Rocker/Intake upgrade advice please...

[MKE - POWER]

Would like to upgrade to roller rockers and change to single plane
intake.
Motor is GenV 454mag,forged bottom,hydrolic roller cam-Gm marine grind@500lift,Gm alum. high rise dual plane intake, with
Gary Williams 750 -4150,EMI Thunders. Heads are large,Rect. open ,088's. Spins to 5000 with a blueprint pump in 21LX Ultra.
Looking to get a few more RPM's without changing the cam.
1) can this be accomplished by installing different ratio rockers?
Stock ratio is 1.7.
2) Will there be significant improvement with a single plane intake
over the stock dual. I was considering the Weiand Team
G#7513 (1800-7300RPM) for clearance restrictions.
What do ya think?
Mark

[MKE - POWER]

Help PLEASE>>>
Somebody must have some thought on this?
?????????

[powerplay230]

Just my 2 cents.. I don't think you would get much of an improvement for the money spent. I know that GM intake is supposed to be one of the better ones out there unless you have a modified motor spinning over 5500. So I doubt you would see much change with just the intake, but I would try hitting up Rexone or Fiat48 or about 6 other guys on here that really know those parts and know there stuff. I myself haven't read any tests on extended ratio rocker arms for the marine big blocks, I know when seeing articles in the past on the 5.0 mustangs etc people were claiming 6-10 Hp gains but there are some guys on this board who really know there stuff and I'm sure would know more about if its worth it. For about the same price you may be able to put one of the 100-200 adjustable nitrous kits on it, ocasional use if set up right wouldn't hurt that motor. Give the guys a day or so to read and respond to your post, if you get no replies pm me and I'll send you a few names...
Rick

[cstraub]

Your putting on "Supporting Parts" that are needed to go upper rpm when you have the camshaft to do so. You may gain a 200 rpm, but the point is if the cam is over at 5000, at 5200 it is just making less power. You need a cam upgrade. If not, save your money, enjoy 04', and rip it apart this winter.
Chris

[Dennis Moore]

You would be much better off installing oval intake port heads and an oval port dual plane Edelbrock intake manifold.
Those large, rectangle intake port, heads were designed for 11.0:1 or 12.5:1 compression ratio engines that run at 6500 rpm and higher. They are way to big for a low compression, low rpm 454 marine engine with a stock marine camshaft (to big for a 502 with a stock cam!). Adding a single plane manifold will make things worse.
Sounds like you have the stock roller camshaft. A better camshaft (aftermarket) would be the best place to increase performance.
Dennis Moore

[MKE - POWER]

Dennis Moore.
" Rect. ports heads too large" ?
The motor is stock Marinepower 454Mag,390hp,8.8-1Cr.,1996 mfgr date.
Why would Marinepower build a motor with heads too large for their application and then put a 2-year mfgr warranty on their product?
My question was realting to enhancing the stock products i have.
If planning to install roller rockers to work with the existing roller
cam/lifters, should I use stock ratio 1.7,or would i benefit from
alternate ratios? I do not want to change the cam at this time.
OBNoxious1:
I understand what you say about a regrind, but it was not my intent to touch the cam at this time.
thanks.
Mark

[Blown 472]

You are not going to see any gain on a stock motor by going with a little diff ratio, what a 1.8 will get you how much more lift? dont waste your money, cam it then worry about that little stuff later.

[Rexone]

I agree with the guys above that a single plane intake and roller rockers would not be money well spent seeking increased performance on the present package. Like Chris said these are supporting parts allowing the engine to go higher when other engine components (like cam) are changed to target a higher rpm level.
An engine must work like a finely tuned orchestra, everyone playing the same notes in the same key with all members targeted at the same level. One or two guys playing the high notes on their own won't make the orchestra sound better.

[Dennis Moore]

Marine Power doesn't build engines. They, like everyone else, (except Mercruiser High Performance) buy complete long block engines from General Motors. They (Marine Power) receive a crate engine, remove it from the crate, install the ignition, wiring harness, bellhousing, carburetion and exhaust system, then paint and re-crate them. The assembly line is not impressive, with only a few people performing all the work. Even the (so called) engine assembly line at Mercruiser's Stillwater OK plant is not impressive (I've seen it).
The two year warranty that Marine Power provides is actually provided by GM (through Marine Power) and only if Marine Power sells the engine to the customer without any modifications.
For many years the only high performance head available from GM was the rectangle intake port cylinder head designed for high rpm, high compression racing engines back in the 60's. To design a better head with optimum sized intake ports for a marine engine was not cost effective for GM. The marine industry simply had to make do with what ever GM made available.
It is common knowledge that the rectangle intake ports are too large for a 454 marine engine.
Dennis Moore

[MKE - POWER]

Thanks for your replys guys.
Looks like the consensus is that cost vs gains don't add up.
I really thought that adding the rockers would free up a few RPM's. Plus they look really COOL!
Thanks.
Mark

[Blown 472]

Originally posted by MKE - POWER
Thanks for your replys guys.
Looks like the consensus is that cost vs gains don't add up.
I really thought that adding the rockers would free up a few RPM's. Plus they look really COOL!
Thanks.
Mark
Who is going to see them under the valve covers? and then you have issues if they dont clear the valve covers and you have to get new ones, then it goes on and on and on.

[powerplay230]

Only reason I suggested a small nitrous kit is because you said you didn't want to go into the motor but cam and head change or little more compression might work as well or better. as even your exhaust might not be helping performance of a stock magnum motor. Guys would a 100 Hp spray hurt that motor and for $450 bucks I thought would be better than changing manifold etc which would probably provide no gains.

[powerplay230]

Well different impeller might be needed if already spinning 5k rpm before adding gas so would need to add that cost also.

[powerplay230]

Would one of the small nitrous kits cause harm or not provide any additional grins? And only reason I suggested different impeller as it looked like he was already near the top rpm range of a stock magnum motor. Asking as I know nothing about jets but do like to learn from you guys!
Rick

[Nucking futs]

the gen v block is a sore subject and piston to valve clerance is very minimal and to recam it you must also put a larger valve releif in the piston.not a good idea to really mess with the engine untill she gets tired and then you can put all the goodies in it.just put a little nos unit on it and that should add the 300-400 rpm your looking for but then your way out of the stock cam curves. just my .02