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Old 01-26-2010, 04:03 PM
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a different 307 sbc build, need some advice

Hey everyone, I got a couple questions on a build i've been working on since early spring last year. To sum it up i put a 307 sbc out of my dad's 73 nova into my 85 rx7 and i've been driving it around for awhile but i feel like i picked the wrong parts to put on it when i built it. heres what i have.

307 sbc, stock bottom end rebuilt, .194 heads refreshed and milled .010, edelbrock performer rpm dual plane intake, holley 600, summit k1104 cam (.465 lift int/exh 282/282 duration), stock exhaust manifolds, points vacuum advance distributor, timing set 8 deg advance. Behind it is a T5 5speed from a camaro and a 3.90 lsd rear end.

The motor sounds great but i feel like theres honestly not enough power for it being a v8, and i feel like the throttle response is better when the hood is up as weird as that may sound and i have a hood scoop just not a very big one. the car can't be more than 2600 pounds and i feel like i never get pushed in the seat when i mash on it. What do you suggest I should do aside from swapping more cubes in? my thoughts have been some kind of different cam, put my headers on (shortys), other than that i dunno. any advice will help thanks alot!

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Old 01-26-2010, 04:09 PM
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Need more info. When you did the build were the pistons replaced? What cc chambers are the heads? what casting number are the heads? Points distributor? best place for points is the trash, get a pertronix conversion unit. 8 degree`s before top dead center is too low. What is the vacuum advance connected to? I manifold full time vacuum source (pulls vacuum all the time, even at idle) or a ported source? Exhaust manifolds belong in the same place points do, however I can understand the cost isn`t cheap for headers for this app.
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Old 01-26-2010, 04:52 PM
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Pistons were reused, they weren't damaged or anything. Casting number i will have tomorrow i don't remember off the top of my head. So you think i should put my headers on and upgrade to HEI or this pertronix? the only question i've had with that is how to set the timing with those. the timings set to 8 deg advance with the vacuum plugged and when it hooks to the carb and the timing jumps to 30 something degrees
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Old 01-26-2010, 04:58 PM
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As above ^^^ Lose the points, more timing. Those Shorty headers are no better than manifolds.
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Old 01-26-2010, 05:03 PM
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Try more Initial timing 12-14deg. Setting the HEI timing will be the same as with the Points distributor. you may need a spring set for adjusting Mechanical advance and adjustable Vacuum advance canister unless you buy a new HEI. They're cheap, check Skip White / Ebay etc..
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Old 01-26-2010, 05:42 PM
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Set the timing to 12 degrees before top dead center with vac advance disconnected and plugged. Lock the distributor, reconnect to a full time manifold vacuum source (one that pulls vacuum even at idle), recheck timing, it should land in the 20 -24 degree area at idle. Test drive and see if you feel any difference. Factory 307`s had 8:1 compression which is pathetic at best.
If the heads you have on it now are stock smogger heads with 76cc chambers the compression ratio is even lower than the factory ratio. Switching to a set of 416 castings off a 305 will be a big step in the right direction. There small chambers will raise compression to 9.5:1, this will help considerably. Make sure you check the mechanical advance in the distributor and make sure it functions smooth. You should install some light advance springs on it. Going to a pertronix conversion kit will give it far better sparking power and it`s alot more reliable. It also removes the hassle of setting points and dwell.
I would also upgrade to spiral core spark plug wires while I was at it. the cheapy solid core parts store wires have very high resistance. For starters, set the timing to the specs given, then let me know how it runs.
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Old 01-26-2010, 07:22 PM
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check you cylinder head casting number here:
www.mortec.com

if you heads are one of the 76cc large chamber smogger 350 heads the cr will be very very very low.

You need to swap on some small chamber cylinder heads.

rob the 1.94 valves from your present heads and build/port a set of #416 305HO heads with the 350 valves and full effort home brewed porting. max shave/mill the 305 heads right to the new intake valve seat edge to reduce the chamber volume and install with thin .015" felpro 1094 head gaskets.

you want as close to 10:1 as possible. you want a finished cylinder head chamber volume of 52cc.

The cam you have requires a modified distributor advance curve.

