So now that my car is complete I have taken it to an engine tuner. You cant believe how hard it is to find someone that can actually tune a car with a carburetor and distributor. Besides the tune they are going to dyno the engine. My question and concern is this. My coded 708271 carb they say has a leak, they were going to repair it but they said that from a performance point of view it is too small for the motor. The motor is the correct 1968 400 HO motor. I thought the carb was 800CFM. Their plan is to put an edelbrock 650 on there. I do want car to run optimal but are these people correct? I know that many people refer to these carbs a Junk, but these tuners are telling me that true 800 cfm carbs are on 600-700 HP race motors and this carb is not that big?
Do I listen because they are correct or do I grab my car and run?
Restored by me. Not a professional. Restaurant worker by trade. YouTube forums and some trial and error built this beauty. Sheet metal replacement. Body work. Paint. Rear gears. Interior. And engine. ALL ME. Toot toot
Your stock 4bbl should be rated at 750CFM. A 650 Edel is going to be even less than you have now. Sounds like your tuning guys just don't like, or want to deal with, a quadrajet. Most mechanics don't have a clue how to make one work well. Sounds like they are trying to talk you into buying something they can just bolt on in a few minutes and send you on your way. It's just plan lazy. You gotta ask yourself what else are they going to let slide because they don't know or want to do the job right?
well I didnt grab my car and run. I told them to skip the carb swap and tune the one I brought, Waiting to get call about its completion. I will post the dyno numbers when they are done. My goal is to be around 350hp and a shade more torque. both should be achievable with my stock carb as those are close to the factory numbers.
Restored by me. Not a professional. Restaurant worker by trade. YouTube forums and some trial and error built this beauty. Sheet metal replacement. Body work. Paint. Rear gears. Interior. And engine. ALL ME. Toot toot
Sounds like you just gave them the green light to do a half assed job. I hope your happy with the results. A Dyno-tune around here runs $500. Personally, I would expect a lot from somebody I gave that much money to.
If they are going to dyno at the rear wheel, you will see a lot lower numbers so don't be surprised. Horsepower rating back in our day was at the crank.
I agree with keeping and repairing the Quadrajet. Not that I don't think you can tune the Edelbrock to work well with your car but you already have the Quadrajet and they are excellent carburetors.
If you have the engine in the car and are going to get it tuned at a chassis dyno, get them to tune the car for the way you are going to drive it. Shooting for the highest horse power you can get isn't going to get you the best street/road machine. It's great to say 'I've got a 500 HP 400" but how often are you going to drive around at 7000 RPM unless you're racing? The beauty of a chassis dyno is the can simulate road conditions and tune your engine to perform for the road. Sometimes a dyno shop will keep changing the tune to get the highest horse power, which will come in at a high rpm, at the expense of low and midrange performance.
Sometimes people get hung up on that dyno HP print out which means diddly squat when your street manners suffer. Sometimes they get caught up in the CFM rating as well. Your engine is only going to take in as much air as it needs regardless of the CFM rating of the carburetor. One can tune a big CFM carburetor for a smaller engine but it's easier to tune a carb that is correctly sized for the CID and the rpm at which the engine is going to be run at.
And as Harold stated the HP rating Pontiac gave your engine was at the crank, you can expect the chassis number to be 20-25% below that. My 428 made 535 HP at the crank and it lost over 100 HP at the wheels.
Back to the CFM rating, mine made more top end HP with a 750 cfm carburetor than it did with an 800 cfm carb. and it's 464 cubic inches.
Well I should wait to comment once the final numbers are in. But my car is complete I just have to pick it up. I dont know the final numbers but I did keep the Quadrajet and they tuned it with it. I think the reason to change the carb was because it had a leak, They chased down the leak and replaced the float. Without the sheet in hand I dont know the total HP it produces but was told they gained 75 HP from when I brought it in. That is a solid number I believe. More info to follow.
Restored by me. Not a professional. Restaurant worker by trade. YouTube forums and some trial and error built this beauty. Sheet metal replacement. Body work. Paint. Rear gears. Interior. And engine. ALL ME. Toot toot
ok so results are back, man what i difference in performance. Went from fun to wow. They gained 75HP on the tuning. Key issues were an exhaust leak at the manifold, leak in the carb also besides tuning replaced float and a pinched fuel line.I dont know what the AFR is or the PSI is on the test sheet. If anyone can tell me that would be great. I feel the RWHP at 292 is pretty great, not sure if anyone knows what that might translate to HP at the crank but I feel it has to be better than stock
Restored by me. Not a professional. Restaurant worker by trade. YouTube forums and some trial and error built this beauty. Sheet metal replacement. Body work. Paint. Rear gears. Interior. And engine. ALL ME. Toot toot
Not too bad really. My first 400 dynoed on a dynojet was real close to the same numbers. It looks like yours could be leaned out a bit. Pretty flat line at 12 and change AFR( air fuel ratio). That's a bit fat. Mine was run at 5800 ft elevation( Reno,Nevada). It ran 297hp/360ftlbtq. Youre at 293hp/340. Pretty close. Thats pretty close to 350-360hp at the crank.
Guys- I'm entering a similar process. Need to tune. Just rebuilt the distributor, nice and solid now (shimmed to .020 to correct the too-much-play up/down, new curve kit, changed advance bushing, new rotor, points (gapped to 0.016) condenser, retaining spring, even glass beaded the body). SO.... to the Quadrajet. Who is Cliff Ruggles, and why is that name familiar? Mentioned before? Can someone send me his contact info?
And by the way, ACENHO: Nice looking Bird you've got! Nice Work
'68 400HO Coupe, 4 spd, 259 interior, Windward Blue. My other car's a Johnson 15 outboard on a '61 Starcraft rowboat... Just sayin'.
It doesnt get any better than Cliff's and his kits. I found his kits are far better than others compared, ready for todays fuel with Ethonol. Cliff also will help you and his Rochester Quadrajet book is very good, and would be a great investment in keeping that car running good for a long time.