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Installing a Holley 58mm TB
&
Porting intake while still on the car

This page will give details and pictures on installing a 58mm Holley Throttle Body (or any TB for that matter!).  The 4th gen LT1 F-Body comes stock with a 48mm TB.  The stock intake is ported from the factory to 52mm.  Installing a 58mm TB requires porting the intake to match in order to get the full benefits of the 58mm.  Installing the throttle body itself is a piece of cake.   Porting the intake to match up with a 58mm TB is a bit more difficult and is what takes the majority of time for this mod.  Because of the need to port the intake when going to a 58mm TB is one of the main reasons why, I believe, a lot of people go with the 52mm TB.  When people ask me about whether or not to go with a 52mm or 58mm TB, I'll always tell them to go with the 58 no matter what their level of mods is.  There have been a few dyno graphs that I have seen that show virtually no benefit of the 52mm over the stock 48mm TB.  However, most who install the 58mm TB do see anywhere from a 10 to 20 hp increase.  I have heard people talk over and over about how if your mods don't support it, the 58mm TB can actually hurt performance.  However, I have yet to see proof of this.  What I have seen proof of though is that it does NOT hurt performance and even helps.  I installed a 58mm TB on my 94Z prior to the supercharger and ran it for a short period of time.  I saw better throttle response and what felt to me like a SOTP difference and I only had a few simple bolt ons.  In fact, my serpentine belt never "squeaked" before during shifts until I installed the 58mm TB.  I believe this was due to the increased power and harder shifts I was seeing... definitely a good butt-o-meter feeling!  Also, there have been a few guys on the F-Body mailing list who have installed a 58mm TB on a mostly stock F-Body and have been very happy.  Bottom line, IMO, it ain't gonna hurt a thing to install a 58mm TB (even on a completely stock car) but it will prevent you from the need to upgrade to a 58mm TB during the later phases of your modding!  You may not get the full benefit of a 58mm TB but, again, it isn't going to HURT.  So, if you find a good deal on a 58mm TB, go ahead and get it even if you may not actually NEED it yet :)  All IMHO of course.  Not everyone shares this opinion with me which is good because I have a 52mm TPiS TB I'll be trying to sell now :-)

Now, before I get to the "good stuff" let me say up front that porting the intake on the car is a controversial subject.  Some say you shouldn't risk getting aluminum shavings in the engine and take it off the car to port it.  I believe, that with proper precautions, the intake can be safely ported on the car.  This is my second car in which I have ported the intake while on the car.  The first time, I didn't actually do the porting.  A mechanic friend of mine did and I was just there watching.  He didn't go to near the level of "precautions" that I did during the port job on this page and it showed.  He only stuffed in a couple rags and started grinding away.  When he was done, he removed the rags and I looked into the intake.  It was like my worst nightmare!  There were probably hundreds of aluminum flakes way back in the intake.   I panicked!  It appeared as though the rag we stuffed in there wasn't "sealed" very well up top and a lot of shavings went over the rag.  I was visibly upset and ready to pull the intake to clean it all out.  During this time, there was another guy in the shop who is very knowledgeable about engines (worked at an engine shop for years) and even has his own full fledge 9.x second drag racing only car.   Now, my mechanic buddy who was doing the porting used to work as an engine builder for about 10 years and did thousands of engines.  Anyway, when I started to show signs of panic about the aluminum shavings in the intake, they BOTH started to laugh at me!!!  I, being somewhat anal about things :) was not happy about this situation!   I ended up rigging up a small tube attached to a vacuum and was able to get most of the shavings out.  I know I didn't get all of them because there were some places way back in there that I just couldn't get at.  I was very upset but both of these very knowledgeable guys assured me that a few "straggler" aluminum shavings wouldn't hurt a thing and would "pass" right through.  Based solely on their experience and trusting my mechanic buddy, I reluctantly bolted up the new TB.  Well, it's been over two years since that "event" and I have ran my car HARD and with 7 psig of boost from a Vortech blower!  My car still runs like a champ and will still hold a piece of paper on the slanted oil filler tube... indicating that I don't have blowby and that I still have a slight vacuum.  So, I am relieved to say that even though I doubted them, they obviously were correct about the straggler aluminum shavings.  Now, I'm not saying that it's OK to get aluminum shavings in your intake, but the few that did get by on me didn't hurt my car :)

Now that my story is complete :)  I believe it can be done safely and since I don't want to mess around with the hassle of removing the intake and the possibility of developing an intake oil leak when it's reinstalled, I chose to port mine on the car.  I don't doubt that it is BETTER to port the intake off the car but if you're like me and want to do a 1/2 hour port job instead of an all day port job, then this page is for you! :)  Also, I'll throw in that if you already have the intake oil leak, then I recommend porting the intake to 58mm while you're getting the oil leak fixed and it's off the car if you even think you might someday want to install a 58mm TB.  If you don't want to fork out the $$$ for the TB at the same time as your intake oil leak repair, all you'll need is the $3 gasket from the company in which you plan on buying the TB from. 

