The March issue of Corvette Magazine has an article on power adders as installed on an LT1. It is eye-opening, to say the least.

They added three very popular mods to the essentially-stock LT1 in a 1994 C4. They were: headers, 1.6 full-roller rockers, and stronger valve springs.
Now, most vendors will claim a 30 or so horsepower increase for the headers, maybe 20 for the rockers (I've seen as much as 40 in some adds), so most forum guys will install these two items, figuring they should get around an additional 50hp, right?

The magazine put the engine on the dyno for a pre-mod (baseline) run and got 275rwhp. After the mods, the car ran a 267rwhp, for a net loss of 8rwhp.

After adding bigger injectors, they ran 287rwhp, for a net gain of 12hp.

I've always said that you should figure about $50 per hp gain when you are buying speed parts....lets see how my formula stacks up:

Headers: I'm guessing $500 for decent Corvette headers, and that's conservative.
Rockers: Crane Gold (what CM used) are about $300 a set.
Springs: (I'm going to omit the price of these, since they add reliability but do not, in and of themselves, produce a power increase)
Injectors: 30lb injectors can be found for about $250 a set.
Total: $1050
Divide that by the 12hp gain and you get $87.50/hp.

In this case anyway, my $50/hp rule of thumb is pretty conservative.

Bottom line:
Anyone who tells you power is as cheap and easy as bolting on this part or that part is not telling you the truth.

Larry
code5coupe

 

Unfortunately most learn that the hard way.

 

And your numbers assume the labor is FREE! If you have a shop do those mods add another $750. That would be $1800 or $150 per HP.
That's why I get irritated with HP claims without proof!

 

Years ago, most speed shops would have a sign posted that said:
"Speed costs money. How fast do you want to go?"

Finding a formula for bucks per unit per horsepower is one thing, but when you break something as a result of applying that HP once too many times, then that repair costs get's added into the formula.

 

Very cost-effective mods like heads and cams or even the mini-ram may go as low as $30-$40/hp, but everything else I can think of is more expensive.

The other L98 intakes and headers for these cars are among the least cost effective mods at something like $60/Hp. But there's no way around 'em really.

I think $50/Hp is reasonable on average assuming a good tune is maintained along with the mods at no additional cost.

With additional tuning costs factored in, I agree the $50/Hp is conservative as shown in the example.

 

This is why I find questions such as, "What is the best part (whatever part is under discussion)for the money?" To me, the two, "high performance" and "cheap," do not belong in the same sentence. I take those questions to be really asking, "How can I get more than my money's worth?" Or, "How can I go fast on the cheap?" It is not going to happen.

 

This is what I've read not what I know as fact: The LT1 stock exhaust is not that restrictive. Therefore, headers alone should not produce more power.

As to the 1.6 RR: It would seem to me that they would require one to put more fuel and air into the intake to take advantage of them. So the 30# injectors make sense.

I would like to see them test the very popular combination of 1.6 RR and the LT4 hot cam with LT4 knock sensor module. Along with port/polish heads and gasket match to intake. Then a proper tune. Even with that I'd still be surprised to find headers making a significant difference. Shorties though are a weight savings and while they don't make power they do make some difference.

 

GeosFun, That sounds like my girlfriend. She says she doesn't feel like she gets her money's worth unless she overpays! That makes her a perfect Vette and Harley owner!

 

In IT projects we have an old axiom: the Golden Triangle of Development. Good, Fast, and Cheap. You can only ever have two of the three.

 

I know Pat, the owner of that car. Here's the deal... the headers were short-tube (I sold them to him), not alot to be gained there. The rest of the exhaust path was stock. So, the only real power mod was the rockers - and 12hp from them is about right.

 

Supercharging provides the highest HP/$ !

 

Ah.... enlightenment.

 

Believe very little of what you read in the magazines as their primary goal is to catch your interest and make the sponsors happy by helping sell product.

I had a car featured in Motor Trend and a good 25% of what was said about the car was made up to make a good story. They for example listed hp ratings for the car and it was never dynoed, they just make the numbers up.

Larger fuel injectors will get you nothing at all unless your existing injectors are at their flow limit or not functioning properly. Mentioned this before in prior posts but one of my cars was the test mule for Haltech to develop a fuel management system for LTx cars. In both dyno testing and road testing the 24lb injectors using 44 lbs fuel pressure maxed out @ 390 rwhp and 6000 rpm. Below or close to that you'll get nothing from peoperly function 24lb injectors.

Id say injectors: Zippo hp on a stock car!!

The very first mod I did was $500.00 long tube headers and a $1,200.00 hand built exhaust and I'd put the exhaust against any made for a C4..Period. We've dynoed the exhaust twice vs open headers and the net difference was 0 hp loss. The exhaust was done by the guy who builds Lou G's (LGM) race chassis.

Headers n Exhaust…..I got a 20 hp gain for $1,700.00.

1.6 rockers and springs in another car got me 7-8 hp for $5-600.00.

Right now I have about 9 grand just in my:

heads $4,500.00
Intake: 2,500.00
Stepped Racing Headers: $2,000.00

That was worth maybe 40 hp.

From gods lips to our ears......The mags are right 100% of the time.

 

Then why didn't the HP increase show up until they did the injectors?

 

Thanks for straightening this out. Sounds like he didn't go for the most effective ways to increase power.

 

The obvious is he had a bad injector or they need cleaning.

I have a spare set of 30 lb SVO injectors that for the most part are new...hey buy them and post what gains you get. If you motor is making less than 380-390 rwhp (providing it's has a standard transmission..less if auto) or your current injectors have have a problem it may be a short post.

OK girls.......line up as I have not one, but two spare sets of the power makers.

 

Probably because the modifications leaned the engine out. IMHO the injectors should have been left out and an adjustable fuel pressure regulator added. I bet that would have allowed them to 'tune' the mixture enough to get more than 12 HP from the mods. A dyno tune would be another option that I'm sure would have netted more HP. Generally I find the 'tech' in corvette magazines to be laughable. Read something else for good tech info.

 

Thats probably nitrous, actually.

 

Quite correct

 

The shorty headers are a waste of time. The cap picked up 12 horsepower at the rear wheels which is pretty good from a rocker swap.
It made an addtional 12 rwhp but it probably made an addtional 12-15 across the board. Why they don't put up they dyno pulls is beyond me.