Can I build a 420 hp 454 with 781 heads? If so how?

no problem, need about 9.5 or 10 comp, port the heads to gasket run a performer rpm air gap, 750-850 dp and a good cam...done...Rob

Yes! And you might be able to get there without upgrading to the larger size valves, but DEFINATELY you will need to replace the stock Merc exhaust with a better breathing/flowing aftermarket exhaust system....something comparable to Stainless Marine, GIL, Dana, etc.

The 781's have the smaller 2.06"/1.72" valves. You MIGHT be able to obtain 420hp without having upgrade to a larger valve size,...but if you want anything much beyond 420hp you may need to consider the larger valves. Whatever size valve you use, you most likely need to upgrade to a stainless steel valve with Inconnels on the exhaust. Also, you will need to install hardend valve seats ($15 each/labor), and definately need to have the heads bowl/pocket ported ($250). Have your cylinder bores "bore notched"---JimV says it is worth about 30hp/tq on the dyno and it only costs about $80 or so---cheap/easy power! Install a hydraulic roller cam.

By the way, you're not too far from JimV's shop----have him port your heads and do the "bore notch" job on your block. Then have your machine work done at WESCO (Dave Wesseldyk's shop). Dave and Jim's shops are within about 5 miles of each other.

This is good news for me. I called Dave at WESCO and he didnt have any long bloks but hearing this mabe I can put my motor back together.

As you may remember I lost a cylinder on my engine and seized the crank.

I had a 454 2 bolt with cast internals, 781 heads, quadrajet carb and edelbrock rpm performer intake.

So my goal is to get to about this 420 mark,,,,Ill need to scrap the old block(I dont want to resleeve it) get a forged crank and pistons new cam and a 750 carb. Plus the valve work mentioned above. Oh yea scrap the stock manifolds too. Ive been watching ebay for manifolds but havnt seen what I want or seen somthing I feel comfortable in buying.

I do appreciate the help you guys have offered. any more advise?

Also tell me who jim V is and what is bore notching?

Do a search, you will find more hits than you will have time to read. Worth every penny you spend

You need to call Dave and explain your bad cylinder condition to him---because he might still be able to sleeve it. If he says yoy can get away with sleeving it then you will be fine. To sleeve one cylinder is about $110...You might be able to save your block!!!

I will bring back one of Jim's head porting threads and then you can see for yourself who "JimV" is.

I did a search about bore notching and got nothing. Do you have a number for Jim V?