utfan01ss

iTrader: (1)

I have a low mile all original 89 IROC-Z L98 car that I'm doing a few things to. Mainly to make it more competetive with newer model cars... since I went from owning a LS1 to a L98. I know there is no comparison between the two, but I'd like to get this IROC a tad bit quicker than it is.

So my plans are...

TPIS Mini Ram

Hedman mid length headers, 3" ORY and Magnaflow catback - I already have all this, just have to install it.

T5 or T56, depending on what I can find first.... prefer a T56 obviously

3.70 gears installed in the 9 bolt rear.

This L98 feels really strong, actually surprised me at how much torque it has. So tossing that TPI and moving some air in and out with the Mini Ram and exhaust, what kind of power would I be looking at? Would it be close to 300 RWHP? Or do these heads and peanut cam restrict it that much?

My honest goal with this car... right now... is to be faster than a buddies Automatic 04 Mustang GT. Ha ha... I'm going to build a 383 next winter for it so this is all temporary supporting mods for my future build. This is not a drag car btw, rather a corner carver as I've swapped the UMI suspension and Koni's from my other car to this one.

Thanks

cuisinartvette

Id do the gears/trans and hold off on the rest til you do the 383 then size headers, etc accordingly. Suppose doing the intake now couldnt hurt.

Orr89RocZ

iTrader: (20)

Exhaust plus miniram ecm tune and stick shift will show around 275 whp. Most bolt ons do 250-260 with a auto. Do some 1.6 rockers as well

Full bolt ons to full bolt ons the 5 spd mustang gt's are hair quicker. Automatics tho, it could be an iroc victory. Now a manual trans L98 well driven may hang with gt manuals but def should win against an auto gt. i spend alot of time racing a friends modded 01 Gt manual car. He'd always be a car length on 1/4 mile, about .1-.15 faster and 1-2 mph

utfan01ss

iTrader: (1)

Thanks Orr89RocZ and cuisinartvette.

If I could at least run with his mustang I'd be happy... we have a friendly rilvary going. lol.. But I'm going to do gears, intake, exhaust and a manual trans swap at least. Hopefully that will put this car in good standing versus a bolt on mustang. So the big draw back to these L98's is the cylinder heads correct?

I'm currently eyeing 3.70 gears, as this is a nine bolt rear end. Would that be a good all around street gear? This car will never see the drag strip, most likely, and will be driven to Florida a couple times a year. We own a beach house in Port Charlotte.... So my highway mileage is somewhat important.

I'll toss some 1.6 rockers in as well, I actually have a set of Comp roller tips from my other IROC. Should be an easy swap. Thanks for the tips! I'm excited to see what this 350 is capable of. It's honestly impressed me for a stock L98, and for being an older car. Definitely more fun to drive than that 98 Z-28 was.

Orr89RocZ

iTrader: (20)

Heads and cam are tiny. Still can cam up and retune to get another 15-25 whp without much effort. Should get to your 300whp goal

I got my bolt on iroc into the low low 13's on average and best of 12.95. That was on light drag wheels. They respond well to intake mods and tune

3.70's are great with miniram and stick

utfan01ss

iTrader: (1)

Awesome! Well, in your opinon... if I tossed in say an LT4 hot cam, while adding 1.6 rockers, would that be worth the effort?

I'm guessing the heads would have to be milled down to accept valve springs to handle that cam though. Wish these motors were like the LS engines, just swap valve springs and toss in a monster bump stick. Your numbers sound like my goal for this car until I get the 383 built.

IrocRoadRacer

If your using stock heads, you would have to use 1.5 rockers.

92g92

To clarify what the person above posted, he should mean that with the LT4 hot cam, you will need to use 1.5 rockers due to the maximum lift the stock heads can take. 1.6 rockers would put you over the "recommended" maximum lift of the heads, which is I think .480. I a buddy of mine runs an LT4 hot cam in his L98 with stock heads and it does just fine, at .492 lift. So take those "recommendations", however you wish.

