I rebuilt my 420 HP engines and noticed a RPM loss on the top end. It went from 5000 to 4600 RPM. In doing the rebuild I replaced the stock 099 GM heads to the Dart iron eagle heads and switched intake manifolds from the stock Dart single plane to the Edelbrock RPM dual plane intakes.
Using Crane hydraulic roller rockers 1.7
I have a the thunderbolt ignition and timing set to 30 or 32 advance. ( I don't remember )
I have a crane cam (Intake 359) &( Exhaust 372)
Prop is a Hydromotive quad 4 22 pitch.
750 Holleys
Gill Exhaust
Compression is great on all cylinders.

How much does the advance in timing effected the RPM loss in this situation. If I increased the advance to 34 what effect on RPM would it have?

Thanks

I would definately increase the timing to 34*.

Which Crane cam do you have??? Those cam numbers don't make sense.

Here is a link to the cam specs:

http://cranecams.com/index.php?show=...41&lvl=2&prt=5

Did you degree the cams in ? where did you set them ?

Degree of Cams -not sure. Left the bottom end untouched. Just upgraded the top end.

Sorry I thought you changed cams. What size intake runner on the new heads

308CC intake runner
129CC exhaust runner
Intake Valve Diameter 2.250 in.
Exhaust Valve Diameter 1.88 in.

The 2.25 valve may be acting like more cam if the stock heads were 2.19. I would try 34 degree of timing like Griff said.

Agreed, on timing that'll buy your some ponies and crisp it up- but listen carefully for detonation.

Well....as long as you degreed and checked everything carefully and everything else is up to snuff,

- id go to the heads and the manifold combo as the reason dual planes usually sacrifice a bit on top for midrange and low end as compared to a single plane. Not so much so in a really high output config 600+ but in a lower HP config this has been true for me.

sorry I dont know your head specifics I've been running Brodix heads the last 20 years almost exclusively, the head/cam/ intake combo is a huge factor in a engines performance

Has your combo been independently tested?
or Did you get a bunch of good used parts here, and

How did you select this combo of parts?


Uncle Dave

My engine builder said I should have used the Brodix hv2000 in stead of the Edelbrock RPM Performer Manifold. Would switching intake manifolds really give me an extra 800 - 1000 RPM?