Paul Workman

On a 90, the primary injector boss can be completely removed. The primary (only) injector is sealed with an "O" ring at the top of the injector.

After removing the primary boss (entirely), the tip of the injector is literally "hanging in the breeze". The tip of the injector(s) accommodate a small O-ring. Some grind the tip to remove the O-ring retainer, but isn't really necessary; is OK "as-is".

Opinions vary, far as transitioning from one diameter (36mm) to another (32.5+mm). Read what you will regarding how/what you think is best for you, when it comes to the actual transition angle vs. reversion, etc. But, I think you'll find that abrupt changes are not exactly performance enhancing. (If you open up the primary port to ~36mm and then blend the runner all the way to the valve guide on BOTH the primary and secondary runners, you'll not get into trouble, IF you keep the centerline straight. And, I know you're gonna like the result!)

For example: Here are a pair of Webber velocity stacks. You don't see any abrupt transitions, right? Nuff said...

Rkreigh

a few things for food for thought and opinions for some very smart fellers

Along the lines of "making the air happy" is there much to be gained from cutting down or maybe streamlining the valve guides? They are kinda "flapping in the breeze" and I remember alot of the comp guys going extra mile with epoxy and "blending the guide better" so the airflow stays more laminar instead of hitting a big round guide (which turbulates flow in a very high velocity area

big valves seems like there is an opportunity here to open up the bowls a bit more. The LPE LSV has them, and Graham was telling me they are maybe worth 10-15 hp. But I believe they are a good foundation for the "upstream work" to realize more out of it. Expensive upgrade though. And the factory valves aren't bad.

Ok, best for last. A fabricated cross ram style intake. The LT5 intakes are both expensive and difficult to port. And the S turn the flow takes due to the shape of the intake runners makes the air make some pretty sharp turns which reduces flow. While the long runners flow well and add torque, I think up top they really do become a hinderance to the overall performance. This might cause some really tough tuning and require a "more gradual" throttle linkage but it would certainly give a nice straight shot for the flow to the valve and pick up the top end charge. I have 4.10s and with the lightweight fidanza and big Stg II cams, low end torq is really not all that great even with the 390 displacement as the lightweight flywheel reduces that initial inertia and the big cams tend to be "soggy" in throttle response below 2k.

The big intake may further exacerbate this problem, but the midrange and top end charge would be glorious. Since no one makes anything remotely like this we look to the foreign parts bins. OBX and others make ITB (*individual throttle body*) setups for a very reasonable price that have a similar port shape to the LT5 intakes. The hard part will be fabbing up the base for the head. Might be able to cut and mill and weld a flange to a set of lt5 injector housings or CNC mill a base.

I'm excited to try this sooo..... gotz to get some fold

check my cars for sale (shameless plug)

cv67

Youll usually gain something from streamlining guides just not much
Porting aside someone that really knows the right valve job to compliment whats done is priceless.
Seen heads lose or gain 15-20+ cfm either way depending on the application. Finding someone who really knows that is the challenge so far only met 3 that could, worth every penny.

KJL

Update:
Still going at it when I can. Taking my time. Almost finished with the intake plenum. I am nervous regarding the injector housings. My first concern is whether to mount the housings in such a way to orient the ports so they are vertical or just clamp them flush on the table and port with openings on an angle.

Dominic Sorresso

How big are u going?

KJL

36mm

KJL

Here are the post plenum porting numbers. It shows about a 25% increase in air flow. I believe the numbers are better than those measured. If I run my flow bench at -6"wg without anything sitting on the orifice, it measures close to 90 cfm. This means my plenum is offering little to no resistance at this flow rate. I should have initially tested at a higher pressure but my digital manometer maxed out at 6"wg. The secondary injector port values will likely run into the same issue. The manometer I am using now is good to 16" so I will retest the injector housings at a higher pressure. This will give me some head room after I open them up.

Here are some updated numbers for the IH's. Not much difference regarding the secondaries. All numbers match much better.

mike100

very interested to see how the I/H'ings come out.

KJL

I did a quick check on the first IH primary port. Not done, just opened up the exit to 36mm and have started to open up the runner. The injector boss has been removed. Tested at 6" with injector installed. Flow increased from 57 to 75 cfm. At -11 inwg test pressure, before porting was 80cfm, after 100 cfm.

KJL

Follow up-
Finished the IH, see below. Now cleaning up the engine, discovered an old mouse nest under the coil packs. Considering removing the secondary vacuum stuff and wiring the blades open. Part of my upgrade will be new all new injectors and o-rings from Jerry's, new T-stat and chip. Decided not go with the 63mm throttle body upgrade. I probably could have spent more time smoothing out the port work but I am really ready to get this car back on the road. Travel for work and other stuff has really prolonged this project.....

