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Old 08-20-2019, 01:30 PM
Murf Murf is offline
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Default Driveablty question

Hi guys! Finally getting the wife’s 65 Lemans on the road. Drives & runs good. I tried to make it a nice highway car but used mostly what I had or could get cheaply.

The details
Approx 27 inch tall tires
3:08 rear
Super T10 with 2.64 low gear

462 @ 9.0 to 1, Performer RPM with a Thermo Quad
Cam is HR 230 int 236 exh 110 LSA installed at 107 ICL if I remember correctly. Exhaust is oversized Ram Air with 2.5 inch X pipe system.

That’s all the info, here is my question.

What is a reasonable RPM for this combo to pull down to without lugging? My second & third gear spacing isn’t great for around town.
I think I need to just keep it in the lower gear a little longer.
It sounds like it’s reving more than needed but I think it might be my new hearing aids throwing me off.

Any thoughts on this would be appreciated!

Murf


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Old 08-20-2019, 01:50 PM
tom s tom s is offline
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Just drive it and see how it acts at 1500 in 4th gear.Big engine should be good.My 455 with about the same cam except on a 112 will pull from 1500 with a 3.31 and a .66 OD.Tom

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Old 08-20-2019, 02:13 PM
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Need more info, what heads are on the motor?

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Old 08-20-2019, 02:39 PM
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Quote:
Originally Posted by tom s View Post
Just drive it and see how it acts at 1500 in 4th gear.Big engine should be good.My 455 with about the same cam except on a 112 will pull from 1500 with a 3.31 and a .66 OD.Tom


Thanks Tom, I was hopping you’d reply. High gear isn’t an issue but it’s the same deal.The engine will pull down to about that. 30 mph in 3rd seems to be about 1400 rpm or so. It kinda tugs at that rpm. I just need to keep it in 2nd gear. It just sounds loud to me. It’s only about 2k rpm I think.
I was kinda curious as to lowest rpm it should cleanly pull from. I think I may have a small carb issue also.

steve25, Heads are 6X-8 milled to about 96cc’s if I remember correctly. They were ported to approx 230 int don’t remember what the exhaust flowed. New SS valves & springs for HR. Thanks for the interest, both you guys!

Murf


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Old 08-20-2019, 05:36 PM
tom s tom s is offline
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I have run street cams from 108-110-112 and 113.The 428 I have going together now is a 113.The 112-113 have always felt better to me in a stick shift car.Seem to chug less.Tom

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Old 08-20-2019, 05:54 PM
Chief of the 60's Chief of the 60's is offline
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Quote:
Originally Posted by steve25 View Post
Need more info, what heads are on the motor?
Why? What do heads have to do with what the OP wants to know.

First off, the engine is too much for it to act like a "normal" car. You build a big engine, you deal with its attitude. If I am understanding this correctly, you want to know what is a good cruising RPM. Well that depends on what your cruising speed is. Around town (30-40 mph) 2100-2200 rpm. Highway speed (60 mph) 2600-2800 rpm. Any less and you are laboring the engine. With an O.D. transmission you can easilly run a 4.30 gear. 3.08's are not a good gear with an O.D.


Last edited by Chief of the 60's; 08-20-2019 at 06:05 PM.
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Old 08-20-2019, 06:12 PM
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He said he has a ST-10 no over drive.The cam he has and the CI he has should be no issue.Just maybe needs a little more tuning to get it where it wont chug at low RPMs.As said my 455 can lug at 1500 in high gear with no issue.Im running a 3310 Holley on a Performer with 12 initial and 38 total all in by 2500. Tom

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Old 08-20-2019, 06:42 PM
Chief of the 60's Chief of the 60's is offline
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Quote:
Originally Posted by tom s View Post
He said he has a ST-10 no over drive.The cam he has and the CI he has should be no issue.Just maybe needs a little more tuning to get it where it wont chug at low RPMs.As said my 455 can lug at 1500 in high gear with no issue.Im running a 3310 Holley on a Performer with 12 initial and 38 total all in by 2500. Tom
I know that, I was giving RPM ranges at speeds. I was also pointing out rear gear scenario with an O.D. 1500 is too low unless you are doing 25mph. Big inch performance engines need either RPM's or a constant supply of spark plugs. I will never understand why people want these engines only to go 30 mph, 5 miles up the road to a cruise night.

