View Full Version : Street Demon/ 302 economizer combo

01-30-2013, 01:25 AM
After getting fed up with a worn out Carter BBD and a lot of research, I have decided to give new life to the 318 in the Scamp.

Over the past year and a half, I have given the car a complete makeover and it deserves more than just a freshened up engine compartment. I'm at a stage in the game where I want to get better fuel economy and a bit more performance when I want it.

Eventually, this car is going to get more gears (stick trans tunnel and carpet are in, with a seam sealed plate over the shift hole until the gear jammer goes in) and it will also be recieving either an 8 3/4 or 8 1/4. I haven't decided yet, I have both.

For now, I'm going to keep the 3.21 7 1/4 and rebuilt 904 behind what is a completely factory engine, with the exception of 360 Truck manifolds with 2" outlets that run dual exhaust.

The engine is in good, running condition. The entire ignition system has new components and it's as tuned as I can get it, but I feel like I'm flogging a dead horse with the intake and head combo.

I have a set of 302, swirl port heads that I am going to use with a new BG(sansBG) Street Demon carburetor.

I am running at about 5450 elevation, give about 2000ft once in a great while, when I drive in the mountains, a few times out of the year, here in Colorado, but most of the time, the car will be in the city at the above elevation.

I have rejetted the carburetor from an .080" primary / .080" secondary sea level tune to a .078" primary / .080" secondary with primary metering rods coming from .060" / .052" step sea level tune to an .064" / .056" step. This combination brings the primaries down .006" on both steps and gives me the correct metering for about 6000ft elevation.

Should I do anything at all with the secondary jetting? Or should I leave it alone and tune the secondary door leaner? This carb tunes just like a TQ, but with a single step metering rod.

I also have access to two different aluminum intakes, but both are for 340/360 runner sizes. I am reluctant to port match the 302 heads, because I'd like to keep velocity and vacuum up, especially at this altitude and when I'm climbing hills.

Will I notice a difference with a small runner intake, like an Edelbrock LD4B over a 302 head port matched to an M1 dual plane? I don't want to strangle this engine, but I do want it to have very responsive throttle and torque. This car is going to be stop and go traffic as well as some cruising on mountain roads, so I want everything up front from idle, even after I put a stick in it.

02-02-2013, 11:41 PM
This is the Carburetor being used-


So, after going over some of the anatomy of this thing, I think I'm going to try the .080" stock jets in the secondaries at this elevation.

I may try a pass up at Bandimere Speedway with some O2 sensors to see what the AFR is at WOT, but I don't think it would be wise for me to go any leaner on this carburetor when I need power.

Right now, I have it set up for 6,000ft elevation in the primary circuit, which is a touch high for 5250-5450 elevation, but if I need power, it's going to be climbing elevation and I think with a richer secondary, it should make up for the 700ish ft of elevation loss in the city and under heavier acceleration loads.

Swirl Port/ 302 casting chamber question for those of you who have experience with them-

Does the area between the valves, where the closed/ flat part of the chamber comes to a peak between the valves cause any detonation problems? Is this a heat sink area? It seems a little sharp and I was considering filing them down a bit to eliminate a possible hot spot, but I'm not too familiar with how these heads take to detonation conditions, like low octane rating, high timing, etc.

Would this area on the chamber cause a problem? Or do the flow characteristics keep the heat off of this spot?

02-03-2013, 10:24 AM
Don't touch the heart-shaped area in the combustion chambers. That is part of the magic of the 302's. Not a hot spot.

02-03-2013, 08:20 PM
Thanks for the insight. It just looks like the peak in the heart shape that is flat, sort of drops off like a cliff edge into the valve areas, but if the flow keeps the area between the valves cool, I'll leave it alone.

I'm after and an Edelbrock LD4B and I think I can get this project underway!

