Thread: Newbie with 307 Questions?

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I'm with Tech 100% on this one - you can not change(reduce) the cfm without changing the physical size of the carburetor body or adding a restriction plate (like sanctioned race bodies require - different story altogether).

That said - If you want a bit of balance between performance and economy, go with a 600cfm carb - like an Edelbrock 1406. Electric choke and very solid design. You may find it a bit rich out of the box and need to re-jet, but try it in the stock configuration first and see if you're satisfied with the performance. I've used a lot of the 1406 carbs very successfully.

Summit SUM-210216 is a 750cfm Quadrajet (rebuild) which is also an excellent carb and was GM's choice for a lot of years on everything from 305 - 454. Great response off idle and there's nothing like those big secondaries when they come to life for a bit of tire chirp in second gear and a wonderful deep growl that lets folks around you know you've got more than a timid mouse in there! This is probably my all time favorite carb but I caution people that it is way too much fun (and perhaps addictive) to kick the gas pedal and your economy goes right out the tail pipe!

Regards,
Glenn

I'm gonna put the whole thing together and run a DynoSim on it, but I'm waiting for a reply from Northern Auto Parts to tell me what the compression height of their Sterling (Federal Mogul???) part #235NP pistons is. Not that you're going to change pistons, but while I'm doing it, I want to start a new thread on a cheapo 307 build using 283 pistons and 400 rods. 307 pistons are hard to find anymore, but there are still 283 pistons available from several sources and they'll work with the 5.565" rods in a 307. I just need to get the compression height nailed down so I know what to say in the thread about block deck height and gasket thickness. If anyone knows this CH info, please post it. I want to use a flat-top piston so I can create a good squish. I hate those fosdick stock Chevy pistons with the hollowed-out crowns.

For now, I will say that the 305 heads look like a good bet for a budget build. I found some information on the 416 heads while surfing and will pass it on. Chambers are 58cc's, valves are 1.84"/1.50" and stock flow numbers are as follows:
0.050" 31 15
0.100 63 37
0.150 92 61
0.200 116 78
0.250 134 92
0.300 157 101
0.350 170 105
0.400 182 107
0.450 189 109
0.500 195 110
The 601 heads may be close to the same. I don't know since I found no flow figures on them.

Having looked at flow numbers on a multitude of different cylinder heads until I'm blue in the face, I would say that these numbers look very realistic. I'll use them on the DynoSim pull.

It has been said that these are thin wall castings, so you probably don't want to go nuts hogging them out or cutting for larger valves if you don't have to. Personally, I agree with the idea that the bowl and valve seat area are where the choke points are in any cylinder head, so maybe a little work in there with cartridge rolls to smooth things out a little and call it good would be the order of the day. I wouldn't try to do any port matching at the manifold/head intersection. You'll end up with a cross-section view that looks like an Anaconda swallowed a pig. The increased volume at that point will slow flow down and may result in fuel falling out of suspension. A real good professional 5-angle valve job with a 3-angle back cut on the valves would probably be worth its weight in gold.

Standard Abrasives has a nice little porting kit that can be used by a home hobbyist to clean up the bowls and chambers. Ideally, an air-powered or electric-powered die grinder would be used with these, but in the old days, I used a 1/4" or 3/8" drill motor to do it. It just takes longer and you have to let the drill motor cool down between grinding sessions. Standard Abrasives also sells individual cartridge rolls and such if you can't spring for the $52 price tag on the kit.
http://standardabrasives.carshopinc....d/52221/260001

If you find that you have to replace many valves in the boneyard heads, you might consider buying a complete set of valves with reduced stem diameter in the bowl area. They'll help the flow figures a little.

And again, if any of you fellow or gals can help me find some readily available pistons for cheap, I'd appreciate you sharing the source. What I need is 283 flat-top pistons, 3.875" diameter with oversizes available up to 0.060" and a compression height in the area of 1.795" to 1.805". Northern Auto Parts has them in the part #235NP for $12.95 each, but I don't know the compression height yet. Thanks, Richard.

Glenn and Richard are dead on......DO NOT ATTEMPT TO CHANGE CFM or tame a carb down by disrupting the air to fuel ratio. Air is air. It needs the proper amount of fuel to be correct regardless of the size rating of the carb.

Tech,

I look forward to seeing the thread.

Originally Posted by techinspector1

Depends on what duty you have planned for the motor. A rule of thumb for a street/strip motor is to use heads with intake runner size at 1/2 cubic inches. 307 cubic inches X 1/2 equals choosing a runner size of 153.5 cc's. Moving up to the first commercially available aluminum cylinder head, if I were tasked with choosing heads for you, I'd choose the Edelbrock #60879 fully assembled units. These heads have the early manifold bolt pattern so you can use any of the standard early Gen I manifolds, although you'll have to use centerbolt valve covers. The small 165cc intake runners and 60cc chambers will be an excellent match for a "stroked 283" motor such as the 307. Springs are rated for max valve lift of 0.575", so you can run just about any cam you want to with them, within reason.

Cutting the block decks for 9.000" block deck height, using an Edelbrock #7310 head gasket and flat top pistons with a 1.675" compression height will put the static compression ratio at 9.74:1 and the squish at 0.038". I'd choose a cam with duration around 225-230 degrees at 0.050" tappet lift and use a 2800-3000 stall converter.

If you want, I'll put all the info into my DynoSim and choose a cam that will be tailored to your application. You may have to change the rear gear though, you can't run this compression ratio and a bigger cam using a stock 2.73 rear gear (for instance).

If I were not going to go to the trouble of building the motor and just wanted some aluminum heads on it, I might choose an Edelbrock with a larger chamber (64cc's), even though the runners would be larger and port velocity would be down some over the 60879 heads.

Please run the DynoSim and see what you get.

Originally Posted by gte436e

Please run the DynoSim and see what you get.

Can you post a photo of the piston crowns in the 307? And can you measure how far down in the bore the pistons are at TDC?

I can't yet, I don't have it broke down yet, or even out of the truck for that matter.

Does anyone know if casting #14102187 will fit on a 307?

14102187 is listed as a cylinder head that fits a 1987 thru 1999 305 engine. It has 55cc chambers and 1.84/1.50 valves (yes 1.84 not 1.94). The useage is listed as boat/car/truck so it was a general use head casting.

mike in tucson