Hello all,

I've lurked on here occasionally for the last 8 years, but never posted. There's a lot of valuable info on here, but I'm not always sure where to start in my search as when it comes to changing too many things under the hood.

Anywho, I'm interested in getting a little more power and fun out of my 225. It is a completely stock engine with the 1-barrel 1920 Holley (the pain in the neck carb that works great when it does work and just awful when it doesn't)... I'm still running points in my distributor. Factory A/C. Power Steering. Not sure what else to include there. I have the 904 automatic. 84,000 Miles. Original time chain.

I have a few ideas thus far. I'd like to get the Dutra Duals, the 4 barrel short runner intake, and an Evil Stick Cam all from Aussiespeed. I'm considering either going with Pertonix II ignitor to replace the points or getting the Performance Ignition Tri-Power Distributor. Either one does require me to swap out the Coil and the Wires... That I'm unsure of what to get for those.

I'm not stuck to any of these things if someone else throws other ideas at me. HOWEVER, I do not want to do any kind of machining to the engine block or heads. I'm not planning to tear it down that far at all.

Thank you to everyone in advance

Sincerely,
Ben

Hi Ben,
I'm no guru on slants, but having two slants myself I'll give you my input. Using the engine as-is, the 2 barrel conversion would probably be your most economical approach. I suspect that the four barrel would hurt nothing, but would not be any better than the 2bbl conversion. Stock slant can move only so much air. Depending on your altitude above sea level, a significant ignition timing change can help. My '63 1bbl woke right up by advancing idle timing to about 10* btdc. For ignition system reliability, do the HEI conversion using a GM HEI module, an electronic ignition distributor and a good coil. If your original differential is still present, it should be a 3.23:1 ratio. That's the best ratio in my opinion.

One of my slants, a '66 Dart has the 2bbl conversion with a ridiculous 2.76:1 ratio--a slug in town. My '63 Dart with 3.23:1 works great.

My take on this is that without significant machine work, it's difficult to add much more pizzazz to the slant. The slant has really good torque at low rpm. Once it's wound up a bit it's needing a shift.

Must not forget exhaust. My cars both have been converted to duals. I put the exhaust manifolds in the vise and hack sawed the front three cylinder portion and used a Dutra casting for the front on the '66. For the '63 I used some small steel tubing to build a front header. Couldn't tell any change from single exhaust. The '63 has dual glass packs and it's kinda loud. I like the cackle on acceleration so that's how it will stay. I'm an old fart and I remember guys in high school had Chevy 235 six cylinder engines with a split exhaust with glass packs and I still think that sounds better than any other engine, to include my '54 Ford 239 OHV that sounded great with glass packs.

I just enjoy driving my Darts even if they aren't particularly quick. These cars will go much faster than I want to drive. Takes a bit of time to get there but 80MPH will eventually happen. Interstate driving is no problem 'til that '66 GTO driver wants to do acceleration runs. I can make more noise than he can. Quick, not much. Love the slants.
Jerry

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Jerry in beautiful Colorado

Hello Ben, and welcome.

Understanding from your post that you want some more fun out of your slant 6. You are in good company in that respect as most of us are leaning in that same direction.

How you go about it is somewhat individual, but the basics that underlie more performance out of your 225 are grounded in Physics. Your feeling of not wanting to change too many things under the hood at once is sound.


If you do not want to remove the head yet, then you are going to be constrained to optimizing what is all ready in place. That is a good place to start anyway, because once you put a 2bbl carb on it, or even change the exhaust pipe size, and increase exhaust efficiency then it will be time to optimize what you have.

A 4bbl won't do a whole lot until you change the camshaft AND bump the compression up a bit.. (Well it looks speedy and that may be enough for some) Dutra duals win in terms of looks, but again they kinda need more head flow to really make the slant sing up the tach.. adding a camshaft may help in the 3000-4000 rpm range, but the head and valves are the cork in this engine.. I would venture to guess, that spending all of your $$ on quality head work would give more performance than adding induction and exhaust parts.. Just saying. Not saying your plan is bad. Just wanting to make sure you know that it will not spin to 5500 with a 4bbl and dual exhaust.

If you want to get started right away, I would look up the HEI conversion. It is cheap to do, and even a stock slant will run better with it. I am unfamiliar with the petronix stuff, Have heard some love it, some do not. I believe the HEI wins in terms of cost..

Let us know what you want to do with it. (daily driver, show vehicle, highway miles, drag racing)

Our family has 4 74/75 slants with the peanut heads. Our chosen plan is Super Six swaps from 1979 or newer Aspens, Volare's, or Lebarons with the attached 904-lock-up converters. (Many posts here about those ideas.) With those late model SS-6 swaps we also take the matching OEM SS-6 electronic distributers (systems) because of the curves (other posts here). Our focus is on slightly more power, but mostly better fuel economy on the highway, making ours better cars for road trips. On one of our Darts we went to the larger diameter exhaust (other posts here) which showed noticeable improvement in breathing. The downside was, on that car, noticeable increase in noise on road trips. (Muffler??) We old folks are getting more sensitive to noise now. Kudos to you on still running points ignition! Installing and adjusting points is now a (nearly) lost skill! Having said that, you will see a definate power increase with electronic ignition, you will spend less of your time fiddling with the points system, and your spark plugs will burn cleaner and last much longer. We are working later model cars, so I don't know if /how these ideas would work on your earlier year slant. But you have lots of early slant folks here to help you out determining those issues. Cheers. P

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"Louise", a 1976 Dart Custom project, (now sadly reverted to being just an "organ donor" to our other project Darts.)