02-10-2013, 02:10 PM
I always liked my 318 combo. Holley vac sec 600 carb and regular Performer manifold. Geared with 3.55s it moved along. Defininately easier on gas than my 340. I think if that goes I'll just rebuild my 318 into a torque motor. Just pay attention to machine work and go.

02-10-2013, 02:52 PM
The Performer is a good intake. It's runner size is dimension matched between the large and small intake port sizes. The 340 is a higher RPM engine and should be set up that way for it's use. I think a 340 would do best in front of a manual transmission.

The machine work on this engine is just as old as the car. It's still in good shape, doesn't smoke and has had good maintenance. I'm going to leave the lower half of the engine alone, until I need to build something else.

The short block will remain intact for the time being. I just want it to have a different breathing personality for traffic. The vacuum secondary Holley is a bit finnicky at my altitude, which is why I went with the Street Demon, even above an AFB, AVS and ThermoQuad. It seems to have the ideal properties of all street carburetors, reverse engineered into it. The CFM is a touch high, but it does use an air velocity door like the AVS and ThermoQuad for the secondary system, so I can tune WOT response. It should get great vacuum signal and response, if I can manage to get the right intake.

02-10-2013, 04:05 PM
I agree. Just saying the ole 318 is a good engine.:) My 340 is set up for rpm; 286 cam and W2s 4.10 gears.
Never used a LD48 intake. I'm using a Mopar W2 dual now. I have a Holley Strip Dom modified to use a TQ. Will see how that goes....

02-10-2013, 04:42 PM
Very cool. I'm at a point with this car that I may just leave a 318 in it forever.

I'm into performance, but not beyond what this 318 can push, for this specific car. The car is a driver. And I mean a real driver. it sees snow once in a while, but it is cleaned and garage kept. The car has been prepped for a 4 speed and I have everything, sans the transmission.

Eventually, I may build something with some Keith Black 9:1 flattops to raise compression, but I'm not going to cut anything past that. This is down the line a ways, but I agree with you, completely. I like this engine and I'm not out to drag race this car. Just have fun and get around with it.

02-10-2013, 05:48 PM
So now I've entered a world of port mismatch and a lot of research.

Here are the port size dimensions for the 4 small block Mopar LA cylinder head sizes-

273/318 intake port dimensions- 1.0 x 1.92
340/360 intake port dimensions- 1.16 x 2.27

The trouble I'm having is that even with the numbers at hand, the cylinder heads in my garage show the same as the above advertised measurements, but all of these intake manifolds are never on target of actual Chrysler cylinder head port dimensions, from what I can find and what I can meausre from what I have on hand.

These are the two intake manifolds that I am considering using, that I have on hand -

Edelbrock 2176 Performer advertised port dimensions - 0.97 x 1.95
Weiand 8022/8007 Stealth/ Action Plus advertised port dimensions - 1.00 x 1.96

My Weiand 8007 does not follow this advertised size, for some reason. It does not have Action Plus cast in it anywhere and it is a pre W logo manifold, so the only characters on this manifold are "WEIAND", 8007 and 180 2P.

I think this is a predescessor of the Action Plus and looks identical in runner and carb design as the other 8007 manifold pictures, but the port sizes are way off.

The actual port size dimensions that I'm getting off of this measurement with a dial caliper are 0.96 x 2.063

This Weiand 8007 looks very similar to the LD4B in it's 180 runner design, but I am sort of guessing blind on port sizes. The LD4B is supposedly the small port size, but so is the 8007 advertised... which isn't what I'm seeing in the real world.

My idea is to keep a small port intake on this engine for velocity, so I really want an LD4B (at least I think I do, but I haven't got my hands on one to measure the ports), but now I'm thinking that due to older casting variations in dimension areas that aren't even advertised (corner radius, etc.) that no matter what I have, I'm going to have a mismatch with aftermarket.

So, with the real world application of this bench racing, should I just gasket match the ports on a smaller port intake with a 318 gasket, do the same on the '302 heads and be done with it?