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post #61 of 74 (permalink) Old Mar 14th, 19, 03:22 PM Thread Starter
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Re: Supercharged '68 updates, upgrades, and tweaks

Back in the states and ready to get back to it! Fixed my trunk lock and richen'd up the carb for the colder weather and freer flowing exhaust install which is happening tomorrow! Real excited to see the difference in feel, sound, and actual dyno power the new headers/exhaust and a good tune will make. It's already making more boost with the cooler air temps - I think I saw 7 psi on a WOT pull where in the middle of summer it was more like 5 psi.

It was Christmas in March when I got home!

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post #62 of 74 (permalink) Old Mar 16th, 19, 10:50 AM Thread Starter
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Re: Supercharged '68 updates, upgrades, and tweaks

And it's done! The ugly, old, small exhaust system is now replaced with the nice new Hooker 3 inch system.

It's amazing what you can fit inside a little Mitsubishi for a good reason...

Old exhaust was 2.5" with no crossover and some Dynomax Super Turbo mufflers (with burnt on gear oil residue from the diff that used to leak..)

Maybe not the best picture to show it but the difference between 2.5 and 3 inch is pretty apparent in person

New system bolted on pretty easily and tucked up about as well as you could hope or expect for 3 inch tubing

Nice and shiny new, no problems with placement or fitment of the new mufflers or X-pipe

And the headers! Guys, these headers. The old ones were little 1.5" midlength tubes and made it incredibly difficult to get to certain spark plugs, were dented to clear the power steering box, etc. These new 1.75" long tubes with their bigger primaries and thicker flange fit perfectly around everything. I can fit a whole finger between the tube and the steering box. I'm not gonna say all the plugs are easy to get to, but they are accessible. It is good that I had a mini starter, as they would not have fit around a full size, but that's about it. I'm super happy with the fitment. And they look sweet. These are the new style from Hooker specifically designed for clearance around common issues and I can certainly say they are as advertised in that respect.

It sounds good too. Idle with the new X-pipe is a bit smoother than before with no crossover and the mufflers are pretty mellow at low RPM/throttle settings. I was hoping the bigger pipes wasn't going to make it a whole lot louder inside the car all the time and they haven't. It's nice. But when I get on it, it's a good bit more aggressive than before. The Dynomax mufflers would get loud and mean sounding too, but they seemed more RPM dependent, whereas the Hookers (which are a fairly similar internal design) are more throttle position dependent. So give it more gas and they'll start making noise from a lower RPM, if that makes sense.

So yeah, pretty pleased with the whole setup. Gonna do a couple minor carb tweaks today after re-tightening header bolts then hopefully dyno next week!

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post #63 of 74 (permalink) Old Mar 17th, 19, 06:12 PM Thread Starter
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Re: Supercharged '68 updates, upgrades, and tweaks

Ran it a few times and tightened the header bolts a couple times. Needed surprisingly little carb adjustment so that was nice. I did up the power valve to a 2.5 so it's not opening at like 1/4 throttle when I'm slowly accelerating. The A/F gauge sure makes tuning a snap though.

Cruise is just right.

And I have it set for mid-high 12's at WOT.

Also got some of those little pills that plug into the MSD controller to give it an electronic redline. Works as advertised. Next will probably be an aluminum radiator and stickier rear tires.

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post #64 of 74 (permalink) Old Mar 17th, 19, 07:55 PM
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Headers and the rest of the exhaust look pretty nice.

1968 Butternut Coupe,
421" Dart SHP block
TKO 600 RR
Dutchman 9" w/3.70 US Gear Lightning r&p
Speedtech torque arm,Ridetech HQ coilovers
Global West arms
Budnik wheels

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post #65 of 74 (permalink) Old Mar 23rd, 19, 04:49 PM Thread Starter
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Re: Supercharged '68 updates, upgrades, and tweaks

After the exhaust install and tweaks to the tune, I hit the dyno. They were having some software issues and the tires spun a little so it wasn't exactly the best data, but ended up with 420hp / 455tq - a gain of about 20 from before. Not bad. Which is exactly 25% drivetrain/accessory loss from what it did on the engine dyno. Makes sense I guess.

