1989 Corvette C4 6 speed manual

As much as I like the Grand Sport, I'd say your car looks better without the flares, the stance is just bang on as it is

Always liked C4 'vettes. They've got a lot of clever engineering that's overlooked because people see 'leaf spring' and 'body-on-frame'.

Nevermind that the leaf springs are composite so much lighter than coilovers (and weight lower down), with later C5 'vettes having a neat mechanism that lets them double as an ARB. The chassis is a little floppy, but the C5 as an evolution of it is not too bad.

You don't happen to know the length of the transverse leaf springs do you? Wondering if I might be able to pinch one for the Sptifire...

I've either been very lucky or unlucky recently with the car depending how you look at it.

The Comp roller tip rockers that came with the replacement heads were the wrong type. From the factory the car has self aligning rockers with a small indent to keep the rocker aligned with the valve stem. The guide plates for the push rods are just assembly guides, not hardened steel. Basically the rocker arm controls the geometry, not the guide plates. Well the Comp rockers can't have been used for long by the previous owner as I soon had a loud valve train and pulled the valve covers off to investigate. The push rods had started to wear down the assembly guides and one of the rocker arms had almost come off the valve stem after chewing it up. I caught it just in time but if I'd known sooner I could have just changed the rockers.





I weighed up what to do next, I needed to pull one head to replace the valve at least. I could have kept the rockers and fitted hardened push rods and guide plates or for a little more get a quality set of self aligning roller rockers. I went with the second option, it was £300 for the 1.6 ratio (compared to 1.5) Scorpion roller rockers. Made in the USA from aluminium and with roller bearings on the trunion and tip they'll greatly reduce weight and friction as well as increased lift. It should be an honest 15-20bhp gain. Certainly the car feels stronger in the higher rev range and eager to rev to 5600rpm. A solid 1000rpm peak gain over the torquey TPI intake from factory.





Aside from the exact torque sequence for the 18 head bolts I could change the head gasket with my eyes closed now, in under a day I was able to pull the head, change the valve and put it all back together. My MOT is due in two weeks and I'm a little nervous as to whether it'll pass emissions with the new tune and intake but otherwise I'm hoping it'll be okay. If I have too many issues I'll just sorn it until the spring I think. It's also decently quick for over 30 years old, the data logging shows it's easy to crack a sub 5 second 0-60 with a decent launch! Or you can be a hooligan and leave black lines all through 1st into 2nd...

Living in Wales and near constant lockdown I've enjoyed reading the threads here so thought I'd do a little write up again. My car mojo has been pretty low, with nowhere to go and the most ridiculous MOT tester. I think I've got the issues sorted and I'm booking the MOT tomorrow morning!

I took the car to a local garage which also specialises in old Jags, thinking they would be reasonable with a 30 year old imported car. With lockdown in full effect and Cardiff a different area even if just 5 miles away, I thought I could just take it down the road instead. Wrong!

Whilst there were some things I needed to sort, such as a broken handbrake cable connector, they were more interested in deriding the car and picking up anything they could. Shame as I would have taken my daily Volvo and the girlfriends Mini there otherwise, not to mention the Corvette.

The rear indicators are in the reverse lamp housings so that the 4 red tail lights can remain. Being an equal distance from the centre of the car, they've never been questioned before. After I pointed this out the tester got his back up, called someone over and declared them “not orange enough”. It's an orange bulb in a clear housing, not exactly an unusual combination? They further picked up on the side markers not being visible from the back of the car and the seats being dangerously insecure, when infact they tilt a bit so you can reach the release lever, just like they came out of the factory. A small crack in the steering shaft rag joint was another serious fail, which had eluded any previous MOT inspection.

My one genuine worry was emissions, and they did allow a quick tweak of the distributor to drop the CO and pass. However I wasn't happy with it running rich at idle and so that was something to sort out.

Having “recovered” the car back home having spent £50 to get very grumpy I set about sorting out the small items.

I painted the reverse lamp housings yellow, hoping to make the indicators more orange, and it looks alright against the plate anyway.





I couldn't find one of these rubber pieces anywhere but after some measuring, a similar item from a Ford Sierra would be a close fit.



The pinch bolt holding the shaft to the rack was a little tight and my trolley jack handle doubled up as a suitable bar.





The third brake light only had one bulb working, not a fail but an irritation. Luckily at a car show someone gave me some C4 oddments in exchange for cold Cider and I was able to swap the innards over from another. The bulb had melted to the housing and cooked the board.



New headlight adjusters since the others were siezed:




The handbrake cable has an integral collar which had broken, no longer actuating the left caliper. The handbrake uses a cam on the brake caliper to push the pads onto the disc, rather than conventional shoes. It can be quite fussy but hopefully a new cable will be all that's required.





The car only has one single wire O2 sensor and it has difficulty staying in operating range with the long tube headers and dual exhaust. Since removing the smog pump I had a spare 12v & ground in the engine bay. Running this to a new 3 wire pigtail connector, I then fitted a 3 wire heated O2 sensor. Now the car goes into closed loop at idle in 3 minutes. Perfect! This should help with my emissions, MPG and performance.



My bluetooth OBD-1 scanner has been a great bit of kit. I used it to datalog with a laptop to tune the car when I changed the intake and rockers. Here I'm using it with an app on my phone to see live readouts and watch it go into closed loop as well as the O2 function.



My throttle body has always had play in the shaft, which is a small vacuum leak and it's required a regular spray of WD40 to keep it smooth. On eBay USA I spotted a billet aluminium Holley 58mm throttle body, open box and 50% off. It's a bit step up from the factory 48mm butterflies and a beautiful piece. With the new intake it lines up pretty well already, although when I next have it apart I'll open up those extra 2mm on the side. It'll future proof any engine tweaks later on too.





