318 rebuild

[alf44]

i have a running 1986 318 with leanburn. its in a 5th. i plan on pulling it this spring and giving it a general rebuild. i plan on,, checking cylinders for size and out or round-taper. if in spec .hone for new rings. has 265,000 miles and very little blow by and good compression on all 8. keep pistons ( cost ). what will be a good cam choise to incresse power a bit, nothing radical. thinking of a comp cam. wanting to change heads with the 1989-91 small block 308 castings to improve combustion chamber and compression. want to use a eddy airgap intake and around a 600 cfm 4 bbl. already has new timing chain. will use new oil pump, rings, gaskets, core plugs, etc... i am not looking for high horsepower just a good increase in power and drive abillity. will use the 904 auto out of the 5th and the rear end ,should be a 81/4? any thoughts on this general rebuild?..

 

[kkritsilas]

Not looking to criticize your choices, but why the 600 CFM Edelbrock/Holley carb? The Thermoquad, at either 800/850 will work on a 318, and probably work better than the 600 CFM Edelbrock/Holley. Chrysler had a good idea when they started using the Carter line of carbs. The Thermoquad. is an air door carb, meaning it meters ayr/fule based on engine vacuum, not throttle position alone. Only part that is a problem with our cars is that there usually aren't any vacuum ports for the distributor's vacuum advance if you want to get away from the ESA/Lean Burn systems, but I have heard that you can have a vacuum port drilled out, and it will work. If you want to use an Eddy Performer Air Gap, it will need the 318-4 BBL/360 heads (larger ports); I don't know if the 308 heads are small port or large port heads. If you did go with an Air Gap intake and a Thermoquad, you may be able to drill out a vacuum port in the spread bore to square bore adapter plate.

Kostas

 

[alf44]

my carb choice is up for debate, just a option along with the thermo, but at 800/850 or so, would that be to much cfm? im just looking at building a good strong engine of around 200 hp or so, and needing to do it at the lowest cost so used parts will be used where it makes the most sence

 

[alf44]

i will read anyones thoughts on this rebuild, the more the better !!

 

[kkritsilas]

No, an 800 CFM Thermoquad was factory standard on the 318-4BBL. Because of the design of the Thermoquad, it meters based on both engine vacuum (or demaind) and throttle butterfly position. Because of that, if properly tuned, an 800 CFM Thermoquad can work just fine on even a stock 318. The Holley, for example, flows strictly on throttle position. So if you put a large Holley on that stock 318, it won't work, or at least not work well. Airflow in a Holley is based strictly on throttle position, no matter what the engine is demanding. So if you floor the gas at low rpm, the Holley will increase its flow, even if the engine doesn't need all the flow. The Thermoquad will flow as much as what the engine needs, no matter how hard you lean on the gas. If the engine demands more, the Thermoquad will flow more. This is very close to the way a Rochester Quadrajet carb works as well.

If you look at a Thermoquad, you will see that there are two places where the amount of air going into the engine are determined. The top of the carb has the engine controlled air doors (operated by engine vacuum), and the bottom of the carb has the throttle butterflies. The engine vacuum determines how much air is going to go into the carb, the throttle then determines how much fuel is going to be added to the air flow. Another thing you will notice is that a Thermoquad has relatively small primaries, and huge (for the 800CFM carbs) or Gigantic (in the 850 CFM carbs) secondaries. That means that the car can get decent gas mileage on the primaries (i.e. secondaries not in use, cruising), yet still flow large amounts of air when needed (using the secondaries, accelerating briskly or hard), all without bogging.

The Holley does have a major advantage in that there are lots of parts available for it. The parts for the Thermoquad are out there, you have to look a little harder for them. The new Street Demon (from what I have read) uses some of the principles of the Thermoquad/Rochester to ensure crisp throttle response. A Thermoquad rebuild by a good carb rebuild guy/service will probably cost about the same as a new or a good used Holley.

