427 quadrajet selection

[AnthonyF]

Hey guys,

First I'll start by saying I'm a rookie when it comes to working on engines, especially carburetors, so I hope I'm not too painful for y'all. Here's a little backstory, last year I picked up a 78 Silverado K30 with a 427 out of a 69 impala in it. I have since broken the truck down and converted my 79 C10 Scottsdale Chevy Sport to a short bed K30. The engine in my 79 is an over the counter direct replacement 454 that my dad put in in the mid eighties. The block of the 454 is a hi perf four bolt main but it is in need of being rebuilt. In the mean time I want to run the 427 in my truck so I can rebuild the 454 on the side. Before I pulled the 427 out of the 78 I drove it around and it seemed to run okay but had a small miss that went away at higher rpms. I got the motor out, checked the compression on all cylinders and found that 7 out of 8 were running about 150 and one cylinder was at about 110. Now this was a year ago, so my numbers could be a little off, but I do remember the low cylinder being over 100 but considerably lower than the rest. If anyone can tell me what I should expect out of a compression test that would be awesome, Internet says the motor is 10.25:1 compression but I'm unsure how that translates to individual cylinders. I pulled the motor out of storage last Sunday and plan on starting it on the engine stand tomorrow and adjusting the valves in hopes that there is just a tight valve causing the low comp. Any suggestions let me know, [img]<<GRAEMLIN_URL>>/smile.gif[/img]

I noticed today that the quadrajet carb on the 427 is the carb off of the factory motor of the 78 Silverado, a 350 sbc. The quadrajet on the 454 is also the factory carb (79). I'm planning on rebuilding the carb for the 454 and running it on the 427. Is it a good idea to use the carb for the 454 on the 427 or should I just buy an aftermarket carb that can handle more power/torque of the 427? Is there a big difference between the two carbs because one was made for a small block and one was made for a big block?

Thanks!

[AnthonyF]

I need to add, after further research, that the compression test on the 427 may have been inaccurate, the engine was on a stand and hadn't been ran in a few days so it was cold at the time of the test. That being said, there was consistency with seven out of eight cylinders with one being considerably lower than the rest.

[WILMASBOYL78]

I would suggest two things...

First...confirm the engine compression problem one way or the other before going any further...all the other tuning and carb issues are academic if the motor is not ok.

Second...talk to Eric Jackson [Vintage Musclecar Parts] his ad is on the right...just give it a click. He can help answer your carb questions and point you in the right direction. Chevy used the QJ carb on everything from 305's to 454's...and lots of motors in between. Some of the later carbs may have more &quot;smog&quot; features built in...Eric can recommend the best way to go. His reputation and quality of service are well known on this site...

good luck with your project...post a few pics for the gang to see.

wilma