Q Re New Motors (off topic?)

Hopefully the legacy of Avanti Motors will put this question within the "on topic" boundaries.....

I read this groups postings every day and value the wisdom of many - at least they are articulate enough to convince me they know what they talk about when it comes to serious wrenching. I have a question about what I should expect out of a newly built motor:

I own a 1990 Avanti 4-door and recently had a 383 stroker motor built and installed. It runs great, but rough. I'm disappointed in how rough it is. I purposely built it for torque and what I thought would be a smooth runner. By my calculations it is at 9.4:1 compression. It has a cam that is only one or two notches above stock. The machine work included extra for balancing everything as an assembly and clearanced for the 400 crank. I'm using Edelbrock Performer RPM aluminum heads with 1.6 roller rockers. There are Hedman headers with

2.5" dual custom exhaust, but currently no cross over. Could it be that a cross over would help smooth out the engine? I get on it every chance I get (:-) and am getting 15.5 MPG with Tune Port Injection. The power is awesome. I know the ECM is programmed just a hair off (originally was a slightly different cam profile) - everything on it is new including motor and tranny mounts. What should I focus on to help this thing run smoother? I have to have a lid on my coffee (which I always do anyway) or it would slosh out just idling.

BTW, on August 18th I'm getting it dyno'd. My guesstimate is it should be 300- 350 HP at the rear wheels and slightly higher torque readings.

Would appreciate your thoughts - thanks!

Rich

Richard Morris Renton, WA

1964 Avanti R-1 #5367 1990 Avanti 4-door #78
Reply to
Rich
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Reply to
Robert W Hughes

Reply to
dwcars

If you are running a 400 crank in a 350 block, make sure you have the 400 harmonic balancer and the 400 flexplate. The 350's are internally balanced and the 400 smallblocks are externally balanced and if you don't have the

400 balancer and flexplate you will have a hellava vibration. thanks, Jerry.

Reply to
Jerry Forrester

Bob - I checked all the injectors and they seem to be firing okay, but I'll dig a bit deeper tomorrow. It would seem strange to have such scary power if it were only firing on 7 cylinders.

DW - I have an aftermarket ECM that was programmed by Scott Hansen of TPI Programming Svcs. The cam I'm running is Crane's #100052 (.216" duration at .050", lobe separation 110 degrees and lift is .454") The ECM is programmed for .214 duration, but that shouldn't cause the roughness. I used slightly dished pistons to yield a touch lower compression.

Jerry - now I'm not sure about the balancer - I remember this was a consideration, but can't remember if I got the right one. I'll double check, but I doubt this is the issue - will let you know.

I think I'll search for a really knowledgeable engine guy and let him look it over.

Rich

Richard Morris Renton, WA

1964 Avanti R-1 #5367 1990 Avanti 4-door #78
Reply to
richarddavidmorris

Rich...look over @ the Chevy Hi Performance magazine web site.Look around and see if you can find recommendations on 383 builds,and science out the answers about ballancers and such.They just did a 383 build in the magazine awhile back.Great technical oriented magazine,unlike the Popular Hot Rod type of picture book.

Reply to
ChampTruckingCompany

Richard, You might want to check the Racing Studebakers website for more thoughts/ideas.

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Johnson

Reply to
Paul Johnson

I subscribe to this mag and, you're right, it is great for tech articles. I'll visit their website to see if I can learn anything. Heck, maybe I'll send my question to the editor. I have to admit, I spec'd out everything done/added to this motor - and most of that came from Chevy Hi Perf mag.

Today I checked and all cylinders are firing - no misses. I also looked up in my receipts - I bought a 383 kit that included an internally balanced 400 crank. The balancer (and flex plate) are neutral.

Has anyone exhaust experience with and without crossovers? I know they'll change the sound, but do they help modulate or balance vibrations. I can't understand why a 383 is inheritly rough idling.

I think any of you visiting the Seattle area ought to come drive it for yourself - not only could I treat you to a great cup of coffee, but meeting some of you face to face, I'm sure, would be a memorable experience.....:-)

BTW, Paul, thanks for the suggestion of The Racing Studebaker website. I'll check it out.

Thanks for all the suggestions and help.

Cheers, Rich

Richard Morris Renton, WA

1964 Avanti R-1 #5367 1990 Avanti 4-door #78
Reply to
Rich

back to basics, check the spark plug routing as the #5 and #7 plug wire being accidently swapped has had many a hair follicle scratched out of the skull, it's a easy and very common foul up, BTDT more than once or twice .

Reply to
oldcarfart

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