[62bandwagon]

I have my new combo with a 350 .030 over about 10:1, 280h Comp Magnum cam, RHS Vortec heads & a Performer RPM Air-Gap. How big of a carb should I need? I have my 600 CFM Edelbrock on it now & it seems to fall off around 5000 RPM & I think this combo should pull up to at least 6000. I have a friend with a 750 vac sec. Holley & he said I could try it. Any thoughts?

Thanks

 

[Mike Goble]

It's probably the stock exhaust system causing the drop-off in power.

 

[62bandwagon]

I have 1.5 valves that have been bowl blended with headers. Do you think the 600 is enough carb?

 

[novaboy009]

What about the rest of the exhaust???

600 should be sufficient for your combo. It might need tuned, as in limiting total advance or fattening/leaning the jets.

Kev

 

[Mike Goble]

The symptoms of marginally too small a carb won't be a dramatic drop-off in power at some rpm. If you were to go from a 2-bbl to a 4-bbl there would be a significant difference, but going from a 600 cfm carb to a 700 cfm carb won't produce that much of a difference provided the mixture remains similar. The primary symptom will be increased manifold vacuum, possible .5" at the top end. EA3.2 predicts an intake vacuum of 1" with a 700 cfm carb versus 1.3" for a 600 cfm carb. It also calculates an actual CFM of 569 at 6000 rpm with your motor as you have described it. Note that the power curve flattens out at 5000 rpm.

RPM···········1500····2000····2500····3000····3500····4000····4500····5000····5500····6000
Brake_Tq······264·····294·····320·····346·····364·····385·····366·····339·····307·····256
Brake_HP······75.5····112·····152·····198·····242·····293·····314·····323·····322·····293
Exh_Pres······.1······.1······.2······.4······.6······.8······1.0·····1.2·····1.4·····1.5
Int_Vacuum····.2······.5······.6······.6······.6······.7······.9······1.1·····1.3·····1.4
Vol_Eff_%·····64.7····68.7····74.3····80.7····86.0····92.2····92.4····91.6····89.9····85.7
Actual_CFM····107·····152·····205·····268·····333·····408·····460·····506·····547·····569
Fuel_Flow·····39.2····55.6····75.0····97.8····122·····149·····168·····185·····200·····208
A/F_Mix_Qal···97.3····100.0···100.0···100.0···100.0···100.0···100.0···100.0···100.0···100.0
BSFC··········.519····.496····.493····.495····.502····.509····.536····.573····.621····.710
BSAC··········6.515···6.222···6.179···6.211···6.298···6.383···6.720···7.183···7.788···8.901
Friction_HP···12······20······29······41······55······75······98······126·····160·····199
Mach_#········.129····.173····.216····.259····.302····.345····.388····.432····.475····.518
Piston_Spd····870·····1160····1450····1740····2030····2320····2610····2900····3190····3480
Piston_Gs·····145·····258·····403·····581·····790·····1032····1306····1613····1952····2323
Overlap_%VE···-4.0····-3.5····-2.4····-1.2····-.6·····1.9·····.5······-.8·····-1.1····-1.2
Int_AvgVel····85······113·····142·····170·····198·····226·····255·····283·····311·····340
In_InertiaPrs·.0······.2······.6······1.2·····1.7·····2.1·····2.4·····2.5·····2.4·····2.2
In_ResTunPrs··0.0·····0.0·····.0······.0······.0······0.0·····0.0·····0.0·····0.0·····0.0
Ex_AvgVel·····120·····160·····200·····240·····280·····320·····360·····400·····441·····481
ExTun_Prs·····.7······.9······.4······-.4·····-.8·····-1.4····-1.5····-1.4····-.9·····-.7
Lifter_Pump_UpNone····None····None····None····None····None····None····None····None····None
Spark_Adv·····19······24······28······30······30······31······32······33······34······34

 

[62bandwagon]

Finally responding...I have dual 2.25 exhaust with 40 series Flowmasters. According to the chart on this post my carb should be the right size. There were a couple guys at the races this weekend (no, I didnt race) that swear I would notice a night & day difference with a 750. I really dont know what to do for sure. I did go over my ignition system & inspect everything & regapped my plugs from .040 to .035 & the motor pulls nicely up to 6000 rpm. It has acted up once since where it dropped of around 5000 so I am thinking that I may need a ignition upgrade. I have a Unilite with an Accel coil & I have considered a Mallory Hyfire...cant hurt I guess. Any more input? Thanks again!

 

[Ironman]

I was running a Holley 750 vac sec. Real responsive once it was dialed in. If you can tune the 600 it should work well for you.

Swap in your buddies carb and see what happens. If he has it set up for his car, it may not react the same on your car depending on how different your combinations are.

 

[69NovaSS]

I have a friend with a 750 vac sec. Holley & he said I could try it. Any thoughts?

Well since you have a friend that is willing to let you try out the 750 I say go for it...you will soon know if it will help or not...I personally am running a 750 on my 355 and found it to be a good working carb....good luck