Am I getting the hint that a 425 with Q-jet carburetor and Q-jet manifold are the way to go on a stock engine.
Yes in deed, if one were to spend $$ on NH head porting, to get the most out of those $$ spent one would need to have the intake flow at least the same amount the heads flow to reap the benefits of the port work or have a custom made that will.
i was the first one years ago to say on the nail head site the intake was the bottle neck when trying to get high flowing heads, actually you need 15-20% more flow for the intake then the heads flow. the eelco 2x4 with port work will keep up.
if anyone is interested a stock square bore iron intake flows 234 avg cfm. an eelco 2x4 stock flows 245 avg cfm with a wide difference in flow between runners. i sent my 2x4 to Gessler he got 264 avg cfm, i sent it to gs Bob our nail head porter a few years latter to check it out and messed with it to get 275 cfm. some where i think there is a thread on the Q-jet intake flow, i know it has a bigger plenum forgot on flow numbers if there better.
well another false hood. Walt posted gesslers Q-jet numbers back in 2013 and the Q-jet intake avg 230 cfm so the same as the square bore of 234 avg cfm. reason why Q-jet performs better it is a 730 cfm and the afb carb is a 575cfm. so put a 750 or 800 cfm edelbrock on your square bore for a cheap way out.
Tom Telesco would know for sure, but I suspect that although the 425 and 401 cranks will interchange, they have to be balanced differently. The 425 has bigger rings and pistons and therefore they would be heavier then the 401 slugs.
So.....over the years i have had at least 25 cars that should have had 425's in them......Riviera GS's....WildcatGS's...Electra's........only 4 of them had the original 425's in them....the rest all had 401 replacement blocks in them.... Why you ask ? Because the 425's had a problem with sand core shift when they cast the block. You had many of them that had thin cylinder walls on the front and rear cylinders depending on how the core shifted.They were fine until the gas went to crap in the late 80's and you could not get premium every where. Get some bad gas on a hot day and get on it and BOOM.....you split a cylinder wall from the spark knock and detonation. I would never build a 425 without ultra sounding the cylinder walls. Plus overbore 425 pistons are hard to find compared to 401's........ How many of you have cars with the original 425 still in them....be truthful...... Peace WildBill
I have 2 66 Wildcat GS's with the original engines. Mine is crated and I am building a mellow 401 so I can drive it again. No more racing the old girl. Jenn's still has the running original engine under the hood. I have had several Nailheads over the years and the majority were 401s
must be the luck of the draw. i rebuilt a 425 28 thousand over bore gs Bob wanted it. then did another 425 needed 38 thousand to clean up plus was stroked to 3.75 that one was blocked filled and always ran hot and fill started coming loose besides. took the crank rods and pistons put them in another block [no fill this time] obviously had to bore that block again to .038 over too.very lucky never had a problem with cylinders on any of the three.
Simplified: 401= 4-1/16" bore 425= 4-3/16" bore Not much difference. Heads, block, crank, all the same. Some camshafts were slightly different, but otherwise not really noticeable . 401's and 425' were painted green and the 65-66 were mostly painted red as also the 401's were too.
