[J.T.]

I have a 67 GTO convertible and have lost my way on the components in my car. Over the years I have made changes that make it not enjoyable to drive now. I would like to try to keep the nice rumble at idle and roar in the exhaust under acceleration. The problem is it will chug at lower RPM cruising and cannot be taken out on the highway for any extensive period of time because of the gearing. I love how I am thrown back in the seat when I hammer through the gears or smoke the tires.
I think I would like to make more low-end torque to make this a fun car to whip around in but still be able to drive long distances. I know I am way over cammed and geared for what I want. What I have now is-
• ’72 400 block bored .030 over
• Stock crank
• Stock rods with ARP bolts
• Forged pistons
• 670 heads- 3 angle valve job, SS swirl polished valves, 7/16” studs
• Nunzi 2043N H/L cam- 308/320 deration, 500/500 lift w/1.5 rockers
• Torker II
• Holley 4150, 800cfm
• Hooker super comps into 2-1/4” exhaust
• 4:11 gears
• M20 4 speed
• 26” tall rear tire
I don’t want to just throw parts at it because that is how I got where I am. I also don’t need to reinvent the wheel. I have read so much on this here and elsewhere, my head is spinning at this point.
I have limited funds for this, but am prepared to replace the cam, gears and carb and intake if necessary.
As a starting point I am looking at
• Lunati 10510702 262/268 deration 468/489 lift
• Performer RPM intake
• 3.08 gear
What would be the winning combination?
Thanks in advance for any help.

[Navy Horn 16]

Start with the rear gear and go from there. I think your four speed will actually help you out in that you aren't working through a convertor.

3.08 is a good gear. You could even go 3.42 and step up to a bigger tire.

See how that works for you and then make a decision on cam. I doubt the carb and intake would impact the drivablity significantly, especially the direction you are trying to go.

[n2ogpsj462]

400s like gear. Might turn into a lopey choppy turd if you drop down the gear that far even with the 4 speed. That being said the voodoos are getting lots of love around here but id look at the 703 unless your truly trying to go to just cruising. The 702 and 308s might work together but with a 28" tire. Like navy said try a taller tire plus 26'' tires usually look lost on a bodies...

[pastry_chef]

Have you calculated your compression ratio?

[Sprocket]

I am no expert but I did sleep in a Holiday Inn last night.

Get this cam: Lunati 10510313, old part number 307A3LUN, it's a 280/288, 223/231, 110 LSA
Change your rear gear to 3.55
Switch to the Edelbrock RPM intake

Bam, enjoy the way!

[Formulas]

Might even use Rhoads lifters if you can stand the noise as you typically let the clutch out under 3000 rpms they will help build more torque when you need it,
Allow you to push the cam a notch or the rear gear.
My experience a 3.750 stroke wont like much cam with a 4-speed and 3.08 everything will be great except take off ... 3.55 - 3.31 area is about where I would go which is what GM did

Wish I could of put Rhoads in my 360 build but I used a low miles lunati 30706 cam mated up to a 3.73 gear

[J.T.]

Originally Posted by pastry_chef

Have you calculated your compression ratio?

I'm not sure how to do that.
I did cc the heads and they were 72cc's. I'm not sure what pistons are in it. When the motor was built we spoke about lowering the compression to run better on todays pump gas but that was some time ago and I don't recall what it was. In the paper work I have it says he used engine kit #R5-4811A311. I have not found anything about that.

I have done a compression test. All cylinders we within 5psi of 165psi, if that helps at all.

[J.T.]

Originally Posted by Formulas

Might even use Rhoads lifters if you can stand the noise

I have thought about Rhoads lifters and have not ruled them out.
I have also thought about advancing the cam timing. It was installed straight up by the timing marks and I do not recall the ICL. I have read that Jim Hand has had this cam at 104 ICL and Rocky Rotella has had it at 108 ICL.

[pastry_chef]

Originally Posted by J.T.

I have done a compression test. All cylinders we within 5psi of 165psi, if that helps at all.

Nunzi 2043
308 / 320
244 / 252
.500 / .500
110

From that pressure I estimate your static CR about 10:1
That is pushing it with the Voodoo 702 without zero deck and ideal tune etc.
I would consider the Voodoo 703, will be a BIG improvement low RPM response over the 2043
Do they make a 3.23 gear for your rear?
I'd try these with the Torker 2

[skullbucket]

3310 style Holley
RPM intake
ditch the cam to something under 230@50 and 110 to 112 lobe separation, ( im done with big lopey high rpm cams)!
308 to a 342 gear.
Tone down the exhaust and buy a fm radio and tune to the oldies on Sunday afternoon.

[PunchT37]

I,m with Pastry. 3.23 gear with a 703 cam is prolly all you need. Keep the rest unless you want it real quiet. Then work on exhaust.

