I was wondering ... if I built a low-compression 383, but didn't have the blower yet, how slow would it be? Assuming 8.5:1 compression and 224/236/114 cam. I think it would have some good low end torque with that cam. But how much will the 8.5:1 compression hurt (compared to 10.5:1)? Could it still come close to 400 RWHP? thanks.

 

General rule of thumb is 4% per point of compression. So expect a 30-35 horsepower dropoff by lowering the compression 2 full points. The car should have decent power and good driveability, but blower cams are not effective at filling cylinder bores naturally aspirated since they don't have much overlap. IOW, it won't be a powerhouse without the blower.

 

I once built a blower motor and ran it NA for a while. It was a 3rd gen with an 8.5/1 360 cid SBC, AFR 210's, GM 847 cam (234/242), Victor Jr, and Holley 750. All of these parts are supposed to kill low-end, but the car ran a best of 11.96 at 114.5 NA - on 87 octane.

Mike

 

Those are good numbers, but the GM847 isn't exactly a "blower cam", so it's gonna be a little tough to compare your motor to Mikey97Z's setup. That 847 has more overlap than a normal "blower" cam, which was great when you ran it N/A. I'm sure your set of AFR 210s didn't hurt either.

 

It will be far from "slow". The loss in hp will be in the 5-7% range.

Rich

 

I don't think the 847 is that far off from a blower cam. A 112 LSA is pretty wide. In fact, mose blower cam experts agree that 112-114 is the range you want to be in. Compare my current 224/236-114 to the 847 and you see that the 847 has 14 degrees of overlap versus 2 degrees in my current cam (@.050). A good NA cam will have more like 50 - 60 deg of overlap at .050". So, I really don't think the extra 12 deg of overlap helped me that much NA.

If anything, the longer duration of the 847 hurt me even more because of the low compression. DCR was especially low with 8.5/1 static combined with 296 advertised duration.

Mike

 

I wouldn't run a 112 LSA on a blower specific motor IMO. Agreed, 12 degrees isn't a huge difference, but it is there.

The longer duration cam would be a help to your old combo, IMO. AFR 210s are "large" runners on a 360cid, and coupled with the Victor Jr. manifold, would lend that engine to do well in the higher end of the powerband; playing right into that cams strength.

 

I think that the converse is true. The "large" runners and Victor Jr. are suited for high end, but not so good on low-end. With the low compression, a short duration cam would perform better because it would help get the DCR up and partially offset the effects of the Victor Jr. and 210 cc ports.

Big ports + Victor Jr. + big cam + low compression = soggy bottom end

On the dyno, with the converter locked, it made 337 ft-lb peak at 5000 rpm. I can thank the Vigilante 3200 for masking the lack of low-end and allowing me to run 1.6 60' times.

Mike

 

put nos on it till you get a blower

 

heh. ricer say nawwwwwz?

now back to your regularly scheduled thread...

 

I think we're saying the same thing. I'm saying:

GM847 + AFR210 + Victor Jr= great top end, thus explaining your great track times with a motor that wasn't expected to be great when run N/A. I definitely agree about the soggy bottom end, but as you mentioned, a Vig 3200 does a great job of band-aiding that.

 

Good timing...I've recently completed my install of a similiar setup to what you describe and I was worried about the same thing initially. I've got an 8.3-8.5:1 383 blower motor with that 224/236-114 cam. With the blower belt on it's "snappy" and super-responsive...with the blower belt off, it's still got tons of torque and power, just isn't as snappy feeling. As soon as you step on it though, it wants to go...I wouldn't worry about it at all, it's made out to sound like far more of an issue than it really is...go for it! Rich told me that's how it'd be and since I trust his opinion, I went for it and have no regrets! P.S. Thanks Rich!!!

 

You are quite welcome! Glad it's working out well.

Rich

 

just out of curiousity, would the same be true w/ a turbo cam in a built 383? it looks like it's going to be a while before i can complete this project and i've already got the cam that Jordon Musser ordered for me in it. i've driven it for a while and haven't really noticed a huge hp loss, but was wondering if it is safe to drive it this way.

 

Cool!! Thanks Brian (and Rich), I am so psyched to start my 383 now!!