Now that I've already almost written a book, I'll get on to the actual install!  If for nothing else, reading the long paragraphs above gave all the images on this page time to load! :-)

Here's what we have to start with.  You might notice that I don't have a stock throttle body to start with.  This is actually a TPiS 52mm TB and I'm upgrading to the Holley 58mm TB.

Notice I don't have the throttle cable cover installed.

1.  Disconnect one of the battery terminals.

2.  Remove the rubber intake elbow and MAF sensor.
3.  Stuff a rag in the rest of your intake!

4.  Remove the 4 bolts that hold the throttle body to the intake.
5.  Disconnect all electrical connections, throttle & cruise cables, and vacuum line.
6.  Remove your inlet and outlet coolant lines.  Be careful not to get coolant on your optispark!  You don't want to have to change that out too! :)  NOTE:  This is a perfect opportunity to do the throttle body bypass mod.  In fact, some TBs require this mod!  My AS&M 58mm TB didn't even have coolant line connections!  All you have to do is either place a shunt in between the two lines and hose clamp the coolant lines to the shunt.  Or, even easier, just connect the passenger side hose near the radiator in front of the car to the passenger side connection near the intake.

7.  Remove all stuck gasket material so you get a clean surface.

8.  Transfer the TPS (2 Torx) and the water crossover (7 Torx) to the new TB.
The water crossover may not be necessary depending on your brand of TB.  If it is though, be CAREFUL when you remove the water crossover from the stock TB!  Most kits don't come with an extra gasket so you'll need to re-use the old one or buy a new one.  This is a thick gasket and came off easily from my stock TB with a little help from a razor blade.

Now for the good stuff!
9.  Take your new gasket and ensure that it matches properly with your new TB.   The punch could have been off or something... you never know so it's best to verify it is "correct" because you'll be using this gasket as the template for your porting!
10.  Take your new TB gasket and install it as shown above, using your TB bolts.   If it isn't snug (the bolt holes are larger than the bolts) then it will be important  for you to center the gasket and line it up so the newly ported holes will be in proper alignment with the actual TB!
11.  Mark where you will port to with either a fine permanent marker or a sharp scribe.
Be sure to mark all the way to the gasket!  You don't want to get sloppy here!

It should look something like this when you are done with your marking.  It is important to note here that not all throttle bodies are created equal!  If you'll notice, the markings above are centered over the stock 52mm ports.  This is for the Holley.  My AS&M 58mm on my 94Z is not the same!  On the AS&M TB, I ended up taking a BUNCH off one side and only a little off the other.  The AS&M does NOT share the same centers as the stock or the Holley.  This is why it is very important to use the gasket made for the throttle body you plan on installing.  i.e.  don't try to get a jump on things and borrow your buddy's extraBBK gasket to port your intake for your Holley, AS&M, TPiS, etc. which will be arriving next week :-)

12.  OK, now it's time to start plugging up some of the small ports!  There are two small ports just inside the intake manifold at the bottom.  I used two foam type ear plugs (see above) per hole to plug these holes.  There is also a hole on the front of the manifold in the center lower section between the two intake ports.  I had some black sticky sheet stuff that I just rolled up into a ball and stuck it in the hole.  You can use whatever you want so long as the holes are plugged up and sealed tight!

13.  Now take some duct tape and tape some rags around as shown above.  This will just help to keep some of the stray aluminum shavings out of your engine compartment.

The above isn't anything you'll need.  I had an idea.  In addition to the rags you'll install (more on that later) I was going to try to rig up something so I could use a vacuum and suck from *behind* while I was porting.  I bought a funnel and some aluminum tubing.  I cut the funnel and used a flame to slightly melt the base so I could bend the spout part over at a right angle.  Well, I thought this would be a good idea but I couldn't get it to work very good and thought it interfered too much with my rags.  So, I ditched this idea :)  Just wanted to let you know about this in case you have a similar idea... don't waste your time :)

14.  Now it's time to stuff some rags in there!  the first rag I put in there was one of those white cotton rags like I taped around the throttle body.  I stuffed that one in then pushed it back a little.  The blue rag above is a medium sized rag.  With this rag, you want to saturate it with oil.  Regular motor oil will work.   This will allow the aluminum shavings to stick much better to the rag and will help "pull" the aluminum shavings out when you pull out this rag.  Now, you want to get the rag as close as possible to the edges, but you don't want to get it so close that you'll run the risk or hitting with your grinding tool!  It's an ugly site when a high speed Dremel gets wrapped up in a rag!  There is also a small "channel" in the upper right of the intake manifold.  If you can get your rag to cover this area, it will save you some time later in the cleanup process.

