How much will I lose ???

General engine tech -- Drag Racing to Circle Track

Moderator: Team

Post Reply
Sodbuster
New Member
New Member
Posts: 24
Joined: Thu Dec 01, 2016 10:19 pm

How much will I lose ???

Post by Sodbuster » Fri Dec 15, 2017 9:41 pm

3000 lb G-Body Bracket car, powerglide, with 5200 converter, footbrake only, 4:56 gears on a 9" slick. Best Time to date 10.42 @ 127 with a 1.44 60'. Currently powered by a 4.155 X 3.875 421 SBC. Profiler 176X, 23 degree CNC heads with 2.125 intake valves, stock 400 block with splayed caps, 14:5.1 compression, S/R Roller cam, Team G single plane with a 950 CFM APD carb. The current engine runs great, but is tired. .006 clearance on mains, front and rear main caps are moving, cam is worn out, and no matter what I do it wont stop leaking oil around the rear main. I found a great deal on a 4.125 bore Bowtie Block, Lunati 3.625 stroke crank, 6" Lunati Pro-Mod rods and Lunati flattop pistons for Brodix 18 degree heads. All of the parts are in new the box. This was a popular combo for a dirt A mod in our area back in the day. I'm considering building this new combo but replacing the flattops with domed pistons (hoping for around 14.1), reusing the Profiler 176X heads, intake and carb, and new S/R cam to match the combo. I don't thing I can afford to maintain an engine that turns much over 7500 RPM. I will be giving up 33 cubic inches and I am concerned that the heads may too much for the smaller inches. How much power and ET do you-all estimate that i will give up with the new combo. Thank you very much for your help and comments !!!

Frankshaft
Expert
Expert
Posts: 639
Joined: Sun Jul 05, 2015 6:01 pm

Re: How much will I lose ???

Post by Frankshaft » Fri Dec 15, 2017 10:53 pm

If your buying pistons, make it 4.155 bore, add a little gear, and a little converter, as it should/could make the same power, but at higher rpm, and it WILL be faster. See 600hp at 6200 or 600hp at 7200 rpm thread, lol.

Sodbuster
New Member
New Member
Posts: 24
Joined: Thu Dec 01, 2016 10:19 pm

Re: How much will I lose ???

Post by Sodbuster » Fri Dec 15, 2017 11:12 pm

Thanks !!!. I have had the same thoughts. The old 421 has lived an long time turning 7200-7500 and i was considering 7500-7800 for the new 388 or 391. Several years ago, the 3.625 stroke was a real popular dirt A-Mod engine in this area. Supposedly fairly torquey and smooth and lived alot of laps at this rpm, but the cam and heads will make a big difference . I dont know if it would ever make 1.5 hp per cubic inch, but losing 33 inches would be almost 50 hp. In bracket racing I guess it doesnt matter, but my ego is telling me different.

Sodbuster
New Member
New Member
Posts: 24
Joined: Thu Dec 01, 2016 10:19 pm

Re: How much will I lose ???

Post by Sodbuster » Fri Dec 15, 2017 11:24 pm

I have read the 600 hp @ 6000 Rpm or 600 hp @ 7200 Rpm thread LOL. If I was guessing 7500-7800 RPM is possible with fair parts, but over 8000 RPM takes GOOD parts and a lot more maintainence and $$$.

Keith Morganstein
Guru
Guru
Posts: 5227
Joined: Sun Feb 19, 2006 10:19 am
Location: MA

Re: How much will I lose ???

Post by Keith Morganstein » Sat Dec 16, 2017 6:00 am

There can be 30 HP improvement from a stock block 400 to an aftermarket racing block, esp at higher power levels. This is because of a much more stable block and cylinders, better ring seal, better machining, lifter bore blueprinting, etc...
Automotive Machining, cylinder head rebuilding, engine building. Old school shop, semi-retired moonlighter. Can't seem to quit #-o

Sodbuster
New Member
New Member
Posts: 24
Joined: Thu Dec 01, 2016 10:19 pm

Re: How much will I lose ???

Post by Sodbuster » Sat Dec 16, 2017 8:09 am

Thanks Keith !! That is good to know.

Post Reply