Changed the oil since running so rich before had blackened it very quickly. Also swapped to a 160* thermostat to see what the cooling system was actually capable of holding. Looks like about 175 on the highway, 185 in town. I'm eyeing a new larger aluminum radiator for the summer months, but we'll see how it does for now. Mostly because I wanted new tires first. The car makes good power but the ol' classic BFG's just can't hold it at anything below highway speeds. I've been planning on new tires for a while, but going to a test and tune night at the local track motivated me to pull the trigger.

I wanted 275's, but the forum seems pretty split on whether they'll fit without rubbing - seems like it often comes down to the individual car. I know 295's rub, so thought I'd be safe with 275's, but then wheel size was an issue. I know people do it and it works, but a 275 on an 8" wide rim seems narrow. My current 245's are on an 8" rim and the sidewall bulges would be huge if the tire was over an inch wider. I thought about looking into having a custom 9" wide set made by Wheel Vintiques since the Nitto 555R's I was looking at don't come in anything narrower. But last night I saw that Mickey Thompsons were on sale so I ultimately decided to take the safer route and go with a pair of 255/60 ET Street S/S drag radials for the rears on a matching set of 15x8 Rally wheels. Super excited to see what kind of traction I can get with these!

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post #66 of 74 (permalink) Old Mar 27th, 19, 10:44 AM
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Originally Posted by SOAR B-1 View Post
It should, shouldn't it? With the 3.42's and the TH400, I got 7-8 mpg. With the 3.55's and 700R4, I got about 10 mpg on my way to Dallas - all highway miles trying to be conservative to make it to the next place that sold 93 octane. And now with the new heads and properly fitting gaskets, it wasn't any better. Still 7-8 mpg. That's with some good on ramp pulls as well as just highway cruising. Right around 100 miles per tank. Lots of smiles too, but not many miles. So that was the first of 2 remaining problems after the head swap.

But then came the second issue. As I was pulling into my driveway after a test drive, I heard a strange noise coming from the engine bay so I popped the hood and watched as my A/C belt fell off. WTF? I had personally tightened the belts during the motor reinstall. Pulled it out and saw this:

The teeth were delaminating from the rest of the belt. How weird. The belts were reused and I didn't actually know how old they were. So I chalked that one up to an old belt, replaced it, and considered how lucky I was that it happened in my driveway instead of while driving where it'd undoubtedly knock off all the other belts.

Next time out, almost the exact same story. As I was turning the corner into my neighborhood, I noticed my voltmeter drop down to 12V and heard a similar sound as the previous day. The alternator belt had liberated itself from the car. Went back and found it laying broken in the road:

So... that one was probably just old too, right? Replaced it, went on with my life.

Next couple drives were ok. I was about to return focus to the rich running carb when it happened again - this time in the way I had feared. On the highway, just after doing a nice pull on the on ramp. Belt flies off, knocks all the rest of them off. In an instant I'm down to 12V, with no power steering, no water pump, temps climbing rapidly, the whole 9 yards. What. In. The. World?

Replaced all the belts. Got them all nice and tight. Nothing appears out of alignment. I'm not super impressed with the quality of the belts I'm getting from O'Reilly, but my pulley grooves are pretty darn skinny and these are the narrowest belts I can find in the size I need. I think I've narrowed it down to happening only at high RPM. I can cruise around mildly all day with no issues. I'd go for drives and keep it below 4,500 RPM. Then 5,000. Then 5,500. All fine. It's only if I get in the 6,000 RPM range that the belts will fall off. It's consistent at this point and I become an expert at changing belts. The confidence I was supposed to have in this motor after all the upgrades is shattered.