Kostas

 

[alf44]

No, an 800 CFM Thermoquad was factory standard on the 318-4BBL. Because of the design of the Thermoquad, it meters based on both engine vacuum (or demaind) and throttle butterfly position. Because of that, if properly tuned, an 800 CFM Thermoquad can work just fine on even a stock 318. The Holley, for example, flows strictly on throttle position. So if you put a large Holley on that stock 318, it won't work, or at least not work well. Airflow in a Holley is based strictly on throttle position, no matter what the engine is demanding. So if you floor the gas at low rpm, the Holley will increase its flow, even if the engine doesn't need all the flow. The Thermoquad will flow as much as what the engine needs, no matter how hard you lean on the gas. If the engine demands more, the Thermoquad will flow more. This is very close to the way a Rochester carb works as well.

If you look at a Thermoquad, you will see that there are two places where the amount of air going into the engine are determined. The top of the carb has the engine controlled air doors (operated by engine vacuum), and the bottom of the carb has the throttle butterflies. The engine vacuum determines how much air is going to go into the carb, the throttle then determines how much fuel is going to be added to the air flow. Another thing you will notice is that a Thermoquad has relatively small primaries, and huge (for the 800CFM carbs) or Gigantic (in the 850 CFM carbs) secondaries. That means that the car can get decent gas mileage on the primaries (i.e. secondaries not in use, cruising), yet still flow large amounts of air when needed (using the secondaries, accelerating briskly or hard), all without bogging.

The Holley does have a major advantage in that there are lots of parts available for it. The parts for the Thermoquad are out there, you have to look a little harder for them. The new Street Demon (from what I have read) uses some of the principles of the Thermoquad/Rochester to ensure crisp throttle response. A Thermoquad rebuild by a good carb rebuild guy/service will probably cost about the same as a new or a good used Holley.

Kostas

thank you for your advice, stillin the planning stage now, i dont know if ill go 4 bblor stick with a 2 bbl though,,,

 

[kkritsilas]

As always, it is your car, your choice. However, it is harder to find speed parts for 2 BBL carbs. There were some Edelbrok SP2P mainfolds made for 2BBL carbs that have been brought up on this forum before. Other than that one, aftermarket intakes are 4 BBL or higher (six pack, even dual quads). For a street car, anything more than a 4BBL is there for bling factor, not for performance reasons. Even the factory six packs and dual quads (other brands) are really just marginal improvements over a single quad, at usually a very steep price initially, and in terms of maintenance and gas mileage. I don't konw if your 200HP goal is even practical on with a 2BBL. You can get a really big 2BBL, I suppose, but then the driveability and gas mileage will suffer. Just an opinion.

In the April 2013 issue of Mopar Muscle magazine, there is an article called "Thermoquad Revival" (starts on page 18) which covers the Thermoquad in great detail, along with how to rebuild it (high level overview). There is also a remarkably detailed 10 Part series on Youtube on how to rebuild the Thermoquad.

Kostas

 

[My imp]

I always go with the TQ. They have vac advance models. I use the smaller one on my 360 & I average 22-24 mpg on the trips to Va. Beach (the only time I closely monitor fuel consumption), combined highway & city. Made the trip 5 times & have the gas receipts to prove it. Not the fastest thing in the world by any stretch of the imagination, but that's not what I'm after. The power is more than adequate, the economy is far above average! A smaller square bore carb will usually get worse economy then a larger spread bore. There are many factors, but if you keep your foot out of the secondaries, you effectively have a smaller two bbl. with a spread bore, than you have with square bore carb.'s. Match all components to get the most of your combo, including eng, trans, convertor, gear, etc...

