saouad

hello i have a 1979 corvette that refuses to go past 90 mph, the car has a 350 with slight modifications such as a edelbrock high rise intake manifold, holley 600cfm carb, side pipes with the catalytic converter delete and a th350 trans. the car hits 3400rpm when cruising 65 mph. and i am just lost as to why it only goes 90 mph, when i hit 90 mph the rpm is at 4500rpm which is right at the yellow line. I feel the engine has alot more power but refuses!
I have an option to put in a 406 if all else fails with the following modscamel hump heads, aggressive comp cam, edelbrock intake, holley 650 db pump, crane cam rockers, hedman headers, high performance fuel pump.

Please help just got smoked by a 2003 mustang is how i know the cars speed limit!

Yeller81USNRet

My 81 only goes to 85 MPH.

Legacy Stables

what is your differential geared at? it sounds like your differential has a high gear. I have a 3.08 so I am going 90 at a little over 3500 rpm. you may need to get a lower gear or improve your engines breathing if you have a need for speed.

One last thing our cars are designed to be less accurate about our mph above ninety so grab a gps to check the accuracy of your speedometer

Doug1

well if it's gearing, if you change it to be better at top end, your gonna lose some off the line.

76strokervette

Your factory camshaft is pretty much done making power at 4500 rpm.
Ther engine will continue to rev but will not make any power.Your options
are a gear swap or a cam swap with the 350.Or just replace the engine with
the other parts that are available.It sounds like you have a 3.70 rear gear.
Have you checked it?I would skip the double hump heads and go with an
aluminum aftermarket head,you'll be much further ahead performance wise.

racegofast

I agree with strokervette more airflow and fuel. Spin that baby up to 6 grand you'll go 130/140. It takes lots of money to go fast. My 383 turns 12.3 in tthe 1340 at. 108.

racegofast

By the way your engine is probably putting about 120 HP to the ground.

garygnu

mite be bad or worn out valve springs.consider a new valve train with good springs ,and a new timing chain .install a modern cam and make some HP.what is your fuel pressure at WOT ?consider new plugs and wires ,and check out your distributor for a possible rebuild.

Avette4me

You must have an overdrive because the stock TH 350 and 3.08's will be much higher than that at 90.

saouad

Thanks for the replies guys, i took it to my mechanic and he said I have 373 gears and I have no clue what the guy put into the engine before I got the car as a surprise, you think I should stay with my engine or swap it out for the 406 I could get for dirt cheap like 500 bucks

gcusmano74

Something is wrong. My '74 L48 w/4 speed, 3.36 gearset, would nearly hit hit the (only 5300 RPM) redline in top gear, completely stock. That should be something like about 125 MPH.
Going down a hill, MANY years ago, I once saw 135 MPH on the speedo. When I realized I was past the redline, I backed off.
As if any of the dash gauges were accurate. Probably not.
All done on empty interstate highways, by the by.
Haven't done anything like that in a long time.
I had no fear those days. That was in my irresponsible youth. Now I'm old and boring. 110 MPH max.

Doug1

what?! really? is that considered a big block now? if so , everything else will have to change, so it will cost much more then $500 when your done, but maybe it's worth it if your really looking for more power and torque

63mako

406 is a small block. I bet your not getting wide open throttle or your secondaries are not opening.

Doug1

in other words, he's running with only 2 barrels on his quadrajet maybe?

saouad

Wait what!? The guy told me everything would fit just the way it's is... Is this not true? He said to put a shifter improver kit and a 3500 stall and I am ready to bolt on an go! And to be honest I don't know very much about carbs and if it is opening a wot or if the secondaries are opening I am sorry for my beginner language, but I am trying!

saouad

And if I do I should get rid of the Holley 650 double pumper?

saouad

And I don't think I want to change the heads to aftermarket because the guy says it makes 450 hp and I heard that's a perfect range for the th350 with an improved shifter kit by tci if I am wrong or I should please let me know you guys know better than I do!

Vette5.5

You've obviously got some problems, as had 4 cyl daily cars with less that 100 hp, that would do better than 90 mph. Sounds like you have a fuel delivery problem. First thing I'd check, is the carb linkage. My brother had a 289 Mustang years ago he put a new carb on. I drove it to school once, and wouldn't top 60. I checked the linkage, and he really messed it up. Thing wouldn't even go half open. I fixed it, and was like a new car.

sly vette

I'm thinking you need to get your car to someone who knows how to work on a car of your vintage and get a good tune up.
A properly adjusted carb and the distributor working as it should will probably bring sufficient results.

saouad

I have taken it to so called corvette experts who only messed things up further two times they adjusted the carb so bad that it would stall everyte at temperature and 400 dollars later here i am. I am attempting solutions myself but there is a guy willing to help me put in the 406 but is there any modifications needed to do this because I don't even know what is in the engine other than why I could see, it looks like nothing major since it still has the original headers