leesvet

.....and is there ANY real improvement in the last L98 designs in flow and performance?

I ask because I am looking for a whole intake 'set' to port match thru the plenum to the intake valve...all 3 pieces of the intake AND the head that they go to, all the way thru.

A converted LT intake is also welcomed, IF I can find one that's ready to bolt on...just need to match the runner-ports to the head.

If the 90-91 models intakes are a better over-all base to work with...so be it. I'll buy the head for that yr too.

if the 90-91's are not much different than the 87-88 intake...then I'll work with what I've got.

I have been told the later yrs had a "D" port...in the exhaust side I'm assuming? supposedly much improved flow OUT of the head, so I'm wondering if there was also some upgrade to the INside of that same head? Again, if there IS then that's what I want to acquire for a winter project while the car is down getting engines swapped out.

bogus

There isn't a lot of difference, really... you have to realize that from 1985 to 1991, the horse power only went up 20... that's refinement, not revolution.

If I was looking for an intake, I would be going after a miniram or something of that nature.

As for heads, they ain't bad, but they require a bit of porting the make really good. I would suggest spending some $$ on AFR heads... you will really be happy.

Where you can really improve L98 performance is with the exhaust. Lose the single cat thing and go with dual, an xpipe and the engine will pick up 30hp... headers another 20, and that's with an otherwise stock short block. Add the AFR heads, roller rockers and associated hardware, with a mild street cam, and your into serious power for not much stress - figure 375hp-400hp.

cv67

Lee the intakes flow about the same I can never get the yr/bolt thing straight myself.

David Frederick sells converted LT1 intakes done can usually find him in the parts section. Doesnt take much to get them to support some decent power on the cheap.

Either the 128 std or 113 D port (little better)could make for a cheap DIY port project. exh on the D is a little better...the intake ports and seats kind of suck least the ones Ive seen. Exh pick up quick on them not much to do the intakes will take more time.

Wouldnt take too much to pick up 20-30 out of the heads on stock valves and intake without marrying the project pm if I can help.

Tom400CFI

...and most if not all of that 20 was roller cam, compression, and exhaust.

leesvet

Thanks for the tips and tricks...!

the goal of this is to take a complete GM intake system and match it all, and port it from TB blade to intake valve. Open it all the way thru and get ALL the detail work done so it can perform as well as I believe it might.

Its not witch-craft in the AFR heads or the stealth ram, its simple attention to the detail and making pieces that work well together. Castings that are RIGHT and given some hand work to make a good finish. Not the "cost effective" mass production stuff that we get on the factory engine that is likely loosing 25% of its potential to flaws and poor quality manufacturing. I want to see if that can be corrected on the table as a matched set of intake parts....all GM parts.

I've seen enough of these things to know that there is probably 25% of the potential that's been LOST to mass production flaws and the lack of attention to detail. That in itself is the single biggest difference between a $50,000 car and one that cost $250,000. The detail work in both the engine and the chassis....

I believe there are ponies hiding in that top end. Many more than people want to believe...They're trapped behind shiddy port alignment, narrowing runners with lumps the size of a good tumor, and all 'round crappy casting. I've ported a handful of LT intakes and all had great results. The last one I did I returned a zip lock baggie with about 3 lbs of aluminum shavings that I took out of the runners and intake ports...and really opened up the runners. There were ports that needed 5-6mm of material removed to match the volume and size of the other runners. Very crappy production parts. low quality stuff. I believe IF I put the time and effort into a GM intake that it will do near as well as many after market systems. I'm NOT a big TPI fan, so the LT intake is really appealing.,. Being 1 piece too.

Yes, I am aware that it will require a LOT of time on the table and that's OK. Its a project that I've wanted to do for some time. I;ve got a motor to build now, so now is a good time for an experiment. It can take all winter....if the insides look good I might do the outside as well.

I cannot remember seeing anyone take an entire GM intake and match it all as a set and see what the end result was.
Its always an AFR head next to somebody else's intake etc etc...then some sort of fresh air induction and a too big TB. Nobody ever takes what is in front of them and fixes whats wrong with it. I cannot recall ever seeing that. Instead of buying a repair, I want to DO the repair, meaning going thru the whole intake system and correcting whats known to be wrong with it. That's easy enough to do. Its not rocket science, just a little work. Not afraid of that.

An LT intake would be an acceptable short cut.....and Cuisinhart, that polished unit in the other thread sure looks nice !