Firstly I'll answer the simple question. Outside of winter time, I use the car as a daily driver/show vehicle. Meaning I'll drive it to work, grocery, hardware store, etc just because I enjoy driving it. However, I do take the time to keep it looking sharp and taking it to shows as well. I don't really ever take it on the highway, I'll take it up country roads first, and drag racing sounds like a lot of fun but I'd definitely blow something up!!

Anyway, I wondered if a 4bbl carb might be overkill without doing the head work, but that was why I liked the Aussiespeed stuff because I could choose a different carb mounting plate. I think going with electronic ignition of any kind will be a no-brainer from what I hear.
I've read quite a bit that opening up the exhaust would help quite a bit because the stock exhaust is quite restrictive.
I've been having difficulty finding exact info on what cams I would be limited to with the stock untouched heads. Any guidance with that?

--Ben

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65 Valiant 200
Holley 1920, 225CI /6
Auto Trans.

Thanks for all the suggestions and ideas! Haha! Yeah this car has soo many original parts it's almost ridiculous! The Points I replaced last, I had no idea how old they were, but they weren't even pitted! I could've adjusted them and put them back. Heck I replaced the cap and rotor at the same time, and I had an mechanic that used to work for Chrysler in the 60s that believed my cap might've been factory OEM! I kept it for posterity.

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65 Valiant 200
Holley 1920, 225CI /6
Auto Trans.

Good reasons to keep old or OE parts around: https://www.slantsix.org/forum/viewtopic.php?t=60552

Also I am having second thoughts about suggesting a 4bbl is not gonna help. Cost aside, it may be a reliable way to put a carb known to be in good shape on the engine.
I am in the planning stages of welding up a stock intake, to accept a Quadrajet. Primarily because of the double boosters on the primary side, and for it's adjustability of the part throttle fuel curve. No expectation that it will add horsepower above 3000RPM, but wanting highest quality atomization in the low to mid range short of fuel injection.

As for camshafts, a search of these two may give some foundational insight: https://www.slantsix.org/forum/viewtopic.php?t=56032

I just about lost it for a second when I read this thread! I actually met DonPal at a car show near me 2 yrs ago at the Ioka Valley Farm. His 65 Dart is absolutely amazing. All his retrofits to the car to make it a year round driver are so darn cool, and he actually had a conversation with me about the cap gap issue when I walked over with him to my car! He's a great guy.
I just couldn't believe how well his car started! Just a quick tap of the starter and it rev-ed right up with Zero Cranking! Okay I'll stop "fan-girling" now.

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65 Valiant 200
Holley 1920, 225CI /6
Auto Trans.

If you don't want to have any machine work done, then put thoughts of 4-barrel carbs out of your mind. They will only provide a noticeable benefit over a 2-barrel once you increase compression and improve flow through the head with bigger valves and a lot of bowl/port grinding. (I should mention that for the price of all those parts from AussieSpeed, you could easily have the head shaved for higher compression and get some valve work done with money left over for more reasonable bolt-ons that would net you more power at the end of the day. But I can understand not wanting to have the car out of service for that long.)

I would suggest finding a used factory 2-barrel manifold, and buying a 2-barrel carb that is easy to work on and you can easily get parts for, with an adapter plate if necessary. I really like the Holley 2300; it uses all the same parts as the common Holley 4-barrels, there's all kinds of information out there on tuning them. It's non-progressive which is easier to tune, although not so great for gas mileage, and even the 350 cfm version might be a little oversized for a stock 225.

Keep the stock exhaust manifold, but have a larger exhaust pipe put on. A single 2-1/4" pipe is plenty for a stock 225. When you re-mount your manifolds, use the expensive heat riser gasket from Remflex. The stamped steel ones that come in every gasket set will leave you with an exhaust leak, unless you're installing pristine factory manifolds with perfect alignment. For that matter, take a straight-edge to your stock exhaust manifold's head mounting surface once it's off the engine. The ends on those tend to warp inward, leaving a gap on the center cylinders. If the runner flanges are more than 0.040" out of flatness, I would either use the (even more) expensive Remflex gasket for mounting the manifolds to the head, or pay a local machine shop $75-100 to have it flattened (or do it yourself if you have access to a big enough belt sander.)

