88 mark4 big block truck motor

65wagon · Poncho Master!

88 mark4 big block truck motor

CdnGMfan · Canadian Poncho Superstar!

I don't know the answer, but I am thinking the Mk VI heads would be peanut ports. Also, how old of a Mk IV? You can put open chamber heads on a closed chamber long block, but not the other way around. More specifically, don't put closed chamber heads on open chamber pistons, at least not before checking clearances. Something like that.

A little knowledge is a dangerous thing. Trust, but verify biggrin

-- Edited by CdnGMfan on Wednesday 12th of October 2022 03:25:35 PM

65wagon · Poncho Master!

its a 88 im assuming its a mk4 .its still got the fuel pump boss, later motors didn't, the mk 6 heads are just a little bigger than peanut ports which is what I have , 1 ton truck, I didn't know if they did anything to the heads that would make them not work on the earlier blocks

LT1Caddy · Poncho Master!

Never assume..... Get the part number off the heads. Check online for the info, that will tell you if it's possible. Tons of info available with some digging, could save you a pile of $$

seventy2plus2 · Canadian Poncho Superstar!

I believe the correct terminology is Mark IV and Gen VI.

65wagon · Poncho Master!

youre right ive watched youtube and hit the forums , but I was wondering if anyone has actually done this here on the site, the chamber on the gen 6 is small and the runners are bigger than mine , its not a race car this thing tows massive loads im just trying to help it out 7.75 is a little low.

silver steak · Addicted!

Well, I don't know what exactly you are trying to find out, but I'll tell you what I have done.

I used a set of GM Iron square port heads last three digits are 781, and I installed them on a Gen VI brand new long block from GM.

From what I read and was told, the Gen V block did not work well, hence the reason they were discontinued, was because of cooling issues and water channels in the Gen V block not well designed, the Gen VI had these issues resolved, my car runs very cool around 190 degrees F with a 185 thermostat, no leaks . The main reason I went with these heads was because they had been worked on porting and such, I seen them perform on a drag car, I believe my 781's are dated mid 80's .

I hope this helps.

Dale

-- Edited by silver steak on Friday 14th of October 2022 07:44:51 AM

65wagon · Poncho Master!

what im attempting to do is run the gen 6 heads on the mk4 block, I know the 781 castings but im not building a street motor, its for towing . the truck is a 1ton the last square body that came out in 88, ive gotta freshen the motor up at some point so the thought of doing up a set of heads and getting rid of the injection came to mind. the gen6 heads were suppose to be right in the middle of the square port and peanut for flow with a little smaller chamber.

65wagon · Poncho Master!

heres another question, when did gm put rollercams in the BB, I think with all the issues im hearing abut might be a wise step for a work motor

65wagon · Poncho Master!

did some research , gen6 are vortech heads 100cc chambers , mine are 120 or so, 1to2 point bump in compression, both the mkiv heads and gen5 are peanut, gen 6small oval and they bolt on with minimal work. roller cams came out in gen 5 which problem engines.