11.5:1 427, AFR 260cc Mongoose LS3 heads (possibly touched up). With proper supporting mods, would you try this combo?

 

If money constraints held me back from putting aftermarket LS7 heads, intake and throttle body on it then yes. You will be leaving some power on the table but the good news is there's room to go bigger.

 

No constraints but I do have the heads on my current setup already. Was thinking about sending them off to Tony for a little more flow. I’m not opposed to going LS7 though since I’ll have to step everything else up at the same time.

 

When Tony gets done the the mongoose heads, they will flow within 18-20 cfm of his LS7 package. I put a set on two of my recent builds for customers….heads from Tony of course….and the engines simply perform amazing. So well in fact, that my next personal big-bore engine will run the MMS 26X heads from Tony. Absolutely amazing performance from a smaller intake port than Tonys MMS 265 LS7 heads.

 

That’s exactly what I was hoping to hear. Thank you for the input.

 

What is the goal of the combo? Why LS3 architecture vs Cathedral or LS7? Give more info on ultimate goal. There are cheaper heads that will make good power and better heads that will make great power vs what you mention.

 

Goal is a nice street/hpde/canyon carver 4th gen F body with a great powerband, excellent manners, and enough power to hang with current later models running around these days. I already have the heads and now the shortblock will be on its way shortly. I am in no rush to assemble as I will be needing to get all of my other ducks in a row first.

It looks like the best bet for success will include sending the heads off for 26X rework unless a different route is taken.

 

Airspeed is the name of the game for what your looking for without a doubt and that's where ALL the stuff I build here really shines.

I just flowed a 290 cc LS7 head that looked huge next to my 265 head. And to be honest the machine work and the finish work looked real good. Just looking at the sheer size of the bowl was intimidating

That head flowed 403 CFM (versus my 265 Stg 2 head that flows 408 and my Stg 3 version that goes 412 with a slightly larger valve). More flow in a smaller port means the airspeed and cylinder packing ability is much higher and that just pays you benefits in so many different ways. Throttle response, better driving manners, and naturally more power and torque across the entire RPM range. Better fuel economy as well....its just a more efficient design. Your LS3 heads will be flirting with 390 CFM when I'm done and accomplishing that thru a conservative sized 260 cc port design.

Talk to people who have run my stuff to get the real 411....Scott and I have certainly worked on numerous builds over the years going all the way back to when DarthV8er was posting alot (really miss that guy on here!).

Anyway.....from a cost standpoint seeing as you already have those heads it's really a no brainer as they are arguably a great fit to do exactly what you want while offering more power potential than a large cathedral port design and similar or at least close to an LS7 build.

With 427 cubes the reworked 260 heads will be really crisp even at lower RPM.....If you were building a smaller engine like a 6.2 I would definitely recommend my medium to large cathedral heads but not for the 427.

This will be an excellent combo with the proper cam selection and Im sure I will be helping you with that as well....and a ported XS 103 intake manifold will be the icing on the cake. Best front mount LS3 composite intake on the market when properly modified

I have been using those now almost exclusively for my harder running LS3 top end set-ups. That intake basically obsoleted the FAST unless your chasing really high RPM power with the FAST mid-length runner design but you pay a big price in low and midrange numbers with that design

Hope you guys had a good Thanksgiving

Regards,
Tony

 

Thanks Tony this is again exactly what I wanted to hear and we will be in touch soon. I see the XS 103 is not compatible with cable driven throttle bodies? What would the possibility be of running a port adapter with the MSD intake? Far fetched or worth looking into?

 

IMHO, far fetched. Tony can answer the adapters question better than I. BUT, though this is hearsay, it's hearsay from a very good source. From what I've heard, the adapters aren't optimal, and cause tuning issues. Again, Tony will know.....

 

Your welcome. Tonys post was valuable here, to back up what I said. Here’s a link to a little 403 I did last year with Tonys MMS 26X heads AND that intake he referenced. I had Tony port the intake also simply to compliment the entire package. My advice to you here on a build like this is to have Tony spec EVERYTHING for you, so that it runs as a combination. Combination is everything in the world of internal combustion engines. Don’t let a buddy talk you into a camshaft selection that his friend had, bla, bla, bla. Don’t do that to yourself. Tony designed the port, and he knows what cam works with his port. It’s not gonna be cheap, but you’ll be happy with the outcome. Again, here’s the link….https://ls1tech.com/forums/generatio...-n-buildo.html

 

If you got creative I bet you could make a DBC throttle body work on the XS103.

 

Yes sir....I just had a customer do it only because I didnt realize it wouldn't just drop on and go.

We mod cars and we make **** work.....that's part of the hobby if your seriously invested in it (and Im not talking financially).

I need to track down that customer and see how he did it. He told me he made some sort of adapter to hold the cable mount.

-Tony

 

Definitely something I wouldn’t want to get into then.

 

Thank you got the great advice. I enjoyed following that build and it previously gave me inspiration on moving forward with this.

 

Tony, if you could find more info that would be great. I just assumed it wasn’t possible.

 

I put those heads on a friend's forged LS3. With a fairly small custom cam, it put down 525whp with a rod-mod LS3 intake, e85, 1-5/8 headers, 3in out of the headers to a single 3.5in exit. We did mill quite a bit off them to get it to 11:1 compression. (pistons were low compression)

 

Jayyyw, you did this thru 1-5/8" tubes?? From what I've read (so it is hearsay) those are restrictive on much lower powered LS engines than 600chp/525whp motors. If the 1-5/8" headers isnt a typo, I'm guessing you left some power on the table by going that small..... @jayyyw

 

It appears running an XS would require cutting the cowl on a 4th gen F body. That would be something out of the question for me with my current low mile WS6 unfortunately. If it was a less desirable car I’d have no problem cutting the cowl. It’s too bad they didn’t make an LS3 MSD.

 

Why not PM that guy and get a few pictures of the bracket they fabbed up?!

That would be a nice addition to this thread

-Tony