Also take a hard look at your ignition system. Electronic ignition would remove a lot of common maintenance issues. A lot of people here (myself included) like the GM HEI conversion, but Pertronix is a lot simpler to install and works just fine. The slant likes a lot of initial timing, so on a higher-compression motor you generally want to "re-curve" your distributor to flatten the mechanical advance curve so you can run ~10 degrees advanced at idle without going over 30ish at high RPM (to avoid pinging). For a stock engine, pinging probably won't be an issue with your stock distributor at high initial advance. But there's a lot more you can do with mechanical and vacuum advance timing that can help your power and economy. Other on this forum like DusterIdiot would know more.

The next step past this would be pulling the head to have it milled for higher compression, selecting a torque-y RV-style camshaft, converting to dual exhaust (either $$$$ for good manifolds, $$ for headers and more installation headaches, or learning how to weld cast iron), and adjusting your ignition's mechanical advance curve. (IMO, a Holley 350 2-barrel is still enough carb for a 9:1 SCR motor with a mid-range cam.)

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Somehow I ended up owning three 1964 slant six A-bodies. I race one of them.
Escape Velocity Racing

I hear what you're saying. Aussiespeed stuff is expensive, but I know it's good quality. Plus there shouldn't be much fuss with it as far as warping and things of that nature. Plus they seem really thorough in their design compared the Offenhauser 4bbl intake, but I'm really just blowing smoke at this point.

I do like the fact that the Aussie intake gives me the option to swap mounting plates between 2 barrel and 4 if I ever would change anything in the future. So if I go with a known good 2 barrel setup, and I get money itching in my pocket to pull the heads and do some machining and porting then I won't have to buy a new intake. I just don't want to put the car out of service for an entire season, ya know? I have to borrow my mechanic's shop for a lot of this work cause A) I don't have all the tools and B) I don't have the space either to do the work... Plus living in the rust-belt I can't drive the car down to the shop some winter day and pull the head during the off-season.

I learned the hard way about the RemFlex gaskets. I've done the manifold gaskets twice in the last 7 yrs because of that thing! Thankfully I had learned about RemFlex when the 2nd time one came around. Even if I go all new stuff for what I'm planning I'm still going to use RemFlex for the intakes because they just work so darn good! You truly get what you pay for.

Besides cost, is there any other reasons soooooo many people like the GM HEI ignition setup over others?

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65 Valiant 200
Holley 1920, 225CI /6
Auto Trans.

The biggest positive aspect after cost, maybe even before cost considerations for the HEI, is that you can get replacement parts at any parts store. Ether off the shelf, or overnight parts availability.

I would be interested to speak with AussieSpeed about the differences between their short runner and long runner intake. It would seem to me that the long runner intake would usually favor street driven vehicles, and the short runner would get the nod for racing and high end power... I could be totally wrong about that, but would have to ask them specifically which they recommend. (And I think a long runner intake has more eye appeal, b/c it is less common)

A trick I heard from DD for having your down time short, when and if you get to doing head work: Get a separate head and do the work in a relaxed manor while driving your car, then you only have it torn apart for a weekend as you make the swap..

I never thought about that. I was choosing the short runner because I was worried about clearance with my A/C Compressor. System isn't in service but is functional, and I'm looking into retrofitting it, but that's a subject for another time...
That's a good tip on the head work! I for whatever reason never thought about that! Thanks for sharing that tip!

-Ben

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65 Valiant 200
Holley 1920, 225CI /6
Auto Trans.

Thought with all this talk I should share some "eye candy"

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65 Valiant 200
Holley 1920, 225CI /6
Auto Trans.

Nice car! Good choice on the Interstate battery; I like NAPA-brand AGMs but those are good too. I like the ridiculous air horns. Plan on a dual-reservoir master cylinder conversion at some point, better yet with front discs. Scarebird offers a kit for small-bolt-pattern front discs; you just have to buy redrilled Chevy rotors from them or find a local shop to redrill parts store rotors. Late Mopar factory discs are better but require a change to large bolt pattern.

I wouldn't sweat the build quality on an Offenhauser or even Clifford intake manifold. It's a pretty simple device at the end of the day, and you can use a 2-to-4 barrel adapter on any of them. Acquiring a second cylinder head for the machine work is an excellent suggestion to reduce downtime. If you were anywhere near Houston I'd give you one I pulled off a parts motor for a 6-pack of Shiner.

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Somehow I ended up owning three 1964 slant six A-bodies. I race one of them.
Escape Velocity Racing

Thanks! Yeah I needed a new battery after my Napa battery gave up after 10yrs. I got the Interstate Batt at-cost from my mechanic, we have a good relationship of I do work for him and he does work for me.

The Air horns I get all sorts of looks with them... And when I set them off going down the road, everyone looks for the General Lee! I do need to do a brake upgrade of some kind somewhere in this, still running 9" Factory front drums and re-po ones in the back. I wouldn't mind converting to the larger bolt pattern cause I have adapters on there right now for the ability to run those larger wheels.

I do think the Offenhauser would fit better than the Aussie because of my A/C compressor... The water jacket in the Clifford intake for some reason always turned me off... I do agree with the adapter thing, that's what I always liked about all of them! I do wish I lived closer to Houston I would totally take you up on that.

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65 Valiant 200
Holley 1920, 225CI /6
Auto Trans.