New to the C4 forum. I've been out of the Vette game for a year. I previously owned a 2009 base with an automatic and left it stock. I just acquired a 1987 convertible with a 4+3 with about 125,000 miles. The interior and exterior are in what I consider pretty decent shape for a 35-year-old car (not perfect, but nice), but I bought it with what is at least a blown head gasket. The combustion gas is pressurizing the cooling system so the top end needs to come apart. With that comes options. I might as well yank the motor that is in there and freshen it up. If I yank the motor out to freshen it up I might as well do a camshaft too. I don't think I want to go crazy and build a 383, but maybe a 355. The problem is that even though I love the look of the TPI system it is just too much of a limitation on making power in the upper RPM range. Tuning an OBD1 is something I've never done. I know the chips come out and you need to burn them each time.

So, maybe I just go and LS swap it. I have an lq4 I could pick up for about $800, with no accessories, and about 160k miles. If I get that it would be at least a cam upgrade I do with it too. I know the LS will bolt up to the 4+3 with a couple of small mods. It should bolt in the car with some motor mount adapters. I see some people have had to notch the k-member and others mention nothing about that. That's something I could do if needed. I've done some minor LS tuning so I think this is also something I could handle. I already have LS headers sitting around at home doing nothing. I would keep the L98 and maybe use it for a truck later if I go this route.

My ultimate goal is to have power similar to my old C6. Somewhere between 400-450hp at the crank (~300-350rwhp). What is your opinion on what should be done? A L98 with almost 400hp and 500ft-lbs of torque would be a blast, so would a 6.0 LS. I'm looking for pros and cons. My budget for this isn't unlimited, but I could do $2-3k (maybe more, but less expensive is always better). The 4+3 is staying with the car. I believe the T10 is a good enough trans for what I'm doing and the OD part of it will be fine if I don't use it under full power. I've always thought it was a decent trans that got a bad rap. The LQ4 and a cam will reach my goals easily. What would the L98 take to do that?

Or just do the head gaskets and leave it stock?

 

Sounds like you know a TPI can do 400hp/500tw...but with a limit of 2-3 I dont think so.
Im more for doing the Gen 1 but if you know the intricacies of doing a proper LS swap and a cam only 6.0 will make you happy..maybe thats the route you should take.
Youll spend on accessories, tuning if you cant DIY. pan, EFI system. May go over budget too and you have an old engine not rebuilt
KNow a lot of guys are ok with high mi engines....guess if you can get them that cheap why not

A junkyard 5.3 is still 13-1500 minimum out here in Ca which is insane. Lol
800 for a 6.0....Id have a hard time not building it they make plenty of tq and like most ls can take a beating.

 

Since you are talking about pulling the block, swapping the cam and going to a 355 (.30 over) why not throw a different crank in and make it a stroker? Then get a set a good flowing heads port the crap out of the intake and runners throw long tube headers on it and there is the power you are looking for

 

I wasn't thinking 383, but I guess nothing is off the table during this phase. The only reason I said 355 is because the motor has 130k on it now. I don't know if the cylinders will need any machine work. If they do, it's going .30 over. It shouldn't be more than an hour more worth of work to yank the motor out compared to just removing the heads. Right now I'm leaning to keep this motor and do some mods to it.

How well do ported and polished l98 heads flow? Similar to aftermarket, slightly worse, or way worse? Enough with a different intake to reach the power levels I'm thinking about and still be drivable? I'm putting a plan together now. Still have a couple more people to talk to that are local.

I would guess a different intake with shorter runners would help move the rpm band up and combined with a decent cam, make more power than aftermarket heads and a cam. Maybe not.

 

If you LS swap don't worry about notching the cross member. I had to do that in my 84. If you need to you just need a piece of steel angle and a welder. It's not hard at all. Nice thing about an LQ4 is that with a mild cam and spring swap you have 400 hp on 87 octane. Or you can swap on junkyard 243 heads and bump the compression up a lot with stock pushrods and no machine work required. Also in your case with a 4+3 you don't have to worry about transmission control like I did and you don't need a higher stall converter. So LS swapping should be a way simpler process.

 

My 2 cents keep it TPI, rebuild it with a cheap Summit 383 crank. You automatically pick up about 30 horsepower just by the extra cubes.
the combination of a 383 on a TPI with a 4+3 and the future 500 plus pound feet of torque would be an amazing animal.
The fact that your car is light weight is also a plus less power to do the same thing. A mild cam, a good set of AFR 195cc heads, Long Tube Headers, and port the crap of of the TPI you would be very happy.
about 430HP and about 500LBS would be the result. Imagine how well these cars move with 240HP look at how they perform once you add 200 naturally aspirated horses to the party!
Well this may be more than 2 cents, lol...

