68 NJConv 454

I'm considering purchasing a slightly used 509 Merlin crate motor. (Merlin II 9.800" deck height, 4 bolt main)
It has a Merlin single plane intake on it with an Hardcore 870 cfm double pumper. The seller had to use a 6" cowel hood to clear this setup in his 74 vette even with an 1 1/2" drop base with 3"x14" K&N air cleaner.
Can anyone recommend a good intake that will flow well on this 509 and clear the L88 hood? I was considering an Edelbrock RPM Air Gap dual plane manifold but some have said this would actually restrict air flow to the 509. The RPM Air gap would flow fine for a 454 or smaller even though the 509 is a low RPM torque engine.
Cam is a Crane Hydraulic Roller 234/242 deg @ 0.050, 610/632 lift
Heads are Merlin Iron Rectangular Port 2.250x1.880 forged valves
Any help is appreciated.
Thanks
-Brett

ZL1powr

The RPM Air Gap works well with an L-88 hood. This link is to a thread where I recently made mods to a base to make a Victor Jr work with an L-88 hood. http://forums.corvetteforum.com/show....php?t=1777588

68 NJConv 454

I've been following your thread. Very nice work. My only concern with the RPM Air gap is I've been told it will restrict airflow to the 509. It works better with a 454 base engine then the bigger cube blocks. Whats your opinion on that?

427Hotrod

It will do fine on the relatively low RPM Merlin 509 combo. Over on the Chevelle Forum there's a guy who did a bunch of back to back testing on his 505" motor in his drag Chevelle. He even has big solid roller etc. When all was done the Air Gap was slightly quicker than a Victor Jr and just a hair slower in MPH in the 1/4. The added low speed power on this combo will be nice with the dual plane. The Air Gap is an amazing dual plane!

JIM

James

I have a 509 CI BB in my 69 vert. The motor made over 550HP on a DTS engine dyno using a Wieand Stealth intake and a Holley 1050HP series carb. This combo fits real nice under a Ecklers L88 style hood with the cold air chamber installed and a L88 air cleaner from Paragon. I have been very happy with the intake, air cleaner, and hood configuration.

69ttop502

The Holley Strip Dominator is a perfect fit with the L88 and airbox as it has the proper back to front slope to it. I am running it on my 502 with L88 hood. On your application I would agree with Jim that the airgap may be the way to go. The other option is the GM 163 manifold, it is the same manifold as the original L88 manifold except the center divider is still there, making it a dual plane. Any one of the 3 will work great on a 500 inch motor.

Little Mouse

I forgot to mention friend of mine has been saving a lakewood
scattershield for me, I have decided not to ues it. Would
not cost nearly as much as new.

427Hotrod

Good point there on the Strip Dominator intake. I got hung up on whether the Air Gap would work and forgot to offer alternatives. Yes,,we know it fits under an L-88 hood for sure. And on Nick's pretty mild 540" motor it picked up literally 30 RWHP over the GM hi rise dual plane!

Then there are my other favorites..the old C-427/C-454 Edelbrock dual planes. Looks sorta stock..just bigger!


JIM

Little Mouse

The merlin people are proffesional engine builders all kinds of access
to dyno work. They used a modest 870 carb on a 509 cube engine
to match its low rpm hydrauilic work. The engine ended up with a
single plane on it. I would think they tested the RPM dual plane
probably several brands of manifolds. The one that made the best overall power for it, more then likely already on the engine.

427Hotrod

I would bet Bill Mitchell used the best combination of HIS parts to build the engines. Lots more profit in it that way. If he was truly after the BEST combination of parts..that 509 would make a LOT more power than it does.

I happen to know a machinist who used to work there...got lots of Bill Mitchell stories for the last few years. Do some searching on Bill Mitchell Customer Service issues and overall quality issues and you'll definitely see a profit is king mentality. And I'm Ok with lots of profit as long as the stuff works.

Don't get me wrong.....they make good parts. I used a Merlin block for my 540 and I've used iron Merlin oval ports in the past. It's good solid stuff. I've seen independent tests of his intake showing it to do pretty well...in fact I believe he even redesigned it to improve it from first design. But that intake has a huge plenum pad on that won't fit under most hoods. Basically works like a regular intake with a 1"-2" spacer on it.