[Squidward]

Originally Posted by PunchT37

I,m with Pastry. 3.23 gear with a 703 cam is prolly all you need. Keep the rest unless you want it real quiet. Then work on exhaust.

Another 703 supporter. The 702 isn't even all that lumpy in my 350. The 703 in my 400 has just enough attitude without getting rude and unmanageable.

I assume you have a BOP 10 bolt? That would mean a series 3 carrier for your current 4.11's, so 3.36 or 3.55 would be a better choice if you want to stick with the same posi carrier. To go smaller, you'd have to get a new posi carrier, and then your options become limited.

Change the cam, make sure your valve springs are matched and/or get new ones, and get into a 3.36 gear. 3.36 won't be an ideal highway gear, but it will be a considerable improvement.

The intake change to the RPM would be better suited to your new combo.

[Goatracer1]

The best change I made to get rid of similar problems was to go to an overdrive trans. My gas mileage went from 6 mpg on the highway to 15 mpg. Temp went down 20 degrees and rpm nose dived. Best yet never lost the power that I had. Now I can drive hundreds of highway miles with less noise and no problems.

[TCSGTO]

Try the Rhodes first. The only other parts you’ll have to buy are intake,valley,and valve cover gaskets. Put moly lube on the lobes and break it in as you would a new cam. It will make a new car out of it.

In another post on this forum a member has a good used 3.36 10 bolt gear. That’s as tall as you can run with your 3 series carrier. I’d keep the 26” rear tires with that tall of a gear and 4speed. Thats your low buck, one weekend of work solution.

I ran a 244 @ .050 110 LSA single pattern hft cam in a stock late 60’s 400 with Rhodes, a 2.52 low Muncie, and 3.23’s and it was ok. Came off the clutch from a dead stop good and didn’t chug too bad at at low speeds in parking lots. That motor was pretty worn out so if yours is fresher it should run smoother.

[steve25]

Increase the rear gear, drop down to a tad smaller Cam and since you have basically stock heads go back to a iron intake or a standard Performer.

Please note Edelbrocks stated power ranges for there Intakes on this chart.

[Half-Inch Stud]

TH400, tight 10" converter2800-3200

Q-JET, Factory Dual Plane

3.31:1 or 3.23:1 or 3.08:1

Keep the 4-speed stuff on a shelf.....

That would be a nice ride for awhile, then you can decide if ya want the 4- speed stuff back in.

[adynes]

Another thing to look at is the distributor advance curve. I did a lot of work on the HEI in my dad's camaro (383sbc, 230/236 110 cam, 4speed, 3.42's) and it completely changed the drivability of the car. It was almost undrivable at low rpms before.

I limited the mechanical to allow for more initial (14*). Bigger cams can handle more initial. I chose springs and set their preload so that the mechanical didn't start to come in till around 1100 rpm (it started coming in at a very low rpm before, making timing erratic). I moved the vacuum advance from the timed port to full manifold. The timed port would make the car lurch going on and off the throttle driving around town. And I limited the vac advance to 10*.

These changes completely changed the way the car drove. It idles better and more stable. It doesn't try to stall any more when talking off from a stop. And it drives smooth at lower rpms around town.

[J.T.]

Thank you so much for everyone’s help. I would still like peoples input. It will take some time to develop a plan to execute. This is what we have so far.
• I like the Idea of doing things a step at a time. Probably start with the gearing (step 1)
• I do have the original rear in the car so it looks like I will be looking at 3.36, unless I change the carrier. Car came with 3.55, that is long gone.
• Will consider the Voodoo 703 cam. Will still look at others. (step 2)
• Will consider duel plane intake, I have a ’72 #485912 in the garage and an adaptor for the Holley. No problem going back and forth from T2. (step3)
• Rear tires are 245/60/15 that are actuarially 26.6” (every little bit helps) I could look at taller tires after I smoke these. (step 4)
• The Rhodes lifters seem like they would help but not get me to where I want to be.
• I had the distributor worked on. I have 0*@800, 5*@1200, 10*@1600, 15*@2000, 20*@2600, 24*@ 3000, 8* vac, 12* initial = 44* all in.
• I can’t imagine changing to an automatic. I love the 4sp, maybe look at a 5sp someday.

[pastry_chef]

As your true static CR is unknown (ran another tool today it said you could be at 10.4)
You could inquire with Lunati about having the Voodoo 703 custom setup with 114 LSA.

[Lemans64]

Another thing to look at it changing the trans to a 6 spd, lower 1st gear to get away from slow speed driving, keep the same rear gear cuz the 6th would be overdrive. Keeps the standard trans as you mentioned you like. More gear selection to keep motor in happy range. Can also move to a 255/70 /15 it's a 29 inch tire. I run that tire only car with 3.9 and a 4spd. With lumpy cam. Just more fuel for thought.