I don't have it pictured here, but I found later (after a second round of porting... DOH!) that if you take some pieces of duct tape and put them over the rag, sticky side out, that this works VERY good!  A lot of the aluminum shavings end up sticking to the tape plus you can get the tape closer to your porting work since the tape is much more forgiving if you happen to hit it with the Dremel :)  Wish I had some pics of this, but I think you get the idea.  So, with the duct tape, you have three lines of defense against the aluminum shavings... the duct tape, the oil soaked rag, and the cotton rag :)

UPDATE:  Here is something else you can do as a precautionary measure.  I think it's a pretty good idea!  My lawn guy (a buddy of mine) stopped by (a couple days after I did the porting and made this page) and saw my spare intake sitting on the table.  I was using this intake to come up with that yellow funnel contraption I have pictured above :)  He asked what I was doing.   I explained to him that I had just finished porting my intake and installing a new TB.  I briefly explained to him how I did it and showed him this web page.  He then gave me another suggestion about using heavy bearing grease along with everything else.  I think this is a great idea!  The idea is you smear/glob the thick grease with your finger just inside the area you will be porting.  Essentially, the grease would go from the back side of the front of the manifold to the duct tape/rags that I explained about above.  This would provide an EXCELLENT seal very close to the area in which you are porting.  You probably wouldn't have any straggler aluminum shavings to deal with if this were to be done.  If anybody tries this heavy grease idea, let me know how it works!

You're almost ready to start porting!  I have found the above works very well!  I used nothing more than a Dremel and a high speed metal cutting bit.  I don't have the part number, but you get the idea what it looks like in the picture above.

UPDATE:  Todd G. read this page and sent me the following email.  If you don't have a Dremel, this is another option for you!
I've done the same exact mod. on my 94 Corvette. The porting job I did was using a 1-1/2" barrel sander, with a corse grit. After I enlarged the holes to 58mm, I then used a real fine 1-1/2" barrel sander and polished each hole. I believe that using a larger size barrel in diameter makes the porting more smooth along the circumfrence of the hole. Using a fine grit after, was just like polishing the edge. The aluminum intake is very soft, so you don't have to use a metal grinder, you can use sandpaper. I went to a True Value and bought the barrel sander that mounts to any drill. The bit was a 1-1/2" diameter rubber barrel that came with a corse grit sand paper and one fine sandpaper. I think the job you've done came out great, but the only thing I would change is the porting device diameter.

15.  I recommend setting up a vacuum as shown above.  I had nobody around to give me a hand so I just placed it as shown.  If you have somebody to help you, you can have them hold the vacuum much closer to the actual porting.  The intent of the vacuum isn't to catch all the shavings, but it will get some of them.  I kept the vacuum running the entire time I was porting... it seemed to help a little.  Also, with all these aluminum shavings flying around, it's a good idea to wear some safety
glasses or goggles!

Now you are ready to start porting!  Now read this because you can learn from my mistake!!!  As you might have gathered from above, I did this port job thing twice.  I did it once, cleaned up everything, pulled all the rags off and found that I didn't get enough off the bottom.  DOH!  Man, I was upset but since I wanted it done right, I redid all the rags and taping and everything and did it again.  Wasn't that big of deal and probably only cost me about 15 minutes, but it was still aggravating! :)  Anyway, what I did was just barely took away my mark when I was porting.  I thought that would be enough... it wasn't.  Also, I didn't quite have the gasket lined up exactly perfect so what happened was I took off just a little extra off the top but not enough off the bottom.  So, I recommend you NOT do it twice like me and port a little beyond your line.  It isn't going to hurt a thing to be a smidgen big but it does hurt to be a smidgen too small! :)

First hole is done!  This is about what it should look like.  It doesn't have to be a perfectly round hole... this isn't rocket science we're dealing with :)  You'll notice how mine isn't perfectly round which is OK so long as the hole is the same size or bigger than the throttle body port.  Your hole will be "smoother" if you don't try to take too much at a time.  The more you try to take (or the more you rush!) the more "wavy" your hole will be.  Nice, light, smooth strokes work the best :)

There!  It's all done.  Looks a bit scary with all those shavings in there, huh? :) Don't worry, though.  It'll all come out!  Also, don't forgot that in the pics above I don't have the duct tape.  I tried this on the second go 'round and it worked very good!  At this point your tape should be covered in shavings and only a few shavings will make it past and stick to your oil soaked rag.

