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Junior Charter Member
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1,032 Posts
Discussion Starter · #1 ·
Hi Folks-

Edelbrock makes two sets of RPM heads for the SBF. One has a 1.90" intake valve, and the other is a 2.02 intake valve.

I'd planned on ordering the heads with the smaller intake valve (won't be consistently spinning the engine over 5000 RPMs) and figured that I'd get slightly better torque at the low end with the smaller valve. HOWEVER I just found a SMOKIN' deal on the heads with the larger valve.

I'm comfortable that the larger intake valve provides at least a negligible amount of additional HP higher up with the recommended cam, but what I'd like to know is all other things being equal, how much do I give up on the low end with the larger valve.

347 short block (piston clearance isn't an issue)
Cam:

Hydraulic roller
Duration at 050 inch Lift: 227 int./234 exh.
Advertised Intake Duration: 298
Advertised Exhaust Duration: 302
Advertised Duration: 298 int./302 exh.
Intake Valve Lift with Factory Rocker Arm Ratio: 0.520 in.
Exhaust Valve Lift with Factory Rocker Arm Ratio: 0.520 in.

Planning on a performer RPM Airgap manifold.

Thanks in advance for your advice.

Chris
 

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Pro FFR Builder and Moderator
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14,785 Posts
Use the RPM heads. You have a really good street mid range cam. The 2.02 will make better power.
 

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section 8
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5,136 Posts
Uhh what gordon said + I believe the port is larger at 190cc on the 2.02 head. Bob
 

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Junior Charter Member
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1,032 Posts
Discussion Starter · #4 ·
Thanks guys.

I guess the question is WHERE will the 2.02" intake valve head make better power than the 1.90" intake valve head? (they're both performer RPM setups.) I don't want to give up low-end torque in order to pick up 4-5 HP at 6500 RPMs...the car will just never see it. If it's likely to give me a small bump throughout the midrange, or not hurt low end/midrange then that's just perfect :^).

Thanks for your time on a Sunday.

Best,
c
 

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Registered
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207 Posts
Port size is 170cc regardless of valve size. As long as piston/valve clearance isn't an issue, go with the heads you can get the best deal on. The performance difference between the two will not be noticable on the street.
 

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Charter Member
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1,576 Posts
I can share my set-up and experience to date (1200 miles). Keep in mind I am no engine expert. I have a 306 with 9.5:1 CR, F cam, 24 lb injectors, gt 40 intake, rpm heads (2.02 valve) and 3:55 gears.

When I was building the engine I wanted a car that was streetable, and could still play with it in the odd autoX and drag and would not boil the hides off every time I got on it.

I have never launched hard in it yet, but have hammered down at about 10 mph. It will loosen the back tires a bit, but no real squealing. As soon as I hit about 2800 rpm it feels like I am on a dirt bike hitting the power ban - I am gone. Shift to second and the same feeling with a bit of spin - the car is very easy to control. Again, 2800 and bang - feels like I have hit the nitrous. The car runs fabulous. It will rip up to 6500 rpm in no time - so quickly that I really only have time to watch the tach, not the speedo.

The only complaint I have is that so much of the power is made at the top end I really only have maybe 3500 rpm that the engine loves to live in. That, and sometimes it would be nice to lay two black patches down.

In hind site I think I should have gone with the smaller valve for my displacement and better low end power. I am no engine expert by any means, but I think a 347 could make much better use out of that valve than a 306.

For what its worth, my .02.

Geoff
 

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FFCobra Fanatic
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12,975 Posts
I'm useing the 2.02" valve heads on my engine. You will not give up any power down low with that head and cam on your 347. You depending on pistons used may need additional machineing to except the increased diameter of those intakes.
The dual plane intake will also help at lowwer rpm's. The difference between an open plane and dual plane and it's effect on low rpm power would probally be a bigger difference then the intake size.
 
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