4.2 with 4.5 inlets,and 4.2 max power

[The AJP Griff]

How many 4.2's are out there with 4.5 throttle bodies and inlets,and what kind of BHP can the 4.2 acheive at max?Whilst there seems to have been a trend of late towards fitting the 4.2 inlets to a 4.5(not for me thanks),i'm wondering if some 4.2 owners may have done the opposite,in order to achieve higher top end bhp?

[The AJP Griff]

Blimey,not much response there then!Don't people tune the 4.2,beyond a re-map,then?Do 4.2 owners just sit back and 'accept' theres little to be gained? I would have though that 400-420bhp should be possible from a 4.2?

[trackcar]

you're new around here aren't you?

[The AJP Griff]

trackcar said:

you're new around here aren't you?

Cheeky!
I'm really surprised that no-one seems to bother trying for more out of the 4.2,unless i've missed it?(the search is a nightmare).I just thought that a 4.2 with the 4.5 throttles ought to be able to make v.good top end bhp,then wondered if anyone had done it sucessfully?

[trackcar]

people do it the other way, but for the life of me i can't think why. the 4.5 setup flows more. you can mod the 4.2 inlets to give you the same as std 4.5 inlets so most people do it that way. with modded inlets, exhaust changes and remapping ive seen 380/390 from a 4.2 .. i think the main problem is finding 4.5 inlets .. try buying some without buying an engine complete and you'll struggle. all the info you'll ever need is in the past threads .. hint don't use the ph search function use google which archives the ph threads very nicely.

why are you interested in the 4.2 engine though mike? does mel want a little sister to the ajp griff now?

[The AJP Griff]

Mel doesn't want another one-thank goodness!She's still pining for the boat that we can't afford.The reason i wanted some info was purely for a good comparison,with the same induction potential.I like your tip for the google-i'll try it,Cheers Joo

[Jester7]

The AJP Griff said:

Mel doesn't want another one-thank goodness!She's still pining for the boat that we can't afford.The reason i wanted some info was purely for a good comparison,with the same induction potential.I like your tip for the google-i'll try it,Cheers Joo

There was me thinking You wanted to put a 4.2 AJP in a TR7

[The AJP Griff]

Jester7 said:

The AJP Griff said:

Mel doesn't want another one-thank goodness!She's still pining for the boat that we can't afford.The reason i wanted some info was purely for a good comparison,with the same induction potential.I like your tip for the google-i'll try it,Cheers Joo

There was me thinking You wanted to put a 4.2 AJP in a TR7

,well we do have a spare AJP.....and you know where theres a nice TR7.................

[Duke Thrust]

So, and please correct me if I'm off the mark - if the 4.5 inlets flow better could that not lead to slower port velocity and 'stall' at part throttle? Hence the 4.2 inlets giving better mid and low end torque?

Doesn't Andy at AMP run the 4.2's on his racer? Can't be all bad then?

Edited by Duke Thrust on Wednesday 9th July 20:55

[trackcar]

Inlet velocity isn't so much an issue on injected cars .. it's a bit of a carry-through from the old days of carbs where it was important to not lose too much velocity through the carb jets to maintain some degree of part throttle emulsion .. the same restrictions don't really apply to injected cars. The 4.2 never makes anything like the low / mid range hp of the 4.5 so the argument isn't really upheld in real life either. The 4.2 inlets flow a lot of air, modded they flow more .. the 4.5s just flow even more still so I don't really know why people are using the 4.2 inlets, the cars would make more on something bigger.

[HarryW]

It really depends on what you are after, out and out top end modified 4.5's will always flow more as they are bigger to begin with.
One aspect of the 4.2 inlets is the butterfly and injector placement, which imho is inherently superior for a road car revving to sub 8k rpm.
Worked 4.2 inlets with the standard butterfly flow similar to the 4.5's. The shortened inlets of the modified 4.5 flatter the cast 4.2 inlets as they reduce the inlet length to that approaching those of the standard 4.2.

A yard stick to me is what inlets does the BossCerb run .

[The AJP Griff]

HarryW said:

.....
One aspect of the 4.2 inlets is the butterfly and injector placement, which imho is inherently superior for a road car revving to sub 8k rpm.....

It's only superior in theory though,Harry.In actual practise,as bad as the 4.5 injector placement looks,it doesn't actually perform as bad as it looks,apparently.Why is the 4.2 inlet so good,otherwise?It all depends where you want your peak torque,surely?

[HarryW]

The AJP Griff said:

HarryW said:

.....
One aspect of the 4.2 inlets is the butterfly and injector placement, which imho is inherently superior for a road car revving to sub 8k rpm.....

