Hot Rods ? For engine gurus, blower cam specs

Current cam is still a mystery for some reason. It's hard to say if "more cam" would be beneficial enough without knowing what's in it now, or watching it run.

However peak power of 400 ft lbs at 4700 rpm means it isn't a high rpm heavy breather or a low end torque monster.

 

I didn't build the long block, so I don't have the cam
Specs. It just seems a little timid from the sound, and the dyno shows me that something is definitely up.

 

While you have the short block apart to put in the dished pistons, maybe you can find a number on the cam that will identify it?

 

Ok, so this engine probably was not built with intent to be under a blower.

 

Would he want to get reverse dome pistons? Or do you even worry about quench in a blower motor?
Or does he need the full dish to get the CR reduction he needs?
I mentioned that we made good HP with this combination NA, but after I thought about it a bit, I doubt if we made that sort of torque, and that's what moves the car.
I'm waiting for you guys to start discussing head porting...

 

The heads....he wants to run old heads, and you can only do so much with the old Fuelie heads. Although finding a set that was ported by someone who really knows what he's doing is a good place to start.

9:1 or more compression is not really in the recipe for a street driven blower motor.

Dished blower pistons have quench around the outside of the chamber. You don't want to run a flat top down in the hole.

 

I had the same thought in mind when i went about building the blown 327 for the 32.
Had to be a small journal and had to have the old "double hump" heads along with the air pump.
Comp was the issue. There were not many piston combinations i could find, aside from custom made, that would drop the comp low enough for the huffer.
A good friend who also owns an engine machine shop and was doing the work on my block came up with the combination.
I ended up running a 6" H beam rod with a 383 piston.
Even though the rods are longer, the piston pin location it closer to the top of the piston thus dropping it further in the hole, dropping the comp to a range that was plenty suitable for a blower application.
Im sorry i cant remember the exact numbers, but it was close to 8:1.
with my drive set up it should put full boost at 7lbs, but honestly i cant stay into it long enough for full boost, the car just go's sideways.
I have to dig out the cam card we used as well, and will as soon as i have a free minute.
But im fairly sure it was basically a comp cam replacement for the GM 302 cam used in the Z-28.
The specs fell right into the range we were looking for.
It all worked real well.
Its a 62 block, 64 heads, 67 blower and runs like a scalded dog.

I'll look for the cam card and be back soon as i can.

Tony

 

Here's the card


In this application it certainly seems to work damn good.

Tony

 

not to sound like a dumb ass or smart ass but figure as much of your motor out and ask the cam companys?
When my blower motor went together as a 'street motor' the builder knows good combinations for blown SBC, but we still used a comp cam that was made for blowers. Cam mfg's have done the research on what works and what doesn't work as well.
This is what i got
http://www.compcams.com/Company/CC/cam-specs/Details.aspx?csid=171&sb=0
383 w/6/71, afb 600's and mild head work on late 70's emission heads...600+ hp and tq.
The cam company's will always pick conservative for you, knowing that you can decide if you wanna step it up a tad....

just my .02

 

Pbrme, how much boost are you running? What is your static compression ? Thanks for the info, I might just call up comp cams.

 

I have a very similar cam (but the big block version) in the 454 that I put over 100k miles on with a blower in my 55....and a little bigger one in the 427 in my Chevy II, which is more race oriented. That cam design works well!

the 55 ran low 11s with a "me in it" weight close to 4000 lbs

 

4-71 on 355 cubic inches at 6psi requires a fast turning blower...could it be parasitic or heat causing the not-up-to-par performance?

 

I was thinking that too, a 6-71 would not have to work as hard. But the look is important too....and swapping to a bigger blower usually means serious changes to how the car is set up.

