Hi guys, new member here. I am waiting on delivery of my 30,000 mile 85 Z51 4+3. I have a group of friends that want too start meeting at the Friday night drags here in Portland this summer, with the goal of competing at/around 13.50 in the 1/4.

what do you all think will be needed to get my car there? I have read that it should run anywhere from 14.0- 15.0 stock. I am open to all suggestions, but would prefer to okeep the car as original as possible. Thanks!

 

Headers (long tubes) would the place to start.

 

Bump the timing a little, ditch the passenger seat for drag events (pretty easy to do) and keep all extraneous items out of the car to shed another couple pounds will help and is basically all free. IIRC magazines reported something like 13.9-14.2 for the 85 model year.

 

Drop some nitrous into it.

 

Remove PreCats and use a Flow master Y pipe and a Hi flow Cat ,
Use Muffler Eliminators.
Use Factory AC Delco Spark Plugs.
Like one poster said remove all loose weight (Spare tire, Jack and Misc)
Use K&N Filter.
Cut Factory Lid opening.
Port The Intake.
These mods may help, worked on my Car.
These cars run on Torque so Launch is Key.

 

85 doesnt have pre cats

Doing anything with the filter also does basically nothing

 

Congrats on the 85 Z51 4+3
That was my first vette given to me by my father around 15 years ago.

I would grab long tube headers and a true dual exhaust with cat and muffler eliminators. Least expensive way to shed the most weight and exhaust restriction. The Hedman 68448 are a good budget long tube header option, I put them on my 1985 and just bought a pair for my new 1989.

I don't know anything about drag racing, but I do know with the TPI C4 corvettes exhaust is the place to start.

 

Many tpis at sea level supposely could turn a 13.9
If you havent run yours before expect mid 14s give or take. I hear the 85 can be a chore to tune sure someone who knows more will pipe in

If it were mine and you didnt want to dig into the engine, Id get some longtubes. true dual exhaust 2.5" is all you need .
Add some 1.6 rocker arms upgrade your valve springs. Port the daylights out of the stock base, get some aftermarket runners and call it a day.

With all the catalog cheap mods my times on an 89 I had were hardly any better than if i did none at all
A 2.5" to 3" to 2.5" exhaust helped a bit so did porting the intake. Was still a 14 sec car in Ca air. Auto, 307
90 Z with 4.10s a too big (3")catback did a best of 13.9 at 110

What Im saying is dont expect road and track times esp if you are new....dont be surprisedif you get say a 15.2...or high 14
the main thing is getting out there and having fun.No bog smoky burnouts it just makes your tires greasy
Leave like you would a red light to get across the intersection quick. Dont dump the clutch

 

Thanks for the tips everyone! It sounds like I should start with exhaust, then maybe move to a cam (or 1.6 roller rockers?). I just need it to get here so I can get it to the track and see what I’m starting with.

 

The 85s have iron heads. If you get a set from an 88+ you can pick up about an honest 10 HP plus lose a few pounds. Port match the intake to the heads you'll probably be closer to 25. Go further with the heads and port those, springs and roller rockers you're 35+.

 

A pair of these will likely get you there as-is: https://hoosiertiregp.com/hoosier-qu...lt-17431qtpro/

Might work better on an 8.5" wheel, though. 16x8.5" wheels should be easy to find on the cheap.

 

I wondered how much drag slicks would help. The car has brand new 255 50 16 Toyo R888R tires on it. I’m going to see how well they hook on the track before trying drag radials. I have read that the Toyos hook very well for a “street” tire.

 

28 x 10 x 16 drag slick could be another option, but a pretty tall tire for a C4 w-3.07 gear: https://hoosiertiregp.com/hoosier-dr...-c07-18153c07/

Not many good choices for 16" wheels left.

I don't see the 28" x 11.5 x 16 QTP listed anymore either, but maybe a few still in stock somewhere: https://www.ebay.com/itm/13378336097...0AAOxyqUpQ8F9F

The M&H cheater slick is another option (and likely a better fitment for 9.5" wheels) if you can find them: https://www.mandhtires.com/M-H-Racem...s/26-11.5-16LT

Note: these are all bias-ply tires which should be a bit more forgiving for manual trans cars.

I have two 1988 16 x 8.5" (+ 50 mm offset) wheels in the garage, so I've been considering 16" drag tires for some time now. I'm still on the fence choosing between either of the QTPs or the M&H Cheater slicks, so I can't offer any conclusive feedback on a specific tire just yet. 3.73 gears give me some flexibility with respect to tire size.

 

I have a different view on it than most I suppose. If I were trying this and I wanted to do it with the L98 I would start with very sticky tires. Then I would swap the rear end gears. With a good tune you shouldn't have any problem hitting your goal. To make it easier the next thing on my list would be to swap the cam.

 

My 86E was almost the same car as the 85, I cracked 13.9s on new rubber once when stock.

You need good tires, really need to redo the entire exhaust, and some heavy portwork on the TPI, and you could get close if you can get your 60' down.

But getting further is going to mean ditching the '624 heads, doing a cam and doing more with the intake setup.

 

I agree with those who said "free mods" (like advancing the timing) and exhaust. The L98 exhaust is not good. Headers, duals and good muffs would make a big improvement and get you close to a 13.5 potential.
Driving the car to that number....that's your job!

 

ill be the first to say, id do nothing but take it to the track as is. with newer rubber i guess, only if they are hockey pucks.

you will need to service the 4+3, flush all other fluids, and more than likely you will discover weak points in the car during first season. ujoints, waterpump, alternator, coolant hoses, radiator fan motors, blower modules, fan relays, fuel pump, deal with the inevitable vacuum leaks and likely seepage from the rear of the intake manifold. That car has hardly any miles for its age. hard brittle things will let go.

all of that ^ completely normal and i dont mean it to sound discouraging at all. you will accelerate the failure of the original systems that are just old, due to your intended use.

i would personally not plan to do a single thing.

instead of comparing times, compare improvements in times with your friends for the first season or something.

that is a gorgeous 85, i applaud you for your plan and i hope you build a thread we can all gollow along your progress.

other than maybe rubber, the *only thing* id do....is alllllll fluids. ps, no synthetic in your 4+3, i used mobil1 non syn atf, and, do not overtighten the pan bolts, if u cant find a vette gasket, a few fords had same gasket. if pan us totally bent up already, use generous application of the right stuff.

Obviously, turn off the OD for your pulls.

 

I think tires will make the most difference if you have problems hooking up, I would wait until you get to the track then go from there.

 

If you want to keep it original, I would start by getting a spare set of wheels/tires for the track and take it there with those first. With some practice you might be able to get fairly close, and then re-evaluate what you will need to change then.
A good set of tires at the track was the difference of almost 2 full seconds for me.

 

I decided to (sort-of) take my own advice and snagged the 28 x 11.5-16 Hoosier QTPs while they were still available.

Update: Tires were delivered today. They look huge, but appearances can be deceiving. The tread width is 25 cm, just a bit under 10". The (un-inflated) diameter is about 26 1/2" while the circumference is about 83 1/2" center of tread. They appear to be very close in size to my normal (but abnormal) 255/50R17 street tires when compared side by side. The QTP was compared against the left front street tire as installed on the car with hood open for ease of access. I'm sure they will blow up a bit when inflated, but these should work just fine for my purposes and gearing (3.73). I'm glad that I went the 28" tire over the two 26" choices already discussed, however a 26" tire is likely the better choice for the OP considering the 3.07 gears.