I have a restored 1960 Plymouth Belvedere with the original slant 6 and push button automatic. I want to add a little performance while keeping the engine looking completely stock. I'm having no help in my friend circles or on other forums, they all say "drop a V8 in it". I don't want that. I'm big on originality. I enjoy driving the car as is but I live in the city trying to merge onto traffic is going to wind up costing me a quarter panel since I can't get out of my own way and other drivers are complete "a" holes in Atlanta. The engine has been rebuilt and is it very good ruining order just trying to move a lot of car. I have to do something or park her. It's just not worth getting hit and possibly hurt. People won't let you over and she does not have the balls to over take a school bus. I was run of in the median the other day and that was not the first time. Notice my damaged valence panel.

A few extra ponies would be great. Is this even possible with the 2bbl and full single exhaust As they will restrict what it can do greatly and I'm trying to do this with only engine internals no nitrous. Not an easy thing to do.
I'm thinking cam, port head, port intake and exhaust manifold and maybe shave head to bump compression. Im not opposed to going roller with it if they even make the stuff for the 6.

Any help is greatly appreciated since you guys know these little engines and what they can and can't do.

I wish I had a better picture of the engine on my phone but I do not.


This is here right now out in the parking lot. I get to look at her while I eat.

Beautiful car! I love the 1960 Plymouths.

Performance upgrades while keeping a stock looking motor are certainly possible. You have already identified the main areas-

(1) improve flow of the head (bigger valves and porting),
(2) improve compression (shoot for 8:1 dynamic compression ratio) (head work alone is one of the best and most cost-efective ways to improve performance),
(3) change the cam (do a search on this website for RV-10 and RV-15 to get some custom cam profiles that you can have reground on a stock cam);. Oregon Cams in Oregon is far from you but has been very good about working with slant six owners and providing good results. You may have a camshaft machine shop closer to you that you can work with.

Porting the exhaust manifold won't really benefit you. There are no off-the-shelf and readily affordable roller valvetrain components for the slant. You absolutely will see gains by switching to a two barrel carb (but you may not be able to use your original air cleaner) and upgrading your exhaust size.

Here is my list of recommended upgrades to do in addition to those listed above:

(4) upgrade the brakes. All go and no woah is dangerous. At the very least upgrade your master cylinder to a dual chamber design that was available on later molars.

(5) upgrade the exhaust. Install a Dutra dual exhaust manifold (search this website for Dutra duals) and modify a stock rear manifold to be the rear manifold. Run dual 2 inch pipes or a single 2 1/4 to 2 1/2 inch pipe.

(6) install a "Super Six" two barrel carb and intake, or modify you original one barrel intake to accept a two barrel carb.

(7) upgrade your ignition. Install an HEI ignition system with an E-core coil (go to the electrical forum on this website, click on the F.A.Q. sticky, and read the HEI upgrade article there). Fine tune the mechanical and vacuum timing advance curve in the distributor for maximum power and efficiency.

THats it. Just remember to plan out the engine as a package and to build it more for low-RPM torque than for high RPM horsepower. You are trying to get a big car moving, so top end HP isn't your goal.

Good luck, and post more pictures!

One can make a slant six perform, just takes some dough, and planning.

This is one way to beef up a stock slant six in a big car not unlike yours. I know you want that stock looking engine compartment, but to get that old girl up and performing a few new doodads festoon to your first year slant as this fellow has done will wake her up. Look here.

Read gives good advice on how to perk up your Plymouth, and get it to stop; I would advise one more step, installing front disk brakes. Check out Aggressive Ted's engine build, he commutes 100 plus miles a day up near Seattle in a slant six Dart, and has no problem getting up to speed with his torque & millage build.

Another aspect to getting going off the line faster is a lower geared rear end. I don't know what ratio you currently have, or if a gear change is easily accomplished with the axle you have due to availability of parts.

When making changes to engine dynamics, one has to look at the whole drivetrain being mindful that one change will make a huge difference in outcome if rear gear, torque converter, and other details aren't all taken into account. I guess what I'm saying is work out all changes on paper first and be prepared to commit to making all changes necessary to reach your goal including some suspension & brake up grades.

Once you have made all necessary updates that car will be a pleasure to drive safely on any road.

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67' Dart GT Convertible; the old Chrysler Corp.
82' LeBaron Convertible; the new Chrysler Corp
07' 300 C AWD; Now by Fiat, the old new Chrysler LLC

It might be plain worn out. The first car that I drove was a '65 Fury I (Savoy) C body with a slant six. Respecting its limits it did okay, could hit 95 MPH. You might want to do a compression check to determine how worn it is . I don't know what your expectations are but I would just do a basic rebuild with increased compression and maybe a two barrel.

