in the induction system first - and maybe not even after that. Remember, a 48mm TB is plenty for the later LT1 engines to make 330 HP and spank most stock L98s, let alone the LB9/305. GM even gets 500+ HP with a 48mm TB on the RamJet 502. You might want to rethink the HP/$$ ratio on that one. In the same vein, don't bother hacking up the stock Bosch MAF. Unless you are going to run the 305 at 7,500 RPM constantly, you'll not need any more flow than the O.E.M. unit can deliver. A 350 can be a little different story, but that's not the question.

The single most significant restriction in the induction system is the area directly behind the throttle body in the plenum casting. If you go that far, take a very critical look at the gasket/port matching on all TPI parts. GM powertrain engineers did a great job designing the system, but GM accountants did a terrible dis-service in cutting the corners and making the mass production techniques introduce so much variability that the mismatch can become a serious hindrance to flow.

Beyond that, the heads themselves are restrictive. If you are married to the stock heads, deep porting on the intake side and some serious short radius blending will yield good results. You don't need huge port volumes on the smaller engine, just good transitions. You are somewhat locked into smaller valves with the stock heads, so almost all flow improvements will have to come with port configuration and cam profile. You can squeeze larger intake or exhaust valves into the stock heads, but the shrouding around the outer edges of the valve seats becomes restrictive. Do the same on the exhaust side and polish up the chambers and exhaust ports well.

You can do a three-angle valve grind as suggested for a bit better flow, but the long-term reliability in street engine is in question with that method. A different and equally effective method of enhancing flow around the valves is to radius the front side of the intake valve margin to allow better flow around the valve faces. The 305 has fairly tight chambers, and any help in that area is a positive change.

Your theory of exhaust modification seems sound. You realize that you will get minimal benefit now, but will build to take advantage of the system later. I fail to see what the fuel pump has to do with the exhaust, however. It's just as easy to reweld the old system in place as it is to clamp up a new system. But if you are planmning to do it eventually, I guess now is as good a time as any. It's your checkbook. Maybe what you'll save on the TB can fund the exhaust parts.

Regarding the increased ratio rocker arms, they make a minimal difference. I installed a set about two years ago and really didn't change the times at all. Still, any improvement over the "LA" cam profile is a plus. Crane at one time advertised a 16.4HP gain with the 1.6:1 rockers on a "LA" 305 TPI. That seems a little optomistic, but that's what they were saying. Frankly, I didn't "feel" another 16 HP, but I haven't had my pants calibrated lately. I guess even a 5HP gain is still 5HP more than you had without them.

As for the thermostat, if you are using the stock PROM, stay with no less than a 170°F thermostat. Even that is on the edge of acceptable, since some engine parameters are set to change to "hot/normal" mode at 176°F in the ECM programming. I've been running a 180°F stat in my 305 for a few years with good results. You'll need to install an auxilliary fan control to take full advantage of the change, however. If you decline to do this, the coolant will still reach 223°F before the fan energizes.

Instead of a prepared AFPR, look into converting your existing unit to an adjustable one. It will take only a little more time than installing the aftermarket regulator and save you about $70.00 minimum. Either way the AFPR will be helpful with the improved cam profile if you decide to spend $250.00 on a cam that you are going to throw away in a few years.

O.K. - maybe that was more than 2¢ worth....

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Later,
Vader
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"No matter how hard you try you can't stop us now..."
Adobe Acrobat Reader 4.0

 

Vader: Thank you for the information. I think I'll follow what you've suggested as far the TB and Thermostat goes.

 

Vader,
I agree about the parts not lining up well. That adds up to a good size loss, especially on the exhaust side if you run headers. The head-port, gasket, and header flange all overlap at different spots.

Now I do have a problem with MAF butchering. My 305 picked up over 10hp from gutting the MAF. This is one of my first mods to the car back in the day. I'm not going to argue airflow from the MAF because it probably just leaned me out some, but still it helped. I also picked up power later from switching to SD and tossing the MAF in favor of a better air-feed tube.

I don't agree on the valve radius doing more good than the top cut 3angle. I do both, and I've never seen any problems. The factory angles are not good for flow though.

As far as increased ratio rockers. They work to a different extent on every car.. better on small cam'd engines. My 383 gained 10hp going from 1.5 to 1.6, then another 15hp going to 1.65
I suggested those because they are easier and cheaper than a cam swap. And like you said why spend money on a temporary camshaft?

The thermostat is totally debatable. There is a point where the cooler temps pay off in increasing intake-charge density and reducing detonation with higher cylinder pressures.

I agree with the rest though.
Always better to get more opinions to choose from.
ODB