View Full Version : So, you really want to build up that 307 eh?

07-18-07, 09:50 AM
Well, one of the "issues" with the 307, is pathetic flow of the heads, right?

Look no further. These heads are a GREAT swap (must use aftermarket or 84 and older intake), and outflow ALL stock GM LS1, LS2, LS4, and LS6 heads. Ported they will outflow LS7 heads boys and girls!

And these as cast are excellent pieces, high velocity, beautiful castings. Even made in the USA!


Make sure John @ RocketRacing knows that I sent you. If there is any interest, IM me and I will talk to John about group pricing for CadillacForums members.

Ok, they are probably overkill for a 307, these are best for a larger inch engine, 350 and 403's, on a 350 with a decent cam are solid 10 second runners in a 3500# car, which it what they were designed after, a head that WORKED first. But there is no reason that you can't make a killer 307 out of these, the name of the game is airflow, how much can you get. A too small head on a 403 will never perform like a good breathing 307. You'll need a good cam (keep it small, do NOT go nutty here with heads that flow this good) and gears to make use of the wide power band this engine would have.

I'll talk to my resident Olds guru about a 307 combo with these heads....

Night Wolf
07-18-07, 11:23 PM
Hmmmm, that would be cool!

Kinda like the big block Cads..... nobody did anything with them, then they started picking up pretty quick.

07-18-07, 11:27 PM
I talked to a friend of mine, he said the Olds 307 bottom end is just to fragile to make any real power. The guys who race super stock use 76 and older 350 blocks sleeved to 3.8" with 330 steel cranks. He said these heads would be just too big and the potential to make high hp would kill the bottom end of the engine....

He said the Olds 307 cranks were pathetic and very very weak, and those are the chief weak point and then the windowed weak block is next. The heads of the least of the 307's issues...

Bummer. So a 350 is STILL the best choice, a 403 is better. But a 350 with a 330 steel crank offset ground or a 350 DX bored 0.125 with a 425 crank would be my choice... and the RocketRacing heads....

BTW, John just ran a 9.40 @ 140+ in his Cutlass with a 482 in Olds and these heads. ROCK ME BABY!!!

07-19-07, 08:28 AM
The 200r4 tranny in the 307 powered cars is very weak. So anything you do to this car will destroy that tranny in no time.

07-19-07, 09:39 AM
Stock yes, but built, it can take more power than the 700R4/4L60/4L60E/4L65E due to the better first gear.