Lots of good advice guys, I appreciate it. Let me give a little more info on the car.

I don't know how "worn out" the engine is. The car only has 88,000 miles on it and the last owner says he had it rebuild at some point. She doesn't smoke at all and fires right up. The carb was rebuilt, valves are adjusted correctly, new points, condenser, plugs, wires, rotor and cap.

The brakes are all original. While not great they will lock the front wheels up in a panic stop. I have considered swapping the master cylinder to a duel chamber for safety but right now I keep on top of the maintenance and make sure the "e" brake is working 100%.

As for rear end gearing it is stock with a 3.31 ratio. I don't know if going to a different ratio would be to much for highway operation, giving her all she has the shift points are 25mph, 45mph and top speed of about 90 (shifting manually). Letting her shift herself puts her in third at 25mph. She is pretty happy around 55 but it makes long drives loooooooong drives.

I read you can shave the bottom of the head .090 to bump the compression ratio from 8:1 to 9.5:1. Mine has 8.5:1 from the factory. The dynamic compression stock is only 7.5:1. Maybe .030 or .060?

I can port the heads myself. If I go with larger valves what would you recommend.

I would like to keep the exhaust stock, I know that chokes it down a lot with only 1 pipe. But I enter this car in a lot of shows as original unmodified. The exhaust system is also new and in great condition.

As for a carb she does have the bigger of the available 1bbl's, can it be opened up any to allow a liitle more in? As for a 2bbl I have one from a 77 vintage 360. It may be to much but I was hoping to find another original air breather and intake to modify to fit it. And maybe no one will notice.

As for cam I found on this site a few people have used a cam from comp cams that is .440 lift .260* duration with a 110* lobe seperation. 1200-5000 rpm. It just seems easier than sending the stock one off to be reground, what do you guys think? To much? Will it work with the stock stall? Kill drivability?

Can you repost the link to aggresive teds engine build, it just pulls up a search page for me.

Thank you again guys?

Well, you are really lilmiting yourself if you aren't willing to upgrade the exhaust and intake. If you aren't willling to make the engine breathe better, then there really isn't much point in bigger valves. Porting the head, maybe, but you are still choking the eninge on both intake and exhaust.

Given your imitations, your best options would be milling the head and/or block to raise compression, changing the cam, and playing with the distributor advance curve. Take the time to calculate your dynamic compression ratio correctly and modify the motor accordingly.


If you aren't going to change the exhaust pipe diameter then I doubt you are willing to change to electronic ignition. You can still fine-tune the vacuum and mechanical advance curves on a points distributor.

In an emergency, your driveshaft-drum type emergency brake will work about 5% for about 20 seconds. If it is in perfect condition. Driving a car with a single-pot master cylinder in actual traffic is a bad gamble.
Too low. Adjust and/or fix the kickdown linkage.
Then what are that fuel filter and PCV system doing there? Neither was original on your '60.
Not really.
I have a 1960 (aluminum, one-year-only) intake that has been custom-modified to accept a highly-regarded Motorcraft 2100 carburetor (and I have a new-not-remanufactured Motorcraft 2100). Send me a PM if you're interested.
Good way to cause yourself a lot of headache. There are much better cams (Dutra RV10M-RDP) available from much more reliable vendors.

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Too many people who were born on third base actually believe they've hit a triple.

If I bit the bullet and went ahead with duel exhaust and changed the intake and carb. What kind of horsepower gains would I be looking at with the cam and head work? She is choked on both ends. It is just bolt on stuff so I can always go back stock. Thanks again guys!

The factory rating of your engine in stock form was 145 horsepower; the small 2bbl and slightly bigger cam setup devised for export (still with small single exhaust) was rated 160.

It's not real helpful to kick around horsepower numbers, though. Leaving them aside, a thoughtfully configured 2bbl intake setup, a good ignition system, and either a bigger single exhaust or (preferably) a set of Dutra Duals (Y into a reasonably-sized single headpipe/muffler/tailpipe) will improve the driveability of the car remarkably. A thoughtfully-selected cam, carefully timed, will likewise make a large improvement. If you do all of this, the car will have a lot snappier pickup from a stop or from a lower speed to a higher one, and driving it will be much more enjoyable and less of a chore.

