You may be right. I thought I saw one this morning, but I’ve been unsuccessful replicating the search. Should have written down the part number.
300hp 307
- Thread starter MadDrOlds
- Start date
That last post wasn’t meant to be snarky. It would be scary to think any block could regularly handle 180hp but would lose it at 300.
I follow your point on the duals, and you are technically correct (which, legally, is the best type of correct). But my state doesn’t care about this stuff (no testing) and if the Feds only complaint about my set up was I was running dual cats, I think I’d be willing to fight that one.Roller engines had the peanut, aka "fun size" ports on the 7A heads. Flat tappet 307s had the "full sized ports" as it were. In any case, 307 heads leave much to be desired whatever their port sizes are. Additionally, 307s and later 350s used 1/2" head bolts where 76 and earlier 350s use 7/16". So there's that. You'd be limited to 77 and later 350 heads unless you're going head drilling. TBH, I don't mess with Frankenblocks like that so I haven't done that much research on it. Additionally, 307 #5A 307 heads are very similar to early 350s in combustion chamber size (around 65cc), but later 350 head chambers are huge and would drop compression ratio considerably. #7A 307 heads are totally useless if you want to make serious power. But if you're going to try and use 350 heads, you might as well use the 350 block, too.
Sorry to piss on the parade, but the biggest issue is going to be keeping it emissions legal as you imply in the OP. Which means YOU CANNOT USE DUAL EXHAUST. So good luck with that. No 307 Olds engine I'm aware of ever came with true dual exhaust, thus in order to keep it technically EPA legal, you have to run those street-legal headers into one cat. Then it doesn't matter what happens after the cat. Just passing an emission test isn't the only qualifying factor for keeping it legal. You can't simply half-azz it. It either meets EPA standards or it does not. Maybe if you get a fat azz cat with 3" exhaust. I don't know. It can be done. Factory 4th gen LS1 Camaro Z28s and SSs ran two cats into a single pipe to the muffler then dualed out from there (a la 79-80 Hurst and 442 style) and their stock rating was 310 HP. My stock 2002 SS with SLP Blackwing intake filter and CME muffler/tails dynoed out at 326 RWHP with just a few thousand miles on it. So it's possible, but a stretch with a 307.
It always comes down to if the Feds want to penalize you and if you're worth it to them chasing you down. You bear that burden. Regardless, it's still illegal under the current statutes, so I'm not saying you couldn't do dual exhaust if you wish, but you can't continue to move the goalposts on getting a 307 to 300 hp and say you're staying within your own rule stipulations and that you're doing it legally. Because you wouldn't be. That's all I'm saying.
It's hypothetical anyway, and I just don't see it happening without machining out new parts and customized ECM action. Hypothetically, anything can be done if you throw enough money at it, but in the real world, ROI matters. I mean, you can spend 30,000 dollars to make 300 HP for your 307, but for oh, guestimate of around 3K-4K, you can do a "proper" 6.2 LS swap and make 400 HP out of the gate since you're going to be illegal anyway. At what point would you say it's worth it? I so badly would love to put a 455 in my 85 442. That would be pinnacle in my book. It's why oldsofb and his build always has me amazed at the quality and workmanship of his build. But my ultimate goal for it is almost a 180 away from Hutch's, and that is to get it completely, or as completely as I can, back to stock specs using as many new GM parts as possible. I mean, who's ever done that? Now that right there's friggin' blowing up an ROI with 40 lbs of dynamite.
The 2.07/1.68 valve size in the soon to be released 68cc version of the Edelbrock head will hit the side of the bore on a 307. There is another solution that would easily hit 300 HP but like everything Olds, isn't cheap or easy. It involves the 4" stroke forged 5140 stroker crank. Cutlassefi(Mark Remmel) is getting a batch done shortly. They will be cheaper at $1200 vs his current billet offering. It is designed with a light bob weight so expensive Mallory isn't need to internally balance, a small amount usually needs some removed on the 350 strokers. Factory 330 cranks need 4 or 5 slugs to internally balance with modern aftermarket rods and pistons. That pretty much pays for the stroker crank. It is designed to use LS rods and would need custom pistons in the smaller bore more than likely. That would give 370ish cubic inches. You could probably hit 350 HP/TQ easy even with CCC and stock looking exhaust. You could up compression and cam size slightly and still work. It could still look stock, running factory heads and block. Honestly if I got an orginal H/O or 442, I would go that route. These cars are too rare and valuable these days to make them not look orginal.
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Edelbrock heads will work on a 307, no different than a 68-69 G block 400 that has a stock bore size 3.870.
Hahaha. long stroke 400...the 307 of the big block Olds. Actually, it was one of the worst bore to stroke ratios ever, even worse than the 307. But it shared crank/rods with the 455. Just had a smaller bore. Like the 307, which shares the same rods and stroke as a 350 (307 crank is lighter, though) it was for better emissions. How I hated that engine. Spinning rod bearings on it was no fun.
I’m enjoying hearing peoples’ thoughts. Having read a lot of the prior threads, I knew this would spark good discussion.
PS-it hasn’t been my intention to move the goal posts. No, I didn’t think “nitrous” was within the spirit of the OP, but a fully functioning emissions set up with dual cats…that’s a closer call.
Honestly, the whole exercise was to explore the possible—most prior threads end in two forks “that’s illegal” or “build a different motor”. My real question is how to get a bit more “go” out of the car I have—I don’t need big numbers, or the ability to take big numbers. For example, I think 400hp is a lot to handle in a corvette with traction control, let alone a squeaky old g body. If I wanted to build something really fast, I’d do it in a 69 cutlass or something, and if I wanted to drive fast, I’d explore something newer.
Thanks for the thoughtful discussion
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