Mark IV BBC - convert from flat tappet to roller questions

[brianwhiteboy]

Hoping some of you gurus can give your advice here. I have a 21’ open bow daycruiser jet böte. I’m not interested in setting any speed records (other than a slow one) just keeping her reliable for the next 20 years God willing.

Got a Mark IV BBC block that I’m doing a refresh on. Currently on stock bore (30 year old boat) that’s going .030 over. Stock peanut port heads with stamped steel rockers, stock valvetrain etc.

It has a hydraulic flat tappet cam, I’m sure a mild grind for whatever the boat companies were using back then. I’d like to upgrade to a roller hydraulic, mainly to avoid break in procedures and ease of replacing lifters down the road. Maybe it’s not the most logical or sensical decision but I’d like to think that it’s a step in the right direction as far as parts upgrades.

That being said, I know I can do a retrofit roller designed for a Mark IV with a cam button, reinforced timing cover etc. It sounds like I can also do a Gen 6 cam since I have the retainer plate holes already tapped and run a Gen 6 timing set and avoiding the cam button.

Looking at the Comp Cams catalog though it sounds like they recommend adjustable rockers for their Gen 6 hydraulic rollers and at this point that may be more than I want to do. I’m ok leaving the stock non adjustable there. I believe they recommend their spec springs for whatever cam you run.

My last boat had a Gen 6 BBC with a hydraulic roller and the same heads and valvetrain and it was reliable. I’m looking to duplicate that set up here without delving into way more head parts.

What says the peanut gallery…other than running it the same way I took it apart lol. Mark IV cam or Gen 6 cam?

 

[rivermobster]

I'd say call the tech department at Comp directly. Get their advice and do what they say.

Or, if you're having someone do this work for you, follow their advice/recommendation.

You don't wanna be the guy that says...

My friend told me that was the best way to do it, when something goes wrong down the road.

Yano?

 

[UltraLucky]

I just did this on an old 454 Mag Mark IV Block. Went with the retrofit cam. Was around $2500 in parts just for the conversion, Cam, Lifters, Pushrods Timing chain and gear set and rocker arms and guides, springs retainers. Teague gathered all the parts so they were compatible with each other and my engage specs.

 

[Shlbyntro]

my opinion is that theres really minimal gain from switching to a roller cam if your not trying to squeeze every single pony out of it (10ish hp like for like)Comp makes really nice complete flat tappet hydraulic cam kits for $4-500. use a breakin additive and really all you have to worry about is the first 20 min.

thats what I ultimately went with for my mkIV Hallett budget build

 

[brianwhiteboy]

my opinion is that theres really minimal gain from switching to a roller cam if your not trying to squeeze every single pony out of it (10ish hp like for like)Comp makes really nice complete flat tappet hydraulic cam kits for $4-500. use a breakin additive and really all you have to worry about is the first 20 min.

thats what I ultimately went with for my mkIV Hallett budget build

Definitely a valid point. $500 flat tappet vs $2500 in roller conversions for minimal gains is something to think about.

 

[brianwhiteboy]

I'd say call the tech department at Comp directly. Get their advice and do what they say.

Or, if you're having someone do this work for you, follow their advice/recommendation.

You don't wanna be the guy that says...

My friend told me that was the best way to do it, when something goes wrong down the road.

Yano?

Definitely my next step. Just wanted to gather opinions and info before I make that call.

The Comp Cam advisor will have to battle the RDP Pro Tech Support when he takes my call!!

 

[Teague_JR]

unless you are going to change the heads, and maybe intake, carb and spin more RPM (make more horsepower)..... Keep it flat tappet just go a little bigger for fun

That being said you could find some used GM iron heads that are way better than the peanuts for cheap... just magnaflux them to check for cracks. it kinda comes down to budget and whether you are happy in the HP ballpark you were or are looking for a decent amount more

 

[obnoxious001]

Looking at the Comp Cams catalog though it sounds like they recommend adjustable rockers for their Gen 6 hydraulic rollers and at this point that may be more than I want to do. I’m ok leaving the stock non adjustable there. I believe they recommend their spec springs for whatever cam you run.

Mk IV heads are going to have adjustable rockers already, and stock rockers can work fine if you see no unusual wear. Non adjustable started with later generation heads.

As John Teague stated, spend a little money on better heads and an improved flat tappet cam. In 40 years of building engines I have never had a legitimate flat tappet cam failure with one of mine. Make sure to get someone who knows what they are doing to set up spring pressures on the heads, and make sure the engine will start and run immediately for the break in.

 

[azsunfun]

I can help you get 100% roller if you want to take in aluminum cans! Should take 6 month's or so.

 

[74 spectra20 v-drive]

Brian, I would take the advice of the experts, Mr. Teague and Mr. Obnoxious, I went down this road building the engine for my Spectra, I had Roller Envy, unless you are going big and bad and high RPM, stick a flat tappet in there and run the piss out of her

 

[brianwhiteboy]

Brian, I would take the advice of the exerts, Mr. Teague and Mr. Obnoxious, I went down this road building the engine for my Spectra, I had Roller Envy, unless you are going big and bad and high RPM, stick a flat tappet in there and run the piss out of her

I agree. After reading the opinions of well respected builders and more engine savvy peeps than myself I really can’t see going roller right now. With the extra costs and peanut port heads it’s not worth it for what I want. I’m not looking for more horsepower but just want a cruiser. I don’t want to make wholesale changes right now.

Comp was closed early but I talked with Summit and got some info. Comp has complete cam kits with lifters, timing chain, springs, rockers etc. I think their mild marine cam setup will be the way to go and I can get all the matching components.

The initial cam break-in is what got me thinking about alternatives. But like anything, take the time to do it right, ask questions and plan accordingly. I rebuilt/reassembled my big block on my last jet boat and she ran well. Hopefully I can duplicate that effort here.

I appreciate all the info gents

 

[mash on it]

Is buying a flat tappet cam twice less expensive than buying a roller cam once?

It's not 1955.

Roller all the way.

Dan'l

 

[farmo83]

Don't you still have to run valves with a flat tappet vs a roller ?

 

[n2otoofast4u]

Big fan of Joe Gibbs break in oil.

 

[renodaytona]

I went with the full Teague hydraulic roller valvetrain when I built my blower motor. Told them what I had prior, what I was changing and they put a complete package together for me.