 

[alf44]

thank you imp, that 2bbl is just a thought as thats whats on it now

 

[alf44]

As always, it is your car, your choice. However, it is harder to find speed parts for 2 BBL carbs. There were some Edelbrok SP2P mainfolds made for 2BBL carbs that have been brought up on this forum before. Other than that one, aftermarket intakes are 4 BBL or higher (six pack, even dual quads). For a street car, anything more than a 4BBL is there for bling factor, not for performance reasons. Even the factory six packs and dual quads (other brands) are really just marginal improvements over a single quad, at usually a very steep price initially, and in terms of maintenance and gas mileage. I don't konw if your 200HP goal is even practical on with a 2BBL. You can get a really big 2BBL, I suppose, but then the driveability and gas mileage will suffer. Just an opinion.

In the April 2013 issue of Mopar Muscle magazine, there is an article called "Thermoquad Revival" (starts on page 18) which covers the Thermoquad in great detail, along with how to rebuild it (high level overview). There is also a remarkably detailed 10 Part series on Youtube on how to rebuild the Thermoquad.

Kostas

do you know whats a good intake manifold to use with a thermoquad?. i would like to find these parts in a good used condition.

 

[jasperjacko]

vac.port

Only part that is a problem with our cars is that there usually aren't any vacuum ports for the distributor's vacuum advance if you want to get away from the ESA/Lean Burn systems, but I have heard that you can have a vacuum port drilled out, and it will work. If you want to use an Eddy Performer Air Gap, it will need the 318-4 BBL/360 heads (larger ports); I don't know if the 308 heads are small port or large port heads. If you did go with an Air Gap intake and a Thermoquad, you may be able to drill out a vacuum port in the spread bore to square bore adapter plate.

I added the vac advance port on my carb. There are instructions online for this. Location of the hole is very important. You can't put in the adapter plate because you'll have advance even at idle. If you put the hole in the adapter, you'll be running on manifold vac. You need ported vac for the vac advance.

 

[jasperjacko]

Edelbrock performer is your best intake for a 318 with the thermo.

 

[alf44]

Edelbrock performer is your best intake for a 318 with the thermo.

thank you jasper, was thinking that as a option

 

[My imp]

thank you imp, that 2bbl is just a thought as thats whats on it now

You misunderstood me. What I meant was that when you are driving under light to medium throttle, you're only running on the primary side of the carb. On a spreadbore, the primary bores are smaller than the secondary bores. On a square bore, all the bores are the same size. The primaries on a spreadbore tend to be smaller than the primaries on a square bore, thereby effectively giving you a smaller two bbl at light throttle when you don't have the secondaries open at full or near full throttle. The TQ is IMHO the best designed, most versatile carb on the market. It's time has come & gone with the invention of EFI, but not everyone has the funds to properly set up their vehicle with EFI. In real world terms, the cost of EFI would take a really long time to recoup if economy is your sole reason for changing from carb to EFI. My Imp gets roughly 16mpg city, up to 24.5 highway, & 19 all around average. My wife's Grand Marquis does 2,pg better in the city, & the same on the highway as my Imp. Why spend $4-6k on EFI. I'd never see the return on investment.

 

[NoCar340]

The Edelbrock Performer is not the best choice with a TQ (or any carb, for that matter). The factory iron 4bbl intake makes considerably more power and torque on the dyno. Remove the EGR standpipe and replace it with a pipe plug, and use the EGR valve as its own block off plate if you don't want to fabricate one. If you don't want to do any fabrication for the rear mount of your AC compressor, it's either an original 4V intake cast late in '77 or newer, or the Edelbrock Performer. I know of no other intake with the rear boss near the #4 intake port. If it were my car, I'd go with the OEM iron piece for this build. The SP2P that I had was a 4-barrel and very similar to the old StreetMaster. Simply put, those are the two worst intakes ever devised for the LA engine for any use whatsoever.

For a mild build like this, I'd stick with the good old TQ. Adjusted correctly, you'll never regret it. It's just an awesome carb. For the record, Holley vacuum-secondary carbs do not operate on throttle position for the secondaries. They work very similarly to a ThermoQuad in that regard, by using engine demand to meter fuel and air. The only piece of linkage from the primaries to the secondaries on a 4160 is a lockout to keep the secondaries from opening too soon or hanging open. Edelbrock Performer carb, a.k.a. Carter AFB 9000? I wouldn't even consider owning one. Carter considered it outdated by the mid-'60s, replacing it with the much-better AVS, which is in no way related to the Edelbrock Thunder Series AVS other than basic principle of operation.

