A little more Horsepower

[patrickt]

Fastd, I'm with David on the smaller carb preference. In fact, I run a Holley 750 (4160) on my FE and I've got a hundred cubes on you.

[olddog]

If your exhaust is two completely seperate pipes, an "H" or an "X" type cross over would help quite a bit. Only one cylinder is pushing high pressure out the exhaust at a time. This will allow each cylinder to exhale through both sides. The "X" is supposed to improve the scavaging affect by creating a ventury, but it gives a higher pitched sound.

Ditto on the 650 cfm carb. A 350 cid at 90% effeciency would have to turn over 8000 rpm to suck in 750 cfm. No way your heads and cam could be up to 90% at those rpm or your hp would have peaked in that rpm range.

Figuring 100% effeciency at 6000 rpm and you would only be pulling in a little over 600 cfm.

[fastd]

Olddog,

Thanks for your input. With respect to the exhaust, there isn't much room to work down there; I am going to keep the exhaust under the car right up to point where it turns out in front of the back wheels. Getting a 3" pipe under there with no H or X is probably as good as I am going to be able to do. Thanks.

Fastd

[fastd]

All,

My tuner came back to me and said he thought the 600 cfm dp would be a better fit than the 650 dp; based on David G's and olddog's post, you guys would probably agree...?

Fastd

[patrickt]

Originally Posted by fastd

All,

My tuner came back to me and said he thought the 600 cfm dp would be a better fit than the 650 dp; based on David G's and olddog's post, you guys would probably agree...?

Fastd

I think that's reasonable. 600 CFM DPs are traditionally good for up to 400CID, even when modified. They're only about $350, so I would listen to him.

[RodKnock]

Just be prepared to potentially purchase a new carb, if and when, you decide to upgrade the cam, intake manifold and heads to achieve 450-500 HP. That's why I recommended "the big plan."

If funds were an issue, then I might opt for the 650 DP now, assuming upgrades with this engine are in your future. Just my $0.02.

[patrickt]

Even if you have to sell your 600 at half price on Ebay, you're still out less than two hundred bucks. RodKnock spends more than that at lunch.

[RodKnock]

Originally Posted by patrickt

Even if you have to sell your 600 at half price on Ebay, you're still out less than two hundred bucks. RodKnock spends more than that at lunch.

It's tough finding a good and cheap Sushi bar around here.

That's why I led off with "If funds were an issue..."

[fastd]

Patrickt,

$350? It is listed at $770 on the Holley site, and $679 on JEGs; without a choke!

Fastd

[patrickt]

Originally Posted by fastd

Patrickt,

$350? It is listed at $770 on the Holley site, and $679 on JEGs; without a choke!

Fastd

Jegs has it for under $350.
http://www.jegs.com/p/Holley/Holley-...46470/10002/-1

[RodKnock]

Fastd was looking at the upgraded HP series of Holley carbs, which is what I would get.

[patrickt]

That would be these. http://www.jegs.com/p/Holley/Holley-...43645/10002/-1 We can poll the collective brain trust as to whether they are really worth twice the price.

[RodKnock]

If I remember correctly, then I believe it was Gunner who thought the Holley HP's were overpriced and POS's.

I like them. I loved my Holley HP 950 on my old Vette. My current Holley 850 is not an HP, but one of these days I may upgrade to Webers or EFI or drop the Cammer in.

[patrickt]

Originally Posted by RodKnock

If I remember correctly, then I believe it was Gunner who thought the Holley HP's were overpriced and POS's.

I like them. I loved my Holley HP 950 on my old Vette. My current Holley 850 is not an HP, but one of these days I may upgrade to Webers or EFI or drop the Cammer in.

I think Jamo booted ol' Gunner; not sure if he's back yet. Remember I run the Holley 4160 vac. secondaries. It is the simplest carb known to man and it runs absolutely flawlessly. Now I know you can get them for under $350. I think the truth of the matter with carbs is that there is a tremendous amount of luck involved. It doesn't take much to make a great carb run crappy. And even a basic, right-sized carb will run like dynamite if everything is just right.

[fastd]

Rodknock is correct - the one that was recommended was the 4150 HP Series, a race carb (whatever that means). I called Holley tech service; they said the difference was better flow, open venturi, and changable airbleeds, resulting in much better low end response.

The current carb that is on my engine now is the 4160 HP 750. The problem I am having is that the secondaries aren't opening properly; my tuner opened them manually one time and that's when we got the 314 hp and 296 torque readings (up 12 hp and 28 ft-lbs). From what I have read, the mechanical secondaries are better suited to a lighter car with manual trans, that doesn't mind the "kick". I will definitely go with the HP series and spend the extra money.

[patrickt]

OK, does your engine builder know that there's a good possibility that you'll want to take the next step of heads and a cam? That might move him up to the 650, or he might still like the 600 even with those additional changes.

[fastd]

Patrickt,

Good question. I talked to the Holley tech guy about that; I know that you guys said don't listen to them but...he said that the 600 cfm should be good for this engine all the way up to about 450 hp; the difference I am likely to feel in the higher end rpms between the 600 and 650 is minimal. If I were to be running above 6000+ rpms, then I would be more likely to need the 650; I just don't see 6500 rpm happening with this engine. I'll talk to my tuner about it also though.

[patrickt]

Originally Posted by fastd

I'll talk to my tuner about it also though.

I'd probably do what he recommends. There's an old saying... Don't hire a dog and then do all the barking yourself.

[RodKnock]

Just based on what I've experienced through the years, I don't remember too many folks running 600 DP's. However, I know a lot of people ran or currently run the 650 DP's.

I'm just speculating, but the 650 DP may be a better value, especially in terms of resale, if you get the upgrade bug again. I know I always do. Its just human nature to move to the next greener pasture, and that's why I think the 650 DP may be the right choice.

[patrickt]

I don't hold much with "carb calculators," but sometimes they're fun to monkey around with. He'd have to hit some high revs with a pretty high efficiency rating to get up in to the 650 range, at least on this calculator. http://www.4secondsflat.com/Carb_CFM_Calculator.html