new 400 build making Pinto numbers on dyno
 

Had a local pro build a 400 for pump gas street driving that after 8k investment it came off the dyno at 191 hp, 262 tq. Didnt get much of an answer other than the quadrajet is a junk carb and should use something else.

Here's what they put together..
1971 YS 400, .060 pistons, crank .010 with factory rods.
#96 heads with new seats, surfaced and .065 head gaskets. Comp checked out to be 155 psi.
Bullet hyd roller camshaft 215/220 dur at .050, 106 degree, hyd roller lifters with new pushrods. Springs, studs and retainers in the cam kit. 1.56 roller rockers.
Factory cast iron intake, Ram Air manifolds, new HEI dist plugs and wires.

Not sure where cam was degreed in at or total timing.
Now maybe its just the carb I supplied that was junk and need to find a better quadrajet.
Big question is in my head, was this cam a good match for the compression?
Thanks in advance for any thoughts!

Verify a full 34* ADV at 2500 rpm.

Verify Quadrajet Secondaries open completely with gas pedal. Wheel dyno or engine dyno?


Time to rejet?

Were you there when they dyno'd it?

Something is wrong I'd say, a 2bbl would probably make more than that?
Are you mechanically inclined?

I'd check timing and full throttle as said. Also check valve adjustment.

:confused:

It should be making a good 300 HP. I would not have used a .065 head gasket though, but that did not cost you all that power.
Stock they were 300 HP and you have a bigger cam.

At what RPM was peak torque and peak HP?

Stan

Thanks guys for the replies. I wasnt there during the dyno session, was on a engine dyno, pulled rocker covers to check out lash (maybe one or 2 were out?) but even though cold engine none were over .003. peak hp was at 4300, tq was at 3600. I dont have the gasket they used under the carb, was suspicious bout that it didnt clear the secondary butterflies but surely they would have caught that.

why the .065 head gaskets? did you ask how far if any in the hole the pistons were? i been afraid to run a .038 gasket with mine .020 in the hole. i cant imagine a .065 gasket being a good idea even at 0 deck

i think your compression was not a good fit for your build.

Your lower than stock 2bbl HP sounds like you’re running on the primaries only, which on a quadrajet are actually smaller than a 2bbl Rochester. Verify the secondaries are actually opening.

A competent dyno operator would have noticed this and tried a different carburetor.

Tripower Motors built for street performance and using 67 and up heads, running off of just the center carb have made over 300 hp.

I say that the carbs secondary’s were not opening.

Does your dyno sheet for the motor have a vacuum column or at least a BSFC read out on it?

Did the builder check if different length push rods
Where needed considering the valve job and those ridiculous thick head gaskets?

Find a new builder/dyno... Something is way off for those numbers with that combo.

A 400 with 96 heads, .065 head gasket, typical 6cc pistons .010 down in the hole is going to be about 7.94 compression. That's with good TRW forgings. Please tell me they didn't use the cast 8-eyebrow monsters? If that's the case, the compression is in the 6s. Put it in your lawn tractor and run it on kerosene, LOL.

250-320 HP would be the expected output if properly tuned.

The tune was WAY off or the secondaries didn't open. Hyd cams don't have lash. Were the valves set correctly?

Low compression heads AND a thick headgasket? WTF is the builder thinking? Some builders don't care about engines that aren't SBC or LS, or don't know the gotchas on other makes.

Did you tell him you wanted it to run on 87 octane? What is the application, a tractor?

I am by no means as engine smart as alot of the minds on this forum but even I would definitely say something is not doing it's job (carb etc...) as this is the Dyno numbers from my stock (bored .030) 350 H.O. so I would think at minimum you should be in this ball park.
Hope you find your issue and it's an easy fix!

With the engine being run on an engine dyno. Could you please post the printouts of the dyno pulls? I would like to see the air consumption numbers, the fuel consumption numbers and the vacuum numbers. That would tell us quite a bit about the "junk quadrajet" Any carburetor can be "junk" if it has a problem, is not jetted properly, or isn't opening most of the way. When I know the engine has been built properly, but the student/customer supplies his own carburetor. If the engine way under performs, we have a "shop carburetor that always works well on anything we put it on". We remove the suspect carb and install the shop carb. I have personally witnessed a 50 HP increase vs a really messed up or mis-matched carb. I am in NO WAY saying Quadrajets are junk. You may have one with serious issues though. I have had many more Edelbrock AFB clones that were much worse before extensive tuning than any Q-jet.

There are allot of things a "Chevy shop" can do to ruin a Pontiac engine build. Did the shop you chose have at least 1 person on staff that had some specific knowledge about Pontiac engines? I ask this because you mentioned they installed new valve seats. All 16? Is there a chance they converted the intake seats to 45 degrees? That can hurt the power. Also, as mentioned, the compression may be really low which will allow any fuel to be used but kill the power. A cam ground on a 106 centerline for this build is not optimal IMO. Lots and lots of little things that may have been done in the Chevy world can conspire to make it run like a Chevy, unfortunately. Low torque and the Pontiac can't make the HP because of the low RPM limits. A little surprised an 8K engine build did not include some form of aftermarket connecting rods. Although that is not costing you any power in this build.

BTW, your reference to Pinto numbers on the dyno is just spot on. We build a 2300 Pinto engine for a student racing a spec. racer hydroplane. It made 235 HP @ 5800 RPM.

Agree that any carburetor can be "junk." When someone says that a Quadrajet is "junk", they usually do not know how to rebuild one, tune one, or make one function correctly. I would be willing to bet that the back barrels were not opening. Something is terribly wrong for that combination to not make over 200 horsepower. Even with close to an 8:1 compression ratio (assuming flat top pistons), I would think that it should make in the 300-325 HP range.

Other than cam timing being way out, I also suspect no secondary opening.

Or just flat out not getting full throttle. I’ve seen that story more than once with some dyno operators saying that’s the first thing they check.

Isn’t that super common with qudrajets or any vac secondary carb on an engine dyno? I know I’ve seen engine masters zip tie secondaries open.

BIG thanks for all the replies!! A few minutes ago I flipped the carb over to look at secondaries and WHOA BOY! Sure looks to me like the linkage on the secondaries is bent horribly, linkage wide open and that is as far as they open up, maybe half way

I've always been a Pinto guy, love them lil ponies! ( my niece says I'm a dork cause of it)

sorry for the poor pics of the sheet, camera is bout to konk out