It's only superior in theory though,Harry.In actual practise,as bad as the 4.5 injector placement looks,it doesn't actually perform as bad as it looks,apparently.Why is the 4.2 inlet so good,otherwise?It all depends where you want your peak torque,surely?

I think the only true answer you will get is try both set ups on the same car and see what works best for you.

Agree the 4.5 does seem to perform well enough to question the theory of injectors up or down stream of the butterfly. Although there are those that build engines and modify the cars who tend to think the sharp throttle response and overall results, be that from the butterfly being further away from the inlet or the injector closer to the valve and away from the butterfly the 4.2 inlet gives the better overall package in practice.

I'd like to say after many thousands of hours testing and comparing the two set ups TVR Engineering decided that when they fitted the 4.2 inlets to the BossCerb it was the best they could do, but I rather think its probably what they had laying around . I'm sure Phil could answer that one better.

[The AJP Griff]

HarryW said:

I think the only true answer you will get is try both set ups on the same car and see what works best for you.....

Somthing i'd very much like to do,and i might just know a man who has a set of fully flowed 4.2 inlets So i'll have to see if he's up for this experiment

[Duke Thrust]

What are you running on yours Harry? What capacity?

[Jester7]

trackcar said:

Inlet velocity isn't so much an issue on injected cars .. it's a bit of a carry-through from the old days of carbs where it was important to not lose too much velocity through the carb jets to maintain some degree of part throttle emulsion .. the same restrictions don't really apply to injected cars. The 4.2 never makes anything like the low / mid range hp of the 4.5 so the argument isn't really upheld in real life either. The 4.2 inlets flow a lot of air, modded they flow more .. the 4.5s just flow even more still so I don't really know why people are using the 4.2 inlets, the cars would make more on something bigger.

BUT surely its all about the velocity and characteristics of the air as it enters the head?? All you are doing with the inlets is changing the way the air enters the head. Two issues as i see it, volume of air and speed of air. The maximum a head will flow is the amount of air the inlets allow it to have at maximum cam lift, you have proved this Joo with the Whirlwind induction. Changing the length of Hose has changed the power/torque curve. What would happen if you added velocity stacks to the tops of the 4.5 inlets?? You would be giving the head the maximum amount of air so you would also be changing the peak power and torque curve. The length and type of induction has to make a difference to power and torque. The other input is cam duration, but lets not go there

[trackcar]

Jester7 said:

BUT surely its all about the velocity and characteristics of the air as it enters the head??

Which is why i was careful to say inlet rather than port velocity. As long as you can keep teh fuel in the airstream in the upper inlet then as long as you achieve good velocity just as the air enters the chamber I'm not sure what benefits you get from a smaller inlet upstream. Like I say : injected cars don't suffer the same problems of carbed cars, you don't need to keep upstream airflow high if you don't want to, as long as you don't fall into problems with fuel drop out. Surely as far as momentum ramming is concerned (which is what we're discussing with smaller ports improving low rev power etc)the combustion chamber couldn't care less what happens in the upper inlet, only the air speed at the very end of the port/chamber area ..?

[HarryW]

Duke Thrust said:

What are you running on yours Harry? What capacity?

Standard (not even worked) 4.2 inlets ontop of a high compression 4.5 engine and making in excess of 430hp/380lbs.

[Jester7]

trackcar said:

Jester7 said:

BUT surely its all about the velocity and characteristics of the air as it enters the head??

Which is why i was careful to say inlet rather than port velocity. As long as you can keep teh fuel in the airstream in the upper inlet then as long as you achieve good velocity just as the air enters the chamber I'm not sure what benefits you get from a smaller inlet upstream. Like I say : injected cars don't suffer the same problems of carbed cars, you don't need to keep upstream airflow high if you don't want to, as long as you don't fall into problems with fuel drop out. Surely as far as momentum ramming is concerned (which is what we're discussing with smaller ports improving low rev power etc)the combustion chamber couldn't care less what happens in the upper inlet, only the air speed at the very end of the port/chamber area ..?

But surely the speed and amount of the air at the port/chamber is dependent on the shape and size of the upper inlet?? You would cause an affect by changing either the upper or lower inlet??

[Duke Thrust]

HarryW said:

Duke Thrust said:

What are you running on yours Harry? What capacity?

Standard (not even worked) 4.2 inlets ontop of a high compression 4.5 engine and making in excess of 430hp/380lbs.

Ooooo! Is the high compression engine the 'GT' engine? I have one of those at home (not in the car yet), might have a play as I have both sets of inlets.