bck

After finding out my blocks were no good I had to repower on a limited budget. The short blocks I got are 540s, 8.8-1 comp, no cam yet. I would like to be able to use my old rectangle port heads for the sake of saving a few bucks. Would they be OK on this motor ? What about the stock GM high rise dual plane intake? Please don't tell me I have to spend money, if you saw some of my old posts you can figure I've already got the most expensive 20 year old formula here. So rectangle ports and a dual plane on 540's--good or terrible? I will spend if necessary, and I would be happy with 600 hp. Thanks.

Pat McPherson

The heads can work but not likely the intakes...

KAAMA

iTrader: (1)

You could use a dual plane intake, but I believe you'll make more HP with a single plane intake with 540cid. A friend of mine had a pair of naturally aspirated 540cid engines built for his boat a few years ago. He used a Crane 741 cam (Hydraulic roller 236*/244* @.050" lift on 112* lobes), Dart cast iron 308cc runner heads with a little bit of port work (nothing major), 8.8 comp ratio, Holley 850cfm carbs sitting on top of some GM dual plane intake manifolds. I can't remember exactly what RPM they made peak power at, but they made 595hp on the dyno---it was somewhere around 5200-5500rpm or so, but I will find out for sure and post here.

By the way, those HP numbers are with full length tubular DYNO HEADERS and for the most part you will be down about 20-40hp with a aftermarket manifold type of exhaust system.

So, agree with Pat Mc on the GM heads, and intakes. The GM rectangle port heads will work for you on 540cid, but a helpful thing to do would be to do some exhaust port work on those heads as they are pretty crude as they come in stock form.

PatriYacht

Be careful if the heads and blocks are different generations. Using Mark 4 heads on a Gen 5 block will cause major water leaks because the water passeges don't line up.

bck

They are gen6 blocks. What I get so far is that the heads aren't the best but OK and intakes being so much cheaper should be changed to single plane. If you could change the heads what would you use? Any other GM heads you would consideder? I was thinking the large ovals would be too small for 540s. Thanks for the help.

PatriYacht

Do some port work on the exhausts, get a couple of used Dart single planes and call it good. A set of aftermarket alum. heads with inconel exhausts will cost 2500+. With cnc porting they're 3000+.

Pat McPherson

The Edelbrock marine aluminum rectangular port heads would be my choice if your on a tight budget.
But if your current heads are in good shape and match the blocks, save you $$ and use them.
I have a friend that built a 540 from a 502 using the stock heads and a Crane 741. I think it dyno'd 565HP at 5200rpm with a 800cfm carb and dual plan intake. Switched to a single plan and 850cfm carb and gain about 25HP.
I also know another fellow that had a 540 built with GM rec port heads, single plan and 950cfm carb. His engine dyno'd at 630+HP, but that was with a solid roller cam at like 5800rpm.

cstraub

The OEM heads are more then capable of making 600 HP on 540 CID, but to do so unported will take a 'healthy cam". Now with some port work and a milder cam you could do it.

The intakes really don't have enough volume for that kind of CID. Will they work yes, but would be a bottle neck for your goal of 600. As stated I would go with a couple of single plane intakes. You can pick up the cheap imorted single planes for BBC for around $180 each. Put a nice 4150 series 950 on them and you'll be set.

bck

Thanks for the advice.

KAAMA

iTrader: (1)

Okay, my friend emailed me the dyno sheet on one of his 540cid engines from a few years ago. It made 586hp @5400rpm, and 635 ft. lbs. of torque @4300rpm. Comp ratio was 8.5