 

Dont waste your time porting L98 heads. Even with larger valves they barely compare to entry level aftermarkets these days.
Rather than focusing on a hp number how do you want the engine to behave? Do you hit the track?
Goal of a time in mind? These arent high rpm big hp engines...they can make super good torque, the hp number takes care of itself.

 

I like the idea of keeping your engine, mine had 230,000 on the clock when i picked up my 90 6spd. I removed engine and transmission, disassemble engine inspect and sent it off to a very good shop, block bored 030 over rotating parts balanced, heads ported and big valves installed. CC flow check in comparison to aftermarket ones.
purchased camshaft, lifters and roller rockers from TPIS. long tube headers, from summit , Hedmen, clutch replaced with a like new DM fly wheel, PO had the wrong dimension fly wheel and clutch installed parts from Jim at powertouque systems, now retired. Z Doc modified my shifter and fork. Regardless about what is said about DM flywheels, my performance is not affected. finished off the rebuild by taking out my differential and sending it to Zip corvette changing from 3:33 to 4:11,
Any way that is my 2 cents about C4 mods, I never contemplated about a LS1 conversion since I want to own a C5 and mod it out. good luck with your car mods!

 

^^^you ever run it down the track, how do you like those 4.11s with the TPI

 

Yes very well 1/4 mile is mid 13s overall average hot days late 13s. I surprise modern cars from a launch, the car hooks up fine. i love the low end torque thats why they made TPI, I have a mini ram stashed away i might try on some weekend and track it.

 

What was your mph? Interesting to hear on st tires? Car hooks well bet its fun light to light
First thing I did when I got my 89 (new to C4s) is took it to my differential guy and said "Put 3.73s" in it..He refuse and explained why

 

Gen1: 383 (if not a 396) with aftermarket heads, cam, headers, and an FFI intake.
Gen3: As you suggested, will cost less but start at 160k miles and require way more work. Long-term power potential is higher.

Note: Mine is a 383 with large-mouth intake, small cam, headers, and AFR 195 heads and is about equal to an LS2. With a bigger cam and a MR you can get 100 more hp. I opted for the BBC torque since I rarely leave town (spending 90+% on city streets).

If an 87 has alum heads, I've seen more than one build where TPIS ported the 113's -- using a longtube TPI setup -- is nearly equal to my build. Without high rpms, porting isn't really a bad option. If HP is your goal, aftermarket is better as CV67 stated.

 

I purchased a pair of summit low profile track slicks i put on the rear when i go to the track. speed at the end is 67-70MPH. is your car a automactic? 3:73 is just about right for a 4L60E. with 4:11 in mine i can pull away in 6th pretty good. 6 speeds have a dana 44 and autos have a dana 36 so a 3:73 wont fit into it. If yours is Auto.

 

Thank you everyone for the input. I won't be doing anything with this until probably January, but I have a bunch of information to put a plan together. I'll post updates as things get moving.

 

Just an update and I will start a new thread when the swap begins. Bought an LQ4 for cheap. I have it completely torn down for a "refreshing." New bearings, gaskets, Sloppy Best cam, PAC 1219 valve springs, 826 heads, and the rest to see what fits when it makes it to the car. Should have the engine back together before Christmas. I'm only spending a few hours a week on it. I have a loose plan for how everything should fit together (clutch, front accessories, ECU, gauges, etc). If something doesn't fit the way I plan I'll modify it.

I'll keep the l98 and fix the head gasket after it's out. I may put it back in the car when it comes time to sell it, but maybe not. So far the swap has paid for itself because it sparked the interest of my 18-year-old son and he wants to spend time with the old man doing this.

 

I'm not sure the LS swap in a C4 is going to make you happy or money. The L98 with the mods the others are suggesting will give you plenty of power and torque, plus keep her correct. The LS swap is cheaper, and future buyers will let you know that. Being a convertible makes the L98 upgrades even more sensible. That car's going to make money in the near future.

 

Not worried about making money and it will be easy to swap back if I choose to. This car has already been changed enough from the original. One of the previous owners already swapped out all the blue interior (on the rpo codes) for gray, the wheels are wrong for 1987 (the left rear is the only one correct), the radio has been swapped, it has 126k miles, already had a repaint (that needs to be fixed in spots) plus its a C4 (highest manufactured model of vettes). The only thing it has going for it is a manual/convertible and even then no one thinks the DN4+3 is worth anything.

Don't get me wrong, it's a decent car for its age, but it will never be a super collectible one. I think the later models of C4 will be, like the LT1, LT4, Grand Sports and obviously the ZR1 and Calloway.

I've never torn apart an LS motor before, but they are the ****. Basically, a 6 bolt main, stout as heck, and kick butt heads from the factory. No reason to build up a sbc anymore.