 

My calcs say that car should do high 10's now. Sumting wong

 

I have a hyd Crower blower cam#00980 for a blown 350 with between 5 and 10 lbs of boost. It specs at 232@50 duration, .459" lift with 1.5 rockers and a 114 lc. Rpm range is 2400 to 6500. It has 250 miles on it before I switched to a roller cam, and it has been on the self waiting for my next project. Pay for shipping and it is yours. Buy some new lifters and give it a try to see if it changes the way that it runs.
Brian

 

I have not run it yet. Maybe it will perform just fine. There's not much weight there. All I really want to know is if I am under sized on my cam.

 

It sure is hard to know, without knowing what the cam is!

Does it feel "soggy" on the bottom end? or does it fall off too early on the top end? how is the idle?

 

It's idle seems ok. It doesn't have much lope to it. I can make
It idle at like 800 rpms. It makes a lot of power early, but it runs out at like 4900 rpms. I don't have any info on the cam. When we dynoed it the guy running the dyno seemed to think it could use more cam. He also said it was in need of a little smaller carbs.

 

The chassis dyno sheet would help for sure I'd bet. In some cases Chasing higher peaks can leave you feeling short and deprived under the curve on the street unless you can get 4000 Rpm off a stop sign.

300 hp 400 ftlbs- at wheels
Peak power at 4700

20% loss in drive train would be at flywheel/crank 375 hp and 400ftlbs @ 4700.

IdK But,,,, there's 450 rpm to the 5250 mark, at least 1000 rpm to a red line of 5700 rpm.

For comparison with no boost

Here's a 375 Hp 350
http://www.proformanceunlimited.com/specs/350_375drop.html

Here's a 375 hp 327
http://www.proformanceunlimited.com/specs/327/327_375_carb.html

 

Sounds good to me. Where are you at? Maybe I got something cool I can send you in return.

 

I will grab the cam tomorrow and give it a good once over to make sure that there aren't any issues and I will let you know.

 

This is the most blower discussion I've seen on here ever. When we built our 355 SBC a couple of years back I don't think I got 10 replies total. First thing we did was call Comps tech line, Holley/Weiand and DSS Racing on a conference call and started the discussion by stating what performance requirements we needed. It cost me a little but has paid good dividends in the long run. We started with a good 4 bolt block and put forged internals on the rotating assembly with 18 cc dished pistons. Then we used the induction cam setup suggested by Comp Cams tech line. We topped it off with a set of 74cc Dart heads with 180cc runners, a 142 cid blower, 700 double pumper blower carb and a MSD distributor with the controller box. Our static compression ratio is roughly 8 to 1. The cam starts in around 1600 and finished just over 6000 rpm. The truck its in is intended for street use and pulling a boat. It runs like a scalded ape and eats late model Camaros for breakfast. You definitely should be getting better out of your setup. Good luck getting it straightened out.

 

Thanks for the reply. I've read what Vizard has to say about porting the intakes, warning about not making the port too big causing a loss in velocity, and maintaining the correct shape for swirl.Is this still a big concern w/ a blower, or could he help himself with some home porting and let the blower do the work?
I read your comment about making the cam suit the RPM range for the street, just wondered if street driveability is as big a concern with the heads, given the blower should help the bottom end torque?

 

The heads have to flow a bunch more air with a blower at WOT, and part throttle performance is usually not a concern on a motor like this. In general, bigger is better

 

As of right now I intend to change the cam out for the cam capt crash has been so cool to offer me. At least then I will know the cam specs.I am also planning to have the heads match ported and a mild polish job. After this I will make another run on the dyno. I'm not going to change out my Pistons. If I were to go that far I would just build another motor.

 

might want to do a little work on the bowls, under the valves, make a smooth radius from the seat to the port. Don't enlarge it, just smooth it

 

Thanks squirrel. I used to do some very minor port work for a machine shop I worked for, but I have never done any smoothing. I might send them
Out to a pro for that.

 

What about porting a set of early heads that have bigger combustion chambers?

 

What are the largest combustion chambered double hump heads?

 

that's the thing....the double hump heads were all small chamber, high compression heads.