I switch to made in the USA Napa belts. They look and feel much higher quality. Maybe it was just an issue with the lesser belts. May have helped a little, but it still happens. Other than that first time, it seems it's always the alternator belt that fails first. Wish I had a way to see what was happening in the engine bay under load at high RPM and figure out exactly what was going on. The only thing I could tell from looking at it is that the belts sit kinda high in the alternator pulley. Like I said the groove was pretty narrow so the top of the belt would stick out above the top of the pulley groove by a few mm. So I removed that and turned down the grooves on a lathe to fit the belt better.

Happy to say that after 20+ full throttle, high RPM pulls later, I have not had any further belt issues. Whew. Confidence returning..

So back to the first issue. Took the car to a chassis dyno because I wanted to see what my drivetrain losses were now that I knew exactly what the motor did on the engine dyno.

I don't remember the exact numbers but it was lower that I was expecting - down about 25% from engine dyno number vs the 18% or so I was hoping for. Guy running the dyno also mentioned how rich it was. I knew it was rich from the smell, the black soot in the exhaust, the narrowband O2 sensor reading, and the aforementioned terrible gas mileage. This was the final straw that got me motivated enough to learn enough about carburetors to fix it. Of note, the dyno headers were also bigger than the ones in the car, plus it has a full 2.5" exhaust, air cleaner, water pump, power steering pump, fan, alternator, and A/C compressor to spin. I'm guessing all that is why the mixture changed as much as it did from engine dyno to in car.

Anyway, got home, pulled a plug, and this is what it looked like:

I'm no expert at reading plugs, but I'm pretty sure they're not supposed to look like that!

So after researching tuning carbs, all the reading plug colors, evaluating sounds, smells, vacuum, etc. seemed too imprecise to me. So first up I ordered a wideband O2 gauge/sensor to replace the narrowband rich/stoich/lean gauge that I had. (And because nothing is ever easy, the bung in my exhaust had some material leftover from the weld that prevented the new wider sensor from screwing in at first until I drilled it out..) Also added a fuel pressure gauge and regulator right before the carb that you can kinda see in the engine pics in my previous post.

Installed in the pillar pod:

If you have a carbureted engine and take nothing else away from this build log, take this: GET ONE OF THESE! Seriously. Having real-time air/fuel data there right in front of you as you're driving at all throttle settings/load conditions is invaluable for tuning the carb. This made it SO much easier.

Setting the idle mixture was a snap. It needed less than the standard 1.5 turns of the idle mixture screws. With the high line pressure of the transmission, the converter is tighter than its rating suggests and I found that the motor likes it a bit rich and a little faster at idle so as to not approach stall when in gear with the a/c running, lights on, etc. So it's set in the high 12's A/F ratio-wise.

Next it was time for a drive to see what it looked like under cruise, part throttle, and full throttle acceleration. Cruise wasn't too bad, in the low 13's. Part throttle acceleration was the worst - 10.0 was as low as the gauge goes and it would hit that often. At full throttle it'd lean out a little to mid 11's. Pig rich, all around.

My plan was to adjust full throttle to within the realm that I wanted first by changing secondary jets, then fine tune that along with part throttle by adjusting primaries, and then see what that did to the cruise A/F ratio. Called Holley to see if they had any starting recommendations, and they said to change the power valve. After looking that up, I realized why. This carb came with a 10.5 power valve. The motor only pulls 7-9" of vacuum at idle depending on load. So basically the power valve was open almost all the time except very light throttle cruise or coasting. Things are starting to make sense...

Put in a 4.5 PV and started swapping jet sizes (after readjusting the idle circuit). Eventually settled on 66 primaries and 75 secondaries if memory serves. Down 8-9 sizes from out of the box (74/84). This gave me high 14's at cruise and a solid 12.5 at WOT. Part throttle mixture still gets rich (down to high 10's / low 11's) when the PV opens, so when I get home I'm going to swap the 4.5 for a 2.5. It'll be cooler so I might jet up a size or two as well. I'll make that decision based on the lovely real time data from the wideband.