So much for photo bucket....

Dominic Sorresso

You will likely need to re-do the fuel map and also a re calibration to enable full time use of secondaries.

KJL

I am having Marc H. do the chip for me.

cv67

Keep at it, the "pretty" stuff on porting is just cosmetic (as you probably know)& in many cases a waste of time really.

the shape of an LSx runner with the complex taper they have would be something to keep in mind if they did a fabbed piece, you get capability of volume and airspeed all in one

Rkreigh

we had that debate as well about the port being "too good" in terms of a mirror polish

fuel can puddle on and wet the port walls and a super smooth port may indeed be more eyewash than benefit and testing is in progress to see!

I saw some really innovative stuff this year with golf ball dimples.

I believe this is a fantanstic idea and may indeed help keep fuel in suspension

I've seen on some cars turbulators to "kick" the fuel up and I'm learning about Tau which is what the tuners calculate for "port wetting" that evaps and the fuel goes back into suspension as the valve opens

with batch flow and older systems, this is a huge factor.

but I believe it also is a factor on the lt5 as we have some tortuous kinks and turns to get the long runner length that gives the sweet mid range torq and throttle response.

Many porters leave the cnc ridges and the port wall slightly rough, others create art, and the dyno tells the truth which is why we test!

Demps has really been doing alot of R&D and sweat equity here and it's very sweet stuff.

I'd love to do some porting on the LSV as there are a few ponies hiding on the table, and the current work is really exciting to see!

With many of the 380 motors pulling nice numbers, for sure with the LT5 the heads and cams make all the difference.

The big displacement motors spank out more torque, but we are flow limited in CFM to feed that many cubes

I'm more into doing "more with less" and using the stock crank and getting the revs upstairs to make the power. I think with some work we can find the flow to get the go.

All of the experimentation done by many of the LT5 faithful, continues on and I'm sure glad to be a part of it!

I can't wait to see history repeat itself and the new ZR-1 hitting the streets.

Dominic Sorresso

If u determine you need a more specifically customized tune, let me know.

KJL

I have a baseline dyno run on the car with just the FlowMaster exhaust. I plan on running it again after she is back together. I will have them measure O2 ratio during the run. Is it worth the money to have the TB increased to 63mm? What type of tuning do you do?

Dominic Sorresso

First of all, I have been tuning mainly Speed Density motors for the last 15years. Started w modified 84 Xfire that ran 13.3s. Over the last 10 years working on the LT5 in configurations from stock, ported top end,
to cammed, and larger displacement motors. Real tuning is a matter of getting part throttle and driveability right first. That needs to be done prior to WOT dyno tuning. Since part throttle requires an iterative process, its not something that you can get right w a "canned" tune. At the very least "canned" tunes are not optimal. Every motor is different and drivers all have their own particular taste in how a car should behave. Having said that, there's only so much a tune can do. The motor must first be mechanically sound w the base systems (ie fuel, ignition, air, sensors) all operating correctly. No vacuum leaks.
If you'd like to know more about how I have helped some other LT5 owners tune their motors, shoot me a pm.

Regarding the 63mm TB, I can tell u that I replaced my stock TB w a 63mm when I ported my top end. But putting a 63mm in front of the stock plenum opening doesn't help unless u port those openings to match. My motor w headers and top end port made 397/375 at the wheels. I could not say that the 63mm had much to do w that. I think once u go w ported heads, cams etc, then there's a greater need for air. I know of one owner who puts down 440hp w a stock TB.

cv67

leave the stock one on there, even a 502 bbc crate comes with a 48mm

KJL

Thanks for info. I am a major advocate of part throttle tuning. My experience (20 years worth) has been primarily with carburetors. I am interested in how the iterative process works long distance. Do I run the car at various speeds on a dyno then send data to you for adjustments? I have a 95 ZR1 as well which is the one I have done the most too. It puts down 400 at rear wheels with headers, exhaust, aggressive top end porting and 63 mm TB. All I did with the heads was port match them to IH's to a depth of about 1.5" blended into the head.

The 92 I just wanted to perk up a little while retaining most of the stock look. The engine runs well but I have not performed a leak down or compression test on this engine yet. Only 25,000 miles on the engine.

Dominic Sorresso

Part throttle tune is even more critical in EFI ECM comtrolled motors because it establishes the baseline for all other fueling. And yeah I tuned carbs way back when which actually helps in understanding what you are doing w EFI.
I can text u my # to discuss remote tuning. Easier to
review the process that way.