Hiya. I got a really nice 2.5" mandrel bent exhaust with magnaflow mufflers on friday. This was to replace the stock-type 2" system with stock mufflers. Before the exhaust upgrade, I could bark the tires good at 15-20 miles per hour, without a kickdown (cable is broken). Now, the tires maybe chirp. Also I seem to have lost some acceleration overall. It's as if flooring the gas has no effect (yes, my secondaries open fully:grin: ). There is no stumble or bog. Now, here's my feeling: I need to re-jet the carb to at least the next larger size, at least on the secondaries. The engine has stock, small valve heads from '74 (all emission junk is history) and large primary headers from TA. the intake chores get handled by an Edelbrock Performer 455 manifold and an Edelbrock performer 800cfm carb with stock jets, under a stock '71 GS350 dual snorkel air cleaner mated to a GS hood. the cam was a mistake on my part, I had looked at specs for 1970 and noticed that the 455 in the Riviera was rated at 370 hp, so I ordered an "rv" cam from TA...come to find out, it's a recreational vehicle cam profile (I did not have the know-how to degree it). Oh well. Car still scoots well enough. The pistons are 10.1:1 pieces, that if I remember correctly, put my compression at about 9.6 or 9.7:1. the engine itself is in fine shape, I rebuilt it a few years ago and it's a sweet idling, quick revving engine that pulls 19" Hg. I may have some nasty deposits on the cylinder tops by now, but that's life. The timing chain's a double roller, I modified the fuel pump arm with no ill effects that I can see, the fuel pump shoves out lots of fuel ( barely a need to prime the carb if I take it off, clean it inside and out, and put it back on the manifold without any gas in it) I use a stock water pump and 7 blade stock fan to cool a 4 row radiator from Modine, the car keeps it's cool just fine. The distributor is a street/strip big cap HEI and I use AC Delco R45TS plugs with 9mm Accel wires. the entire engine was blueprinted and balanced by a damn good machinist (Thanks again, Tom Cavuto:TU: ) and assembled by me, the car sees regular street duty as a daily driver and the engine has proven itself very reliable. OK, so much for the background on the motor. I have rebuilt any number of side and downdraft aircraft carbs at school. I can rebuild this Edelbrock almost blindfolded. I have no qualms about yanking it apart again to re-jet it. Yes, I should send my 800 cfm Buick Q-jet out for rebuild, but let me get a job, first:grin: What is all y'all's take on my situation? I feel it's the carb that's robbing me of performance right now. I'd appreciate your input.
Chris, I think the bottleneck is the cam!ou: If you want the performance of your engine to come to life, take that rv out and toss it. Also, unless you decked the block (I had to go .050") I kinda question the compression ratio. It could be a good bit lower than you think~~
Well, I'm a bit confused...yes, I know the cam is the weak link, but I'm not looking to make killer power right now, but rather, why did I lose a bit of power, and where should I look to get it back. I am considering the TA 212 cam for the future. But the probelm is: I had MORE power on tap before the exhuast upgrade. Seems like the four barrel is acting like a two barrel but the secondaries definitely open all the way. The Edelbrock Performer 800 I have is the AFB clone, square bore. I have Tubular headers from TA performance necked into their 3" collectors, then down to a 2.5" head pipe to the mufflers, and then to the mandrel bent 2.5" tail pipes.. I didn't replace my headers; there is nothing wrong with them, but no, I do not have exhaust manifolds anymore, I got the bundle of snakes.
Hi Chris - With my stock Stage1 carb (jets 68/42), John Osborne jetted me (a rebuilt '71 800 CFM carb) to 76/48 after a new exhaust (ported manifolds, 2.5 mandral bent w/X-pipe, walker 17749) The car is a completely different animal :Brow: Think about rejetting.
:TU: With that RV cam I can probably afford to lose it, and it will be easier to drive in the rain! Mmmm, chocolate doughnut
I'm not thinking about it anymore, I'm doing it. I sooooo want my Q-jet back on my car. I just don't have the dough right now. I won't build it myself, I'll have John Osborne go through it for me when I scrape up the dough. I suppose I'll pick up a strip kit for the one I have and find some nice deserted road early in the morning at like 4, hook up the G-tech and do a little "research":grin: I thought maybe I was going a little nuts when i felt the car had lost a step. It's good to hear I might be on the right track. I guess I was a lil bit confusatory there before, I try to give out more information than I probably need to.