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Old 08-20-2019, 06:51 PM
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I drive mine from off idle to about 2200 and shift,im on the highway at about 2000-2100 in 5th gear.3.31s and .66 OD.No issue at all and the same set of plugs has been in the car for at least 3 years and right at 13-1 on the EGTs at 2000.FWIW,Tom

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Old 08-20-2019, 06:55 PM
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2200 - 1500 = 700

Big difference.

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Old 08-20-2019, 06:56 PM
Murf Murf is offline
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Quote:
Originally Posted by tom s View Post
He said he has a ST-10 no over drive.The cam he has and the CI he has should be no issue.Just maybe needs a little more tuning to get it where it wont chug at low RPMs.As said my 455 can lug at 1500 in high gear with no issue.Im running a 3310 Holley on a Performer with 12 initial and 38 total all in by 2500. Tom


Thanks Tom, it’s actually acting better than I had feared. I’m sure it would be better with a wider LSA but for now she’ll just have to live with it.


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Old 08-20-2019, 07:05 PM
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Quote:
Originally Posted by Chief of the 60's View Post
I know that, I was giving RPM ranges at speeds. I was also pointing out rear gear scenario with an O.D. 1500 is too low unless you are doing 25mph. Big inch performance engines need either RPM's or a constant supply of spark plugs. I will never understand why people want these engines only to go 30 mph, 5 miles up the road to a cruise night.


The road to the car show has a 30 mph sped limit?

Chief, thanks for your input too.
I’m not sure if all of it applies to me but I appreciate it.
I think around town it will just meet staying in second longer.
With the tall tires & 3:08 gears it’s pretty nice @ 70mph.

Murf




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Old 08-20-2019, 07:09 PM
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Sounds like just a little more tuning will get you there Murf if you have the time and patience. Shouldn't be much to it with the combo you have. I would suspect the thermo quad might need attention in the transition area from idle to the main circuit. That's where most carbs need attention to address issues like this.

For example, our little 302 with a 254 @ .050 on a 112 lsa will lug down to 1000 rpm in 5th gear, and it pulls out fine without complaint. That's with a .64 overdrive and 3.55's out back. I spent a bunch of time on the 780 holley idle and transition circuits to get that area perfect so it would putt around town with minimal shifting necessary.

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Old 08-20-2019, 07:58 PM
mgarblik mgarblik is offline
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Quote:
Originally Posted by Formulajones View Post
Sounds like just a little more tuning will get you there Murf if you have the time and patience. Shouldn't be much to it with the combo you have. I would suspect the thermo quad might need attention in the transition area from idle to the main circuit. That's where most carbs need attention to address issues like this.

For example, our little 302 with a 254 @ .050 on a 112 lsa will lug down to 1000 rpm in 5th gear, and it pulls out fine without complaint. That's with a .64 overdrive and 3.55's out back. I spent a bunch of time on the 780 holley idle and transition circuits to get that area perfect so it would putt around town with minimal shifting necessary.
I am thinking the same thing about the Thermoquad. That's a carburetor I haven't worked with much other than straight clean-up's and rebuilds. If you want to science this out a little further, I would drive it around some with a vacuum gauge attached to manifold vacuum. See what the vacuum is at the speeds where the engine seems to lug or buck. Then you need to figure out what a Thermoquad does to richen the main metering circuit for this situation. Possibly a small main jet change or cutting a coil off a power piston spring will give it a little more fuel to run better in this loaded condition. Possibly someone who is more familiar with Thermoquads can chime in as how to make the power circuit a little richer.

