Anyone have any idea what kind of HP you can make with these?

Not good heads compared to what’s available today, they are a knockoff of the GM 990 head. That said they will support at least 750HP

quote:

Not good heads compared to what’s available today, they are a knockoff of the GM 990 head. That said they will support at least 750HP

Ed is correct, but he's prejudice towards anything 990 related
Merlins are reportedly much heavier than oem GM stuff so that sucks. I have a set of Grumpy Jenkins heads I just acquired, I believe they are the same thing. I'll weigh them.

650-700 is easy on a 454, 700-800 on a good 496 but you suffer the weight penalty.

The Merlin heads I saw many moons ago were Dart heads, they had improved exhaust ports for sure. Don't remember how much better the intake ports were off hand. They certainly weighed a lot more than stock steel heads for sure. I don't know what Work Products did with them since. The Grumpy version of those heads were better also. Weight is the big factor,, I wouldn't be surprised to hear that they are 20 to 25 lbs heavier per pair than stock heads.

I weigh a set years ago, I believe they were 76lbs each heavy sobs for sure. Jegs list their shipping weight as 88lbs.

Ran Merlin's on 555ci motor for a short while. Car ran 9.8s in 3700lb 67 Chevelle.

Switched to 335 Dart Pro 1, no other change. Car went 9.6@144.

Huge weight difference and obvious HP gains. All in all, the heads performed well.

Fuse ignited. Wait for it.....

You can make them work well for what they are, but I've never held a heavier cylinder head.

Even the '990 or '188 heads are boat anchors like all BB iron heads

Last time I did a pair of '990's my back was not happy lugging those things around and in and out of my pickup

The aftermarket heads are even heavier for sure....

They can make good power though.....all of them....

Dart Pro-1's Aluminum are scary lightweight heads.....Even compared to a regular Dart like a 320 or a Brodix....

They do work well and I've used them a few times....Dart Pro-1 325-335. The weight savings is gonna be around 80lbs over iron anything......

At 80lbs each, you’ll bust a gut putting them on the block. I had bought a set when World made them. Definitely better than your std LS6 head.