You can use up to 24deg base timing at idle and 34-36deg at max advance.
Shorten the mech advance curve to allow this. 20deg is typical stock. you want 10 to 14deg adv travel.
vac adv should be 10 to 15deg.

use champion RV8C or AC delco R42T spark plugs in your new killer "poor man's racing head" #416 heads and use 92 octane gas.

get some headers.
http://www.grannysspeedshop.com

Last edited by F-BIRD'88; 01-26-2010 at 07:27 PM.
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Old 01-26-2010, 07:26 PM
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Changing parts would be a bit more costly, but I'd try a different cam...smaller. Something in the 204, 206 @.50 range. Maybe an Isky 256 or 262 Supercam or Comp Cams XE 249H-12 or XE 256H-10 at most. You might not like the smooth idle, but you'll like the lower RPM torque results. The milder valve timing will give you a better dynamic compression ratio.

Another inexpensive solution to up the compression a bit if you do have the smog heads is to switch to a shim style head gasket that is about .015. If it is indeed an 8:1 engine, as Double vision notes, even with the head mill job you probably lost what you gained because most of the rebuild kit head gaskets are the .040" Felpros whereas your factories where probably .026 or so.
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Old 01-26-2010, 07:32 PM
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Or stick with the low compression ratio and bolt a 144 weiand blower on it.
And hang on tight!
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Old 01-26-2010, 08:21 PM
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Quote:
Originally Posted by F-BIRD'88
check you cylinder head casting number here:
www.mortec.com

if you heads are one of the 76cc large chamber smogger 350 heads the cr will be very very very low.

You need to swap on some small chamber cylinder heads.

rob the 1.94 valves from your present heads and build/port a set of #416 305HO heads with the 350 valves and full effort home brewed porting. max shave/mill the 305 heads right to the new intake valve seat edge to reduce the chamber volume and install with thin .015" felpro 1094 head gaskets.

you want as close to 10:1 as possible. you want a finished cylinder head chamber volume of 52cc.

The cam you have requires a modified distributor advance curve.

You can use up to 24deg base timing at idle and 34-36deg at max advance.
Shorten the mech advance curve to allow this. 20deg is typical stock. you want 10 to 14deg adv travel.
vac adv should be 10 to 15deg.

use champion RV8C or AC delco R42T spark plugs in your new killer "poor man's racing head" #416 heads and use 92 octane gas.

get some headers.
http://www.grannysspeedshop.com
ok i'll look at the casting numbers tomorrow and adjust the timing, and i can't use grannys headers my slave cylinder bracket on the bellhousing is in the way of the longtubes. i'll see if i can find a set of 305HO heads around here. what should i set the plug gap to if i switch plugs?
also i used a thicker headgasket because i didn't have them deck the block although i probably should have would it still be ok to run a thinner headgasket?
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Old 01-26-2010, 08:38 PM
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Plug gap with Points .035", with HEI .045"
If the Deck Height is stock, usually .020"-.025" you could still run a thin .015" shim gasket.
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Old 01-26-2010, 08:40 PM
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Could you use a hydraulic clutch release/throw out bearing and long tube headers?? That would eliminate the external Slave Cyl.
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Old 01-26-2010, 11:24 PM
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I picked up a copy of the March 2010 "Hot Rod Deluxe" magazine, and they did an article/engine build using a 283 block, referring to the engine as a "stroker 283". In reality, they juist used .060 over 283 pistons that had a 1.67 327 pin height, aftermarket H-beam rods, and a 327 crank for 316 cubic inches. You might want to review that article for some of the tricks they used. Butch/junior stocker.
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Old 01-27-2010, 12:03 AM
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Quote:
Originally Posted by SSedan64
Could you use a hydraulic clutch release/throw out bearing and long tube headers?? That would eliminate the external Slave Cyl.
technically yes but we're talkin 400 somethin for headers and 200 for the hydraulic throwout bearing and even bigger pain in the *** takin my trans out lol.

i'll have to look for that magazine see what its about.
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Old 01-27-2010, 07:42 AM
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Do what F'bird said. I was going to post the exact same reply until I saw he already did. One thing I would not do is mill them more than you have to, they are a thin casting and I would not chase after every last cc that way unless its for a race only application where its do or die.

I would run a little less initiail timing to start with as well, I'm just conservative about some things I guess. You can always add more as you go.



416 ported heads with pinned studs 1.94 valves
HEI ignition (a cheap ebay unit will work fine for now, you can upgrade it when it becomes a problem down the road) set at 16 initial, 34 total.

Those two changes will make a BIG difference.
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