That sounds right. The machinist would have a better understanding of the intricacies, and therefore a finer calculation. Ha, of course!

 

I'm sure you've this, or data similar, but I thought I'd throw it your way. It concerns exh. pipe diameter and the max hp with each.

How To Calculate Muffler Size and Exhaust Pipe Diameter - Exhaust Videos | Exhaust Videos

 

I've never actually seen that before, that's really interesting stuff.

If that's the case, I have just about the right size exhaust with 2 1/2" pipe.

 

Yes, you could be right. I was thinking closer to 240-250 hp with your engine though. Is that high? I guess it is the 1.75" restrictions in the efi's that hinder ... wouldn't you think?

 

I'm curious about that too. 250 is roughly what the builder and I are thinking, but won't know for sure until it's done.

As for the exhaust... I didn't really have any plans of putting a bigger exhaust on it, but hadn't thought about it either. I'm curious what a difference it'd make.

As for the EFIs:

1.75" diameter = 2.40 sq/in area.
2.40 * 2 = 4.80 sq/in area combined.

My exhaust:

2.50" diameter = 4.91 sq/in area.

So they're very closely sized matched to each other.

It'd be interesting to know the HP difference by putting a larger exhaust and headers on it... without having to pay for it first.

 

I think that with the exhaust you have you will, of course, notice a huge difference from what it was. Whether you will notice a difference after running it that way and then converting to higher volume exhaust system, that is questionable. I think you would notice an improvement. The data points toward that conclusion, but we can't say w/o trying. And of course you have to consider the price. Would a theoretical performance gain justify the expenditure?

What do I think will happen? I think you'll be thrilled with the new engine, but after a year or two you'll make the jump to a hp exhaust. Time will tell. Just enjoy your engine!

I wish I had had my buddy get on it when I drove in his hot rod. His engine is similar to yours, and, as I mentioned b/f, he runs the efi's. With that light weight frame and tiny body, I image it hauls. But truth be told, his steering was so squirrely it scared the heck out of me, lol. But I would have loved to have felt the performance with efi's.

Oh, after rereading your post: Granted, your exhaust is well matched to the efi's. But, I believe the point is whether the efi's, that are designed for an engine with much less flow and hp, are vacating the gasses adequately, and allowing your engine to breathe as freely as it is now trying to.

 

You keep bringing up the fact about how restrictive the EFI manifolds are. But you do realize the outlets can be ported and opened up quite a bit don't you. I've ported them in the past but never measured them or took any pics. I recently bought one just to see how much they can be opened up. But I'm not going to be able to do anything with it until spring. I'm building headers for my 240/300's. But I was just curious about porting the EFI manifolds again.

 

+1; Is there a post or thread with pics on porting efi manifolds? I generally like manifolds better for street driven engines due to their durability. I've got a set now that I want to put on my 300 along with some other bolt on mods and would like to know more.

 

Update:

So, the springs we ordered were outputting way more pressure than they advertised. They were advertised at around 336lbs at 1.1" and they were outputting 370lbs @ 1.1. Figured there's a bad batch of them out there right now.

Instead of exchanging for another of the same and ending up with another set that didn't work, we found another spring part number that worked.

Sent the previous ones back and ordered the new ones. They came in today and we measured them at the shop this morning and they check out great.

Crane Retainers: CRN-99946
Crane Springs: CRN-96803


Here's how they tested:

The cam I'm using has a 0.504in lift, so:

Installed height: 1.700in - - 105 ft/lbs
Compressed Height: 1.196in - - 285 ft/lbs
Coil Bind: 1.026"

Shouldn't be long now.

 

Great. Is that the seat pressure the cam requires? Wasn't it an Erson cam you used? And the springs are double springs? My Isky springs were 134lbs. Using only the outside spring they dropped to 117lbs.

Fordman: Of course the EFI can be ported out, but to what ID? 1.80"? 1.85"? and then the 1.75" pipes attach to it. However you spell it, it means restriction, clear and simple. The EFI were designed for an engine with what, 140HP?

I'm only saying that is seems ludicrous to spend $1500 to port, install larger valves, bigger cam, etc., everything to make the head/engine breathe better, and then slap an exhaust system on it designed for an engine with 100 less hp than AB's.

I know too well the shortcomings of headers, but HALF of my header (232 max hp) is flowing more than 2 efi's (217 max hp). (data from How To Calculate Muffler Size and Exhaust Pipe Diameter - Exhaust Videos | Exhaust Videos

cheerio

 

I don't recall seeing any post with pics of ported EFI manifolds. I'm going to port the one I picked up sometime this spring/early summer. I'll take some pics and measurements when I do it and will post them.

That's sucks that first set didn't work out. Did you consider going to a different brand for the second set. I'm leaning towards Crower for everything for mine but the lifters.

Glad the second set checked out and will work for your set up. Can't wait to see how your engine turns out.

 

I'll let you know on the amount sometime this spring/early summer when I port the one I picked up. But I'm pretty sure I could easily open it up to at least 2.00" if not a little more. They are pretty beefy at the outlets. What the EFI manifolds were designed for doesn't really matter. It's what you can improve them to be good for. Remember these engines were "designed" for only 140hp or whatever. It doesn't stop us all from building them and making improvements. Same with the parts for them.

It's not like we are talking about the piston choice here. We are talking about bolt on parts. They can always be changed out at any time if more performance is needed or wanted. And if AB isn't changing the exhaust then headers aren't going to improve a whole lot. It's just moving the "restriction" down stream.

And there is a difference between a race vehicle and a street driven vehicle. If you are looking to squeeze every single hp you can out of it. And are willing to live with the headaches that come with them. Then yes run the header/s. Most people aren't. And they are more then willing to sacrifice a few hp to gain the reliability and less issues of the manifolds.

I'm not bashing headers. I like headers and all of my 240/300 powered vehicles will be running them. But there is more then one choice when building these. Not everyone needs to run headers.

 

The previous springs were dual springs whereas the new ones are a single with a dampener.
I don't have the specs on the cam (he has the printout that came with it down at the shop), but he was extremely specific about the pressure ratings he was looking for, so I imagine it's right within spec.

He also had to hunt and peck around because, after pulling the studs and shaving down the bosses for screw in studs, the install height changed slightly, and he was taking that into account in his measurements.

Fortunately, since they were out of spec, Summit covered the cost of the return. And the new springs ended up costing less than the previous ones. No real complaints. Just set me back a week or two which is nothing in the grand scheme of things to be sure it's done right.

As for EFI vs. headers, I agree fordman. I love the durability and complete hassle-free nature of the manifolds. Right now I'm running a 2.5" exhaust, which I think is more than ample. The only bottleneck is right at the manifolds. Bore them out a bit and then have a shop rebuild my Y-pipe (which I want to do anyway) and I think I'll be more than pleased. Will it have the peak hp that headers could supply? Probably not.

And there's certainly nothing limiting me from putting on headers in the future. It's just not in the budget/plans right now.

 

105# installed is pushing the upper limit of how much seat pressure a flat hydraulic cam will endure. Above about 110# there is a strong likelihood that cam life will be adversely affected, depending on other engine conditions and operating parameters. Perhaps that is what is weighing on your machinist's mind.

 

I'll be interested in seeing how they will modify those manifolds. I too like the trouble free manner of manifolds and will go that way with mine, altho my little hop up is way down on the scale vs what you're doing with yours. But still, good to know how to go about it and results from worked over manifolds.

I do have 2 sets of efis, so can go ahead and get the first set on, and save the 2nd for anything learned here that I may want to do later.