Wanted: Advice on L98 Engine Upgrades
 

Hi Folks, I have a 90 L98 Vette. I'll state my problem first; I am going to take my L98 in for a rebuild and before I make that big jump I would like to have some of your suggestions for improvements. Some things I thought of were timing chain and oil pump. I would like some performance mods but I don't want to alter the ECM very much. In other words, what can I do with the engine internals only. Thanks so much for your help. Skip, 90 L98 Vette, 91 ZR-1 Vette

Here is one I'll give, although I don't know if this is what you're looking for. Get good high quality head gaskets or you will pull the engine back apart sooner than you want. Don't purchase the cheap AutoZone set.

If the engine is being rebuilt why not stroke it to a 383 then install a mild cam and have the heads ported and freshened up and install matching valve springs if you want to stay with your factory heads and then you can upgrade your intake system and exhaust system either when you rinstall it or at a later date.

:rofl:

Here's one. Insert an LS3 :D

No, that's an LS9 :lol:

If you want to do a stock rebuild, I would go with some flat top pistons and H series clevite bearing with a decent sized cam.

If you want to modify internals, go with a 383 stroker build.

:iagree:A 383 is not that much more time or money these days.

Pete, I thought you wrote the book. ;)

Just alot more power!!!..:yesnod:..WW

..... not getting a custom chip...just go for good parts. I would have the rotating assembly balanced. This consists of the crank, pistons, rods, balancer and flywheel. Balancing is about the most you can do for the bottom end. You could go for higher compression pistons, but you are at that fine line with your chip being able to handle this or not.

To get a little more out of the engine (again not touching the chip), go for a good set of heads and upgrade to roller rockers. Take a grinder to the intake, runners, plenum and gasket match by taking out the excess material to match the gasket holes. You can do the same for the exhaust manifold. The gasket matching will not provide much in the way of HP....but it all adds up.

Want power.....get the cam and pay the $$ for the custom tune....you will be much happier.

Changing to "a good set of heads" will absolutely require a retune (ie: a chip) in order to maximize power gains and to get the engine running at optimum. In fact, any change which significantly impacts air or fuel flow will require a retune.

To the OP:
The answer(s) to your initial question are:

1. How much are you willing (or looking) to spend?
2. What are your final objectives for the car (race-only use, road-burner, reliable daily driver, etc...)?

Generally speaking, if you're looking to just 'freshen-up' the engine on a modest budget, then upgrading some of the 'weaker' items is a great idea. Spending those extra dollars for a true double-roller timing chain, high-volume oil-pump, and (if your budget allows) a forged crankshaft will be money well spent. If the stock connecting rods are in good condition, you can have them balanced before being reinstalled; stock L98 connecting rods are a lot stronger than most people give them credit for. If I am not mistaken, 1990 L98s came with forged pistons as stock items. If this is the case, replacing your old pistons with OEM units will keep yours costs down. Approaching a rebuild with the mind-set to only replace the weak-points with stronger alternatives will go a very long way in helping the engine live a long life as a daily driver and will not require any sort of retuning. The best part is, it will give you a solid base for any future modifications since you'll know the foundation will be solid.

Why would anyone suggest a 383 on a TPI setup ( a huge waste of money )
the intake is all wrong for that power and flow

he said not alter the ECU (I'm guessing he meant eprom tune)
a 383 would need all upgrades Injectors, fuel pump, eprom tune,
heads, a small based circle cam to clear the 3.75 stroke
pistons you should use forged and so on

Balancing/blueprinting, maybe boring it to a 355. Upgrading weaker parts like rods or crank (which I don't think is really necessary if youre not doing anything to really upgrade power). Porting of the heads and intake manifold, 1.6 RR.....

If you don't want to change the cam, which generally necessitates a chip change, then theres not too many things you can do to the inside of the engine to give outrageous power gains. A little here and there is what you'll get.

LS engines the only way to go.

Better HP
Better mileage
Less engine weight

engine rebuild
 

Here's my take on your question:
First off, you need a plan starting with a budget. It's real easy to get carried away once you start the re-build and begin to look at parts and accessories. If you motor is just tired and with excessive mileage, get a basic re-build, ie, rings, oil pump, valve job, timing chain,etc., and maybe a slightly better cam and 1.6.1 rocker ratio increase, to go with the build. This won't require any ecm mods and you will end up with a nice fresh motor with a little more pep.