Orr89RocZ

iTrader: (20)

You can try beehive springs which have a thinner retainer. They are suppose to give you more lift clearance than typical double springs.

Another option is .050" worth of shim under spring seat and +.050 offset locks with a good drop in single or double spring. This raises assembly .050" off guide boss valve seal area giving you max lift closer to .520"

Lastly a place called alex's parts sells a double spring kit for vortec heads which have grinded down retainers giving you .550" lift they say. One member here runs a .540" cam on stock vortecs with those springs. Vortecs are said to have a max lift of .470" but it all varies depending on casting differences and how the seats/guides were cut when originally made.

Best bet is to measure retainer to guide/seal boss clearance and see what you can get away with. Lt4 hot cam only mod would be very fun when tuned. With miniram it would compliment well and be a cheap swap since its a popular used cam. Just run 1.5 rockers unless you get the alex kit and verify you do have clearance for .525"

Johngypsy

Got a 90 Iroc z, came with a 305 Tpi and a 5-spd, I am a parts supplier for 3rd gens, so I had some to all the parts needed to make it a real quick car,

Done this last year:

1) installed all brand new suspension sys, every nut & bolt, pan bar, adjustable all, new(er) 10 bolt 3.23 limited slip from 91 Rs, had a 1989 Trans am Gta come in, so the quest for a 5.7 was in mind, 2 weeks later, it was in my car, again new all, cleaned, painted, and looking nice, did a denisty swap at the same time, kept all wire harness, and added a 5.7 knock sensor and denisty,

Finally- added from my stash
1) 58 mm BBK performer tb
2) 1.6 short roller rockers to compinsate for the valve covers oem,
3) 255 walboro same as grand national
4) brand new cluch set from a bc4 police inceptor, same as 91rs L98,
5) 24 pond fuel injectors, adjustable fuel regulator,
6) msd 6AL,,,not yet installed, taken out because rpm went nuts, and damaged my sending unit for my cluster, so it's off for now,
7) flow master muffler, 3inch short exhaust to 2 inc out back to muffler,
Has factory cat, which is good,
8) hi voltage wires, 8mm, stock cap & rotor, & plugs gm ac Delco,
9) k&n air filters going to stock box inlet,
10) Slp siomise runners,
11) ported runners with it, intake ported, pentium also all 3 ported to gasket match set up.....

My mechanic adjusted the fuel to stay wide open at some where at 48 psi, he said I need more fuel? Also have stock headers,

My timing is off, it's not lab top, and stock ECM,
Did a test drive, it went 16.7 I'm the 1/4 mile, and felt like it was holding back, like if I had a truck and was pulling a house on my rear bumper, if I punch it in first gear, it's slow and feels like it was holding on to dear life, straining life if it's a old man trying to walk up 30 flights of stairs,,,, yea I laugh to.....

I need a good honest assessment of what's wrong here? What's my issue,
Thanks so much all you guys & gals. I would love to do atleast 13.8, I'm not asking for 12 sec car, I wish, but want it a little better then normal,

And also, with this combo? What's the proper cam and heads I need to do, I do have a friend who has a machine shop, and can do vortec heads from a 5.7 silverado truck, the shop will do the machine work to get it on right,
So please help me out, it would mean the world to me as I am a Iroc guy who just wants a decent power, and don't wanna be beaten by a 1991 Honda civic anymore!
John

VincentZ28

iTrader: (2)

Just a full Exhaust system will wake the car up. A 5 speed with 3.42 gears will beat your friends mustang. The car will run about 13.3 in th 1/4 mile @ 105mph. But used Dyno Don with dual cats to get that results.

utfan01ss

iTrader: (1)

Yeah a manual trans swap is next on my list. After reading that long post, wow... my brain hurts. Lol...

Once I get it the way I want it I'll post results. It's going to the body shop for paint next week.... then on to making it faster