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Old 08-20-2019, 08:01 PM
Chief of the 60's Chief of the 60's is offline
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Quote:
Originally Posted by Murf View Post
The road to the car show has a 30 mph sped limit?

Chief, thanks for your input too.
I’m not sure if all of it applies to me but I appreciate it.
I think around town it will just meet staying in second longer.
With the tall tires & 3:08 gears it’s pretty nice @ 70mph.

Murf
What are you turning at 70?

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Old 08-20-2019, 08:21 PM
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What are you turning at 70?


Chief, I ‘m unsure. I’m using a portable tune up tach right now. It only reads to 2500 and it’s slightly past that. If I had to guess, I’d say 2600-2700. It seems to be right in it’s sweet spot about there.

Thanks
Murf


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Old 08-20-2019, 08:33 PM
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Originally Posted by mgarblik View Post
I am thinking the same thing about the Thermoquad. That's a carburetor I haven't worked with much other than straight clean-up's and rebuilds. If you want to science this out a little further, I would drive it around some with a vacuum gauge attached to manifold vacuum. See what the vacuum is at the speeds where the engine seems to lug or buck. Then you need to figure out what a Thermoquad does to richen the main metering circuit for this situation. Possibly a small main jet change or cutting a coil off a power piston spring will give it a little more fuel to run better in this loaded condition. Possibly someone who is more familiar with Thermoquads can chime in as how to make the power circuit a little richer.


Thanks, I’ll try checking the vacuum out. I’d love for someone with experience with it to chime in.
I have a book on Carter carbs but it’s pretty lacking.

Formula, thanks to you also!

Murf


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Old 08-20-2019, 08:45 PM
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Quote:
Originally Posted by Murf View Post
Chief, I ‘m unsure. I’m using a portable tune up tach right now. It only reads to 2500 and it’s slightly past that. If I had to guess, I’d say 2600-2700. It seems to be right in it’s sweet spot about there.
Murf

You gave us all the info to calculate your RPM's at 70.

3.08 gears, 27" tall tires, no OD @ 70 MPH = 2683

Your guesstimate was pretty close.

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Old 08-20-2019, 09:17 PM
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My 455 carries milled, lightly ported 6x8’s with a 230/236 on a 110 HR cam. My trans is a TKO and the rear is a 3.73. The carb is a Qjet I built. With the OD I can find the engine turning lower rpms fairly regularly on the country two lanes around here. 1300/1500 depending on the situation. Pulls a lot like a big inch v8. No issues. No complaints from the plugs.

I have a couple of 9800 Thermoquads though it’s been 6-8 years since I ran one. I found them to be good carbs. Easy to work on. BIG.


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Last edited by David Jones; 08-20-2019 at 09:33 PM.
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Old 08-21-2019, 12:15 AM
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Cool, a 9800. Haven’t seen one of those for a while. They are big, shave the choke housing off and they are up around 1200 cfm.

The Thermo-Quad used metering rods on the primary and secondary circuits. It also has 2 floats. Plus it IRC, air bleeds that can effect the mixture. I might be a little rusty, haven’t had to mess with one for a while. I have 4 cars still running them though, lost count of how many I have ran in the past. We have a lot of parts if you can’t find something.

It sounds like it is running a little lean on the primaries? Making it surge and not carry the load? The thinner rods progressively make it richer. It would be up in the partial throttle section of the metering rods. I don’t know which model carb you have, some of the emission carbs had vacuum ports that changed the mixture. The float level setting also has a small range that effects the afr. It is a very tunable carb, but some folks tune themselves into a corner and the setting are hard to get back to square one.

Here is a link to some info on them. Metering rods are pretty easy to play with, you can scroll down and see the steps in rods size they used to meter the fuel for different throttle positions.

https://www.carbkitsource.com/tech/C...de-Vaanth.html


Last edited by Jay S; 08-21-2019 at 12:17 AM. Reason: Edit
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