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Discussion Starter · #1 · (Edited)
I am moving along w/ the planning stages of my 65 Riv roll race/1 mile events/general destruction mobile. Got oiling system, connecting rods(6.125 Manley 300M) and block(s). It's going to be at least a 427(4.125/4.00), but I may go bigger, probably 4.155 bore. It will be pump gas, may run E sometimes, but a pump gas combo. Shooting for 750whp or more, which is going to not be a so easy combo on pump. I know the automatic answer is go LS7 architecture, but had a thought to maybe go large bore big valve LS3 architecture as I am hood limited and would like to run dual 4150's on a Holley LS3 low ram. I know I can adapt the low ram to LS7 heads or a just have an intake fabbed. Just had the thought that I have never seen a 900hp+ LS3 build of any cube size or fuel, I was curious if anyone had seen/heard/built one?
(This is no relation to the PRC LS3 head question before this-those are going on an LS2 if I keep them.)
 

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350 cfm will make 850 hp.There is more than enough potential for 400 cfm plus in these heads these days.Tall deck height easy to build cubes and compression.Those low rams are killer also for rpm.Our best ls3 program is 125 hp higher than your goal.900 is no big stretch of a goal imo.Plenty of port and valve to work with.
 

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Discussion Starter · #7 ·
350 cfm will make 850 hp.There is more than enough potential for 400 cfm plus in these heads these days.Tall deck height easy to build cubes and compression.Those low rams are killer also for rpm.Our best ls3 program is 125 hp higher than your goal.900 is no big stretch of a goal imo.Plenty of port and valve to work with.
To give some more combo info, a main goal of the car is I want to go 200mph in my own car I built. I did some rough math and with 8000+rpm and 3.00 rear gear w/ the th400, it's possible on paper. Aero will be difficult, but that can be powered through. The TH400 is going to get a low gear kit and Gear Vendors at some point, that will probably happen later once the base combo is built and somewhat tuned. I am shooting for a wet weight of around 4000-4100lbs w/ me in it. I know you are right regarding the E vs pump gas, but I plan to really drive the wheels off the car, like 3-4hr trips etc. Because of this, I want to build as big as I can afford and I have it as easy to operate/reliable as possible. It's going to be a dry sump motor, so cranks are a little more complicated/pricey once you get out of the std 4.00 or 3.622 strokes. I agree on the cfm of the heads on the market, I know 400cfm is enough to make 900hp, but I just had not seen to many actually do it on a LS3 architecture. You have some of the best LS3 combos, by far, you did really well with those. If you look at the majority of big inch LS3 stuff, it's all lackluster and breaks a sweat making 650hp on a 440. The low ram is pretty much going to be THE intake I want to run, for several reasons. I am open to aftermarket LS3 heads, I just want this to make a real wide range of power. I am looking at the Mast LS3 large bores as cast and maybe have Greg Good work them, even considering an Ebrock Vic Jr LS3 head, but have seen zero testing on them. I did start the conversation on the cam w/ [email protected] so probably going to do a road race lobe w/ around .7-750 lift. Probably shooting for peak power around 7500rpm or so and have it rev out to the 8000's, Any insight is appreciated! Take care and Happy New Year to you!
 

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If you are over 4.125" bore you should be looking at LS7 port config. 13.5:1 will run on pump e85.... The few times you run it on the street I'm sure you could get away with pouring in some 100 octane or similar. 12:1 compression easily runs on 93 octane. As you know you only gain about 3% power going from 12:1 to 13:1 etc.... To make real power you need compression and CUBES N/A plus some killer head/intake flow and RPMs.

Why not just go to a single turbo and have a/c too? My 88mm turbo 376ci LS9 with MAST LS3 heads (380cfm) and stock LS3 intake/90mm TB has a baby cam... is totally streetable and makes 600-1200rwhp with a keystroke on the computer running $2/gal e85. I run a 100% stock T56 Magnum in my car.... it even had a cast factory crank in it for a few years.

An N/A 750rwhp LS will drive like sh*t on the street that is for sure... plus you will need some $$$$ heads to make it happen. Also some stepped/custom LT headers, and lots of exhaust fab. A single turbo will be easier and you could make the bottom of the car flat if needed with much less effort.

In 2009 at the TX Mile we had a 440ci 595rwhp LS in the silver RX-7 and it went 196mph with 275mm tires up front and street ride height.... there were C5/C6 Vettes needing 1000rwhp+ to go over 200mph that day. Top speed is all about aero... or having excess power to overcome the drag. I don't think 900hp flywheel is going to hit 200mph and the TH400 will suck up a bunch of power not helping your cause. This silver RX-7 now has the turbo LS9 setup and does 196mph in 1/2 a mile.
 

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Discussion Starter · #12 ·
GNX7/Stevieturbo, I appreciate the insight and I don't disagree w/ what you are saying, but boost isn't my thing. Car is going to go NA for sure, for a few reasons. The main thing being budget/build time, that is that if I go boost, I am setting up to make 1400+whp and go hunting bigger fish. That will cause me to have to re-chassis the car and a 25-30k build will turn into a 80-100k build overnight and take years. I want the car on the road and rocking within the next 1-2yrs, which is why I am leaving it a TH400/Gear Vendors because it bolts in and I do not have to re-engineer anything major to make it work. It is going to be pump gas for sure, as I don't want any real limitations on when/where I can drive it. I want to hop in an go and fill up as needed without breaking my brain on where to get E. I know what you mean on aero and that is going to be a big thing, but I want to just get it together w/ the basic necessary math to theoretically do it and adjust/build/add as necessary to achieve the goal. Here are a couple of pics of what I am building. Mine is the black one, the white one is my customers car which I also built and mine will have a similar look. My body is painted, chrome is done, I have 15in Brembo's F/R for it, just need a trans core, order a 9in rear, and put it together.
 

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1967 Camaro | 5.3 LS | S485 Turbo
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How about get a GM 454 LS crate engine, cam it and run 2" headers...
 

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Discussion Starter · #14 ·
The 454 won't work for me. Need a dry sump crank, factory LS7 heads have too many issues, and rotating assembly won't hold up to 8000rpm+, I just need to build what I want. Building off of an LSX block is not a bad idea, but I already have alum blocks waiting to get sleeved.
 

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I think you’ll need 1300 - 1400hp. I would gear it for just over 200mph if that’s the goal, the 9” will let you swap pumpkins with relative ease.

On the note of the TH400 + GV combo. If you want to stay auto, I’d run a glide + GV. A top speed run is just a high gear pull. Lockup would be a nice to have for the top end charge, don’t know how the GV would like it though.

On the note of fuel. You could always plumb in a second fuel system with a tiny cell for some Q16, M5, VP 50/50,…, in the future. I think either of those would make a big difference in a mile run.
 

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Discussion Starter · #17 ·
You are probably right on the hp estimate, but I am going to build it as is and see where it ends up. TH400 is for sure, car is going to be multi-purpose, roll race, 1 mile events, Hoonigan shit, all types. Yes, I do intend to have more than one 9in pumpkin for it for different occasions. Most of the time in the car will be Sunday cruising w/ the kids and late night Mexico runs w/ the German/JDM retards around me.
 
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