The 308 heads are awesome, but remember that with an '86 non-AHB engine you'll need to replace the pistons or your compression will be in the basement. Like, 7.5:1 or less. The '85-up roller longblock kind of sucks for a build because of that and the fact that the OE 302 swirl-chamber heads don't flow worth a hoot. Spend $1,000+ for professional porting and you might get them to flow as well as as-cast 308, X, or J/O/U heads. Realistically, even with the favorable 1.85 rod:stroke ratio and high nickel content of Mopar blocks, it's more than likely at 258K miles you'll need to bore it and use new pistons. Just get ones listed for an '82 or something rather than the correct year. With a .020"-.030" shave to the heads and Mr. Gasket's thin head gaskets, this will put you very close to (or slightly over) 9:1 compression. More power and better economy right there. Make sure that for every .010" taken off the head-gasket face of the heads, .0095" gets shaved from the intake face of the head or your intake won't fit correctly.

Camshaft? The easy choice here is something very similar to an original 340 camshaft, such as Summit's inexpensive K6900, or one step up to the K6901. Nice, mild camshaft in either situation. No need for added stall, deep gears, etc. The smaller cam will be a little better on fuel, but not dramatically so.

Get a vacuum-advance distributor (points or electronic) and pull out the contact/pickup plate to gain access to the mechanical advance mechanism's flyweights. You'll have to remove the rubbing block or reluctor, but you can do that with two screwdrivers. Get the Mopar Performance lightweight spring kit, but use only one. Replace the lighter of the two factory springs with it. Put the pickup plate back in, reinstall the rubbing block or reluctor, and toss the points or pickup. Install a Pertronix Ignitor, red wire to coil + and black to coil -. Done. Never think about it again. I've sold hundreds of them since they were introduced and have never seen, nor even heard about, one failing. Disconnect the ESA (Lean Burn) and pack the connectors full of clear silicone so they can't short, and just leave 'em hang. Set timing using the "Big Fat Friend on a Steep Hill" method. If you get spark knock at part throttle or cruise (not likely), get a vacuum advance canister with less total pull; the amount of advance is stamped on the arm.

Quick recap:

• OEM cast or Performer intake
• Carter TQ w/vacuum advance port (easily added if yours doesn't have it)
• 308 heads milled .020"-.030"
• Earlier pistons ('76-'84 flattops)
• Summit K6900 (or K6901) camshaft kit; stated goals tell me the K6900
• Vacuum advance distributor w/1 light flyweight spring & Pertronix Ignitor I
• Tell everyone it's a 360

Candy from a baby. This will put you well over 200HP (net) with the factory cat & single exhaust. If the cat falls off and a pair of true 2" duals grows in its place, figure more like 240-250HP at a usable 4,500RPM. It should pull like a freight train from slightly off idle to about 5,000RPM. Headers and 2.25" pipes are probably good for another 30 beyond that.

I've built this combo three times, once with J heads and twice with 587s with the smog humps ground out. It works. To be honest, though, you could probably forego the cam and heads, rebuild your shortblock with the stock-style '86 pistons and be very happy with intake/carb/distributor and free-flowing exhaust. I did exactly that with an '84 Fifth Avenue, and it was a very enjoyable car after a swap to 2.94 gears from the abysmal 2.2 ratio originally in the car. Fuel mileage actually increased with the lower 2.94 gear. It was lugging too much with the ultra-high 2.2 cogs.

 

[kkritsilas]

NoCar 340:

Thanks for the info regarding a good street setup. I have two factory 318-4BBL cars (one 1980 Cordoba Crown, one 1981 Mirada CMX). Both are (of course) ESA/Lean Burn, and would like to get rid of them on both cars. I do have a couple of questions regarding your recommendations.

