Exact same Supercharger to be used on both........

Some say larger cubes is better.......some say smaller cubes is better......

Whats the deal.......? Some say stock cubes.....some say 390....408.......some say go 427 or bigger.......

---and no, I still haven't figured it out as long as I've been here......LOL

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Spec the motor and blower to the intended rpm range, boost range, cam size, etc. The blowers have CFM ratings so you can work out power, and have max Rpm speed so you can estimate with a given pulley size and boost.

No point in running a tiny blower on a massive motor and no point in running an F1R blower at 3psi on a 346.

 

A 347 with a large centri and a 427 with the same centri will most likely have the same peak power capabilities. The 427 will make more torque at lower rpm.

 

@ddnspiderand@BCNUL8R

So I just bought a Harrop 2650. I also purchased all ZL1 front engine accessories that bolt up to my LQ9 iron block. This gives me the proper LSA SC'er alignment that the Harrop 2650 belt needs. With the ATI lower damper my accessories and the ZL1 AC compressor also line up for the other two belts.

I have a well built 390ci with Callies crank and rods, with Diamond pistons. I also just put my name on a set of Brodix BR-7 heads and I bought the Holley 105mm TB that fits it. Also, TSP 2"/3.5" LT headers merging to a 4" pipe at the Y back to my Magnaflow. I'll be usimng the big Afco Mustang heat exchanger with a Killer Chiller and 3 way bypass valve.

I have a brand new 4L80E level 4....1,500 HP transmission. I also ordered a P59 PCM programmed to work with my 1998 car and new 4L80E segment swap and a new complete wiring harness with a complete 4L80E harness plug-n-play ready to go in.

New cam to be spec'ed by someone and purchased.

I have a set of 18 x 12.5 widened rims with 335 Michelin Pilot Sports for daily driving, great in dry and in wet. Then I have another matching set of rear rims in 18 x 10.5 that I will mount some kind of good street drag or slick.....Hoosier, M&H, etc...... For good weather fun days.....

So, I think everything in my combo is pretty damn good, can't really get a whole lot better. 100% STREET CAR......no drag racing at a track.

BUT....if a larger Cubic Inch engine like a 427 will do better, I will sell my 390 to someone and build a new LSX 6-bolt capable 427ci. My builder has two LSX blocks and the parts needed to assemble the engine....it can literally be built in one week and then I can swap the engines. BUT ONLY if t will make more power that I will notice and be a totally different animal.

Being a Positive Displacement SC'er.....unlike a Turbo its going to have massive instant torque and instant power everywhere from 500-6800 rpm.

I keep asking professionals and keep getting different answers.

This is my last dilemma to deal with......stay with my 390ci.....or go bigger cubes.

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Any difference in power can be overcome with a couple more PSI, that's what's great about boost. It is a replacement for displacement. I would only consider swapping to the 427 to get the 6 bolt clamping force if you were planning to run high boost (>20 psi). I also don't think you'll hook up in 1st or possibly 2nd with an 18" by X drag radial anyways so the extra torque of the larger cubes will only help on the high way potentially. The torque curve will be too vertical with a blower like that and assuming some type of 3600ish stall.

 

Roll racing is what I'll be doing.....I don't plan on trying any serious dig racing on the street. I have an FTI Triple Disc 3200....they built it for specifically for 40-50mph punches......

I am planning 20psi with my 390ci......ARP head stud kit is already on it, should be ok.

So staying 390ci seems like the smart choice. 427ci would be nice, but probably won't change a roll race too much......

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Yup, I'd stay 390.

 

 

Until you experience the difference first hand between larger cubes and smaller cubes using the same supercharger, it can be difficult to explain or comprehend .

Most of the times they will make relatively the same peak HP.
The tq.and hp across the board will be quite different though.

 

Not turning a bunch of RPM and doing a LSX block I would go 427.

If you were going to spin it to 8k and make 1500hp I would stay smaller cubes to keep piston skirt wear to minimum.

 

More than likely, at some point you're going to want more than 20 psi. Since you have the option available, I'd go with the six bolt block and head combination now. Bob

 

Ask them their reasons why......it depends on what blower, what fuel...what speed you'll be spinning the blower, actual usage etc etc etc

But a big PD blower on a larger engine. Can all your parts handle that torque ? Can you put all that torque to the ground ? Torque breaks ****...torque at very low rpm breaks even more ****.

 

Well, I'm after 1,100 RWHP or so. I think thats gonna be about all I'll ever need with a 100% street car. So if I can make that, which everyone agrees the Harrop 2650 will do on my 390ci, I won't need more power. Maybe a different car some day.

Yes, I can go ahead and have an LSX built, but it will cost $6,000+, so if I can get where I need to be with my 390ci....just an insane roll racer and a mellow round-town driver....I'll be set.

I guess some builders that I spoke with just like to give their input and some over the past couple months have said I should not use a 390ci, its too small...and not a good choice for the combo. So I'm trying to clear it up with everyone here that my 390ci WILL absolutely make a very nice size engine for this Harrop 2650 in my 100% street car and nothing is actually negative or wrong with using a 390ci. I'll save $6,000+.......

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I'm starting to think most comments from professionals I've talked with......NOT THE MEMBERS HERE........mostly talk and have pure drag racing on their minds. So maybe thats the reasoning. These are quick back and forth emails asking questions. I always say "street car". But the conversation usually gets back to making the most power possible, this guy runs 150mph in the 1/4, at this weight, this one runs 8's.......conversations are always turned towards 1/4 mile stuff. I know its popular racing.....and street roll racing and daily driving not so exciting to most.
Maybe thats the reason.......

I'm ending this here by asking members here.......no more talking to different shops.

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If everyone agrees the Harrop 2650 will get you 1100 rwhp with the 390ci, then it sounds like a done deal. You'll need zero spark knock so you don't push water. Bob

 

I can spin the engine to 7000 rpm with the 8.75 lower and a 70mm upper and the supercharger speed is 22250 rpm. So I think 6800 or 6900 will by max rpm.....keeping it just under 22,000 rpm SC'er speed is the highest recommended for the Harrop 2650.

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Just hope its a good roll racer, mile racer....and daily driver too.

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It will be interesting, you'll have to post up what it does. Bob

 

Cool.......390ci it is.........

We'll see what this experiment does..........might be the first F-Body with a Harrop 2650..........

Thanks for the comments.........

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Thick bore walls, keep CR sensible, good or 1/2" head studs etc etc.

Again, making the power is easy, making it last the power reliably is fairly easy. But that thing will make a **** ton of torque too which will be much harder on parts.