[Billnova70]

I am at a crossroads where I am not sure where to go with my build. I would appreciate some advice.

I have a 70 Nova with a 307, turbo 350 rebuilt in 2014 with stock stall converter and a posi 3.73. At first it was a no brainer, ditch the 307 and get a crate motor then I found out the engine has been modified with the following:

Engine built in 2014: Bored 4 inches over, Z-28 cam (unknown specs), World Torquer SR 305 heads, roller rockers, Edelbrock manifold, Holley 600 carb, MSD billet distributor and 6AL box.

Here is the dilemma, the performance isn’t what I would expect from the motor and rear diff combo. I don’t need a 11 or 12 second car, but 13’s would be nice. My guess it is in the 15’s now. The engine could use some fine tuning which will help some, but not sure what else would get me my most bang for my buck. Stall converter, shift kit? Do I give up on the built 307?

Thank you for the opinions.

 

[wht73]

It’s a 307 bud. A nice 10” converter “could” help. I have a street fighter converter in my basement that worked real well with the 3.73’s
You could start by replacing it with a 350 or more. This would be a large improvement.
I took out a 575+ hp 406 and put a 89 iroc 5.7 in over the winter and had fun clicking off 13.80’s
Used 29yr old engine with a huge single plane intake. It was actually fun going 3.2 seconds slower! Lol
Purrs like a kitten!

 

[Billnova70]

Thank you for taking the time to reply. I was full in on getting a 383 stroker, but when the engine builder told me it was bored 4 inches over and was basically a 350 and all of the other upgrades, I thought it could be salvaged.

I am sure the engine could be tuned better or could use a new carb, but I’m not sure how much more I would get out of it. What stall speed for the converter do you think?

 

[wht73]

Honestly I don’t know what stroke a 307 has. I’ll have to look it up.
So “if” it is, I’d start with raising base timing to at least 18* if not more and limit it to 36’ish.
If your base timing is low that will feel like a wet fart out of the hole. What intake and carb is on it? Is it a solid lifter “z28” cam?

 

[wht73]

Looks like a 307 has a 3.25” throw so that would equate to a 326ci unless he put a 3.48” crank in it. Then you’d have a 350” engine.

http://www.aces.edu/~parmega/sbc.html#307

 

[Billnova70]

It has an Edelbrock performer intake and a Holley 600 carb with a 1 inch spacer. I get the occasional backfiring only when letting off the throttle completely.

 

[wht73]

I'd also remove spacer for now (unless it's an adapter/spacer)and check timing.

 

[Billnova70]

Makes sense on the spacer. Also, I saw the same thing about it being 327 and not a 350. The builder has been trying to find the book where he wrote the specs. Might be a 350 crank, but I don’t know.

Outside of it running less than perfect, I feel that the transmission is holding it back. Tossing around the idea of converting to a manual, but might do the less expensive of changing the converter and adding a shift kit.

 

[wht73]

How many inches of vacuum does it make?
2500/3000 converter and the timing set and you will be happy! :yes:

 

[Sheepdog]

Do a 5.3 LS and 4l60e swap. Throw in a nice cam and you should be good to go.

 

[wht73]

That didn't take long! LOL!

 

[Billnova70]

Just took the carb spacer off and saw a slight improvement in the rolling starts with still some back firing. Haven’t had a classic car in 25 years so I need to buy a vacuum tester and a timing light. Also, the MSD distributors come with different springs, so I am not sure which is the right one.

Also, you are right about the LS, just can’t swing that right now though.

 

[Billnova70]

Just got off the phone with the engine builder and it is a 350 steel crank, so with the bore, it should make it a 350.

 

[wht73]

Just got off the phone with the engine builder and it is a 350 steel crank, so with the bore, it should make it a 350.

Cool! Service on Sunday!
Ok do the stuff I mentioned.

 

[Billnova70]

Thanks for the help, as you can see by my above post, I took the spacer off. The guy who built the engine said that heat was boiling the fuel in the carb and making it vapor lock, so he added the spacer.

 

[wht73]

OK next time you talk to him ,ask if he blocked off the heat risers in the heads if they have them. Never had that problem as my heads don’t have them.
Is this a vacuum carb? Open or 4 hole spacer? Tomorrow do timing and report back.

 

[wht73]

See what springs are in the dizzy. If the two heavy silver ones are there, put blue ones in.

 

[g2072]

The 307 engine came with a 3.875 inch bore and a 3.25 inch stroke. To make it a 350 inch engine you would have to bore it to a 4.00 inch bore and add a 3.48 inch stroke. At some point you have to ask yourself if you feel comfortable throwing performance parts on a factory GM block that is already bored .125 AND the weak point of the whole engine is the block. Do yourself a favor and go find a decent 350 block and start from scratch on a short block build. You can always use your upper half if they are in good shape. The way the 307 came out was they used 283 blocks with 327 cranks with a 5.7 rod.

 

[wht73]

Its already done. He just wants to tune it better so he could save for a 406.

 

[Billnova70]

I hear you on the 4 inches over. That is the limit on those blocks. It is my understanding you can’t even go that far on blocks made a year or two later.

It is already done, so I would like tune it and add performance to the transmission and what ever else I can do that would be a benefit now and for when I eventually drop the money on a bigger/better motor. It is technically a 350 now, so I imagine I can get some decent performance with the correct tune and mods. All recommendations are appreciated.