Next week I'll start shopping for some heads. The cost of building a set of bare heads is actually more than taking some that already have some mods done...there are lots to look at.....and cost is all over the place. To do this right and stick to the project goals, I have to have ALL the top end there sitting on the table in order to match it all and achieve the goals that I've outlined for myself, and this motor. Why not? I've got all winter...Guess I'll look for the D-port head and see if a modified LT intake will fit. That D-port stuff still confuses me.......

BTW, long tubes are included in the build, and some other 'upgrades' outside the block. The bottom end will be forged so it will be a good solid platform to work with no matter what I bolt on top. I don't expect to do it overnight....the plan IS to take the time and do it right. Do what GM cannot do in mass production.
Thanks again for the info !

cv67

Sounds like a challenge and a fun project. If i had a TPI car Id do the same thing: make the most of whats there already without getting carried away with huge valves, ports that turn the head intoa sprinkler system etc. Even better design a "blueprint" type cam..something with increased duration not too crazy on ramps/valve timing, conservative on lift depending how everything flowed;stockish bottom end maybe with a touch more compression...OEM like reliability drivebilty and low cost. Lingenfelter did it except the cost part lol
Anyone can use high buck parts and make some #s.
A true drive on the (kinda) cheap.
Keep us in the loop.

ghoastrider1

there is a TPI manifold ,runner and Plenum and fuel line on Indy craiglist for 75 bucks. Seems maybe a good start to look in your neighborhood for the same.

leesvet

yessir, I might look that up to see about the base. There are a couple local salvagers that might also have some good stuff at a decent price. craigs list is actually how I found my block...I always check that place for misc C4 stuff.

I've already got a couple plenums, and runner sets but no base. I was recently looking at a stock base next to a big-mouth and there is a TON of difference in just the casting....so I might cheat and look for an after market base...I've already tossed the stock runners in favor of some SLPs that I've gouged out big enough for a golf ball to roll thru. So much metal was removed that I have to go get some welding done on the outside to close up a couple "thin" spots that you can see thru...a little.

I'll match those to a base IF I decide to keep the TPI. Its sure tempting to get the LT intake and run with the one piece system. With the modified LT intake, all I have to do is match that to a head. The LT intake can also get lots more air thru its short meaty runners...Its then getting close to a stealth ram in flow characteristics.

That's the point. I see these aftermarket parts that someone DID spend the time to mfg RIGHT and they DO offer real results. That's why they cost more. That's all the aftermarket does.....they take the factory part and improve on the design or simply fix whats known to be wrong with it. Its not voodoo...its a game of numbers. Whats cost effective and who can afford to do it. Most times the bean counters are in charge of production cars. In after-market, the consumer is.

But if you look at these NICE parts next to the stock parts thru a dirty pair of glasses, you cannot tell the difference. They are the same design, same shape, same objective. One is just made better and finished out better than the other. That's what the difference is. One works while the other works real WELL.

I think we all accept that a couple of the stock pieces are hopeless...namely the runners and probably the baseplate. The stock TPI base has very little meat to work with and is not very forgiving when it comes to the shape. There is just nothing there to open up...its too thin. The runners? Short of cutting the tubes OFF and welding in larger replacements OR adding room onto the plenum
( Lingenfelter style) and then dropping short runners straight down to the base, there ain;t much that can be done.


Building the lingenfelter style plenum is not difficult, not at all, BUT it gets costly in TIME and materials, so why not just BUY one instead? OR replace it with the only other real option, the SLP. I actually designed a bolt-on box that would have done the same thing as the big lingenfelter plenum...except I was going to use silicone tubes for runners to avoid the cost of even MORE welding and machine work. Just bolt on the box to the siamesed ports (plenum) where the old runners went, and clamp the silicone tubes to the under side where some 1.5" diameter nipples were hanging down to clamp onto a plate with nipples for the baseplate. Easy. Might have worked too,...

I've already cleaned out a plenum and the SLPs are Siamesed to mate up to that. Now The base and heads. There is a LOT of science here that I'll damn sure never fully understand but there ARE a lot of folks out there that DO "get it" and can advise along the way when shopping for these parts. I need to get off my *** and start looking for more hard parts. I found the bottom end 'kit' I want....forged flat tops, forged I beam rods, nice steel crank, all Scat stuff, Probe pistons IIRC. Balanced and ready to assemble with their own flex plate and dampener. That's got my name all over it ! Merry Christmas to me !