I bought some bucket seats for a bargain price too, Sparco Torino II's. Not many seats fit in the C4 because the transmission tunnel accounts for half of the cabin and the handbrake is down by the sill. These should have fitted but the recline knob lined up perfectly with my seat belt reel and it was a no-go. I passed on the deal to someone who drove up from London. They were going in a track car replicating one their Dad built before passing away. The chances of finding another set must have been slim and they were thrilled.

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Then just about ready for MOT I had a setback. After changing the valve cover gasket on the passenger side and tightening the cover down it cracked! I was a bit miffed as I'd hardly snugged them down. I emailed the manufacturer Proform and asked for a replacement, as a new pair would be circa £300 delivered from the USA. I got them second hand with the heads in the summer and now with the roller rocker arms I couldn't go back to factory covers. To their credit, with no receipt they agreed to send me another one if we split postage between us. £32 later I was back in business. Although they sent it via the US postal service so it took a couple of weeks before it even showed up in the tracking at Chicago, but once it was on the system it arrived quickly and marked as a commerical sample worth $1 I paid no duties either. Result!



I didn't like the look of the bucket seats in the car and it made me realise the best course of action is to redo mine and take care of the cracked leather and worn bolster. It's only £400 for a complete carpet set and that had me thinking, if I do both, perhaps I should go for a red interior? It would look great against the black I think! In the summer a shares saving scheme with mature and I could redo the whole interior for about £1500 if I do it myself. It's a temptation and I think it would add so much to the car. It's going to be a bit longer before I can really swing a complete engine build anyway.



The other thing that has happened is my big shed arrived too! In the summer I made the base out of some sleepers and a mere 3 ton of limestone to level it out. A local company supplied the 10x8 pent shed and it's great quality, no chipboard to be seen. At 6'2 there's plenty of headroom for me too. I made a workbench and finally have my tools and stuff organised, it's so nice to have everything in one place for the first time in my motoring life!



(excuse the winter tyres)









And this week 10 years ago I started my first thread on here after buying my white 924 for under a grand.



10 years and 30 countries later here's hoping 2021 will provide more automotive adventures!

Thanks, that's a good idea! I would like to do that in the future but the only access to the wiring is through the numberplate aperture and the PO must have cut the wires before. The red tail lights also double as fog lights.

I thought about those hamburger LED lights too, it's just a standard 80mm round light

That's a good idea!

The wheels still look like the day I had them done. The chrome powder coat requires no more maintenance than any other powder coat finish. I can't be bothered will polishing/detailing stuff really so I wanted a durable and low effort finish!

Came across a bit of a bargain on eBay and had to go for it!

A complete engine from a 1988 Corvette. Shiply was great for delivery too, ended up costing £60 to get it on a pallet from Watford to Cardiff. The seller had a C4 as well and was very helpful on his end getting it ready to send to me. It has 121k on the clock but has been used with a Procharger and 150 shot of NOS so a bit tired probably! I wanted a later SBC block as it has a 1 piece RMS and hydraulic roller cam as standard. To get one complete was a real bonus, I can sell the heads and intake to recover the cost of purchase. All the ancillary brackets will make useful spares or again have value, along with the bolts and little connectors and sundries. I've been stuck for a couple of days before waiting on electrical connectors so having a little supply of my own will be good.

As for plans I have the CNC ported heads in my loft ready, which flow 40% more than the stock aluminum heads. Mated with my aftermarket intake and a suitable cam will see an easy 400bhp. I'm going to strip the block down, hopefully it's still on the original bore. If it checks out okay the idea is to make a 6.3L 383ci stroker. This should make 500bhp a realistic goal, however I'd be happy to settle for a strong and reliable engine rather than a number. For $800 a complete 383 kit can be bought, that's new crank, rods, pistons, bearings and rings. Double that for forged components, although I want a strong NA engine and can't see myself adding a supercharger in the future.

It might be I could get away with a more basic rebuild of the bottom end but I have a feeling for the extra money I'll regret not going for the 6.3L

Yesterday I took the ancillaries off as well as the exhaust manifolds, it's certainly easier to take the plugs out in this situation! The all looked consistent at least. I might do a compression test out of curiosity too.

“Honey, there’s a small block Chevy in the garden.”

I recall Callaway, in prepping C4 engines for their elegant twin turbo upgrade, machined the block to take 4-bolt main caps and used a Callies crank, can’t remember which rods (prob Carillo) and Mahle or Cosworth pistons. I think at that time (C4 R2BK) they left the heads alone, but I could be wrong.

Their Sledgehammer, which set a serious record of 254.76 mph (think about that) was, obviously, a much more involved job.

I like your car.
John

Another good article on the Sledgehammer:

link

Just read this from start to finish.. I've never really "wanted" an American car before. Il admit I was of the "leaf springs and pushrod engines, what is it the 60s,how do they only get 200bhp from 6litre" mentality... Not helped by an old school mates older brother having a transam when we were younger that left me positively underwhelmed (my parents chavalier was faster)..

But.... I don't know if it's the way it's written, the car itself, the look of it, or perhaps I've matured haha. But I really really like this.. I mean I like everything with a V8 but this is brilliant. Seeing how you've worked through upgrading as you go, the road trips (even commuting in my car seems risky haha) and the scenic photos all make it a good read!

Bookmarked for the journey, now off to look for a thread about a 924 I've no interest in either 😂😂