All done!

16.  Clean up time!  Pull out your duct tape, and oil soaked rag.  Before you pull out the three plugs you installed (two in the intake and one on the front) clean out the straggler aluminum shavings in the intake.  First off, use a vacuum and get what you can when the vacuum.  Next, and what I did that worked quite well, was take another rag and rip it into about 4 inch strips.  I then saturated these strips in oil and used them to wipe the aluminum shavings out of the intake and away from the ear plugs I had inserted.  Once again, the oil makes the shavings stick to the rag.  Look closely in the upper right of the manifold at that small channel I told you about earlier to make sure that you get everything out of there!  Also, don't forget the back side of the front of the intake manifold!  Some like to hang there.  Once you've gotten all that with your rag strips, pull out the three plugs.  Use your oiled rag strips again to get any remaining shavings... being careful not to push any into the ports you had previously plugged! :)  Once it looks like you got all the shavings out, you can remove the large rag that is still in the intake.  If you did your tape and oil soaked rag properly, you will have ZERO shavings on this rag in the back.

I'm happy to report that THIS TIME and with the precautions I took, I ended up with ZERO aluminum shavings after the cleanup was done.  No shavings even made it to the first air intake port.

17.  Now it's time to check your work!   Take your throttle body and gasket and a couple bolts and "test fit" it as shown above.  You don't have to tighten the bolts much, they're just holding the throttle body in place.  Now, manually move the throttle body blades with the actuator on the right and, using a flashlight, look inside there to see how good of job you did.  You can even stick your finger through there and feel around to see if you feel any edges/ridges.  If you're lucky (and took my advice earlier!) you'll be ready to bolt things up!  If you didn't take my advice and ended up like me still needing to take more (a little less than 1/16") off the bottom, you'll be taking everything off and starting the process over again!  Trust me, you don't want to do that!  If everything has gone well for you so far, you'll find that this hasn't taken long at all!

18.  Once you're happy with your port job, it's time to bolt up the throttle body.  Mine called for 18 ft. lbs. of torque.  Yours may be different.  Also, you'll need to connect your TPS connector, vacuum line, and the hose going to the valve cover.  If you didn't previously have the throttle body coolant bypass mod, you may need to refill and vent your coolant system!  You'll also need to connect the throttle cable and cruise cable.  My cruise cable gave me a bit of a problem.  See picture below...

The cruise control cable "stud" on the throttle body had a head that was slightly too "thick."  The plastic connector that snaps onto this stud is supposed to move freely and rotate around.  Mine didn't.  I fixed this by removing the stud and using my Dremel and a grinding/cutting wheel.  I pressed the top of the stud onto the cutting wheel.   This made the head a little thinner which allowed the plastic snap on piece to rotate freely like it did previously.  I'm not sure if my car came with a different black plastic snap piece or if this is going to be a problem with all the Holley TBs.  Not a big deal and it has an easy fix :)

Well guys, that's it!  Time to reconnect the intake elbow and forever hide those very pretty Holley TB blades :)  Also, don't forget to reconnect the optispark vent (if yours has this) and the MAF connector.  And, of course, the battery you disconnected in step 1.

Time for the test and to start her up!   Everything should work properly without adjustment.  AFAIK, all TBs come set from the factor for proper idle.  On both TBs I have installed, neither needed any adjustment.  You may need to adjust the idle screw but you shouldn't have to adjust the TPS sensor.  In fact, there really isn't much adjustment on these.  The LT1 computer "learns" what proper idle voltage is and adjusts accordingly.  It will adjust for proper idle so long as your are within a pretty big band.  There is no reason you should be outside of this band but if you do, for some reason, need to adjust the TPS, you'll need to make the TPS holes slightly oblong so you can get some movement out of the TPS.  I've seen acceptable idle voltages anywhere from .4 volts to .9 volts so the band is pretty large!  Take her out for a test drive and enjoy the new found horse power!

I know I made this page fairly detailed, but I wanted to make it so even the minimally mechanically inclined would know what was going on :)

If you found this page useful and informative, please let me know!  Also, if you have suggestions for improving it, let me know too!  You can send me email at

bfranker@tampabay.rr.com

Enjoy!