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一期一会
Too many people who were born on third base actually believe they've hit a triple.

This used to be an old topic everyone was tired of talking about. I'v searched with do diligence and can't find what I need to know. In a stock engine, in a truck, I converted to 2 bbl and spent a lot of time getting a stock manifold right. Now I have to have the exhaust done because the angle of the pipe and manifold doesn't match. But I always wanted to make it larger anyway. Do I remember correctly - 2-1/4 from the manifold, then 2" out the back?

Still working out a wreck. Found parts made of unobtainium - the best kind. Had them shipped from TX to GA. Now working to get them stripped, primed and talk a body shop into working on an old truck... They don't like that for some reason while restoring mustangs in their spare time.

I have everything but a front bumper and a tailgate if anyone knows of either...
Thanks, danny

Not an easy choice, as everything needs to work together to make it work right...

The first step is to set a goal on what you want:

Sounds like streetability with some pep, and MPG on pump gas...

Limitations are:
Big Heavy Car
Auto Transmission with stock convertor
stock 3.31 rear ratio

Rear Ratio looks good to help make it easier for the engine to move the car, so we are good there (although upgrading the brakes should be a priority as it is a lot of car to stop once it's moving).

The torque build is going to get you what you need, and there are a couple of ways to get there depending on what you want to do...

the comp cam 264 is docile and is not suitable for the torque build, and doesn't get it's sweet spot until you are way up in the power band...the MP244, Comp 252, Delta 254, and OCG equivalents will work perfectly from idle to 5000 rpm (and I have used the comp 252 with a hyperpak intake and the engine was still pulling past 6000 rpm in 3rd with no problem...)...lately comps' QC has not been that great, so most of us would rather have an original cam and lifters reground so as to not have the dreaded oil pump gear failure...

You will need to pull the engine, take apart and measure the combustion chamber size, the depth of the piston in the bore at TDC and the width of the bore to determine what to tell the machinist to cut off the deck and the head...also note that going to new valves and seats can change your combustion chamber volume depending on how they sit...Slant sixes changed a bit over the years and I can say that the 1963 truck engine I used as a core when I measured it was sitting in the 6-7 static compression ratio range, the stock 1967 engine was much nicer but still in the very low 8:1 range...and the 70's motors tended to be closer to their advertised CR...much like a book at a store, you don't know what's in it until you open it up and check it out.

If you are going to stick it out with a 1 barrel and go to a bigger exhaust this cam will work OK and be fine for daily driving, some minor clean up of the ports will get you more gump but going to 9:1 compression isn't going to make big dividends with the restriction on the intake side....

If you take the plunge...going to 9:1, adding the 2 barrel, and getting the 2 1/4" exhaust to the muffler then 2" out, will be good bump up in power...note that there are more gains to be paid by upgrading the ignition system from points to EI (more stable timing, no points to wear out and change), and recurving the distributor will gain both power and some mileage.... Even in this configuration a little porting and stock valves still work fine and can save money for later improvements...
don't forget to degree the cam and set a few degrees advanced to get a bit more torque out of it (with the slant every "little" thing is like saving pennies to get a dollar...some things add up...some things work together and make a dime...) Overbores don't gain "cubes" like they do on bigger bore engines...if your engine is shot then an overbore will be needed...if you are going for larger O/S valves and need to keep them from being shrouded an the chamber more blended with the bore, then you may need to step up a bit....for street in a fairly modded engine 1.70/1.44 valves are fine...(in a 10:1 street engine with the 4 barrel, and good exhaust they are a must).

If you are going for even more power then the bigger 2 barrel or small 4 barrel is next on the list, along with dual exhaust, and oversized valves and a bit more porting (don't go hog wild in there...if you open them up too much you can cause the engine to go "flat" when the velocity can't be maintained in the port at certain throttle positions...)....that being said when you enter this end of the field the transmission is next to go and really good brakes are mandatory.


Right now, figure out if 1 or 2 barrels are staying or going, how much exhaust you are wanting to install, and measurements on what it will take to bump the engine up a bit...

Last item of concern, ask around as to who the reliable and quality machinist is in town and go by to talk to them...look around and see if they have anything "interesting" they are working on....if they just do V-8's and frown at the slant or won't take your suggestions (and our advice), then keep shopping... One machinist I use does everything from 4 cylinders, to drag race engines, to diesel 16 cylinder utility engines...he like the "off" project, just to say he's done it...and done it right, and he even asks questions and likes to see if anything he's picked up from other brands works...