- This carb was real rich out of the box. Obviously. It's made for boost and richer is safer for boost so I get it, but I do question the use of a 10.5 PV.
- I can see via the readout the moment the PV opens. A/F ratio drops about a full point. The vacuum rating of the PV is accurate.
- The car sounds and feels much happier and healthier. More eager to rev more quickly, no bogging. (Before this, I wouldn't have described anything the engine did as bogging, but in comparison, with the corrected mixture it just seems so much peppier)
- Gas mileage is DRASTICALLY improved. Instantly doubled - on the highway I now get almost 200 miles per tank (almost 15 mpg vs 7-8 mpg before the tune)
- The engine runs hotter. It was using so much gas before that the fuel was contributing noticeably to cooling. Coolant temperature is probably an average of 9-10 degrees hotter now. This is the one thing I'm not as excited about. Idling in traffic in the hot Texas sun with the A/C on, it will climb over 210 degrees and that makes me nervous.

Regarding the last point, I'm interested in what you guys would do to address it. I've started using a higher ratio of pure water in the coolant. Helped a little. Have a 180 or 185 degree thermostat from Napa that's supposed to be their performance line. New aluminum radiator? Expensive electric fans? Other options? Richen it back up some?

BTW, here's what the plugs look like now:

Can't wait to get home, get the new PV in, make any other minor mixture tweaks that may or may not be necessary, and give it another go on the chassis dyno. Overall it's running so much better!
I kept throwing belts with my 454. I tossed all the standard pulleys for deep groove and never had an issue since. I have a 500 hp 383 stroker with 6 speed tremec and 3.73:1 gears. Your build is making me consider a turbo or supercharger.
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post #67 of 74 (permalink) Old Mar 28th, 19, 06:21 PM Thread Starter
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Re: Supercharged '68 updates, upgrades, and tweaks

Many, many full throttle pulls later and no further belt issues - machining the alternator pulley down to a deep groove seems to have completely cured it.

One of these smaller blowers is fairly simple bolt on horsepower, in comparison to other methods of boost. Just watch the compression ratio. Some people recommend crazy low, like in the mid 7's - 8's. Assuming you aren't trying to run a crazy amount of boost, higher is fine. Mine is 9:1 with the AFR aluminum heads. Yours sounds pretty healthy N/A so I'm guessing you already have good heads on it.

The 142/144 size blowers are about maxed out making 6-7psi on a 383. If you can fit the 174/177 size it could do more.

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post #68 of 74 (permalink) Old May 4th, 19, 03:44 PM Thread Starter
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Re: Supercharged '68 updates, upgrades, and tweaks

Got the Mickey's mounted on the new wheels and bolted on the car. They're about an inch taller than the BFG's. I like the look - a little more aggressive but not ridiculous. And they make a whole lot of difference. Tail doesn't kick out going around a turn during a 1-2 shift. First gear is usable. I can still spin them a bit, but way less than before. They hook way better than the Radial T/As. I'm happy.

Trying to decide if I should go to the trouble to get the fronts remounted with the white lettering facing in so they match the rears. Meh. Higher priority is tweaking the governor springs/weights to get the WOT shift point right where I want it. Right now it shifts at like 6400 RPM. I want it at 6000 or just before. Just up on jack stands in my shop, I can't the the cover for the governor off. Seems like you really gotta get it on a lift and move the crossmember to get at it. So much for an afternoon project...

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post #69 of 74 (permalink) Old May 6th, 19, 03:54 AM
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Re: Supercharged '68 updates, upgrades, and tweaks

I think you just talked me into getting an air/fuel gauge!
On a different note, I know it has been discussed to great length already, but the air cleaner is a huge issue - especially while tuning the carb as you are. Been through this with my build and talked extensively with Sceptre and Edelbrock on the matter. I have a 572 so I need a touch more air than you, but minimum recommendation for me was a 5" filter WITHOUT a drop base. For you I would see a 4" without a drop base. When I inquired about the drop base because of my height issue, the consensus from both companies is that they take away airflow so a 5" filter with a 1" drop base is typically a 4" filter defeating the purpose. Short of cutting a hole in my hood, I went with a drag racing screen to see if I could get by. It originally had a outerwear pre-filter on it. That was a joke - car ran good upto 3000 rpm and felt like it had a rev limiter. Took it off and made a world of difference. My point is, get your air cleaner figured out first for max airflow or you will be tuning just to tune again.

