Build a 420 hp engien with 781 heads???
02-14-2009, 10:19 AM
#3
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.
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.
02-14-2009, 02:01 PM
#5
Registered
Thread Starter
Join Date: Sep 2007
Location: Gaylord, Mi
Posts: 2,573
Likes: 0
Received 0 Likes
on
0 Posts
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.
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.
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?
02-15-2009, 07:46 AM
#8
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!!! 
