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| Holley 350 cfm carb help pls https://slantsix.org/forum/viewtopic.php?t=64126 |
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| Author: | Scoote6982 [ Thu Oct 10, 2019 9:17 pm ] |
| Post subject: | Holley 350 cfm carb help pls |
Hi all Looking for some assistance on setting up my idle and accelerator circuits on my holley 350 cfm. What jets, squirter, and accelerator pump cam should i use? Engine specs 9.8:1 compression, port matched head, long runner intake, 252/252 duration 0.435/0.435 cam, hei distributor. I have read placing paper clips into the fast air bleeds will help, but I am hoping some can explain how and why I might want to do this. |
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| Author: | drgonzo [ Fri Oct 11, 2019 6:06 am ] |
| Post subject: | Re: Holley 350 cfm carb help pls |
I've never owned a 350cfm Holley 2V but my 500 runs well with 68 jets vs. the 73s that came in it. I changed the 31 pump shooter to a 28 and that delivers a longer pump shot. All else is as it came from the box. I would just bolt it on, check the float level, tune the idle mixture screws and give it a go. I suspect it will want smaller jets, say 58s or so. 2 cent charge waived. |
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| Author: | DusterIdiot [ Fri Oct 11, 2019 6:28 am ] |
| Post subject: | D |
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| Author: | Scoote6982 [ Fri Oct 11, 2019 6:55 am ] |
| Post subject: | Re: Holley 350 cfm carb help pls |
It wasn't a typo, that should be my CR. I shaved .090 off my head and with my deck hieght I came up with 9.8:1. Gosh I don't want to be doing a cam swap now. Would a higher grade gas prevent pinging in this instance? What about the PV? Leave at the 8.5 that it came with? I ran a formula for CFM size and felt a 350 was on the larger side and this steered away from a 390cfm 4bbl. |
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| Author: | SpaceFrank [ Fri Oct 11, 2019 7:37 am ] |
| Post subject: | Re: Holley 350 cfm carb help pls |
Shaving 0.090" off the head shouldn't get you quite that high, if the block is uncut and you're using stock-type pistons. What other measurements are you using to calculate SCR? Deck height, final bore diameter, head gasket dimensions? Stock 225 crank, rods, and pistons, or something fancy? Is this a "long-rod" build? |
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| Author: | Scoote6982 [ Fri Oct 11, 2019 7:44 am ] |
| Post subject: | Re: Holley 350 cfm carb help pls |
It was a friend who did the head work that actually ran this calculation. The rotating assembly is all stock. Deck height was .010, std head gasket, .030 bore over. |
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| Author: | SpaceFrank [ Fri Oct 11, 2019 8:04 am ] |
| Post subject: | Re: Holley 350 cfm carb help pls |
Unless this is a 170, that deck height isn't right for a stock bottom end. |
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| Author: | Scoote6982 [ Fri Oct 11, 2019 8:33 am ] |
| Post subject: | Re: Holley 350 cfm carb help pls |
Hi SpaceFrank; Can you help me out? What do you mean? This is indeed a 225 block. I checked the codes, it is a '68 year made 225. |
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| Author: | Joshie225 [ Fri Oct 11, 2019 8:37 am ] |
| Post subject: | Re: Holley 350 cfm carb help pls |
NHRA blueprint deck height for a 225 is 0.145" down. My experience across a number of 225s is that the pistons are about .185" down give or take. I had one 225 that was only about .170" down and with .080" off the head it came to 8.5:1 with a Felpro head gasket. Give us good numbers and we'll find the truth. |
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| Author: | Scoote6982 [ Fri Oct 11, 2019 10:08 am ] |
| Post subject: | Re: Holley 350 cfm carb help pls |
Thanks Josh Apparently, I am not as versed as I thought I was on my engine's deck dimensions. Short of pulling this apart to another set of measurements, I don't know what the accurate deck height might be. |
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| Author: | drgonzo [ Fri Oct 11, 2019 10:56 am ] |
| Post subject: | Re: Holley 350 cfm carb help pls |
Perhaps the machinist took .010" off the deck. If it were mine I would bolt that carburetor on there right out of the box, break in the cam and then take it for a spin. |
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| Author: | Joshie225 [ Fri Oct 11, 2019 1:46 pm ] |
| Post subject: | Re: Holley 350 cfm carb help pls |
Quote: Thanks Josh
Chances are the static compression ratio is fine for your short duration cam, but it's also likely far less than expected. What's also likely is that the cam was not installed with the best valve timing. Again with that short a duration it's not as important. These are the a couple of areas where many engine builders fall down when first building a 225. The compression ratio is usually far lower than assumed and the intake valve closing point is usually too late. Together these lead to a very low dynamic compression ratio and poor performance. I have first hand experience here. My first "performance" 225 build was a flop, but it got much better with .100" off both the block and head, bigger valves and head porting.
Apparently, I am not as versed as I thought I was on my engine's deck dimensions. Short of pulling this apart to another set of measurements, I don't know what the accurate deck height might be. |
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| Author: | SpaceFrank [ Fri Oct 11, 2019 2:41 pm ] |
| Post subject: | Re: Holley 350 cfm carb help pls |
I would press your friend for more information about how that number was calculated and what measurements were taken. If we assume your friend meant 0.010" was removed from the block deck surface, then using this site, typical Fel-Pro head gasket numbers, and a kludgy guess for your head combustion chamber volume based on heads I've had machined (and the standard 0.00667"/cc number given by DD), I'm getting somewhere around 9.2 SCR. Whether this is a good match for your cam I'll leave to others on this forum. |
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| Author: | Scoote6982 [ Fri Oct 11, 2019 3:14 pm ] |
| Post subject: | Re: Holley 350 cfm carb help pls |
Thanks Spacefrank and joshie225. This is my first build. And in consideration of your comments, I would be inclined to agree with you. I think the 0.010 was the amount taken off the deck height of the block. I didn't degree in my cam, although it was recommended that I should. In retrospect, I probably should have. All lessons learned. Spacefrank, your numbers indicate that maybe I am ok with my cam (whew)! I'll iron out my carb issues and drive my car whilst I start working on plans for a future /6 upgrade. s |
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| Author: | DusterIdiot [ Fri Oct 11, 2019 4:54 pm ] |
| Post subject: | D |
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