As fare as mod's go, there aren't many that will boost performance much without dropping more and bigger bucks on that build. One thing that will give you better performance and a good boost in the seat of the pants acceleration would be to change the rear ring and pinion. If you are currently running with a 2.59 rear ratio, go to a 3.07 or 3.45. The throttle response will be much improved and very noticable. Personally, I like the 3.75 I put in my car. You can often find a complete differential on this site at a reasonable price, or buy a new ring and pinion and have it installed.

If you are not going to do the engine build yourself, I highly recommend Carolina Machine Engines in Johnson S.C. ( www.cmengines.com) , as they do excellent work with a good warranty, and are very reasonable and quick. They did mine and the entire build only took 3 weeks including shipping the block back and forth.

Good Luck with your build! :flag:

Parts and pieces purchased from members on the CF:

Used 383 rotating assy -
Cast Scat 9000 crank
Scat 5.7 I beam rods
Used LPE 219 roller cam w/new stock roller lifters
1.6 ratio Comp alum body rockers
Accel Super Ram Plenmum and runners w/Eldebrock Hi-Flow base (limited port and polish).
Old style AFR 195cc race ready 70% CNC ported cyl heads.

Something that I had laying around:

96 Vortec 5.7L truck short block that turned out to be a 2bolt and Will put 4bolt caps on it.

Bought new:

KB/Icon forged PN 9926 pistons (18cc dish)
Hastings Plasma Moly ring set
King Accular brgs
I had a new old stock Melling M55 (heavy casting) oil pump
PBM fluid damper
Rollmaster timing chain
TFS 7.150 5/16 .080 wall pushrods
Victor Reinz gasket set

Clearance worked out to:
.002 Main
.0025 Rod
.007 Thrust
.003 Piston to wall
+.005 piston to deck (quench .040)
.020 Top ring
.021 Second Ring
Piston to valve -
.083 Intake
.122 Exhaust
LPE 219 Cam was degreed in @ 107 ICL with 112 LSA

Other engine Specs:
Displacement 382.6 cubic inches
Bore 4.03"
Stroke 3.75"
Rod length 5.7"
SCR 10.25
DCR 8.1

As you can see this is a "budget build".

Alvin at PCM for less mail order tune. The car is a 91 with Hooker 1 3/4" long tube headers, Y pipe into a single 3" converter to a Magna Flow cat back, ZF 6spd trans, new old stock Dual mass FW, LUK clutch, 3.45 rear gear, 315/35R17 Nitto NT05 tires on A molds.


336RWHP
400RWTQ

:iagree: :lurk: :D

Your computer can compensate for a head change without the need for a new chip. If you change the cam, then you will need to get a custom chip. The better flow of a good set of heads, better intake or similar modifications do not necessitate a chip change. Only when you alter the cam from stock with higher lifts, change in duration and overlap will you need to change the chip. If you don't agree, ask a good tuner in your area.

I would suggest any modification that requires new injectors needs a tune. I would suggest heads could create that need.

I also wonder if Skip, the OP will even return to this thread. (It's already been 2 1/2 days since his first/last post). And, I wonder if people read his original post thoroughly. John obviously did (though I respectfully disagree with the answer). I'm not sure about everyone else. Vader's reply about balancing/blueprinting sounds more like what the OP might want.

There's not a whole lot you can do w/o a chip change/tune. I'd probably qualify the limit as intake/exhaust improvements. Even then, headers may require adjustment depending on O2 location and accuracy. OTOH, there's nothing that says a stocker can't benefit from a tune. Member "Neat" proved that.

If you're wanting to keep the car/rebuild for a long period, balance/blueprint is a good idea -- especially if the intake/exhaust are upgraded to allow more revs. Otherwise, large runners/base and/or exhaust improvements are about the limit here. I'm not sure I'd even vote for an upgrade in the OEM timing chain or oil pump. Those original parts do a good job compared to the lifespan of other components used in the car.

This particular debate seems more beneficial to address piston upgrade (if any), ring size change, head gaskets, sensors, fasteners, intake gaskets, etc... IOW, the pieces that sometimes cause an OEM motor to fail. Along with that, suggest what minor changes he could install that would REQUIRE a tune.

I'm not sure what Skip means with his comment about not changing the chip "much". WTF...Either change it or don't, Skip! What are you trying to limit yourself to? Changing the fan temps?

I kinda have the same attitude as Pete, but for different reasons. If/where is this thread really going?

:crazy: