BHP- Fact or Fiction?

[PeteT]

I am in the process of building a DAX Tojeiro and will be considering ordering my Engine shortly. I have the chassis jigged up to fit a Chevy small block,Tremec 5 spd, through to Jag 3.31 powerlock final drive.
I am amazed at the different BHP and TORQUE figures some of you guys state that you think?? you have.., QUESTION FOR THOUGHT though..HOW MANY of you HAVE had your Cobra Dyno`d and can sleep at night with the comfort knowing that YOUR vehicle is punching out the BHP and TORQUE that you was lead to believe when you purchased your engine.!
Love to hear from you, - wonder what the best and worse scenarios would be? Are these figures we are lead to believe, when we spend our hard earned cash-
FACT or just FICTION???.... Get your Answers in now.

[David]

I was in Atlanta, Georga, USA in September last and I went shopping for a Camshaft for my Chevy 350. I put this question to the guy and his reply was that when Chevy were making 350's in the late 60's and early 70's, they were reconed to produce 1 horsepower per C.I. It was really just a rule of thumb. So using this rule, every 350 C.I produced 350 H.P. Then the rules changed. Some legislation came into effect which standardized the horsepower into what we know today. Therefor some of the die-hards and also older literature regarding these engines maintain that the figure of 350 H.P ie 1 H.P per C.I is still relavant today. As it turned out when the standard was changed there was a huge outcry because somebodies beautiful, powerful shiny Chevy, and Ford V8's had lost, on paper, about half its power. As you can imagine, ther were alot of @?&&*$ off people around.
That is the explanation given to me. If anyone knows different, it would be interesting to know other theories.


David

[robert]

Well, A bit of faction and fict

When I bought my engine from a bloke in Nottingham at All American Autos, he told me he was building a 350HP chevy with new this, new that etc. I should have know when the engine turned up that he was rubbish as the engine has a broken water jacket, not very good for a new engine.

After a lot of hassle, he replaced the engine, or rather just dropped it off at GD for me to get it installed. The second engine was only firing on 7, and the pressure on each bank was very low. After some investigation, we found out that the pushrods were bent, and had been used before. Anyway I digress, just think twice before you buy from All American Autos.

On to the BHP figures. This chap at All American told me the engine would produce around 350BHP. I was very sceptical after the problems I have had with the engine, so I took it to a local rolling road in Northampton.

The engine was putting out 180BHP, nowhere near the 350 he told me it would. We finally managed to get the engine up to about 250BHP after a lot of messing around etc.

Over this winter I have had the engine re-built by Ken Coleman of Engine Data. We have used turbo pistons, etc etc. The engine has been blueprinted and balanced and normally aspirated porduces 350BHP. With the blower at 12psi, we produce around 520-530 BHP, and then add the intercooler on and it adds about another 50BHP.

These figures are purely vapourware at the moment as the engine has not been dyno'ed. The engine will be dyno'ed at the end of the month and I will let you know what the actual figures are.

I reckon the figures will be spot on as Ken has been doing this for a long time and has the experience to know what an engine will do based on the components he has selected.

Best Regards

Rob

[paul]

When I ordered my engine from Real steel I took the option of them running it up on their dyno it cost an extra £200 (fuel.fresh oil&filter.etc,)but I now have a print out showing me exactly what I got for my pennies.(BHP.Torque.Carb air flow.Oil pressure.etc,)
Having said that I know it's not telling me what's at the wheels but then what the heck I'm happy

[alex]

Robert,

When you say your engine initially put out 180bhp was this at the wheels ? If not what did it put out at the wheels ? It seems to me that you loose a hell of a lot of horsepower through a Tremec/T5 & Jag rear end. I have chatted to guys from the Australian Cobra Club and some of them have had engines dyno'd at over 400bhp at the flywheel(one example was a Ford 351 Windsor with an Edlebrock rpm package). When installed in the car they where getting about 280bhp(208kw) at the wheels through a manual box and Jag rear end. My Dax has a mildy modded Ford 351 Cleveland/Tremec which put out 230bhp(170kw) at the wheels. Even though the carb needs jetted properly. I figure this is over 300bhp at the flywheel. All this talk about flywheel horsepower is bollocks anyway it's what goes to the road that matters. I think a better mesurement is performance. I have timed my car 0-100 in about 11 secs. Can't complain at that. There was an article in Car & Car conversions recently about a Dyno Day with a Lotus seven club. This rolling road was able to measure rolling resistance by slipping into neutral at high revs and measure resistance as the revs dropped. This way they could predict flywheel horsepower from wheel measured horsepower. There was a Ginetta(I know its not a seven) with a Rover V8 that put out 210bhp at the wheels but predicted flywheel power was over 280bhp. Don't know what kind of box/rear end this has but I reckon it's probably not as heavy duty/power consuming as a typical Cobra transmission.

Bhp figures are a waste of time in my opinion.
If u look at some figures in some books/mags etc.
What u find is a load of boll$%^* most of the time.
e.g. a cossie engine in full tune at say 400bhp is only a fraction quicker than one at 300bhp if u look at the (here comes the magic word)TORQUE!!!!
Figures theres not a deal of difference.

In my opinion the winning combination is high torque-correct gearing-
the weight of the car and last how u get the power onto the road!!

BHP is just a bi-product of rev-ability and torque.

If u dont agree the look at it this way:-

Put a 160 bhp fireblade engine which revs high into a 5-tonne truck
Then try a 165bhp Rover v8 in and lets see which one will actally move!!!!

Ya see bhp what a load of crap.

Its those three little letters that get the unwise to reach for their wallets though

[robert]

Roger

Couldnt agree with you more, its the torque which equates to acceleration and top speed.

Mind you, my supercharged engine puts out about 500lb foot torque.

I once read an article which detailed in laymans terms what the difference between horses and torque was, I will try an dig it out.

Best Regards

Rob

[alex]

I agree with the comments about torque. However surely the max torque isn't the only important consideration. The torque curve is important which is reflected in the BHP figure. If you compare like for like an engine with a broader torque curve will give better performance throughout the rev range and hence have a higher BHP rating.

Agreed but the torque has too be there.Fact!
In my eyes the ideal engine would be one to give good flow
right through.
I don't like 16 valves much cause i like to feel a bit of "punch"
(caused when then engines flow/timing/cam r just right)
But they rev higher which gives a broader "canvas" to paint your
curves on.
My rover engine is only really good for upto around 5500 for street
use but i have put the (i hope)right parts on to work from 1500-5000
so it should all come in together
So really if someone could put together a light revy 16v v8(say chevvy)
My guess that it would be a good engine in standard form.

The other way of thinking is weight.
Stick a revy engine in a v.light weight car and u have your speed back

So do u go for swing or roundabout?

For longevity give me torque any day!(i've never seen a 12000rpm bike engine do
200,000 miles!!!)

[robert]

Alex

All the figures quoted were at the wheels.

Regarding loss through the transmission, at the start of the session we were seeing losses of about 45bhp through the transmission, and when the dif oil etc warmed up it got down to about 30bhp loss through the transmission.

Best Regards

Rob