383 SBC quad 48 IDA 200hp 248ftlbs ???

[Jac Mac]

Certainly looks & sounds like the dyno op was getting out of the throttle early, having said that I would suggest that your getting into a lifter pump/valve train problem when you ran it up to 7000 in the garage. Depends what you want, low speed driveabilty 'might' suffer with larger chokes, but somehow I don't think that's gonna worry you It might help a little if you fit at least the top of the hood/bonnet to keep the hot radiator air under and away from the intake trumpets. The dyno you intend visiting might do a trade on the 37's for 42's, but as virtually every set of IDA's come with 37's they might be a bit meagre on the exchange.
Hope you never have a head on prang, the feds are gonna be weeks working out how fast you were going to drop the head gaskets and camshaft out the front!!

Now all we gotta do is convince you to fit that engine in a Lola T70 or McLaren body!!!

 

[mike hall]

Hahaha those would be harder to get legal on the roads over here it's easier to plop a 80year old body on a new chassis and be done the heads are coming off and new cam valve train this winter yah there is not any protection from anything in any kinda accident

 

[mike hall]

So I'm not crazy then with questioning the dyno results?

 

[Jac Mac]

So I'm not crazy then with questioning the dyno results?

No, I would say your spot on, look at it like this, the operator by only using an observed ~5000 rpm limit treated it much the same as you pulling out to pass a car and accelerating to say 80 mph then lifting off to maintain that speed, which is probably why both your tq &hp lines on the readout peak fairly early and then drop off slowly since the rollers are no longer being accelerated at the earlier rate.

On the cynical side it could be seen as a means of drumming up further business for that dyno shop, good thing is you didn't fall for that line! Like most things mechanical you often have to look past the obvious to get to the bottom of the real problem.

An early Scarab or similar era sports car must be getting close to an 80 year body these days....... I would suggest a Ferrari TR , but one of those would really get the establishment upset..

Bugger, forgot my Ford Blue Text............

 

[Robert May Eng.]

Aside of the webers there is not much going on in the way of power builders in this engine. The cam profile which would be quite a mild cam even in a 350 would not be as hot in a stroker, you could fit quite an aggressive cam in a 350 chev if it is being stroked. If you look at a 400cu sbc you will see they are rated at about 150 to 265 hp so without a lot more breathing,comp and cam you may not see 300hp. Stroker alone is only the cubes you need to compliment the rest of the package

Bob

 

[mike hall]

Well the jury is back and the numbers are 215hp and 325ftlbs of torque at 5100rpm I guess time to get new heads and cam shaft bigger venturis my curve is nice and my afr on the main circuit is perfect my idle circuit is rich as hell we did 6 pulls consistent with the same numbers give or take a hp or ft lbs I will upload the data later when I'm near my computer

 

[Paul fortin]

my two cents if your spinning tires and making the wife nervous. I think your doing ok. try a different shop to do the dyno before you do anything to your car.

 

[mike hall]

Yah I think where the ftlbs is coming in at 2500 and pulls to 5100 on the curve my top speed was 140mph I think it is what it is and I'm sure with bigger venturis full rollers and new heads I can pick up some decent gains I was planning on putting new heads on anyways this winter I'm looking at maybe getting those raptor venturis the dyno shop I went to my buddy was running the dyno but if they do a half off dyno day somewhere I'll pop in and get another base pull done and see the difference then average the three I guess but he also dynoed a 383 tbi and it only put 290hp 320ftlbs so I guess I'm not that far off from a stock 383 however my horsepower to torque ratio was much higher then that one I guess that accounts for the nice jack rabbit starts from a stand still

 

[mike hall]

here is the dyno graph

 

[Ron Earp]

Air fuel ratio is horrible for two of the runs, and not all that good for the other. I target around 12.8ish @ WOT. But sadly a better A/F isn't going to magically create 150 hp.

 

[mike hall]

Your correct on that on no it's not but I can get that air fuel ratio under controls free the winter but no point in doing anything with that until after I change heads cams and venturis

 

[Robert May Eng.]

The heads you have should support power north of 350hp, with the webers a bit more , something is holding it back. I think you need to double check what you have in the way of compression ratio and swap in a cam that will allow those extra inches to breathe.


Bob

 

[mike hall]

That may be Robert I'll try that first rerun on a dyno any advice on cam selection I'm gonna go with 42-44mm venturis I know ideal is 115 set lobe separation but I find cams with that separation usually doesn't have a higher lift

 

[Robert May Eng.]

The 383 is a well documented build and there are dozens of articles on them so it may be an idea to have a read up on a few. I would call up a cam shop give them all the info like axle ratio ,vehicle weight and intended use, they should be able to point you in the right direction. I would also be curious to know how it would run on 750 or bigger double pumper even if it was just to set a bench mark, a 48 ida is not a big carb for a 400 cube engine.

Bob

 

[Howard Jones]

.480 lift and 280 duration cam with a 10.5 to 1 CR and decent 2.02 heads should be making at least 1.1 to 1.2 HP per inch (421-460HP) Subtract 50-60Hp in loses and you are still at 350-400Hp at the wheels.

Even with that lean AFR costing another 10% I would still expect 325-340 at the wheels. Something is way off here. Check combustion chamber volume against piston type to verify CR, check cam degree timing, and who did what to the heads? Wrong springs? Overly optimistic port job? I think I would even check spring pressures If noting else turns up.

Run a compression check and let us know what each cylinder is making.

Put a 750 Holley on it with a descent intake for a baseline setup when you figure out what's wrong. Then mess with the Webbers.

 

[mike hall]

Cyl 1 -170psi
Cyl 2 -170 psi
Cyl 3 - 169 psi
Cyl 4 - 171psi
Cyl 5 - 169 psi
Cyl 6 - 173 psi
Cyl 7 - 169 psi
Cyl 8 - 170 psi
These are wet checks
And I think when whoever did the heads they looked fantastic but that doesn't mean anything you might be onto something with the springs and yah the only thing with changing the carbs and going with a dual plane 750 I may end up selling the webers and turn into another neigh sayer and call them junk lol and I really don't want to be that guy but from all accounts of other builds most guys only see a 20 hp loss between weber 48ida and say a victor jr so either I'm starving the engine or something is a fuckary

 

[Jac Mac]

As an indication I have a build sheet for a 365 cu in chevy with 48's, 11 to 1 comp, no jetting info unfortunately. Cam on 112° lobe centers, 300° duration, .465" lift, 76° overlap. 491hp / 405 tq. As Howard suggests you might have a spring issue, is there any visible standoff or reversion above the trumpets thru the rev range.

 

[mike hall]

Nothing spitting out the tops or anything that's what I was wondering too was reversion but I don't think reversion would cost 100hp would it?

 

[mike hall]

I think I may have to pull this engine down re check the cam and heads and springs lifters all the good stuff see if there is any signs of reversion in the intake

 

[Jac Mac]

Nothing spitting out the tops or anything that's what I was wondering too was reversion but I don't think reversion would cost 100hp would it?

Not if its 'normal' reversion, but if its due to the inlet valves not seating or following the cam profile, Yes. Remember your 'shed' video where you claimed ~7000 RPM, & I suggested valve train noise seemed to increase!