That 870 carb is a hybrid deal that he originally configured as a replacement DP for the ZZ502. Works well on the 509 with hyd cam also.

They are using 345cc ports on that 509 with a hyd cam. No way it's going to rev to where those heads want to be. Might as well help them all you can.




JIM

68 NJConv 454

Alright, doing a little research on the intake manifolds.
I do agree that Merlin would put the best intake on there to match the engine but I also agree that they are a company to make a profit and would bennefit most from using their own parts. The seller has a dyno sheet showing 579hp with the merlin single plane intake. I'd keep it if it would clear the L88 hood but I am told it won't. The seller had to buy a cowl hood to clear the intake/carb/aircleaner.
The seller is willing to install an Edelbrock RPM airgap in place of the merlin intake if I'd like. But is that my best choice??

Here's my research...

Summit shows two listings for Holley Strip Dominator. What are the differences and which one do I want for my 509 application??
http://store.summitracing.com/egnsea...00752&D=300752
Both say the single plane opperates from 4,500-8,000.
I was hoping to lower the power band on an already high RPM engine.
Is that a good plan? Its a street car so high RPM HP won't be seen very often.
$199.95

Then we have the Weiand Stealth dual plane intake that is good from idle to 6,800 rpms. "Weiand dual plane Stealth intake manifolds feature long, separated runners for bottom-end and mid-range power, plus a special runner design and larger plenum to flow the air needed for high-rpm horsepower. They mount single, square-mount 4-barrels and make power from idle all the way to 6,000 rpm. That makes Stealth manifolds the perfect choice for your street/strip vehicle."
http://store.summitracing.com/partde...8&autoview=sku
$215.95

The Edelbrock RPM Air Gap which is said to be good between 1,500 and 6,500. Summit website does note: "Will not fit under stock hood of Corvette." are we sure it will clear an L88 hood?
http://store.summitracing.com/partde...2&autoview=sku
$239.95

What do you guys think? I'm on a budget but they all seem to be in the same ballpark. The seller is going to throw in his Mcload scattershield bellhousing for $100, so thanks anyway LittleMouse, I appreciate the thought and offer. If we can work out the details and final $$ I might be purchasing this engine at Carsile in 10 days wooohooo. Thank god I'm not married or my wife would kill me when the next bank stmt came in with a $5 balance.

69ttop502

300-5 is the Holley you want, for rectangular port heads. I agree that on a low rpm engine the airgap may be the ticket although I think the Holley would run good too. Maybe give you some room to grow later too. Check Ebay as there are usually a few 300-5's for sale at anytime.

ZL1powr

The RPM Air Gap will fit. I have used it on my 71 with an L-88 hood.

J and H

Go for the rpm air-gap unless the engine will spend the majority of its time above 5000rpm-then go single plane.

68 NJConv 454

Alright, so I'm hearing a lot of votes for the RPM Air Gap.

Any words of wisdom of why the Weiand Stealth dual plane is not a good choice? or are all of you guys old buddies of Vick?

James

I can't give any hard facts on why the Wieand Stealth is a better choice than the Air Gap but I can tell you this. The person that built this motor for me mainly builds and repairs hi-performance motors for people all over the midwest. (i.e. hi end blown boat motors, injected sprint car motors, alky truck puller motors, drag car motors, etc.....) The only way people know about his shop is by word of mouth. I guess for me I described the motor I was interested in building and he picked the parts for it. That is how I ended up with the Stealth intake. I let someone that has a long history in performance motors make the choice for me.
Here is the configuration of the motor:
Merlin II block (4.5in bore x 4.0in stroke)
Eagle forged crank
Eagle H beam rods
SRP Pistons (12.5:1 Compression)
Merlin Rect. Port heads
Crane custom ground solid roller cam (he config'd the specs)
Jessel shaft mounted rockers
Wieand Stealth intake
Holley 1050HP carb
MSD Dist and 6AL box
Hooker headers and sides with JCL inserts.
On his DTS dyno the motor made 546 Ft/lbs of torque @ 4600 and made a little more than 550HP @ 6200.
I'm on my 5th summer with this setup and so far so good.
Either way I don't think you can go wrong but I sure do like how the Stealth has worked out for me.