Carb choice

Petrol Head

Senior member
Mar 16, 2004
West Sussex
Cruising area
Solent + south coast
Boat name
Black Widow
Boat make
Donzi 30' sportsboat
2* 454
Hi Guys

I am upgrading my 454's to try to get close to the 540HP mark as quoted in the edelbrock dyno

The spec calls for 750 cfm carbs.

I have 600 holley's right now, so they have to go.

I would like you're advice on what you think I should buy the holley or the edelbrock?

What manifolds/exhausts are you running?
IN's as per package, performer RPM

EX's are stainless marine.
To really get anything out your cam you're gonna need true 'seperate runner' headers, or close to it.
The spec sheet quotes the normal 2 1/8" dia x 32" headers
Thanks for that Jon

I cant do everything by their book for sure.:cry:

Which would you use.

Holley's or the Edelbrock's?
I think I'm right in saying that a the edelbrock's are only re-badged holleys or Carter quadrajets, so i'd go for holley's.

There used to be some really nice cast ali manifolds that had long separate runners, originally by a indipendant exhaust manufacturer, they are now marketed by an engine builder, Keith Eickert I think, or could be Paul Pfaff.

They were also fitted to the 600hp Volvo motor
It is KE,

Here they are


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I'll have to look out for those pipes on the volvo stand. This year.

I havent had the risers off yet but Tony and Cronky say these have sperated runners up to the riser joint. They have that cast ally design too. I cant understand why the dont rot off, but stainless hadnt had one back in ten years??

I have Gil butterfly tips to work externally into the transom some time and I guess the best time to redo the pipes is when I rework the transom for these.

I heard that the Edelbrocks are carters.

I didnt know they used holleys too.

I was supprised to find that just fitting Stub stacks and freeflow arrestors was enough to put the 600 holleys out of tune. I dont see much point in retuning these things when they are already at the extreme of their operational range.
Hmmmm. I like them !
I personally don't like Carters, so would have holleys every time, with vacume secondaries, not the manual type
Are Carters easier to service and tune than holleys??

The blocks ,standard two bolts.

Reversion hasnt been a problem to date. I think if anything the current valve sizes are probably restricting this.

It might become a problem as the gas flow and C/R improve though.
Are you already using the #7162 cam then?
Matt said:
Wouldn't it be cheaper, and less hassle, to put a pair of blowers on?

This is not hassle to me. I enjoy it.

Simply bolting on the heads that matched the manifolds and cams already in place was the original plan. No hard and fast aims.

A bit of fun

Then I saw that flippin Graph!
jon fuller said:
Are you already using the #7162 cam then?

Cant say for sure I havent read the numbers on them meself.

Tony told me he bought and fitted the performer rpm inlets with matching cams.

The manifolds are marine performer RPM's.
Vacuum versus Mechanical

jon fuller said:
I personally don't like Carters, so would have holleys every time, with vacume secondaries, not the manual type

why whould you go for vacuum secondaries jon??
Much less likely to get flat spots.
If you open the taps real quick with manual jobbies, and the motors are at low rpm's, it may well have trouble 'carburating' till the revs are up, resulting in a nice big flop in the power, vacume secondaries wont let that happen. just MHO
Thanks for that.

I would like the Vac secs too . I would prefer them to function with load rather than just follow track the primaries.

I ask because I am anticipating a problem .

I think the bigger valves and higher compression ratios bring with them less idle vacuum and a generally a more unstable idle?
here,s 4 edelbrocks,carters,webers,federal mogel call them wot you want,they are not edel brock quadrajet spread bores .
these are750 cfm marine carbs and work well on these 700hp blower motors with no flat spots from 850rpm-5250 at 6psi boost.they also give better fuel returns than holleys ,tried both


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hutchy said:
tried both

Thanks for that, hve you run them on motors without blowers too?

I imagine you have a good idle vacuum with that setup!

Very nice.

More pictures please!


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