Hey folks, looking for cam/turbo advice on my oddball turbo project, 1976 K5 blazer street/show truck. Goal is maybe 750 crank hp on pump 92, focused all on low/midrange torque. Obviously high rpm power/speed is not a factor for this one. Stoplight to stoplight fun factor is all I'm looking for.

Parts I already have:
Gen 4 iron 370
Forged 12cc dished pistons
Forged H-beam rods
Stock crank

Heads with CR according to Summit's calculator:
823 rec ports 68cc 9.2:1
243 cat ports 64.5cc 9.52:1

Built 4l80e & treadstone A2A

Looking for cam and turbo combination that will deliver snappy low end torque at the expense of top end. Cam can be off-the-shelf or custom grind. Single-turbo only. I already have 3 other cars on twins so going single this time. Not interested in a Whipple or Procharger. I'm a turbo guy. Thanks!

 

If you just want low end grunt, just keep the stock cam.

I am running a 7875 in my LQ4 with the stock cam. GOBS of low-end quick-spooling grunt. It's hilarious on the street.

 

Gears will help more than anything to move mass quickly

What trans ratios are you running? What final ratio?

I would be looking for a 3.5-4:1 first with a 4.33 or 4.56 final if your goal is stoplight to stoplight

 

Good to know. What a/r on your 7875?

 

Well the 4l80e is 2.48, 1.48, 1.00, 0.75 and my axles are 4.10 on 33" tires. Deeper gears would help but I also want reasonable rpms at cruise. I think the right cam/turbo combo should be able to make up the difference.

 

That's a gorgeous K5 my friend.
The easy button of course is the billet VS 7875 but with the room you have under the hood I'd also consider a billet S475.
This guy would still spool up very quickly on a 370, keep the back pressure reasonable and still be able to rpm decently.
VSR 75mm Billet 96×88 Turbine 1.32ar T6 – VSRacing
For a cam any Stage 1 Turbo cam will be sufficient, but you could certainly ask the question to any of the cam gurus like Baker, BTR, Martin Smallwood, Pat G, etc.
I'd run the 243's as well, I ran as much as 15.5 lbs. with about 9.5/9.75:1 compression on pump gas with no knock.
Now your rig is much heavier so you probably won't get quite that high, but you could always use water/meth to keep detonation at bay at higher boost levels.

 

Thanks! Agreed there are several options right in the same ballpark (7875, 7883, S475) any of which would probably work fine. Just hoping the pros can help me zero in on the details. I was thinking 7875 with a tight a/r would light up quick even if it chokes on the top end. Don't really need high boost or room to grow on this one, it will probably never see 80+mph.

I confess that pic is just my photoshopped rendering of the end goal, but I'll share pics when its done. Just for fun here's my other truck thats taken me about 2.5 years to build.

 

your current combo is turning about 2000 RPM at 65mph. I wouldnt worry about spinning the motor at 2500 or 2800 at 65 however your rear ratio total is only 10.17 in first

I would look into a 6-speed, like a 6L80e or similar with a 4.03:1 first, especially running 33" tires and now adding reasonable RPM's at cruise as a criteria. same final, so the gear ratio total is 16.5:1.

 

I had one of those!
It had a BBC 454 with big oval heads, it would light the 35's at will and got 5-6 mpg lol.
I loved that truck but I put two or three cams in it because it sat all the time and it kept flattening cams, so I sold it to a friend of mine.
Honestly, I'd probably just do a 7875, it'll be way easier to package and get you where you want to go.
There's a gent on here who did a great comparison of the VS 7875 and the VS 70/70 on his 5.3 and the 70/70 lit up very quickly and still made good power, might be worth looking at.
Just be careful with boost at low rpm, the rods don't take too kindly to that sort of thing lol.

 

Nice!! This one has a Gen 6 454 with the roller cam. I built it to be mild and reliable but now I wish it had more power...lol. Sounds like you're thinking what I was thinking. VS7875 might be the sweet spot with an a/r around 1.10 or similar. Last time I looked I think they even had a few turbos with that T-51r mod to make the whistle louder. That would be fun.

 

I think you're right-on with that assessment, but I already have the 4l80e.

 

You also already have the 454. Why not turbo it? If you are set on swapping engines, a little garrett clone 67mm turbo put a lot of 6.0 escalades deep in the 12's for 1/4 mile times. Those things will brake spool full boost.

 

The 454 is in the truck. The turbo 370 is going in the K5 blazer.

 

My bad. I was skimming the posts instead of looking closely. Probably going to be hard to beat that 70/70 turbo mentioned a few posts up. people sometimes forget that some of us don't care if the truck turbo chokes out at 7000rpm, or if backpressure hits 2/1 on a street only vehicle. Instaspool is fun in a heavy truck.

 

Exactly! So you're leaning towards the 70/70 instead of the 7875? I'll have to search for some posts and read up on that. Thanks!