'68 Camaro with RS conversion
Moser 9" with 4:11
Martz Chassis 4-link and Front Sub-frame
Tremec T-56 Magnum 6 speed
572 BB - CM Engines
Wilwood 6 piston front and 4 piston rear disc
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post #70 of 74 (permalink) Old May 6th, 19, 05:57 AM
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Re: Supercharged '68 updates, upgrades, and tweaks

Here's a good air cleaner to try ; a 1-1/4" drop base and use a 4" filter with it since you have the cowl hood :

And if you can fit a 5" tall filter, I'd like to know - I have a cowl hood too

68 Camaro convertible, 6.0 LQ4 with LS3 heads, Vintage Air, 750 street demon carb, eddy perf rpm, GM hot cam, Hooker headers, 4L80e, 12 bolt, 3.55 gears
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post #71 of 74 (permalink) Old May 6th, 19, 03:31 PM Thread Starter
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Re: Supercharged '68 updates, upgrades, and tweaks

Right now with the 3" filter on the dropped base, the lid is already basically touching the hood brace. If I cut that out, I could go taller, but not sure how much. I didn't try with and without the filter on the dyno last time due to the issues they were having, but they said they don't usually see much difference. I would like a taller filter setup but not sure if it's worth cutting metal on the hood. At that point I'd be tempted to get a new, non-cowl hood and cut a hole in that for an Enderle style air scoop.

Other than that, the new tires are working great. Darn near dead hook on concrete, and a bit of slip on asphalt. I'm also going to be getting some parts to fix the parking brake, interior dome light, and the trunk weatherstripping that someone pointed out was on upside down when my ROTM prize shows up. Once I get the governor tweaked to lower my shift RPMs a bit, it'll be done until I decide what to do as far as suspension upgrades.
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post #72 of 74 (permalink) Old Jun 16th, 19, 09:27 AM Thread Starter
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Re: Supercharged '68 updates, upgrades, and tweaks

Well I had hoped this was going to be a positive update after fixing a few minor things, but for the most part, it isn't. I got the parts to replace the trunk weatherstrip, interior dome light, and parking brake, all of which should have been pretty easy.

- Trunk weatherstrip - this is the only one that was successful. It seals well.
- Dome light - replaced the housing that had melted at some point, got a new LED bulb that won't be as hot, and... it stays on all the time. Is there anything else other than the 2 little plunger switches at the front of the door jambs that trigger the dome light to turn on and off? I figured that was it..
- Parking brake - got all the linkage to connect the existing cables coming off the pedal and 2 drums. After connecting and tightening, no braking action. Take the rear drums off, and the parking brake cables aren't connected to anything. The lever is missing. Tried to get a pair from a local store but ended up being the wrong part, so off to the internet.

And finally, at some point during my weekend cruise yesterday, my trunk lock liberated itself from the car. So that's great. Just to confirm, when I get a new one, the pins can be adjusted to match the key I have for my door locks, right? And which style retainer is right/better?


Or this?

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post #73 of 74 (permalink) Old Jul 10th, 19, 12:34 PM
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Re: Supercharged '68 updates, upgrades, and tweaks

Great build man, looks like you really woke up the car with all of your tuning revisions.

And for the trunk lock, I used the second part you have pictured.

Project: 1968 Camaro 5.3, T56, Z51 brakes, 12 bolt, etc.

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post #74 of 74 (permalink) Old Jul 10th, 19, 07:41 PM
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Re: Supercharged '68 updates, upgrades, and tweaks

Technically you should use the first one as it has a screw point to anchor it to the internal upright inside the trunk. I'm not sure why the trunk is different from the doors but that's how the factory did it - must be a reason.

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