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Anyone have a Holley 650 dp I can borrow?


hpfiend

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Hey all! Looking for a Holley 650 double pumper to borrow a few days... I have a dead spot below 2500 rpm I can't get rid of- I am thinking with the low compression (dished pistons) 355 sbc, 2.56 gears, and supposedly a 3000 rpm stall- maybe the hp750 I have is too big...the cam should have good bottom end though it sounds more lopey than I would have expected for such little duration.
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Hey all! Looking for a Holley 650 double pumper to borrow a few days... I have a dead spot below 2500 rpm I can't get rid of- I am thinking with the low compression (dished pistons), 2.56 gears, and supposedly a 3000 rpm stall- maybe the hp750 I have is too big...changed the cam to known mild specs and it's still there

 

I dont have a 650 currently, but I can tell you that a 750 is to much carb for a 355.

 

650 should will help wake it up and make it more responsive.

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Thanks guys! I thought I could pull it off as we bought the car this way but the Holley calculator calculated a 600cfm carb as ideal... Replacing the pro stock sounding cam has helped but still pretty lazy and downright abominable below 2500- gas consumption is unreal as well
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Thanks guys! I thought I could pull it off as we bought the car this way but the Holley calculator calculated a 600cfm carb as ideal

 

Wow, that's the first time I've ever seen it be somewhat accurate. It's normally off in never never land with calculations(suggests to big).

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I've ran with a 1150 on a 355. Key is does the motor need it. Yes a 750 is too large for that motor as it is. My motor has a 750 and needs a 850 or 950 badly. Key here is my motor shifts at 7800. Has big dur big lift big runner heads. Went 11.02 at 127 on motor with a 950. You should really change the gears. Not many motors at all would wana run with a 2.6 gear. Evan if your motors peak rpm is 6000 rpm a 3.50 gr would barley get u there. Mileage would proably get better letting the motor pull the car easier. Plus ud likley never feel the true stall of 3000 rpm I'm shure that motor strugglin with the gear. Id make the gr change right away.
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  • 1 month later...

I posted a lot of this in my gremlin build thread but as an update to this thread...

 

I bought a "650" double pumper off of craigslist as it appeared to be a good deal... having a hard time indentifying for sure what it is. The metering blocks say it is a 700 dp. If anything it is smaller than a 750 and can be a parts carb/practice carb for my hanger18 blow through modifications when the time comes...

 

In the meantime, I disabled the secondaries on the installed/converted hp750 and tried to tune the primary using shooters and different accelerator pump cams. After much trial and error and pump cam curve analysis, I came up with the blue cam in position 2 with a 31 shooter and then after connecting the secondary linkage a green in position one in the back with a 40 shooter. The dead spot was pretty much eliminated from a standstill (Knock on Wood) and it absolutely murders the one rear tire now.

 

I then read that the hp main body is setup for a 4 corner idle adjustable carb and I only have 2 adjustments in the front. Apparently it was discovered by this fellow that by switching the high speed secondary air bleed for one the size of a non-hp 750 he had much better idle and throttle response... so I put a set of 28s in place of the 75s as he did and tried it out. It did seem to idle better and have a little better off idle response...

 

In order to try and band-aid this oversized carb situation further I bought a linkage to be able to adjust the secondaries for idle from the top rather than pulling the carb every time. I cracked open the back and reduced the front opening to prime the rear transfer slots and it seems to run pretty well now. I did have a situation where the dead-spot was back once from a mid throttle cruise with a stiff punch but I am wondering if that was at the point of the primary to secondary transition on this little engine and the transfer slots couldn't make up for the load of the high rear gears... who knows.

 

It will have limited slip 3.73s in it the next time I pull it out of the garage so this could all be for naught.

 

It does pop in the tailpipes after tuning the accelerator pump circuit which I believe is now indicative of an over-rich condition??? But I feel I can now make a clean run from a standstill...

 

Any thoughts?

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