1. To add a vacuum port to the factory standard Thermoquads, do I find an carb spacer with a port in it, or do I have the carb drilled for the vacuum port? If I get a carb spacer, do you know where I can get one? If I need to have the carb drilled out, I think I will have that done when the carbs are out for a complete rebuild. I'd like to keep the original carbs, as both cars have cruise control, and it may be a problem to get any other carbs to work with the cruise control.

2. Regarding the ignition, do I need a new ignition box, and with the Pertronix Ignitor, do I take out the ballast resistor or leave it in?

The Cordoba Crown is a little odd. It was bought used, and sat in a field quite a long time. It needs work (almost all of the cars in the wild do), but the odd part is that somewhere along the line, the previous owner(s) took out the restrictor plate that prevented the use of leaded gas in the filler neck. From the sound alone, it sounds like there may be headers already installed, and I know there is a dual exhaust in it (two working tail pipes). I won't really know until I can get underneath, and with the winter in Canada, that won't be until the spring.

Kostas

 

[alf44]

wow,, thanks NoCar340 and myimp.. a lot of good info, just a fast review of my plan.. 79 volare with a super /6 .904, 7 1/4 rear ,gearing unknown. electronic ignition. plan is 86 318 with L B now ( not to be used ) a general low cost rebuild to make reliable, want that 4bbl. will use the trans and rear from the 5th. new rear springs, ( all mine are weak ). i am looking to spend up to 400. on rebuild so looking for good used parts. i know with this price im not going to get fancy-good heads and pro porting is out. 200 hp is just a goal im not going to get to but as close as i can get and ill be happy. 318 has 265,000 miles, little blow by, very good compression from 150 to 165, new timing chain already. so a cast iron 4 bbl intake and a good used thermo quad are wanted. ill need to use as much of the old parts as i can- crank- rods- pistons ,( depending on condition ) rering and bearings, oil pump, gaskets. have all parts to convert LB to standard electronic on hand. the k6900 camshaft and lifters sounds good. with that combo of cam-intake -carb. what used heads will i need? i know there is A LOT of differant ways i can go but i need to keep cost down.. ill use the whole v8 k frame- suspension- brakes.. so give me your best ideas like you already have... thanks to all.

 

[My imp]

I agree with Kostas. I bought the correct (year & engine) TQ off of eBay BRAND NEW for $165. There's a web site that tells you everything you'll need to know about a TQ. If rebuilding one isn't your forte, contact Dave @ Demonsizzler. He'll ask you about your entire combo (cu.in., cam, heads, comp. ratio, exhaust, torque conv., trans, gear, etc..), be honest, tell him what's there now, not what you plan on running! Get any weight out of the car you reasonably can. Hot rod stripped a Caddy, & as they cut stuff off, they made passes at a track. Every 100 lbs. improved their time by .1 th! They got a junk yard Caddy running 10's! Wasn't street legal, or even remotely safe. But that wasn't the point of the article. ALWAYS use new lifters with a new cam, be careful where you save your money! Good things are not cheap, & cheap things are not good! With that many miles I'd be surprised if someone hasn't been in there before. Craigslist & eBay are full of deals. If you know what sounds good vs. what is good. Summit's good with prices on master kits, + they price match. Machine shops aren't cheap, & finding a good one is imperative! You won't have to change it, but a lower (higher numerically) gear will definitely help. A 3.21 in your 8 1/4" would go a long way.

 

[alf44]

thank you my imp. as far as weight of car, lighter is always better. will be a v8 car, no power window- no power seat, has buckets and floor shift console but a colum shift. just a basic 2 door, will add some weight,, rear spoiler- home made front spoiler. want to add sub frame connecters. not much else for added weight

 

[slant6billy]

Help me on that vac port thing and drilling one or using a carb spacer with a vac port. I set a car up on "timed" vacuum and it ran 100% better. The guy who set it either did not know or was not paying attention. What impact does this play into with Thermoquads?